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ONKALOUnderground Characterisation and

Research Programme (UCRP)

P O S I V A O Y

F I N - 2 7 1 6 0 O L K I L U O T O , F I N L A N D

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F a x ( 0 2 ) 8 3 7 2 3 7 0 9 ( n a t . ) , ( + 3 5 8 - 2 - ) 8 3 7 2 3 7 0 9 ( i n t . )

September 2003

POSIVA 2003 -03

Pos iva Oy

POSIVA 2003 -03

September 2003

ONKALOUnderground Characterisation and

Research Programme (UCRP)

P O S I V A O Y

F I N - 2 7 1 6 0 O L K I L U O T O , F I N L A N D

P h o n e ( 0 2 ) 8 3 7 2 3 1 ( n a t . ) , ( + 3 5 8 - 2 - ) 8 3 7 2 3 1 ( i n t . )

F a x ( 0 2 ) 8 3 7 2 3 7 0 9 ( n a t . ) , ( + 3 5 8 - 2 - ) 8 3 7 2 3 7 0 9 ( i n t . )

Pos i va Oy

ISBN 951 -652 -117 -7ISSN 1239 -3096

Tekijä(t) – Author(s)

Posiva Oy

Toimeksiantaja(t) – Commissioned by Posiva Oy

Nimeke – Title

ONKALO UNDERGROUND CHARACTERISATION AND RESEARCH PROGRAMME (UCRP) Tiivistelmä – Abstract

The purpose of the ONKALO Underground Characterisation and Research Programme (UCRP) is to explore Olkiluoto rock conditions and thereby enhance the current geoscientific understanding of the site, to allow the submission of an application for a construction licence for the deep repository. The characterisation programme has the following geoscientific goals:

• to develop and demonstrate techniques for detailed characterising volumes of rock from the underground,

• to update the current descriptive model of Olkiluoto bedrock and to increase confidence in this model such that it will serve the needs of construction and the Preliminary Safety Assessment Report (PSAR) in the construction licence application, and

• to identify volumes of rock that could be suitable for housing parts of the repository.

The development of ONKALO will be based on coordinated investigation, design and construction activities. Mapping data from the tunnel front and data obtained from short probe holes will constitute most of the data needed to control the construction of ONKALO. Pilot holes will be drilled along the tunnel profile as the excavation proceeds and investigations will be carried out for geological, rock mechanics, hydrogeological and hydrogeochemical characterisation. Investigations cover more detailed mapping and sampling in parts of the tunnel, mapping and sampling of potential groundwater inflows to the tunnel and investigations from characterisation bore holes drilled from ONKALO. In addition, monitoring is planned in surface-drilled boreholes, in boreholes drilled from ONKALO, and in ONKALO itself. Monitoring will reveal changes in bedrock conditions and thus provide important information for site characterisation.

The information collected by characterisation and monitoring will all be assessed in an integrated modelling effort. The aim of this modelling is both to successively enhance the description and understanding of the rock volume around ONKALO and to assess potential impacts of ONKALO's construction and operation. Basically all geoscientific disciplines, geology, hydrogeology, geochemistry and rock mechanics follow the same workflow. Integration between modelling in different disciplines is essential and an integrated modelling task force will be formed.

Posiva will also use ONKALO for tests and experiments, in which the site-specific conditions at Olkiluoto have to be taken into account. The detailed programme for such testing will be developed once the tunnel progresses further. Already at present specific tests are planned related to construction and characterisation issues. These involve exploration of the mechanical and chemical impact on the rock and the impact of grouting.

Avainsanat - Keywords underground characterisation, disposal of spent fuel crystalline rock, geoscientific modelling, Olkiluoto

ISBN ISBN 951-652-117-7

ISSN ISSN 1239-3096

Sivumäärä – Number of pages 142

Kieli – Language English

Posiva-raportti – Posiva Report Posiva Oy FIN-27160 OLKILUOTO, FINLAND Puh. 02-8372 (31) – Int. Tel. +358 2 8372 (31)

Raportin tunnus – Report code

POSIVA 2003-03 Julkaisuaika – Date

September 2003

Tekijä(t) – Author(s) Posiva Oy

Toimeksiantaja(t) – Commissioned by Posiva Oy

Nimeke – Title ONKALO – MAANALAISTEN TUTKIMUSTEN OHJELMA

Tiivistelmä – Abstract

ONKALOn maanalaisen karakterisointi- ja tutkimusohjelman (UCRP) tarkoituksena on selvittää entistä tarkemmin Olkiluodon kallioperän ominaisuudet ja olosuhteet lisäten siten nykyistä geotieteellistä ymmärrystä loppusijoitus-paikasta. Tarkka käsitys loppusijoituskalliosta on edellytys rakentamisluvan hakemiselle loppusijoitustiloille. Karakterisointiohjelman tavoitteet ovat:

• kehittää ja osoittaa käyttökelpoiseksi tekniikoita kalliotilavuuksien yksityiskohtaiseksi maanalaiseksi karakterisoimiseksi,

• päivittää ja tarkistaa Olkiluodon kallioperää kuvaava malli sekä lisätä mallin luotettavuutta niin, että malli täyttää rakentamisen ja alustavan turvallisuusarvion (PSAR) edellyttämät vaatimukset rakentamislupaa haettaessa, sekä

• osoittaa loppusijoitukseen soveltuvia kalliotilavuuksia ja määrittää niiden ominaisuudet.

ONKALOn karakterisointiohjelmaa toteutetaan ja kehitetään koordinoimalla tutkimus-, suunnittelu- ja rakentamis-toiminnot. ONKALOn rakentamisen ohjaamiseksi tarvittavat tiedot saadaan pääosin tunnelin perän kartoittamisesta ja lyhyehköistä tunnustelurei’istä. Etukäteen kairataan niin kutsuttuja pilottireikiä tulevan tunnelin profiiliin. Näistä rei’istä suoritetaan geologisia, kalliomekaanisia, hydrogeologisia ja hydrogeokemiallisia tutkimuksia. Tutkimukset käsittävät myös tunnelin joidenkin osien yksityiskohtaisemman kartoituksen ja näytteiden oton, vesivuotojen kartoi-tuksen ja vesinäytteenoton sekä ONKALOsta käsin tehtävien karakterisointikairausten mahdollistamat tutkimukset. Lisäksi laaditaan monitorointiohjelma seurantamittauksille maanpinnalta kairatuille rei’ille, ONKALOsta kairatuille rei’ille ja ONKALOssa itsessään tehtäville seurantatutkimuksille. Monitoroinnin avulla voidaan paljastaa mahdolliset olosuhteiden muutokset kallioperässä ja saada samalla arvokasta paikan karakterisointitietoa.

Karakterisointi- ja monitorointiohjelmissa kerätty tieto arvioidaan integroidusti eri tutkimusalojen yhteisessä mal-linnustyössä. Tämän mallinnuksen tavoitteena on sekä vaiheittain parantaa ONKALOa ympäröivän kalliotilavuuden kuvausta ja ymmärtämistä että arvioida ONKALOn rakentamisen ja käytön mahdollisia vaikutuksia ympäröivään kallioon. Työn kulku kaikilla geotieteiden osa-alueilla, geologiassa, hydrogeologiassa, geokemiassa ja kalliomeka-niikassa on pohjimmiltaan sama. Integrointi eri alojen kesken on välttämätöntä ja mallinnuksen erityistehtävää suo-rittamaan perustetaan ryhmä (task force).

Posiva suorittaa ONKALOssa myös kokeita ja tutkimuksia, joissa Olkiluodon erityisolosuhteet otetaan huomioon. Yksityiskohtaisempi tutkimusohjelma tällaisille kokeille laaditaan rakentamisen edettyä pidemmälle. Tiettyjä ka-rakterisointiin ja rakentamiseen liittyviä kokeita on suunniteltu jo nyt. Tällaisia ovat kallioon kohdistuvien mekaa-nisten ja kemiallisten sekä tiivistämisinjektointien vaikutusten tutkiminen.

Avainsanat - Keywords Maanalainen karakterisointi, käytetty ydinpolttoaine, loppusijoitus, kiteinen kallio, geotieteellinen mallintaminen, Olkiluoto.

ISBN ISBN 951-652-117-7

ISSN ISSN 1239-3096

Sivumäärä – Number of pages 142

Kieli – Language Englanti

Posiva-raportti – Posiva Report Posiva Oy FIN-27160 OLKILUOTO, FINLAND Puh. 02-8372 (31) – Int. Tel. +358 2 8372 (31)

Raportin tunnus – Report code

POSIVA 2003-03 Julkaisuaika – Date

Syyskuu 2003

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TABLE OF CONTENTS

1 INTRODUCTION 7 1.1 Background 7 1.2 Conclusions of the 2000 RDD Programme review 8 1.3 STUK�s review of preliminary ONKALO designs 10 1.4 International experience 11 1.5 This and associated reports 11

2 OBJECTIVES 13 2.1 Needs 13 2.2 Geoscientific goals 14 2.3 Goals related to testing and demonstration 15 2.4 Experience, training and R&D 15 2.5 Expected outcome 15

3 OVERVIEW OF CONSTRUCTION PLANS FOR ONKALO 17 3.1 Planned facilities 17 3.2 Scheduling 19 3.2.1 Excavation and construction 19 3.2.2 Characterisation and research 21 3.3 Compatibility of ONKALO with the final disposal facility 23

4 CHARACTERISATION PROGRAMME 25 4.1 Characterisation strategy 25 4.2 Stage 1: Surface based investigations 28 4.2.1 Investigations needed for construction 28 4.2.2 Characterisation 28 4.3 Stage 2: Investigations during construction of the access tunnel 29 4.3.1 Boreholes drilled from the tunnel 30 4.3.2 Tunnel mapping 33 4.3.3 Additional characterisation activities 36 4.3.4 Characterising the main level from the access tunnel 39 4.4 Stage 3: Investigations during construction of the characterisation levels 41 4.4.1 Investigations needed for construction 42 4.4.2 Characterisation on the main and lower level 43 4.4.3 Characterising the intended repository area from ONKALO 44

5 UNDERGROUND INVESTIGATION METHODS 47 5.1 Geological investigations 47 5.1.1 Objectives 47 5.1.2 Measurements - Data 47 5.1.3 Expected results 50 5.2 Rock mechanics and thermal properties 50 5.2.1 Objectives 50 5.2.2 Measurements - Data 51 5.2.3 Expected results 60 5.3 Hydrogeological conditions 60 5.3.1 Objectives 60 5.3.2 Measurements - Data 61 5.3.3 Expected results 64

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5.4 Hydrogeochemical conditions 65 5.4.1 Objectives 65 5.4.2 Measurements - Data 67 5.4.3 Expected results 68

6 ASPECTS OF THE MONITORING PROGRAMME RELEVANT FOR CHARACTERISATION 71

6.1 General 71 6.2 Monitoring on the surface and in surface based boreholes 72 6.2.1 Rock Mechanics and Tectonic Events 72 6.2.2 Hydrogeology 72 6.2.3 Hydrogeochemistry 74 6.2.4 Surface hydrology 76 6.3 Monitoring in ONKALO 77 6.3.1 Monitoring the construction process 77 6.3.2 Rock Mechanics 77 6.3.3 Hydrogeology 78 6.3.4 Hydrogeochemistry 79 6.4 Monitoring during repository construction and operation 80

7 EVALUATION MODELLING 81 7.1 Modelling Strategy 81 7.1.1 Data processing and interpretation 82 7.1.2 Discipline integrated descriptive modelling 82 7.1.3 Modelling scales and stages 86 7.1.4 Modelling impacts of ONKALO and its construction 90 7.2 Geological modelling 91 7.2.1 Model components 91 7.2.2 Evolutionary aspects 93 7.2.3 Lithological description 94 7.2.4 Fracture zone description 95 7.2.5 Fracture network model 95 7.2.6 Rock mass model 96 7.3 Rock mechanics modelling 97 7.3.1 Descriptive modelling 98 7.3.2 Evaluating the rock mechanics impacts of ONKALO 100 7.4 Hydrogeological modelling 102 7.4.1 Descriptive modelling 103 7.4.2 Evaluating the hydrogeological impacts of ONKALO 104 7.5 Hydrogeochemical modelling 108 7.5.1 Descriptive modelling 108 7.5.2 Evaluating the hydrogeochemical impacts of ONKALO 111

8 R&D RELATED TO CONSTRUCTION AND CHARACTERISATION 115 8.1 General 115 8.2 Mechanical and chemical impacts on the rock 116 8.3 Impact of grouting 116 8.4 Site specific tests on grouting technology 119

9 INSTRUMENT DEVELOPMENT 121 9.1 Equipment in surface-based boreholes 121 9.2 Equipment to be used underground 122

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10 DATA MANAGEMENT 127 10.1 Objectives 127 10.2 Features of the data management system 128 10.2.1 Data 128 10.2.2 Users and accessibility 130 10.2.3 Integration 130 10.2.4 Maintenance 131 10.3 Long time span of the project 131

11 MANAGEMENT, ORGANISATIONAL AND QA ASPECTS 133 11.1 Organisation and management 133 11.1.1 Practical design and construction work 133 11.1.2 Underground characterisation 133 11.1.3 Tests, demonstrations and monitoring 134 11.1.4 Liaison 134 11.2 Quality assurance 135

12 REFERENCES 137

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PREFACE

This report has been produced by a team of Posiva staff and consultants working on behalf of Posiva. Among others, consultants contributing to the report include Johan Andersson (editor), Henry Ahokas, Pekka Anttila, Mel Gascoyne, Pirjo Hellä, Erik Johansson, Paula Keto, Lasse Koskinen, Ari Luukkonen, Petteri Pitkänen, Reijo Riekkola, Pauli Saksa and Margit Snellman.

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DEFINITION OF SOME TERMS USED IN THE REPORT

ONKALO: The ONKALO underground research facility, which is to be constructed on the Olkiluoto site, in the municipality of Eurajoki, Finland is a system of exploratory tunnels accessed by a shaft and an access tunnel. The main objective of ONKALO work is to enhance the current geoscientific understanding of the site to allow the submission of the application for a construction licence for the deep repository. ONKALO is an acronym based on the Finnish language expression for �Olkiluoto Rock Characterisation for Final Disposal�. The word �onkalo� also means a �cave� in Finnish.

Main characterisation level. The main characterisation level envisaged at a depth of 420 m includes characterisation tunnels for characterisation of the bedrock and approximately 400 metres of tunnels used to test and demonstrate the disposal concept. In addition, for instance a rescue chamber, a repair shop, a parking area and the main access to the shaft are located on the main level.

Lower characterisation level. The lower characterisation level, 100 m below the main characterisation level at a depth of about 520 m, consists of approximately 350 metres of tunnels for auxiliary rooms,, which can also be used for characterisation purposes.

Depth (m) is the depth from the ground surface. Depth is also used as a measure of distance from starting point along steeply dipping boreholes (depth in borehole, meters).

Level refers to the vertical z-coordinate with the sea level defined at 0.0, i.e. underground levels usually take a negative value.

Regional scale models. Models representing the geoscientific conditions surrounding the island of Olkiluoto. Typically they cover ten or some tens of kilometres around the island.

Site scale models. Models covering the investigation site and the whole repository area (about 2 km2 surface area).

Local scale models. Models of various sub-volumes investigated from ONKALO (100 � 500 m scale).

Detailed scale models. Models of detailed resolution, e.g. for describing deposition tunnels and holes (10 to 100 m scale). Very detailed scale models refer to sub-volumes described at a scale less than one meter.

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1 INTRODUCTION This report describes the Underground Characterisation and Research Programme (UCRP) to be carried out at the ONKALO1 underground research facility that is to be constructed on the Olkiluoto site, in the municipality of Eurajoki, Finland. The purpose of UCRP is to explore the Olkiluoto rock conditions at the actual repository depth and to produce detailed knowledge for the application to construct a final repository for spent nuclear fuel in Finland.

1.1 Background On the 18th of May 2001 the Finnish Parliament ratified the Decision-in-Principle (DiP) taken by the Government that �[construction of the disposal facility for spent nuclear fuel] � at Olkiluoto in the municipality of Eurajoki is in the overall interest of society� (Parliament brief EK 8/2001 vp � M 7/2000 vp). As stated in the report of the Parliament's Finance Committee, the DiP means that the disposal project can now proceed to the construction of an underground investigation facility and more detailed, site-specific studies. The need for underground rock characterisation is also expressed in the YVL Guide 8.4 by the Radiation and Nuclear Safety Authority (STUK), listing the construction and operation of an underground research facility as the next main milestone after the selection of the disposal site (STUK 2001). The Decision-in-Principle is valid for 15 years from the date of the Parliament's ratification, which means that the application for the construction licence has to be submitted to the Government during this period.

In January 2001 Posiva published a programme for research, development and technical design work (RDD) in the pre-construction period (Posiva 2000). In this programme the general goals and objectives were defined for the RDD work that has to be carried out before the submission of the construction licence application. In general, the principal areas of the planned work consist of site investigations, technical design and development work, and research into the long-term safety of disposal. However, the programme laid special emphasis on the ONKALO underground rock characterisation facility, which should provide important information for all these main RDD areas. The information and experience from the ONKALO investigations, experiments and construction work was seen as key input for the Preliminary Safety Assessment and the application for the construction licence for the disposal facility, which will be submitted in the early 2010�s.

The ONKALO UCRP is based on the same goals and considerations as the RDD programme but gives a more detailed description of the planned underground work. According to the RDD programme, the underground investigations are particularly designed: 1 ONKALO is an acronym based on the Finnish language expression for �Olkiluoto Rock Characterisation for Final Disposal�. The word �onkalo� also means �cave� in Finnish.

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• to enhance the current geoscientific model of the site by a more detailed description of the explored volume of the rock mass,

• to collect data that cannot be obtained from surface-based boreholes,

• to test interactions between the rock and the engineered barrier system.

A particular purpose of the underground investigation programme is to assess whether the present conclusions on the suitability of the Olkiluoto site for the spent fuel repository can be confirmed by investigations carried out at the actual depth of the repository.

Three stages were distinguished in the programme. Each stage has its own �products�, which represent contributions to the work process in going underground and in meeting the main objectives. The stages were defined as:

• Stage 1: Surface-based investigations before the construction of the access ramp commences. The main products are an improved description of the target rock volume and the access locations of ONKALO and the establishment of baseline conditions.

• Stage 2: Construction of an access ramp and a shaft down to the planned repository depth accompanied by parallel investigations on the surface. The main products are monitoring responses of the geosphere to the construction activities, the improved characterisation of the target rock volumes and the completion of the detailed design of ONKALO.

• Stage 3: Completion of ONKALO's construction at the target depth, together with underground investigations, including site-specific tests of repository technology and experiments related to the long-term performance of the multi-barrier system.

A fourth stage will follow later, the repository excavation stage. Excavations will continue over the operational lifetime of the repository, since detailed characterisation of the whole rock volume needed for the repository space is not practicable at once, either from the surface, or from the underground rock characterisation facility. Therefore, the underground characterisation of the site will continue to be an important activity during the operational period, especially when designing and constructing the deposition tunnels.

1.2 Conclusions of the 2000 RDD Programme review Posiva�s RDD programme of 2000 was reviewed by the Finnish Nuclear and Radiation Safety Authority, STUK, and their team of international experts (STUK�s letter Y811/35 to MTI, 26 September, 2001). Most reviewers found the overall programme well thought-out and well structured. The division into different stages was found to be logical despite some overlapping and imbalance between individual chapters.

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The reviewers also identified several development needs. The following points are particularly relevant for the UCRP:

• There is a need for a logical framework for R&D planning. The guiding principles for developing R&D needs should be stated, as well as the means applied to identifying and prioritising R&D needs.

• Adequate time is needed to collate and assess data, to integrate it into a performance model and to have the model and its conclusion approved by audit.

• Posiva should develop a basic data accessibility plan in consultation with STUK, in order to enable external review.

• An iterative prediction-confirmation programme could be envisaged. Once sufficient understanding of the existing situation can be demonstrated the exercise would evolve logically to predictions that could be tested in the shafts and tunnels.

• The Baseline Report is judged to be essential with the main argument being that Baseline conditions need to be defined before the construction of ONKALO commences.

• The previously used wording that ONKALO should �confirm� predictions made from the surface is misleading. The objective of ONKALO is to allow the exploration of conditions underground and at scales unattainable from surface-based investigations.

• There is a need to consider transport characterisation also in this phase of the work. Quantitative flow and transport modelling make it necessary to address all important issues from the outset and whereby inconsistencies are less likely to occur.

• There is a need to develop a better understanding of how the chemistry of the groundwater will change in the future and to consider interactions between geochemical and hydrogeological processes. Special studies are also required on whether the exposure of rock could result in it losing its reducing capability. Calculations are required that consider the primary porosity and not the whole rock in the redox buffering capacity.

• Copper corrosion in the chemical conditions prevalent at Olkiluoto may require additional attention. In this context special emphasis shall also be focused on the occurrence and significance of ammonium at Olkiluoto. Interactions among barrier corrosion products, involving copper and iron corrosion products and fuel need to be studied.

Posiva is developing the framework for RDD planning. As stated in the RDD programme Posiva takes the safety concept as the basis of RDD priorities and has applied this thinking to the RDD programme formulation. It also forms the basis for the UCRP programme. To make the planning logic more systematic, Posiva has started the

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development of a requirements management system, which will show the logical connections between the current design specifications and the corresponding design requirements and make it easier to recognize the constraints of and possibilities for modifying the system or component designs. The logic will be applied to future programme planning and reporting, which from the year 2003 on will take a new form. At the end of the year 2003 Posiva will publish a report (�TKS-2003�), which includes a summary of the progress made during the years after the DiP and an update of the RDD programme report with focus on the next three years. In the future a similar report will be produced regularly every three years. The 2006 report will include the updating of the UCRP as well.

RDD priorities are also being discussed in many international contexts at present, one example being the NET.EXCEL project of the European Union�s Fifth Framework Programme, in which Posiva is a partner.

It is admitted that as yet it cannot be known, whether ONKALO will really confirm the suitability of the Olkiluoto site but, on the other hand, that is, of course, what Posiva hopes to achieve with the planned activities at Olkiluoto. Only with such confirmation will it be possible to proceed to the application of the construction license.

Posiva has reconsidered the timetable of the ONKALO programme and allowed more time for the pre-construction planning and other activities, such as baseline description and monitoring system planning. A special report will also be published on the expected disturbance caused by ONKALO to the Olkiluoto bedrock (Vieno et al. 2003). Due attention has been given to the other recommendations, as well.

1.3 STUK�s review of preliminary ONKALO designs In February 2003 STUK expressed their comments on the conceptual alternatives for ONKALO (STUK�s letter Y811/37 to Posiva, 13 February, 2003). Some of the comments, which are partly based on a review report on the geological and structural characterisation of the Olkiluoto site by STUK�s IMGS team (Cosgrove et al. 2003), have bearing also on the planning of the UCRP. In STUK�s opinion, the access routes to ONKALO should be designed so that they will not be above the rock volumes meant for disposal, nor in their vicinity; this would decrease the possibility of chemical or mechanical disturbances to the repository. On the other hand, STUK also recommends that the access-ways should not cross well-flowing fracture zones or be located in ground-water discharge areas.

According to the general safety requirements for spent fuel disposal the design of the characterisation facility as well as the underground construction and investigation methods must be chosen �in the best manner with regard to retaining the characteristics of the host rock that are important to long-term safety� (Government Decision on the Safety of Disposal of Spent Fuel, STUK 1999). As most of the expected disturbance to the host rock is expected to be due to changes in flow conditions, the minimisation of inflows to ONKALO has been one of the central requirements in the

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design of ONKALO layouts. In practice this means avoidance of high-transmissivity zones, as STUK recommends. However, most of the rock volumes outside the high-transmissivity zones would also be suitable for repository tunnels, which implies that the tunnels and shafts will necessarily be located in rock volumes that are potentially suitable for disposal as well. Therefore, the requirement that the access routes should not be close to the repository tunnels means that the area beneath and close to access tunnels becomes unavailable for disposal. This has consequences also to the planning of the underground characterisation strategy, as it makes it more difficult to obtain an early borehole access to the potential host rock volumes. The current characterisation strategy takes the risks of undesired chemical and mechanical disturbances in the repository area seriously, yet tries to facilitate early characterisation of the rock masses of interest for the repository purposes.

1.4 International experience Experience on constructing underground research laboratories (URLs) and on conducting underground experiments has been gained in several countries during the past few decades. In recent years Posiva has participated in the R&D work of several of these facilities and utilised this experience in the planning of the ONKALO facility and the related underground research and characterisation programme. The Hard Rock Laboratory at Äspö in Sweden has been of particular interest, and the co-operation is intended to continue even after the construction of ONKALO, as several generic type experiments (e.g. those related to barrier functions) will be carried out at Äspö or in other suitable URLs.

A recent publication of NEA (2001) gives on overview of the underground laboratories constructed so far and of their role in the nuclear waste disposal programmes of several countries. Posiva has also produced a summary report (Hagros 2001) of work carried out previously in foreign URLs with emphasis on laboratories that are in a similar geological environment as Olkiluoto, i.e. in crystalline rock.

The development of the ONKALO programme has partly been based on the experience from other URLs, and this report provides some examples of the contribution of this experience. However, all currently existing underground laboratories in crystalline rock are of the generic type, i.e. they are not located on the actual disposal sites and have been designed for generic studies only. Compared to these facilities (such as Äspö HRL in Sweden and the URL in Canada) the underground research programme of ONKALO is to a greater extent focused on the characterisation of the site-specific properties of the rock mass, and specific underground experiments are mainly related to tests and experiments in which the site-specific conditions at Olkiluoto have to be taken into account.

1.5 This and associated reports Posiva's plans (2000) need to be further developed and made more specific before the actual construction of ONKALO can commence. More detail needs to be added and the

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points raised by the reviewers should be considered. For this purpose Posiva has produced five reports that are separate, but yet linked with each other.

Activities regarding Stage 1 (Surface-based investigations to support construction) are only briefly summaries in this report. They and all issues related to the baseline are reported in Posiva (2003a). The strategy for the construction and investigation planning is presented by Saksa et al. (2003). The details of the monitoring programme are to be described in a separate monitoring report. Vieno et al. (2003) discuss assessment of disturbances. Current construction plans and layout are given in Posiva (2003b).

The current report focuses on Stage 2 and Stage 3 of the continued and detailed site characterisation process. Chapter 2 presents objectives. Chapter 3 outlines the construction plans. Chapter 4 provides an overview of the characterisation programme, both for engineering and pure characterisation purposes, related to the different stages of ONKALO's construction. Chapter 5 presents the investigation methods to be applied within the different disciplines. Although the monitoring programme is presented in a separate report, essential information also for characterisation is derived from monitoring. These aspects of the monitoring programme are presented in Chapter 6. Chapter 7 describes how all the information assembled will be interpreted in an integrated modelling effort covering the various geoscientific disciplines, i.e. geology, rock mechanics, hydrogeology and hydrogeochemistry. Chapter 8 outlines some of the research activities that will take place in ONKALO. ONKALO-specific instrument development activities are presented in Chapter 9 and the data information system is presented in Chapter 10. Chapter 11 outlines the planned management, organisation and overall quality assurance structure.

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2 OBJECTIVES The findings from ONKALO will be needed as one important basis of the application to construct a final repository for spent nuclear fuel at Olkiluoto, supported by a Preliminary Safety Assessment Report (PSAR). This overall need and the requirements specified by authorities lead to specific geoscientific goals. In addition, there are goals related to testing and demonstration, experience, training and R&D.

2.1 Needs The findings from ONKALO will be needed as one important basis of the application, supported by a Preliminary Safety Assessment Report (PSAR), to construct a final repository for spent nuclear fuel at Olkiluoto. The demand for underground rock characterisation is included in the General Safety Requirements specified by the Government, which state:

�At the planned disposal depth, blocks of bedrock with adequate size and intactness shall exist for the construction of the emplacement rooms. For the design of the emplacement rooms and for the acquisition of data needed for the safety analysis, the host rock shall be adequately characterised by means of investigations performed at the planned disposal depth� (STUK 1999).

The aim is to carry out such characterisation by the early 2010�s. The individual results of the studies need to be integrated into overall understanding of Olkiluoto geology. On that basis it should be possible to judge whether the previous assessments on the suitability of the Olkiluoto site are valid. According to the General Safety Requirements,

�The geological characteristics of the disposal site shall, as a whole, be favourable for the isolation of the disposed radioactive substances from the environment. An area having a feature that is substantially adverse to long-term safety shall not be selected as the disposal site.� (STUK 1999)

The regulatory guide YVL 8.4 by STUK further explains that

• �the characteristics of the host rock shall be such that it adequately acts as a natural barrier�, and

• �the characteristics of the host rock shall be favourable with respect to the long-term performance of engineered barriers�(STUK 2001).

According to STUK the host rock conditions of importance to long-term safety should be stable or predictable for up to at least several thousands of years. As factors that indicate unsuitability STUK lists (STUK 2001):

• proximity of exploitable natural resources

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• abnormally high rock stresses

• predictable anomalously high seismic or tectonic activity

• exceptionally adverse groundwater characteristics, such as lack of reducing buffering capacity and high concentrations of substances, which might substantially impair the performance of barriers.

The location of the repository should be favourable with regard to the groundwater flow regime on the disposal site and the disposal depth should be selected with due regard to long-term safety, taking into account at least

• the geological structures and lithological properties of the host rock and

• the trends in rock stress, temperature and groundwater flow rate with depth (STUK 2001).

Finally the YVL Guide (STUK 2001) requires that:

�The structures of the host rock of importance to groundwater flow, rock movements or other factors relevant to long-term safety, shall be defined and classified. The waste canisters shall be emplaced in the repository so that adequate distance remains to such major structures of the host rock which might constitute fast transport pathways for the disposed radioactive substances or otherwise impair the performance of barriers.�

The guidance from STUK has been used as a basis in the programme formulation and combined with more practical goals of the overall development of the spent fuel repository at Olkiluoto.

2.2 Geoscientific goals The main objective of ONKALO work is to enhance the current geoscientific understanding of the site to allow the submission of the application for a construction licence for the deep repository. In this respect ONKALO should make it possible:

• to revise the current description of Olkiluoto bedrock and place it on a scientifically firm foundation so that it can serve the needs of site evaluation, safety assessment and technical design for the construction licence application,

• to show how bedrock can be characterised and classified for the purpose of identifying suitable volumes of rock for disposal tunnels and deposition holes

• to identify volumes of rock that would be suitable for repository tunnels and describe these volumes in detail, and

• to explore the response of the host rock to the repository construction by monitoring and modelling the various effects of ONKALO in the vicinity of the excavations.

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While the early phases of ONKALO work may focus on the testing and development of methods for characterisation of underground rock conditions and on characterisation of typical Olkiluoto rock, the investigations must eventually reach the actual rock volumes of interest for the repository. However, the characterisation programme must not jeopardise the use of potentially useful volumes of rock that would otherwise have been suitable for locating parts of the repository. This necessitates certain restrictions in the design of ONKALO�s layout.

2.3 Goals related to testing and demonstration Posiva has a bilateral agreement with the Swedish SKB on testing and demonstrating repository technologies at the Äspö Hard Rock Laboratory. As explained in the RDD Programme of 2000, Posiva will take advantage of the benefits of co-operation and the available infrastructure at Äspö and only use ONKALO for tests and experiments, in which the site-specific conditions at Olkiluoto have to be taken into account. High groundwater salinity and rock mechanics conditions in terms of rock strength versus rock stress are aspects that may require Olkiluoto-specific testing and demonstration. Most of such work will be postponed till the time that the ONKALO access tunnel reaches the actual repository depth. The detailed programme for such tests will be developed by the time the programme is approaching Stage 3.

2.4 Experience, training and R&D ONKALO project will gain Posiva experience in investigating, planning, constructing and operating deep underground facilities, which will be of use in the development of the actual disposal facility. In addition, the project will mean the start of a monitoring programme, in which the whole repository site is monitored, in particular the parts of the rock that are expected to be influenced by construction activities. The project will also contribute to the development of techniques and know-how to be applied during repository development and allow experiments to be carried out for the testing and exploration of barrier functions specific to the Olkiluoto site conditions.

2.5 Expected outcome The Underground Characterisation and Research Programme will produce:

• a coherent picture of the geological, hydrogeological, geochemical and rock mechanical conditions in typical repository host rock at Olkiluoto

• the characteristics of the host rock needed to assess the long-term performance of the planned repository and to complete the technical design of it

• increased information and understanding of the barrier functions of the host rock in �prevailing in situ conditions�

• a procedure for the progressive development of the repository layout by coordinated investigation, design and construction activities. The procedure will

16

embody a practical application of the rock classification system that is under development.

• improved rock characterisation methods and skills for use at the repository construction and operation phases

• knowledge and experience in the performance of repository technology in actual site-specific conditions, and

• general skills and experience in work in the Olkiluoto underground rock conditions.

The characterisation and monitoring programmes will include investigations of geological, rock-mechanical, thermal, hydrogeological, geochemical and migration properties. Subject specific plans have been developed, where each sub-plan is presented in a standard format stating the objectives, the methods and the expected outcome of the work. The overall characterisation and modelling programmes are based on the integration between these areas of work.

Additional surface-based boreholes and other types of surface-based investigations will also be needed in order to characterise additional potential repository rock volumes located outside the area of ONKALO. Such plans are to be reported in the 2003 update of Posiva�s RDD programme.

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3 OVERVIEW OF CONSTRUCTION PLANS FOR ONKALO This chapter provides a brief overview of the construction plans for the ONKALO underground characterisation facility. The dimensions and details presented stem from the current plans as they appear in the main drawings report (Posiva 2003b). These may, however, change during subsequent planning stages of ONKALO.

3.1 Planned facilities The main element of ONKALO is a system of exploratory tunnels accessed by a shaft and an access tunnel (Figure 3-1). The exploratory tunnels are planned to serve the actual repository in the future as part of the network of transport tunnels or as auxiliary rooms. The actual layout of the exploratory tunnels will be determined before the construction of the access reaches the designated depth. The tunnels will serve three purposes:

• provide an opportunity for exploring the potential host rock volume in more detail than would be possible from the ground surface,

• allow the monitoring of the response of the host rock to excavation and,

• provide adequate space to allow experiments and tests.

In current planning, the main characterisation level (see Figure 3-1) will be located at a depth of 420 metres. Demonstrations and tests related to repository technology will mainly be carried out on the main level. In addition to underground facilities ONKALO also comprises buildings and areas on the surface such as office facilities, laboratories, storages and the headframe of the shaft.

The total underground volume of ONKALO is approximately 330 000 m3 and the combined length of tunnels and the shaft is 8 500 m. The access tunnel from the surface to the lower characterisation level, envisaged at a depth of 520 metres, consists of approximately 5 500 m of tunnelling with an inclination of 1:10. The access tunnel is 5.5 metres in width and 6.35 m in height.

The vertical shaft will be excavated down to a depth of 520 metres by using a shaft slashing method. The preliminary inner diameter is 5.7 metres with concrete lining. The shaft will be equipped with ventilation routes and a man cage for personnel transport. A connecting tunnel from the access tunnel to the shaft at every 1 000 to 1 500 m will facilitate the ventilation and evacuation of ONKALO.

The characterisation carried out in ONKALO concentrates on the access tunnel and the two characterisation levels:

• The access tunnel itself, shaft accesses and exploratory niches will be used for characterisation purposes. The layout design of the first tunnels on the main characterisation level will be based on drilling investigations from the access

18

tunnel, below the main sub-horizontal fracture zones (R20A and R20B, see the Baseline report, Posiva 2003a, for a description of the current bedrock model).

• The main characterisation level at a depth of 420 m includes ca. 1 200 metres of characterisation tunnels used for the characterisation of the bedrock and approximately 400 metres of tunnels for tests and a demonstration of the disposal concept. It consists of a tunnel loop occupying an area of ca. 350 m x 350 m. A separate area, consisting of a few short drifts, will be reserved for site-specific demonstrations and development work. In addition, for instance a rescue chamber, a repair shop, a parking area and the main access to the shaft are located on the main level.

• The lower characterisation level, at a depth of about 520 m, consists of approximately 350 metres of tunnels used as auxiliary rooms, and also for characterisation purposes. The main pumping station is located on this level.

Figure 3-1: ONKALO layout

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3.2 Scheduling The ONKALO project can be divided into three main stages: Surface-based investigations before construction, construction of the access tunnel and shaft and completion of the ONKALO construction at the target depth. Figure 3-2 presents the current preliminary schedule and phasing. Excavations will be started in mid 2004 and the construction of ONKALO will be completed by the end of 2010.

3.2.1 Excavation and construction

The underground excavation and construction works are divided into three construction packages. Construction package 1 consists of the access tunnel to -300 m level (approximately) including a ventilation raise to the same depth. Construction package 2 consists of the access tunnel from -300 m down, i.e. to -520 m level. The main characterisation level at a depth of 420 m is also included in package 2 as is also the shaft slashing from the surface to the bottom. Construction package 3 consists of permanent construction work, such as concrete structures, air, water and power lines and shaft installations.

The construction schedule is based on the following assumptions:

• Five weekly working days

• Two eight hour daily shifts

• Round length 4.6 m

• Pre-grouting 46 %

• Temporary reinforcement after every round

• Permanent reinforcement after every four rounds

According to the plans the access tunnel will advance 20-25 m per week, i.e. approximately 1 000 m per year. The total duration of the ONKALO Project is 6-7 years.

The tunnels will be excavated by the drill and blast technique. The shaft will first be raise bored with a diameter of 2.4 m - 3.1 m and later slashed up to 6.0 m by using the drill and blast technique. The tunnels and the shaft will be reinforced by bolts, shotcrete and possibly also steel mesh reinforcement. Cast concrete structures may also be used.

In order to limit groundwater ingress the tunnels will be pre-grouted and post-grouted according to the results of the probe holes (see Section 4.3.1). The methods and the amount of reinforcement and grouting will depend on the local conditions, and may thus change even within a short distance. This requires coordinated investigation, design and construction activities to recognise the most probable, favourable and unfavourable conditions in advance and to pre-establish design alternatives based on these conditions and to handle both predicted and unexpected changes in the layout of ONKALO.

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According to current construction plans (see Figure 3-2 and Figure 3-3):

• Stage 1: should be completed by mid 2004

• Stage 2: should be completed by early 2008 (i.e. a duration ca. 3.5 years)

• Stage 3: should be completed by mid 2010 (i.e. a duration ca. 2.5 years).

Figure 3-2 ONKALO main schedule.

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Figure 3-3 ONKALO construction schedule

3.2.2 Characterisation and research

The scheduling of the characterisation and research work is closely related to the scheduling of the ONKALO construction programme. Given the various activities outlined in the following chapters some important activities and milestones can be identified.

At stage 1 these include:

• Surface-based investigations to support the construction process.

• Assessment of the available information to allow descriptions of the potential access sites to be developed.

• Decision on the selection of the access site.

• Establishment of �baseline� site model.

• Prediction of mechanical, hydrogeological, hydrogeochemical impacts of construction.

In the construction of the access tunnel to the -300 m level important activities (part of stage 2) include:

• Surface based monitoring

• Additional surface-based boreholes for characterising the upper layers

• Probing and mapping of the access tunnel

EXCAVATION OF TUNNELS

Access tunnel 0 ... -100 mAccess tunnel -100 ... -200 mAccess tunnel -200 ... -300 mAccess tunnel -300 ... -420 mAccess tunnel -420 ... -520 mCharacterisation level -420 mCharacterisation level -520 m

SHAFT

Raise boringSlashing

CONSTRUCTION WORKS

HOIST

INSTALLATIONS

2004 2005 2006 2007 2008 2009 2010

EXCAVATION OF TUNNELS

Access tunnel 0 ... -100 mAccess tunnel -100 ... -200 mAccess tunnel -200 ... -300 mAccess tunnel -300 ... -420 mAccess tunnel -420 ... -520 mCharacterisation level -420 mCharacterisation level -520 m

SHAFT

Raise boringSlashing

CONSTRUCTION WORKS

HOIST

INSTALLATIONS

2004 2005 2006 2007 2008 2009 2010

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• Exploration niches for characterisation boreholes and the drilling of these holes.

• Inflow measurement weirs

• Hydrogeochemical sampling

• Rock mechanics sampling

• First tests of geophysical techniques for identifying major fracture zones prior to intersecting them.

• Combined and updated modelling description of the upper volume and model prediction of the main and lower characterisation levels. Comparison with predictions made at the end of stage 1.

• Detailed planning for stage 3 R&D at the ONKALO

During the construction of the access tunnel from the 300 m to the 520 m level (also part of stage 2) important activities include:

• Several cored boreholes will be drilled from the lower parts of the access tunnel to explore rock conditions on the main characterisation level.

• Test drilling of some pilot holes.

• Probing and mapping of tunnel.

• Exploration niches for characterisation boreholes and the drilling of these holes.

• Hydrogeochemical sampling.

• Inflow measurement weirs and other hydrogeological sampling.

• Rock mechanics sampling.

• Characterisation of the ventilation shaft.

• Combined and updated modelling description of the entire volume of the rock mass and the development of model prediction of volume of rock around the main and lower characterisation levels. Comparison with earlier predictions.

• Detailed plans for characterising the main and lower levels and the first repository panels.

During the investigations made in the tunnels on the main and lower characterisation levels (stage 3) important activities include:

• Monitoring

• Characterisation work (details to be developed during the previous stage, see above).

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• Carrying out selected experiments.

• Site-specific tests of technology.

• Final integrated modelling, including comparison with previous predictions and delivery of descriptions of the repository panels such that they can be used as input to the PSAR.

All these different activities will be further described in the following chapters.

3.3 Compatibility of ONKALO with the final disposal facility The ONKALO rock characterisation facility is designed to later serve as part of the repository for spent nuclear fuel (Figure 3-4). The repository concept may be based on KBS-3V (canisters in the vertical position) or KBS-3H (canisters in the horizontal position) and disposal may take place on one or several levels. The repository layout will consist of panels each comprising a set of disposal tunnels.

Figure 3-4 Example of layout adaptation with repository

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4 CHARACTERISATION PROGRAMME This chapter gives an overview of the ONKALO characterisation programme. The characterisation serves the dual purpose of supplying information necessary for the construction of ONKALO as well as for detailed characterisation of the rock volumes surrounding ONKALO. The actual investigation methods will be described in Chapter 5 and the associated monitoring in Chapter 6. Furthermore, the acquired information needs to be interpreted and modelled. This is described in Chapter 7.

4.1 Characterisation strategy Based on the overall objectives, specified in Chapter 2, the strategy for characterising ONKALO rock volumes and a typical repository host rock aims at investigations that integrate the different disciplines, and are also adapted to the construction and excavation work. Most of the planned underground investigations serve both research and construction purposes.

The characterisation facility will be constructed in a rock volume estimated to meet the requirements specified for repository host rock. The large geological database acquired so far, compiled in the Baseline report (Posiva, 2003a), and the preliminary layout design of the ONKALO facility and the repository form the background for the strategy. The following facts also affect the characterisation programme:

• The programme will be conducted in stages following the excavation of the underground facility as presented in the R&D Programme (Posiva 2000, see also Figure 3-2 and Figure 4-1). According to current plans the construction of the access tunnel will start in 2004, detailed characterisation at the disposal depth will start in the beginning in 2008 and the application for the construction license will be submitted in the early 2010�s.

• The characterisation activities are planned such that disturbances on the site are minimized and the plans will be revised and adapted to the observations made along the tunnel.

• Characterisation should cover the different disposal alternatives, such as a one or two-storey repository layout, and the alternative disposal techniques still under development.

• Investigations will first be focused on the 2 km2 area planned for the repository. This area is also the area best covered by the surface based investigations.

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Figure 4-1: Main stages of construction and characterisation

The characterisation programme will develop stepwise as the underground excavation proceeds, based on the investigations and updated models of the site at different scales. Initially, the focus of the characterisation programme and rock modelling will be on the volume around ONKALO itself. Later the focus will shift onto detailed characterisation of the rock mass intended for host disposal tunnels, i.e. outside the ONKALO region. The characterisation process can thus be considered a diverse learning process, in which knowledge from different sources is compiled to better understand the rock conditions most important to the construction and long-term safety of the final disposal repository. The current understanding of the site as compiled in the Baseline report (Posiva 2003a) is an obvious starting point for this process.

The current phase of characterisation and modelling will thus:

• demonstrate that detailed characterisation of a volume of rock covering a typical disposal panel can be carried out from the tunnels before excavation commences

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and, in particular, devise means of detecting larger fracture zones and significant minor fracture zones before they risk being penetrated by the tunnel being excavated,

• provide the information needed for a �classification system� for different volumes of rock, in accordance with the STUK Guide YVL 8.4 on long term safety of spent nuclear fuel disposal (STUK 2001),

• produce a geoscientific model encompassing ONKALO volume's geology, rock mechanics, thermal properties, hydrogeology, hydrogeochemistry and migration properties, including a rock volume suitable for disposal use.

The rock volume characterisation should also assess the reliability of the model descriptions by applying procedures that can be used to test and confirm and demonstrate the progress made in the level of understanding of the rock mass.

The identification of suitable disposal volumes requires the establishment of criteria or guidelines for locating disposal tunnels and deposition holes. Such criteria are currently being developed as part of the programme �Host rock properties and classification.� Some results of this work have already been published. Hagros et al., (2003) consider the properties of the host rock and how they influence both the long-term safety of the disposal system, the layout of the repository and the constructability of the rock mass, concluding that the following rock mass properties are important:

• Fracture zones provide the most significant controls over the location of the disposal tunnels. It is essential to develop an understanding of the major fracture zones in the entire repository volume. Smaller features may control the layout of specific disposal tunnel sections and the distribution of the deposition holes.

• The location, orientation and hydraulic properties of hydraulically conductive features and the network they form are significant factors to be taken into account in the location of the deposition holes.

• The in situ stress and rock strength, in particular the strength/stress ratio, will play a significant role in controlling the depth of the repository and in the orientation of the disposal tunnels.

• Groundwater composition, salinity in particular, also has potential impact on the repository depth.

Consequently, the underground characterisation programme primarily aims to explore these factors. On a general level these important factors have been well established in the programme for a long time, see e.g. Posiva (1999) or Andersson et al., (2000).

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4.2 Stage 1: Surface based investigations

4.2.1 Investigations needed for construction

During 2001-2003 surface investigations were conducted in order to locate the ONKALO access tunnel in a rock mass of suitable quality. Alternative locations for the tunnel portal at Olkiluoto have been explored. Further detailed and supplementary surface investigations will be conducted before the construction commences and at the initial stages of the tunnelling work. Table 4-1 presents the surface investigations needed for both the construction of the access tunnel and for the determination of baseline conditions on the construction site.

Table 4-1 Stage 1: Surface based investigations to support construction

Investigations Obtained knowledge

Percussion drilling and refraction seismic surveys.

The location of rock surface beneath the overburden. Rock quality of the bedrock at the surface.

Core drilling: geological investigations with core logging and possibly also borehole-TV / video surveys.

Identification and intensity of fractured zones, fracturing, fracture filling, rock types and foliation.

Geophysical borehole investigations (single hole and cross-hole).

Identification (orientation and continuity) of discontinuities and other inhomogeneities.

Investigation trenches. Location of fracture zones. Fracture pattern in the upper part of the bedrock.

Hydrogeological investigations: hydraulic conductivity measurements, pressure monitoring, interference tests, cross-hole tests and possible tracer tests.

Hydraulic conductivity data in the ramp area. Identification of fractures and fracture zones with high rates of groundwater ingress.

Hydrogeochemical sampling. Groundwater chemistry at different depth levels (pH, Eh, salinity (EC, TDS), main cations and anions, dissolved gases and isotopes).

Rock mechanics investigations (rock stress measurements using the overcoring method and laboratory testing on core samples).

In situ state of stress at different depth levels, strength and deformation properties of the rock prior to ONKALO construction.

4.2.2 Characterisation

Most of the surface based investigations primarily performed to support construction (see Table 4-1) are also utilised for characterisation and modelling activities. As these investigations concentrate on the ONKALO area, investigations on the outskirts of the possible repository area and studies to determine site-specific geological features are also to be done during 2003-2005. Furthermore, the monitoring of hydrological,

29

hydrogeochemical parameters and rock movements is continued in order to characterise the baseline of the site before the construction work begins.

At this stage characterisation will produce:

• information to support the decision of the location of ONKALO's access tunnel,

• a description of the selected construction site, and

• an enhanced knowledge of the entire repository volume.

Surface-based investigations will continue during all the stages, including studies of surface properties as well as investigations from deep boreholes. There are four main reasons for additional surface-based investigations in boreholes:

• Characterisation of the upper parts of the rock mass around the access tunnel and the shaft and to locate and characterise fracture zones that the tunnels or shafts could potentially intersect. Excluding major features that influence the main characterisation level is of particular importance.

• Characterisation of deep bedrock properties in advance from a few boreholes, by means of for example rock mechanics studies and groundwater sampling from the anticipated depth, might be required. Further drillings from the surface down to a depth of more than ca. 300 m have to be considered carefully in order to minimise possible flow routes between the repository depth and surface.

• Enlarging the potential repository area, as the underground boreholes from ONKALO cannot cover the entire volume needed for the estimated amount of spent fuel to be disposed. A supplementary characterisation programme to examine additional areas of interest will be carried out.

• Regional surface based studies would supply additional understanding of the regional setting and properties.

Apart from additional boreholes with related investigations and continued monitoring in the existing boreholes, additional surface-based geophysical measurements, such as reflection seismics, will be carried out.

4.3 Stage 2: Investigations during construction of the access tunnel During stage 2 the access tunnel to the underground characterisation facility is being built. Stage 2 investigations provide complementary and detailed information about the host rock and also include monitoring of disturbances caused by the construction activities. Most of the stage 2 investigations related to construction aim to ensure successful excavations, reinforcement and sealing and are also used in ordinary tunnelling projects. Some of the investigations are specific for this project, such as the pilot core holes along the tunnel profile (see section 4.3.1). When the access tunnel

30

progresses deeper, specific attention will be paid to the impact of high groundwater pressure on the construction and investigations activities.

Investigations essential for the construction activities can be divided into probing, mapping and drilling of pilot core holes. Again, most information acquired for construction purposes will be essential also for characterisation. Additional investigations for pure characterisation purposes will also be carried out. These comprise essentially drilling and exploring specific characterisation boreholes, additional tunnel mapping and monitoring.

4.3.1 Boreholes drilled from the tunnel

Boreholes are drilled to assist in the construction of the access tunnel and other facilities, as well as for the characterisation of the repository site. The boreholes can be divided as follows:

• Probe holes

• Pilot holes

• Characterisation holes

All water for underground drilling will be tagged with an Uranine-tracer to distinguish �undisturbed� groundwater from production water.

Probe holes

Probe holes are short holes, typically 10-25 m, to be drilled by the drill rig forward from the tunnel face. The primary use is to estimate the need of pre-grouting and rock support, and to plan the drill and blast pattern. Also, borehole video data can possibly be utilised for assessing certain rock properties before the excavating the next round.

Apart from the drilling of probe holes, probing includes hydraulic tests and possibly a video survey of the holes. The primary purpose of probing is to estimate the need of pre-grouting and to select the most appropriate grouting material and grouting pattern. Data from hydraulic tests and video surveys are used to locate and initially characterise transmissive fractures and fracture zones and to establish the hydraulic conductivity of the rock mass (e.g. Lugeon value, pressure observations). Hydraulic injection tests are proposed to be carried out at two or three different pressure levels. The possibility to use flow logging in probe holes will also be tested in the beginning of the excavation of the access tunnel. In addition, data on drilling rate, drill cuttings, drilling water pressure, the colour of sludge water and the rate of water loss provide additional information on rock properties which can be utilised in the excavation procedure to some extent.

The probe holes will be drilled systematically in ONKALO. According to the current plans two to four probe holes will be drilled after every 4th round (round length 4.6 m). The length of the probe holes typically varies from 10 to 25 m with an average overlap

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with the next probe hole set of at least 5 metres (see Figure 4-2). According to the current plans the probe holes can be drilled outside of the tunnel perimeter (some 4-5 m off the tunnel sidewall at the end of the hole) at least down to a depth of 300 m. Below the 300 m depth they will only be drilled inside the tunnel perimeter in order to avoid shortcuts for groundwater flow.

The decision on pre-grouting will be made after the borehole survey. The purpose of pre-grouting is to minimise the ingress of water into ONKALO to avoid disturbances on groundwater chemistry and draw-down of the groundwater table as well as to improve the general underground working conditions.

Figure 4-2 The principle of probe hole drilling in the upper parts of the access tunnel (above - 300 m). Probe holes can be drilled partly outside the tunnel perimeter in the access tunnel in order to limit ingress of groundwater. The overlapping section of adjacent probe hole groups is at least 5 m.

Probe hole drilling and related borehole investigations in deeper parts will be of special importance if water-bearing fractures or fracture zones are intersected. Due to the high water pressure at these depths packers or other methods will be needed in order to control inflow of water into the tunnel.

Lengt of the probe holes 10-25 m

Round 1

Round 2

Round 3

Round 4

Round 1

Round 2

Fracture/fracture zone �intersecting the tunnel

Fracture/fracture zone �adjacent to the tunnel

Overlapping section of�

adjacent probe hole�

groups (5 m)

� �

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Pilot holes

Pilot holes are cored boreholes to be drilled along the tunnel profile. The length of the pilot core holes typically varies from several tens of metres to a couple of hundred metres. The pilot holes will mostly aim to confirm the quality of the rock mass for tunnel construction, and in particular at identifying water conductive fracture zones and at providing information that could result in modifications of the existing construction plans (i.e. they are an integral part of coordinated investigation, design and construction activities, see section 3.2). The pilot holes will be also used for the comparison of the drill core and the tunnel sidewall mapping, particularly on the characterisation levels.

Furthermore, at the repository construction phase, long pilot holes (200 � 250 m) will likely play an important role in the assessment of rock mass conditions before the disposal tunnels are excavated. For this reason, it is important to gain as much experience as possible of their use at an as early stage as possible. A number of pilot holes will thus be drilled already in parts of the access tunnel. Decisions on the location of these pilot holes will be based on the bedrock model and other relevant data, possibly assisted by statistical analyses. Such boreholes may, for example, be drilled into major fracture zones or other structures of interest.

Pilot holes will only cover part of the access tunnel. According to the current bedrock model and the latest layout about 1200 m of pilot holes are needed above the main characterisation level. The pilot holes in ONKALO will be drilled inside the tunnel profile to avoid disturbances in the surrounding rock mass. This will interrupt the construction schedule and this has to be included in the contract documents.

Characterisation holes

Characterisation holes are cored boreholes drilled from the tunnel or from a separate niche, and directed outward from the tunnel. Their purpose is to characterise larger volumes of rock.

The location of the characterisation holes is more flexible than of the pilot holes. The drilling of such boreholes will not be allowed to interrupt excavation work so the drilling sites need to be located in the niches or other enlargements of the access tunnel. For the ramp section of the tunnel the most suitable sites would be the corners of the ramp, with the boreholes directed outward to reach distant parts of the rock mass surrounding the tunnel and the ramp area. The corners are also appropriate locations for drilling of pilot holes running parallel with the line of the tunnel. Niches should be located in the rock between fracture zones. Their size will depend on the drilling equipment used, but they should be large enough to accommodate all the necessary activities related to drilling.

The drilling of long boreholes underground differs greatly from drilling from the ground surface. The Strategy Report (Saksa et al. 2003) discusses the requirements related to the boreholes, with respect to:

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• groundwater inflow and stability of a borehole - how inflows are to be handled, borehole stability and avoiding the creation of short-circuited flow routes,

• sealing of boreholes,

• borehole deviation and length.

The experience gained from the Äspö HRL and from other underground excavations will be used in the planning of the borehole drilling programme.

Techniques for borehole investigations are well established. All characterisation holes (and some of the other holes as well) will be subject to a basic investigation package comprising:

• core mapping, sampling and laboratory tests,

• fracture mapping and mapping of fracture mineralogy,

• geophysical measurements including resistivity, acoustic, magnetic and temperature logs,

• reflection seismics with high (kHz) frequency, cross-hole, tunnel-to-borehole,

• digital borehole-TV imaging (optional),

• flow logging (part of hydrology, see section 5.3.2).

A selection of boreholes and cores will be subject to additional measurements such as:

• rock mechanics measurements (see section 5.2.2),

• directional borehole radar,

• interference and other hydraulic tests (cross-hole flow logging) between boreholes (or between packed off sections) and pressure monitoring

• other cross-hole geophysical measurements (electrical, high frequency electromagnetic) and hydraulic experiments,

• seismic tomography,

• groundwater chemical sampling (part of geochemistry, see section 5.4.2),

• rock movements, microseismic measurements (see also section 5.2.2).

4.3.2 Tunnel mapping

Tunnel mapping is integrated with construction activities. In practice, geological mapping will primarily be carried out during probing and the pre-grouting and drilling of blast holes or charging. This tunnel mapping is divided into two steps (see Figure 4-3):

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• Step 1: Tunnel face mapping. Every round will be mapped prior to temporary reinforcement. The duration of face mapping varies between 0.5�2 h.

• Step 2: Tunnel window mapping. Window mapping will be carried out after every fourth round. Mapping the walls and the roof will take about 8 hours. Window mapping can be carried out simultaneously with probing and pre-grouting but before permanent reinforcement.

In special cases, for example where the tunnel intersects a highly transmissive fracture zone, the situation will be considered on a case-by-case basis (an example of coordinated investigation, design and construction activities). Simplified mapping, like digital photos, or other means of immediate mapping before reinforcement, will be used if an essentially immediate reinforcement of the fracture zone is needed.

For characterisation purposes supplementary studies (�Step 3�) and mapping may be carried out. Step 3 investigations consist of detailed and supplementary investigations for special characterisation and research purposes (see section 5.1 and Saksa et al. 2003).

Figure 4-3: The principle of mapping steps (from Saksa et al. 2003).

Tunnel face mapping

Step 1, tunnel face mapping consists of preliminary geological mapping, digital photographing or video scanning. Ingress of groundwater, failures (e.g. spalling) and water conductive fracture zones will be inspected and reported. Face mapping is carried out after temporary reinforcement. Important geological characterisation data will also be obtained from the tunnel face. However, more detailed mapping will be carried out in step 2.

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Window mapping

Step 2, tunnel line/window mapping includes geological and rock mechanics mapping, photographing and/or digital imaging (scanning). Samples may also be collected. The main emphasis is on documenting the tunnel walls for characterising the ONKALO host rock with a secondary objective to assist in determining the level of permanent support. The investigations require that the tunnel sidewalls and roof have been properly washed, temporarily supported and that a precise co-ordinate grid is provided. Powerful lighting and a mobile platform are also needed.

Step 2 mapping covers the walls and the roof of the tunnel. To develop a comprehensive understanding of the geological features, the tunnel floor should be mapped in certain sections of the access tunnel. These sections can include floors under water collecting dams and certain special sections in the access tunnel.

In summary. step 2 investigations cover:

• rock types and their properties (grain size and texture, colour and alteration, degree of weathering, foliation and folding),

• sampling (rock types, fracture filling, groundwater),

• structural geological mapping (both ductile and brittle structures),

• fracture data (position, frequency, orientation, fracture trace length, type of fracture, aperture of open fractures, thickness of fracture filling, filling material, alteration and weathering, shape of fracture and roughness),

• water leakage and chemical characterisation (see also section 4.3.3),

• rock quality boundaries,

• determination of the Q´-value or the Q-value (modification of Q-value for deep tunnels should be taken into account in the deep parts of the facility),

• stress failure or damage to the tunnel surfaces.

If a fracture (or a fracture zone) shows any features of faulting, additional information will be gathered, e.g. fault plane orientation, fault displacement vector, sense and amount of displacement, indications of block rotation, physical characteristics of faulting (description of gouge, brecciation, damage zone, etc., including mineralogy, sampling), width of crushed zone and damage zones, relation between fracturing in the fault damage zone and fractures in the surrounding rock mass.

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Monitoring of impacts of construction work

Apart from tunnel mapping, the tunnel will also be inspected and monitored for impacts of the construction work. This includes exploring the development of EDZ and the time dependent behaviour of excavated tunnel surfaces (see Chapter 6 for further details).

4.3.3 Additional characterisation activities

During stage 2 the surface based studies are continued, but tunnel mapping and monitoring of changes induced by the excavation of the access tunnel will provide new information also for characterisation purposes.

At this stage investigations will focus on ensuring that the characterisation levels will be located in good quality rock. A particular goal is to exclude the possibility of major zones intersecting the main characterisation level.

Fracture zone and rock mass characterisation

Pilot holes will be drilled, where the tunnel is expected to intersect an important fracture zone. Measurement results from the pilot holes will be compared with the tunnel mapping results, providing the first opportunity to test the host rock classification system and possibilities to upscale borehole data to tunnel scale.

Fracture zones that the tunnel is estimated to intersect for a second time at a greater depth will be instrumented and characterised in more detail. The same level of interest will also be applied to wider (> 5 m) fracture zones and large fractures if they dip towards the main level area of ONKALO. A small number of additional short holes will be drilled, and basic logging (geophysics, digital borehole imaging), chemical sampling and flow measurements will be carried out. Geophysical techniques for identifying major fracture zones before a borehole or a tunnel intersects them will be tested and their functionality evaluated. Figure 4-4 illustrates the consequences of a tunnel intersecting a fracture zone and the time spans and predictions regarding later intersections with the tunnel (for more detail see Saksa et al., 2003).

To date, fracture zones have been categorised using partly the Finnish engineering geological classification system (Korhonen et al. 1974, Gardemeister et al. 1976), but also other parameters have been involved. A new system for classification of fracture zones will be developed in the Host Rock Classification project (Hagros et al. 2003) discussed previously. It will mainly be applied to defining respect distances to modelled fracture zones, but the classification system will also allow tunnel sections to be classified as probable fracture zone intersections, when new (unmodelled) fracture zones are encountered during tunnelling. Thereby the fracture zone classification will fit the coordinated investigation, design and construction activities.

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Figure 4-4 Characterisation and prediction of a fracture zone intersected by a tunnel

Additional characterisation boreholes drilled outward from this section of the access tunnel toward major fracture zones or other hydraulically significant features need to be avoided because of the risk of substantial inflows of groundwater. The investigation of these near-surface zones can instead be easily carried out from surface-based boreholes. Grouting used to minimise ingress of groundwater will also prevent hydrogeological and chemical studies taking place directly from the access ramp, but nearby surface based boreholes can be used instead. Investigations will take place at locations that are judged to be hydraulically important, and where the monitoring network indicates hydraulic connections to the tunnel or where changes in flow are thought likely to occur.

Geochemical groundwater sampling and monitoring

Geochemical groundwater sampling and monitoring (see also section 5.4) should be performed prior to excavations from existing surface based boreholes. After the excavations sampling and monitoring will also cover the water flowing into the tunnel. Monitoring will focus on salinity, pH and redox parameters as well as on the possibility of inflow of oxygenated and CO2-rich water. In addition, the evaluation of surface water inflow into the tunnel is of interest and exploration of suitable tracers is included in the programme. Continuous monitoring stations will be set up in the tunnel at intersections with flowing fractures. Other activities are occasional or on-demand based (e.g.

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complete characterisations, flammable or radioactive gases, etc.). For example, complete chemical (see section 5.4) characterisations will be done if remarkable changes are noticed on regularly measured geochemical parameters or in order to get detailed information for site characterisation purposes.

Groundwater flow monitoring

Groundwater flow monitoring will involve the installation of weirs for measuring the ingress of groundwater. A basic set of measuring weirs is planned to consist of a weir installed at the lower end of each straight tunnel section (length 200 - 300 m). At tunnel bends the tunnel is widened and the weirs installed just above the widened part. Additional weirs will be constructed to measure the flow from individual fractures or fracture zones. The total frequency of measuring weirs is estimated to be one per 100-200 m of tunnel length, but in favourable situations, where the rate of groundwater inflow is small, this frequency may be reduced. Similar measurements will be carried out in the shaft with special measuring rings.

The selection of monitoring points of inflow on the walls and the roof of the tunnel will be carried out on a case by case basis. To obtain an overview of the ingress of groundwater into the tunnel, measurements need to be performed also in the rock between the fracture zones. The water content of the ventilation air may also need to be considered.

Modelling

Modelling, see also Chapter 7, is to a large extent a continuous activity, as new information gets available. However, for the model integration and consistency checks it is also essential to define suitable milestones, or �data freezes� where different disciplines use all data available at a certain time.

The access tunnel enables characterisation of geological features and determination of rock properties (descriptive modelling, see section 7.1.2) at a smaller scale than has been possible previously. A suitable milestone for the integrated assessment is to produce an integrated model based on the data from the upper part of the access tunnel, possibly after a depth of about 300 m has been reached, see Chapter 7. In order to do this, the data from the characterisation and monitoring programmes (e.g. hydrology, chemistry, microseismics, GPS) are integrated with the structural model. Predictions of rock properties along the next ramp section would be a good way to test the level of knowledge of the site and the prediction capabilities. The information, including the results of the comparison between model predictions and the data assembled later, will also be used to test and modify, where necessary, the rock mass classification system specific to Olkiluoto (see e.g. Hagros et al. 2003).

At the end enough knowledge will have been acquired to decide the location, area and depth of ONKALO's characterisation levels and other facilities. This stage is also

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important in the learning process and for the further development of the characterisation methods.

4.3.4 Characterising the main level from the access tunnel

Characterisation of the main level of ONKALO, representing a rock volume typical of the repository near-field, can start when the tunnel reaches a depth of approximately 300 m and the emphasis will be on a depth range of 400 - 500 m. Investigations will be performed from tunnels, drifts and boreholes. Investigations will be carried out in campaigns and borehole-to-borehole measurements will be utilised extensively. The purpose of the drifts is to cover larger areas and to enable characterisation activities without disturbing construction work.

Borehole investigations from the access tunnel

Tunnel mapping and monitoring activities together with boreholes drilled from the tunnel and the associated measurements and analyses form the basic set of investigations. Below the �300 m level the number of surface-based boreholes drilled to characterise ONKALO or the repository volume will diminish. Underground surveys minimise the possibility of hydraulic connections between the surface and the repository area and are therefore more favourable in terms of long-term safety. The shorter length of boreholes required is also a clear advantage. Some surface-based boreholes within or close to the tunnel (distance less than 100 m ) can be used for cross-hole/tunnel studies or for monitoring purposes. Their presence will allow correlations to be made between data obtained from the surface and from underground. The measurement of rock mechanics, hydrogeological and hydrogeochemical data is planned to take place simultaneously in the tunnel and in the boreholes.

Pilot holes will be drilled more extensively along the tunnel line. Pilot holes at this depth range will be important for the development of the rock classification system before entering the main level and comparing the borehole and tunnel data. For the tests data on at least a couple of hundred metres of borehole length is needed. The pilot holes enable groundwater sampling, and especially salinity, potential inflow of oxygen and CO2-rich waters should be monitored, as well as pH and Eh. Other tracers could also be included in the programme for the evaluation of potential surface water components in the inflowing water. At the planned repository depth, in addition to salinity, pH and redox parameters there is a need for detailed analyses of major components of groundwater, which are of importance for the long-term behaviour of tunnel backfill, buffer, canister and spent fuel.

Apart from pilot holes, there will be several characterisation boreholes drilled from the access tunnel to explore rock conditions and allow groundwater sampling on the main characterisation level and in the possible repository area. In order not to interfere with excavation work special niches or even short tunnels are required for the drilling and it is estimated that at least 10 niches will be needed along the access tunnel. According to

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the current plans the access tunnel will make borehole characterisation possible on the main characterisation level, to choose favourable locations for the drilling of the characterisation holes. Boreholes will only be drilled from the access tunnel to or slightly below the main level in locations below major sub-horizontal zones.

There are three major objectives to be achieved with the boreholes (see also Figure 4-5):

1. Observations from tunnels, boreholes and associated surveys should provide information on zones that affect the layout of the characterisation tunnel area on the main level of ONKALO and therefore require special attention in subsequent underground work. In particular, the location and orientation of any vertical or steeply-dipping fracture zones should be determined accurately, so that major zones can be avoided and taken into account in the planning of subsequent stages of ONKALO. Horizontal zones are important in determining the depth level of ONKALO, but major horizontal zones should already be known after surface based investigations. This is depicted with drilling activities labelled with A in Figure 4-5.

2. Additional emphasis will be laid on investigating the different rock rooms and tunnels immediately linked to the shaft on ONKALO's main characterisation level, see Chapter 3. The boreholes have to be directed steeply toward the rock rooms (item B in Figure 4-5). They will be vertical and penetrate the main characterisation level. The possible surface boreholes on the shaft site will also assist underground characterisation.

3. The third objective is linked to the continuation of the access ramp into a depth of 300 � 400 m. Pilot drillings with a gentle dip along the tunnel will be carried out to study expected intersections of the tunnel with fracture zones. A sub-horizontal borehole along the tunnel marked as C in Figure 4-5 serve an example for these pilot holes.

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Figure 4-5. Lower access tunnel parts with potential exploration holes at -300 m level and an example of a pilot hole.

Modelling

At least 6 - 9 months can be spent on the performance of investigations from the access tunnel toward the main characterisation level before the excavation reaches the main characterisation level. This time will be used for the interpretation and analysis of the results, as well as for making predictions about the conditions on the main level for the tunnel design. With the access tunnel at 300 - 400 m depth, investigations are likely to add new results to be assessed before deciding on the final orientation and shape of the characterisation tunnel and construction can then begin according to the revised plans.

The ventilation shaft itself, together with associated geological mapping and other observations will produce data at a larger scale than what has been obtained from the boreholes in its vicinity. The results obtained from the construction of this shaft can be compared with the predictions made beforehand and used to test the models of the site.

4.4 Stage 3: Investigations during construction of the characterisation levels

Stage 3 is aimed to �produce detailed site information necessary for the safety assessment and detailed design of the repository as needed for the application for construction licence� (Posiva 2000). The research tunnels at the main characterisation

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level will be excavated into a volume of rock considered to represent typical repository host rock.

4.4.1 Investigations needed for construction

The basic construction-related investigations, such as probing, are basically the same on the main and lower characterisation levels as in the access tunnel. The plans for the investigations to be carried out on the main and lower characterisation levels still need to be updated before stage 3. Again, most information acquired for construction purposes will also be essential for characterisation.

Mapping at this stage follows the guidelines set out at stage 2 (see section 4.3.2). The details of the mapping parameters will be defined later, based on the experience gained from access tunnel mapping. In order to characterise the first set of potential repository tunnels an Olkiluoto-specific host rock classification system (see section 4.1 and Hagros et al. 2003) will be developed, tested and applied to ONKALO.

Other investigations on the main and lower characterisation levels are divided into regular and more specific investigations. Continuous monitoring of groundwater ingress rates will be carried out on the main and lower characterisation levels and will not disturb other activities.

Pilot holes will play an important role on the main characterisation level to prevent the tunnels from unexpectedly intersecting fracture zones, which would result in large groundwater inflows, and to make it possible to consider such intersections in advance and carry out appropriate pre-grouting. According to the current plans all the research tunnels need to be explored by means of pilot holes before construction. Pilot holes are also fundamental for acquiring reliable in-situ data on the host rock. The boreholes must be designed, assessed and constructed so that disturbances to the host rock (e.g. undesirable hydraulic connections, uncontrolled leakages, etc.) are minimised and the natural integrity of the host rock is not jeopardised.

Special investigations and tests will be carried out during construction phase 3. For example, full scale tests on excavation and sealing methods may be possible before phase 3 excavations are started. In addition, investigations on the response of the rock mass to the construction activities will be carried out in a controlled environment in a specially constructed tunnel loop, in order to increase the knowledge of the rock mechanics of the site (see section sections 5.2 and 6.3.2).

Investigations made in the ventilation raise

The exact location of the shaft will be confirmed on the basis of surface investigations. For construction purposes, the shaft area can be investigated by drilling and borehole investigations.

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The raise bored shaft can be surveyed before commencing shaft slashing to provide detailed geological and rock mechanics data on the surrounding bedrock. During shaft slashing mapping (similar to Step 2 mapping in the tunnels) can be carried out before permanent reinforcement. In special cases, the shaft will be mapped immediately. Water measurement rings are installed below hydraulically conductive features.

4.4.2 Characterisation on the main and lower level

Characterisation on the main and lower characterisation levels will essentially include the same measurements as on the higher parts of ONKALO, but the degree of detail will increase since this part of ONKALO is at the proposed repository depth. The studies will also concentrate on characterising the rock intended for the first disposal panels and finding suitable methods for the characterisation. Tunnel mapping and monitoring will continue.

Investigations

Further details of the characterisation plan will be decided on as the characterisation work proceeds. In further planning the following factors should be considered :

• a large amount of new data will be available before the repository level is reached,

• new requirements may arise regarding characterisation, demonstration and confirmation activities,

• the waste disposal concept is under development,

• the criteria and safety-related requirements for underground construction are to be further developed,

• instruments, data acquisition and processing techniques will evolve.

Based on the earlier characterisation activities the degree of knowledge and understanding of the conditions on the main characterisation level is likely to be high on the site and at local scales (features at a scale of 100 m) before construction begins on this level. The degree of detail achieved will to a great extent depend on how representative, comprehensive and well analysed the results from investigations carried out from the access tunnel below -300 m are at the time.

The entire length of the main characterisation level will be explored by means of pilot holes. The host rock classification method based on comparing the observations from the pilot holes with those made from the tunnel will be tested as will also methods for detecting features that make the use of a certain rock block unsuitable for the deposition.

The results from the volume characterised in detail will be compared with the earlier assumptions and predictions. Predictions will be made and compared with the outcome

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of the investigations regularly to demonstrate and build up confidence in the understanding of the rock conditions. Also a comparison between the properties of a representative subsurface volume and surface based information can be performed.

The investigations on the lower level will mainly aim to explore the possibility of a two-storey repository alternative. The lower level will consist of short tunnels used to study whether the rock mechanics properties in particular and the salinity of the groundwater allow the construction of the repository on two levels.

Modelling

When the construction of the main level of ONKALO is completed, the tunnel and borehole data will be analysed, interpreted and integrated with earlier observations and geoscientific models (see Chapter 7, for details on modelling approaches). This will provide the basis for the planning of a preliminary safety analysis and a detailed characterisation of the disposal tunnel areas and individual tunnels. It will probably take a minimum of one year after the completion of the tunnel loop before the characterisation programme, the analysis of its results and the associated modelling will be finalised.

4.4.3 Characterising the intended repository area from ONKALO

According to the draft design, the first disposal tunnels can be drilled from the main level tunnels of ONKALO. Should anything be encountered, which would prevent the use of the volume investigated from ONKALO as part of the repository, the investigations will be expanded to new areas. The characterisation holes from the access tunnel will already cover the potential volume for the first disposal tunnels. If building the repository connected to the ONKALO proves appropriate, pilot drillings for the first disposal tunnels can be performed from the characterisation loop. The estimated distance between the holes, to be suitable for cross-hole studies, is 50 to 200 m.

There are alternative methods of local- and detailed-scale characterisation of the main and lower levels and the experience gained can be utilised in characterising the other parts of the repository. They are discussed with examples by Saksa et al., (2003). In short, these alternatives are:

• Using two levels for characterisation; with a separate characterisation tunnel constructed above the target area. The target area will be investigated by drilling boreholes from the upper level and by performing different surveys to characterise the lower level. If the ONKALO facility is built according to the current plans this technique could be tested and finalised, as part of the access tunnel will run above the main level tunnel.

• Characterising the rock volume from one level, using a characterisation tunnel or a pair of tunnels and (sub-) horizontal boreholes in them. Again, cross-hole soundings can be made between the tunnels and holes to cover larger areas. Surface based

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boreholes will produce additional data. This type of approach is suitable, when larger underground areas are to be investigated and the bedrock above is not to be inferred. This approach is very likely to be used for the characterisation tunnels at the repository level (one storey repository) or at the upper repository level in the case of a two-level repository. Also, if the access tunnel is located so that no tunnel section runs above or within reach of the main level tunnels, the main characterisation level has to be characterised by applying this approach.

Another issue is whether the characterisation programme on these levels is to be based on a direct approach or on an observation-based adaptive approach. The direct approach would mean that the main level tunnel loop would be constructed in a straightforward manner, with a design that was determined in advance, based on the results obtained from the access tunnel. Research along the tunnel will only marginally affect its construction. With the observation-based and adaptive approach of the coordinated investigation, design and construction activities, the final design of the excavation would be decided in stages, based on the findings of the characterisation programme.

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5 UNDERGROUND INVESTIGATION METHODS This chapter presents the underground investigation methods to be applied within the different geoscientific disciplines, i.e. geology, rock mechanics, hydrogeology and hydrogeochemistry. For each discipline this chapter aims to describe the objectives of the investigations and the proposed measurements. The evaluation of this information and the descriptive modelling (i.e. modelling made for characterisation) is covered in Chapter 7.

5.1 Geological investigations Geological investigations, i.e. geological mapping and borehole drilling, and associated measurements in boreholes, form the basis for the bedrock characterisation programme to be carried out in the access tunnel and other underground spaces. Although the methods have already been used in surface investigations, several new aspects must be taken into account when adapting them to underground conditions, e.g. restrictions set by construction activities and, especially, the high groundwater overpressure relative to the tunnel that will influence borehole operations.

5.1.1 Objectives

The objectives of geological characterisation are:

• to enhance the understanding of geological features and processes (geologic evolutionary history of the site),

• to update the geological database

• to update the current bedrock model while considering the information needed in hydrological, hydrochemical and rock mechanics analyses,

• to provide data for tunnel construction,

• to test investigation methods most suitable for detecting and characterising fracture zones to be avoided in the construction of repository tunnels and disposal holes.

5.1.2 Measurements - Data

The geological characterisation carried out from the tunnels will mainly comprise:

• Geological mapping of tunnel walls, roof, floor and faces.

• Drilling of boreholes from the tunnel.

• Borehole investigations.

• Testing techniques for identifying potentially problematic fracture zones before a borehole or a tunnel intersects them.

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Most of these basic characterisation methodologies have already been outlined in Chapter 4 (sections 4.3.1 and 4.3.2) and will not be repeated here. Some additional remarks can still be made.

Geological mapping

Tunnel mapping is described in section 4.3.2. The underground investigation stage facilitates direct observations in three dimensions from the excavated rock surfaces, and thus provides more favourable conditions for characterising the geological features than surface outcrops or boreholes. Although the observations are local in nature and restricted to a tunnel with a limited cross-section, the continuous length of 4 - 5 km of tunnel will also help in investigating large-scale features. In addition, the shaft, the auxiliary rock rooms and the boreholes to be drilled from the tunnel will supplement and expand the information beyond the tunnel volume.

Geological mapping has three major goals:

• To assist in the overall rock characterisation programme for the design and construction of the ONKALO facility and the repository.

• To serve tunnel construction operations, and provide the necessary information for blasting, grouting and reinforcement measures (see Chapter 4).

• To document all the available data with particular reference to the tunnel sections, which are to be covered by shotcrete or concrete due to, for instance, poor rock quality. The documentation process is also needed in long-term maintenance of the tunnels and in monitoring.

As already mentioned, mapping will be performed in a stepwise manner. Steps 1 and 2 provide information to support construction work, but will also provide important characterisation information. Tunnel face mapping will not allow thorough observations, but will provide an insight into the geological conditions. Window mapping and sampling in Step 2 will constitute the main rock mass characterising phase and will also assist in the design of permanent rock support. The aim of this detailed geological mapping is to develop a better understanding of the geological environment of the repository area, and to provide data for the modelling of the most significant structures with respect to the design and construction of the ONKALO facility.

One of the key questions to be studied will be the relationship between tectonics and fracturing of the bedrock. Apart from the fracture zones, foliation is regarded as one of the main tectonic elements influencing fracture orientations, and hence, special attention will be paid to the observation of foliation.

After the detailed geological mapping additional investigations will still be needed to complete the rock characterisation programme. These supplementary studies constitute Step 3 and consist of activities, which might be more time-consuming, or which can

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only be designed based on the results of previous mappings. Typical activities for this supplementary study phase include the establishment of different measurement stations for monitoring and sampling.

All the mapping activities have to be carried out before the rock surfaces are covered by shotcrete, concrete or any other material that would hinder observations. This needs to be safeguarded in the tunnelling contracts and also calls for good co-operation between the construction and mapping staff. If mapping of the tunnel floor should be considered, it needs to be carefully designed before construction commences because of special requirements, such as manual cleaning of the rock surface. It would, therefore, be preferable to perform the floor mapping exercise not in the access tunnel proper, but somewhere else, such as in a niche, for example.

Boreholes and associated investigations

Boreholes will be drilled in connection with the construction of the access tunnel and other underground openings, and as part of the characterisation of the repository site. Different drilling techniques will be used for the boreholes, depending on the use that is to be made of them. Section 4.3.1 describes the various planned borehole types, i.e. probing holes, pilot holes and characterisation holes, and outlines the planned investigation programme in these holes.

Because of the heterogeneous and anisotropic nature of the Olkiluoto bedrock, a special methodology for data acquisition and processing will be developed, see section 7.2 in Chapter 7. This will be based on presently available techniques for borehole investigations, which are well established.

The drilling of boreholes, together with the associated measurements, will play a central role also in the underground characterisation of the rock mass and in the evaluation of the overall suitability of the site for disposal purposes. A comparison of the results from the boreholes with geological mapping that will take place during excavation will be an important part of the geological modelling. This will improve the reliability of predictions based on borehole information and promote the understanding of their uncertainties. As the characterisation of potential repository panels will be based on borehole data, this evaluation is crucial for reaching the overall objective of being able to characterise potential repository volumes. In addition, combining the data from boreholes with the data from geological mapping will serve as the basis for the observational method to be applied during construction, and also for the host rock classification.

Techniques for pre-identification of fracture zones

Geophysical techniques for identifying major fracture zones before they are intersected by a borehole or a tunnel will be tested and the functionality of the methods will be evaluated in site-specific conditions. Suitable techniques in this area include seismic

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reflection (high frequency kHz, ahead-of-the-bit and other configurations), electromagnetic surveys and radar reflection. All are applicable both to tunnel and borehole configurations.

5.1.3 Expected results

The further interpretation and use of geological data in geological modelling is described in Chapter 7. Geological characterisation including geological modelling should result in:

• understanding site geology and geological parameters that are of importance to the repository layout and the placement of disposal holes,

• a detailed description of the lithological and structural properties, including fracture statistics and fracture mineralogy, of the ONKALO volume as well as of the first panels of the repository,

• site models and detailed models of certain sub-volumes (see Chapter 7),

• tested data acquisition and modelling methods and

• better understanding of the relationship between geological and hydrogeological, hydrogeochemical and rock mechanics properties.

An important aspect is to understand the relation between the deterministic fracture zones and the fracturing in the rock mass between them. These are not two fundamentally different things, but instead two related aspects of the same phenomenon. What is regarded as a fracture zone and what is included in the rock model is a matter of scale. The object of description is brittle deformation at all scales, including geometry, kinematics and dynamics, not fracture zones and fractures in separate compartments. Geological characterisation will lead to enhanced confidence in the understanding of the bedrock and its properties at different scales and in different locations in the Olkiluoto area.

5.2 Rock mechanics and thermal properties The rock mechanics and thermal characteristics of the rock include mechanical properties of intact rock, of fractures, the rock mass and the fracture zones, the in-situ stress and the thermal properties of the rock.

5.2.1 Objectives

The strategy of the rock mechanics programme can be summarised as follows:

• Acquiring a sufficient amount of data in order to specify the mechanical properties and boundary conditions of the rock mass at Olkiluoto, especially at the anticipated depth of the repository. The quality of the data should be high enough to ensure sufficiently reliable rock mechanics analyses and modelling.

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• Developing and testing methodologies for characterisation of rock mechanics in the ONKALO context.

• Performing rock mechanics analyses in order to describe rock mass behaviour and to evaluate the mechanical stability of the disposal rooms during the excavation and operation of ONKALO and the repository. The rock mechanics programme is very important in the deeper parts of the repository where higher stresses are encountered in the rock. The results are needed for the repository construction licence, to prepare the technical plans for the repository and to confirm the constructability of the rock mass. The rock mechanics analyses will also support performance and safety analyses.

• Acquiring data and measuring the response of the rock mass during excavation and operation of ONKALO and the repository by means of the rock monitoring programme, to compare the measured results with the analysed data and to ensure the long-term mechanical stability of the disposal rooms.

Additional rock mechanics properties may need to be assessed to analyse long term mechanical stability. This will be discussed in future RDD programmes.


Hagros et al. (2003) discuss the effects of host rock properties on the long-term safety of the disposal system, the layout and location of the repository and the constructability of rock mass. According to the authors the most important rock mechanics properties at the repository scale are strength/stress ratio, orientation of fractures, foliation and in situ stress. At the tunnel scale, the report suggests that the most important rock mechanics parameters appear to be location of minor fracture zones, fracture frequency and frictional (strength) properties of fractures. Thermo-mechanical properties are also important.

If the stresses in tunnelling are sufficiently high in relation to rock strength (i.e. the strength/stress ratio is sufficiently low), damage in the excavation roof or walls becomes apparent, and may result, for example, in the loosening of slabs of rock, a process known as spalling (cf. borehole breakout). Based on preliminary pre-ONKALO rock mechanics analyses and on data from the surface investigations (Johansson & Rautakorpi 2000), this stress damage is probably only likely at depths exceeding 300 � 400 m, see Figure 5-1.

Rock mechanics research in ONKALO will mainly be focused on increasing the understanding of the in situ stress regime and the strength-deformation properties of rock. Excavation of ONKALO will provide an opportunity to conduct larger scale and more reliable tests to determine the in situ stress state, and will give a more detailed description of lithology at the repository depth to complement the rock strength-deformation tests. ONKALO will also provide an opportunity to study oriented samples

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for anisotropy tests and to carry out in situ testing to study the effect of scale on rock properties.

The thermal properties of the rock mass are needed for the dimensioning of the disposal panels and deposition tunnels and for the evaluation of thermal stresses caused by to heating.

In addition, mappings during the excavation of ONKALO will provide a more detailed picture of fracturing and foliation in the rock mass and will increase the reliability of rock mechanics analyses. Preliminary analyses of jointed rock at Olkiluoto have shown the importance of fractures in relation to the orientation and support of the tunnels (Rautakorpi et al. 2003). ONKALO excavations will also reveal fracture zones and provide opportunities to determine their properties to a greater degree of accuracy, which will allow a better assessment to be made of their effects on tunnelling and on long-term safety.

Figure 5-1: Calculated mechanical state of ONKALO access tunnel and corresponding maximum displacements. Results are shown at different depths for a case where the major in-situ stress is parallel to the tunnel (left) and for a case where the major in situ stress is perpendicular to the tunnel axis (right). Orange blocks indicate the location where crack initiation strength has been exceeded.

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Stress state

One essential input parameter in rock mechanics analyses as emphasised in previous chapter is the stress state. Stress measurements made underground mean shorter boreholes and more reliable results and boreholes can be more easily directed to the target area. Accordingly, stress measurements, using direct and indirect methods, will be made underground at the various construction phases of ONKALO as shown in Table 5-1.

Table 5-1 Stress measurements at various construction phases of ONKALO.

ONKALO phase

Stress measurement method Objective/outcome

Access tunnel 3D measurements in one deep borehole (a. 500 m) from surface at the ramp location (prior to excavation)

2D or 3D measurements short boreholes (a. 30-50 m) in rock mechanically important fracture zone, if ramp penetrates such zone (option)

rock response measurements in 3-6 cross-sections¨ at depth level of 300-500 m

mapping of possible stress induced damage

in situ stress state (magnitudes and orientations) at ramp depth of 200 � 500 m

stress state in the vicinity of a fracture zone

input values for ONKALO stability analyses

damages in access ramp

Main level 2D or 3D measurements in short boreholes (a. 30-50 m) and stress change monitoring in specific test tunnels

2D or 3D measurements with short boreholes (a. 30-50 m) in rock mechanically important fracture zone, if tunnels penetrate such a zone (option)

measurements of excavation responses in specific test tunnels

mapping of possible stress induced damage, AE monitoring in specific test tunnels

detailed understanding of in situ stress state at main level

secondary stresses and damages around tunnels

comparison with anticipated and modelled results

possibly more detailed understanding of stress state in the vicinity of a fracture zone

Lower level 2D or 3D measurements in short boreholes (a. 30-50 m)

mapping of possible stress induced damage

to check in situ stress state in �extreme� conditions, to ensure stability of disposal rooms

Shaft, raise etc. mapping of possible stress induced damage complementary information on orientation of major in situ stress component

Conventional, well-established techniques, such as overcoring and hydraulic fracturing, will be used as direct stress measurement methods. In medium long (50 m � 200 m) and long (200 m � 500 m) boreholes only overcoring will be used. In general, the long boreholes will be used to measure the in situ stress state far from the excavations and the short boreholes to control the loading condition (secondary stresses) around the near-field of tunnels and in the vicinity of fracture zones.

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Rock response measurements, stress damage mapping and Acoustic Emission (AE) monitoring will be used as indirect methods. In a rock response measurement method the in-situ stresses are evaluated by back calculating stresses from displacements caused by excavations (i.e. rock response). This method will be used to evaluate stresses in a considerably larger volume of rock (a scale of several metres) than in borehole measurements, and since these measurements can be carried out in the exact target area or at the target depth, they will give a more reliable estimate of the magnitude and orientation of the stress field. The rock responses are to be monitored in a few cross-sections in the access ramp and on the main level in specific test tunnels that are constructed for rock mechanics studies (e.g. a tunnel loop, in which case measurements can be performed in various directions with respect to the maximum principal in situ stress).

Another indirect method is the mapping of stress damage at excavation boundaries. If the stresses are sufficiently high in relation to rock strength, damage will be apparent round an excavation in the form of, for example, loosened slabs of rock, i.e. spalling (cf. borehole breakout). Such damage may indicate the direction of the maximum principal stress. According to the plans, monitoring of stress damage will be carried out systematically during the construction of ONKALO. Mapping of stress damage has been tested in the Pyhäsalmi mine and is reported by Hakala et al. (2002) and Matinlassi (2002). Based on the preliminary rock mechanics analyses (Johansson & Rautakorpi 2000) and the mapping of core disking (Sacklén 1999) the possible visual stress damage at Olkiluoto, as shown in Figure 5-1, is only expected to occur at depths exceeding 300 � 400 m.

Another way to monitor stress changes and related stress damage is by acoustic emission (AE) measurements. With this method stress changes (damage to the rock) that are not perceptible by visual mapping can be located within the rock mass. The method can also be used to validate the direction and magnitude of the maximum compressive stress by comparing the monitoring results with the modelled results. AE monitoring has been used in the Äspö HRL in Sweden and in the URL in Canada with good results (Juvonen 2002).

In addition to stress measurements, R&D work in the field of stress measurement will continue. An interpretation method for overcoring measurements is under development, in co-operation with SKB, designed to improve the reliability of the results (Hakala 2003a). This aim of the work is to develop an interpretation method for use on rock with anisotropic properties, provided the anisotropy parameters are known. This will make it possible to reinterpret the old overcoring results from Olkiluoto. Preliminary laboratory test results on Olkiluoto mica gneiss indicate that the anisotropy ratio of the rock is about 1.5 (Hakala 2003b), which suggests that there is an obvious need for an interpretation in which the level of anisotropy is taken into consideration. The stress analyses may also reveal links between the geological structure model and the understanding of the stress field.

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Development work in stress measurement methods may also be carried out by participating in a proposed project financed by TEKES (National Technology Agency). The aim of the project is to develop a stress measurement instrument especially adapted to the needs of the Finnish civil engineering and mining industry.

Strength-deformation properties of intact rock

In order to be able to make detailed and accurate estimations of tunnel stability the stress/strength regime should be known as described above. According to the plans the current data on intact rock2 stress-strain properties will be complemented by laboratory tests on core samples taken from borings during ONKALO's construction. Samples taken from stress measurement boreholes could in many cases be used for these laboratory tests. The construction of ONKALO will provide a more detailed description of the lithology and could possibly reveal rock types, for which no determinations of intact rock strength-deformation properties have been performed or the number of determinations is insufficient. The statistically sufficient number of determinations in different rock type environments that would be required is dependent on the geology. Laboratory loading tests with the different rock types on Posiva�s investigation sites have shown that for isotropic, homogeneous rock about ten (10) specimens for each loading test would be statistically sufficient, whereas in an anisotropic, heterogeneous environment, represented by most rock types in Olkiluoto, about 20 specimens per test would be necessary (Hakala & Heikkilä 1997).

The test programme for ONKALO would be to a large extent similar to the programme executed in 1996 - 1999 and described e.g. by Hakala and Heikkilä (1997), with the addition of investigations on the effects of sample size and anisotropy. Underground excavations will provide the opportunity to collect larger size samples (scale effect) and to acquire oriented samples for anisotropy analyses. Anisotropy testing has been developed and the first tests have been performed using existing material from deep boreholes (Hakala 2003b). Posiva also participates in the large-scale pillar stability experiment, known as APSE, in the Äspö HRL. One of Posiva�s objectives in participating in this test is to gain experience for carrying out a possible large-scale test on the main or lower level of ONKALO.

Fracture properties

The rock mass at Olkiluoto is typical in Finland, in that it is characterised by high in situ stresses and fractures. The fracture sets in the rock mass at Olkiluoto have been examined on the basis of information obtained from deep boreholes and from surface mapping. Few analyses of the fractured rock mass have been made so far, as the main emphasis has been on evaluating and understanding the stress-strength regime in intact

2 The intact rock refers to rock without visible fractures � in accordance with the normal vocabulary within rock mechanics.

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rock and because of the lack of the required fracture data. Although it is not essential to consider fracturing for stability considerations, the preliminary analyses on fractured rock have shown that fracturing is an important factor to consider in optimising the orientation and support requirements of the tunnels (Rautakorpi et al. 2003). The extent of fracturing is also relevant in terms of assessing the long-term safety of the disposal system, as has been demonstrated, for example, in the work by LaPointe & Hermanson (2002) where movements on fractures caused by earthquakes have been estimated.

There have been some attempts to build fracture models at repository depths for rock mechanics analyses, such as the ones presented by Johansson et al. (2002) . However, the fracture model available before the construction of ONKALO is subject to considerable uncertainties, since it is based on surface mapping and core logging of deep boreholes. ONKALO offers good opportunities to improve this model as detailed data on fracturing will be acquired from the geological mapping and modelling programmes, see section 7.2. A model for the fractured rock mass will be constructed on the basis of these results and subsequently used in rock mechanics analyses, see section 7.3. Creating a fracture model is a dynamic process, because the amount of data increases continuously and the model has to be updated constantly .

In addition to fracture geometry, the strength and deformation properties of fractures should also be known. This is clearly a more demanding question to solve. In earlier phases of the site characterisation programme (e.g. Hakala et al. 1993) attempts were made to determine the strength properties of fractures using laboratory tests, but the results were not encouraging. One main problem of laboratory tests is the scale factor, i.e. the small size of the laboratory sample (L = centimetres) in comparison with the natural fracture (L = several metres). The development of different testing methods will be investigated. Another and potentially a more meaningful approach is to estimate the strength properties of fractures by means of some empirical rock mass classifications. For example, the Q-classification used by Äikäs et al. (2000) could be adopted for this purpose. The mechanical properties of the fractures are dependent on the waviness and roughness of the fracture surfaces, occurrence of slickensides, the quality and thickness of the fracture fillings, as well as on the strength of the surrounding rock. Fracture mapping as part of geological mapping during the construction of ONKALO will provide more accurate data for the estimation of these properties of fracture surfaces than what is obtained from core logging.

Fracture zone and rock mass properties

The starting point of repository planning has been to leave a sufficiently large respect distance (50 - 100 m) to significant fracture zones. This is considered to eliminate any obvious interaction between the repository and the fracture zones and, for this reason, these weakness zones have not been taken into consideration in rock mechanics analyses. However, the central tunnels of the repository will probably run fairly close to these zones or even intersect them, which could result in a need to analyse their effects

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(e.g. respect distance, displacement behaviour, requirement for rock support) more closely. In addition, some deposition tunnels might intersect minor fracture zones.

An essential and a difficult task is the parameterisation of fracture zones for the analyses, at Olkiluoto. One solution is to use a rock mass classification system as described in the context of fracturing and another is to conduct in situ measurements in the zone itself, something that has been tested in the Äspö HRL. The development of methods in this area needs to be followed and it may be possible to make such measurements in ONKALO, provided that a suitable zone can be located.

In rock mechanics analyses, the properties of fracture zones (weakness zones) can be treated in different ways depending on the scale and the structure of the zone. In principle, this also applies to the rock mass between the fractures zones. Figure 5-2 summarises the commonly used modelling concepts and the associated mechanical material properties.

When a fracture zone is treated as a discrete discontinuity (A in Figure 5-2), the parameters used in its modelling are identical to those used for individual rock fractures but corrected with a scale factor. If a fracture zone has a significant width in comparison to the studied problem, it is modelled as an equivalent rock mass (B-D in Figure 5-2), but often characterised by lower strength and deformation properties than the surrounding rock matrix. Since laboratory testing and in situ measurements on fractured material in deep boreholes are extremely difficult to perform, other indirect methods have been developed.

The most common procedure for determining the properties of fracture zones is the use of rock engineering classification systems such as Q- and RMR- (Rock Mass Rating). They provide a shortcut to rock mass properties that are more difficult to assess. The classification schemes consider a few of the key rock properties, and assign numerical values to the classes within which these parameters lie for a given rock type/environment. The RMR scheme defines six parameters: the uniaxial compressive strength of intact rock, the RQD (Rock Quality Designation)-value, discontinuity spacing, the condition of discontinuity surfaces, groundwater conditions and the orientation of discontinuities relative to the engineered structure. The Q-system also assigns six parameters: the RQD-value, the number of discontinuity sets, the roughness of the most unfavourable discontinuity, the degree of alteration or fracture filling as well as water inflow and stress conditions. As rock mass properties, e.g. deformability and strength, are also functions of intact properties and discontinuity properties, the classifications can be used to estimate the rock mass modulus. Empirical relations to estimate rock mass modulus (Erm) are available for both Q- and RMR-systems (Barton 2002).

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Figure 5-2 Modelling approaches for fracture zones and associated parameters (Johansson et al. 1996).

Besides empirical procedures, there are also some simple analytical methods, in which the properties of intact rock and fractures are superimposed to yield fracture zone properties (see e.g. Hudson & Harrison 1997. p.p. 141-144). It should also be recognised that the use of empirical methods has its limitations � and involves a significant degree of expert judgement. The progress made in direct mechanical modelling (see e.g. Andersson et al., 2002a) will also be explored.

Measuring excavation responses

Rock response measurement involves measuring the diametrical changes in a tunnel caused by progressing tunnel excavations (rock response). The use of this method can supply valuable information on rock properties, which can be estimated from a considerably larger volume of rock (over a scale of several metres) than in borehole measurements. It is proposed that the response of the rock mass be monitored in a few cross-sections in the access ramp and on the main characterisation level in specific test tunnels constructed for rock mechanics studies (e.g. a tunnel loop, in which case

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measurements can be made in various directions with respect to the maximum principal in situ stress).

Thermal properties of the rock

The thermal properties of the rock will mainly be acquired by conducting single hole in situ measurements with the new equipment under development (Kukkonen et al. 2001) and by complementing these with laboratory determinations of thermal properties carried out on samples taken from ONKALO. These will also include tests on thermal anisotropy. Multiple borehole experiments in the tunnel may also be conducted, where a heat source is placed in one borehole and the spreading of the heat pulse is observed in a set of other holes.

As with rock strength, the scale effect is considered important when determining the thermal properties of rock. The main emphasis is currently on the development of in situ measurements (Kukkonen & Suppala 1999, Kukkonen et al. 2000, Kukkonen et al. 2001). The in situ test instrument, which is known as TERO and will be used to make measurements in boreholes, is under construction and planned to be used in some investigation boreholes in ONKALO, see also section 9.2. Procedures developed by SKB (Sundberg, 2003) will also be considered.

Development of laboratory test instrumentation is nevertheless also being carried out. Laboratory tests or parameter estimations for the main rock types at Olkiluoto have been performed (Kukkonen 2000, Huotari & Kukkonen 2003), but complementary laboratory determinations of diffusivity, thermal conductivity, heat capacity, coefficient of thermal expansion, rock anisotropy and the temperature dependency of parameters will be carried out using samples taken from ONKALO. The construction of ONKALO will provide an opportunity to develop a more detailed description of the lithology and could possibly reveal rock types for which no determinations have been carried out or the number of determinations has been insufficient.

Long term mechanical properties

The long-term properties of rock have previously been examined mainly by means of literature studies (Tuokko 1990, Eloranta et al. 1992). The most important long-term property of rock is its long-term strength, because some excavations, e.g. the central tunnels and the shafts of the repository, will remain open for several decades. According to the plans, the long-term behaviour of the rock mass will be studied in situ by mapping the level and form of the damage suffered by the underground facility during and after excavation, by monitoring displacements in the rock mass, by measuring acoustic emissions (AE) and by means of microseismic monitoring (MS).

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Further interpretation and modelling of rock mechanics data to produce a rock mechanics description is presented in Chapter 7. To summarise, the rock mechanics characterisation will result in:

• A detailed description of the rock mechanics and the thermal properties at the Olkiluoto site in 3-D.

• An assessment on which predictions are supported by obtained data and which predictions are less well supported will be produced.

• Evaluations and predictions of the mechanical stability of the excavated rooms.

In general, modelling will be a supporting tool of the design work and enhance confidence in understanding the mechanical behaviour of the rock mass.

5.3 Hydrogeological conditions

5.3.1 Objectives

The primary objective of hydrogeological characterisation is to describe the hydraulic properties of and the groundwater flow pattern in the rock mass. The groundwater flow regime will influence the chemistry of groundwater and is also one of the determining factors in radionuclide migration. A description of the migration of radionuclides may require a resolution of the flow field at a decimetre scale. Such a fine resolution can, of course, only be attained in a statistical sense and it can only be obtained in tunnels close to the volume being investigated and in boreholes originating from such tunnels.

In addition, hydrogeological characterisation should monitor and explore the impact of ONKALO itself. Inflows of groundwater into ONKALO will result in changes to pressure and flow fields, and these changes will provide important information on the hydrogeology of the site. This subject is discussed in more detail in Chapter 7.

In addition, the results of and the experience in hydraulic tests at depth will be useful for the planning of the construction work (optimising grouting etc.) and other investigations, such as groundwater sampling.

More specifically, the objectives of hydrogeological characterisation are, thus:

1. Updating the overall hydrogeological (descriptive) model at the site scale. This comprises determining the position, extent, orientation and transmissivity of site scale fracture zones and upscaled hydraulic conductivity of the rock mass between the fracture zones.

2. As part of the tunnel wall mapping (see section 4.3.2) to gather basic data on fracturing on ONKALO tunnel walls and to detect fractures with water leakage, where also TDS and the gas content of leaking water should be analysed.

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3. The analysis and understanding of the relationships between geology and hydraulic properties ― such as fracture transmissivity, fracture gouge porosity and gouge diffusivity ― are essential for conceptualising the flow and transport modelling at different scales and for supplying data that can be used in migration calculations for the safety analysis.

4. Developing a high resolution, but statistical, description of flow and permeability in a volume of rock representing the first potential disposal panels. This model will allow a statistical description of the transport resistance (WL/Q) at depth.

5. Determination of the open tunnel skin arising from EDZ, grouting, degassing of dissolved gases, and adsorption of air on crack surfaces on the tunnel walls.

6. Investigation of the phenomenon of saline upconing and groundwater drawdown through monitoring pressure changes, the changes in the TDS of water leaking into ONKALO tunnels and in the boreholes drilled from ONKALO, and through exploratory numerical modelling.

7. Testing methods for detailed hydrogeological characterisation inside disposal tunnels (i.e. to test means of determining whether individual disposal holes are suitable; the selection of the locations for such holes will depend on the criteria to be developed).

8. Supporting hydrogeochemical investigations and experiments.

9. Providing data to guide and support actions directly related to tunnel excavation (such as grouting).

The hydrogeological characterisation will also investigate the presence of gas in the groundwater and assess the extent to which the gas may affect hydraulic or other measurements. In general, hydrological investigations should not be strongly correlated with just geological investigations but also with hydrochemical studies. The former are required for the development of the attempted fracture network model, while the latter will help in further refinement and serve as a consistency check for the modelling.


Hydrogeological information will be obtained by monitoring the impact of ONKALO's structures and from various characterisation measurements. The information from hydraulic measurements will consist of:

• Local transmissivity distribution along boreholes inferred from hydraulic test responses measured with the difference flow meter of the Posiva Flow Log (see Figure 5-3) or a double packer device to be used in the boreholes drilled in ONKALO tunnels.

• Monitoring of pressures in packed-off sections of boreholes drilled in the tunnels and on the surface.

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• Measurement of cross-flow in borehole sections and locations round excavated tunnels, especially in boreholes drilled on the surface and in the planned locations of each deposition hole.

• Interference tests between boreholes using the difference flowmeter (flow responses) and multi-packers (pressure responses) at selected locations.

• Monitoring of groundwater inflows in different sections of the tunnels and in individual fractures or fracture zones at chosen locations, using dams and specific collecting devices.

• Tests aimed to determine the EDZ (e.g. pressure monitoring close to tunnel walls in order to determine skin) and to assess other factors (e.g. grouting, shotcrete), which may locally affect inflow to the tunnels (see also section 7.4). The main source for this type of assessment is the comparison of data gathered during excavation (e.g. hydraulic tests in probe holes etc.) with tests made in boreholes after grouting and excavation.

Figure 5-3: Posiva Flow Log. The device measures the (net) flux of water between the borehole and the surrounding rock between the rubber disks. The hydraulic conductivity characteristics for the distance separating the rubber disks can be inferred on the basis of certain assumptions.

Updated geological and structural information will also be needed for modelling (see Chapter 7). DFN-type fracture statistics, in particular, would be needed for a very detailed characterisation of the rock volumes round potential disposal tunnels. In addition, an assessment of groundwater composition (gas, salinity) will be needed in order to get a handle on the effects of degassing and density differences.

W inchPum pM easuring com puter

Flow along the borehole

Rubberdisks

Flow sensor

Single point electrode

EC electrode

M easured flow

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Tunnel �skin� and the EDZ

The excavation of a tunnel will give rise to a thin layer (possibly a few tens of centimetres thick) with altered hydrogeological properties , which is referred to as the tunnel skin. While fracturing caused by blasting tends to increase the hydraulic conductivity of rock (i.e. an EDZ develops), in the case of an open, i.e. air-ventilated, tunnel it is likely that a skin will result in decreased hydraulic conductivity. This wouild also be benefitial.

One reason for development of a skin is the adsorption of air molecules onto crack surfaces and the degassing of groundwater. Degassing takes place because water under the considerably reduced pressure experienced in the tunnel, compared with that in the surrounding rock, cannot prevent dissolved gas from forming its own phase. In addition, grouting will contribute to the formation of the skin. Because the tunnel wall is a mechanically free surface, the local principal stress perpendicular to the surface has a zero value and fractures can dilate causing enhanced conductivity. The other two principal stresses are both parallel to the tunnel wall and will vary in magnitude round the tunnel periphery. In case of a high horizontal in situ stress, this leads to high stresses in the roof and the floor, which can increase or reduce conductivity depending on fracture orientations.

Some aspects of the hydrogeological character of the skin round open tunnels are rather easy to explore because the skin very clearly manifests itself as an abrupt change in groundwater pressure in the immediate vicinity of the tunnel wall. In this respect the emergence of the skin can be seen to be beneficial, as it tends to decrease the hydrogeological impact of the tunnel excavation within the surrounding rock mass. Thereby, it is possible to determine whether changes in the ingress of water are due to skin effects or to a more general lowering of the water table. However, pressure measurements alone will not be sufficient for exploring potential effects on permeability along the tunnels.

As the tunnels are closed at the end of the operating stage of the repository, the formerly open tunnels will begin to re-saturate. The gas phase in the cracks on the tunnel walls and inside the backfill material will either dissolve into the groundwater or will be displaced upward due to hydrostatic buoyancy. Chemical reactions and microbes will quickly consume any oxygen present and the removal of any gas will lead to an increase in the hydraulic conductivity of the tunnel skin.

The hydraulic conductivity of a saturated rock mass adjacent to an underground opening is likely to exceed the conductivity level before excavation, due to an increase in the fracture density - at least in the un-grouted portions. This effect will be present even if the saturated hydraulic conductivity of the bentonite-sand backfill remains low (as it is expected to do) � whereby the more conductive tunnel skin will surround the poorly conductive backfill material. A complicating factor is the effect of the bentonite swelling pressure and the change in the rock�s stress state on the properties of the tunnel skin, a subject that will need to be investigated in detail. Saturated tunnel skin will,

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therefore, be examined using a dedicated experiment (see section 8.2). In addition to establishing the change in the hydraulic conductivity of the tunnel skin, this experiment will be used to provide quantitative information on the saturation process itself and the associated biochemical changes.

Near-field

In addition to providing direct support to tunnel excavations, the specific objective of the near-field characterisation programme is to develop a high resolution, statistical description of flow and permeability in a volume of rock representing the first potential disposal panel. This will allow a statistical description of the transport resistance (WL/Q) for that part of the rock mass.

A very detailed description of the flow and transport properties of the near-field has to be obtained, since performance assessment and hydrogeochemical tests essentially deal with the migration of contaminant dissolved species from a very small or point-like source, although diffusion implies a lower limit (in the order of 0.1 m) for the scale that needs to be resolved. For this reason, near-field investigations involve an estimation of the geometrical characteristics of fracture networks and flow and of the transport properties of individual fractures.

The characterisation of fracture networks for discrete fracture network simulations is based on detailed mapping of the trace lengths, intensities and orientations of fractures on the tunnel walls used as primary sources of data. Information obtained on groundwater flow along individual fractures (e.g. visibly leaking fractures on the walls of tunnels) is also useful. The geometry data will also be supported by borehole core-log data on the intensity and orientation of fractures. Complete characterisation of the fracturing also involves an analysis of fracture infillings.

In the case of individual fractures, only a fine resolution of a few centimetres can be dealt with in statistical manner. The data required for such a statistical analysis will be obtained from borehole core-logs and rock samples obtained in the excavations. The determination of the fine scale variability of fracture apertures in the core-logs and in borehole-TV will be accompanied by measurement of the hydraulic conductivity (using the difference flow meter) of corresponding locations in the boreholes. This is expected to facilitate the analysis of the relationship between the observed apertures and the fracture transmissivity. This analysis, together with the results of fracture network simulations, will provide information on the connectivity of the individual fractures.


Further interpretation and modelling of hydrogeological data to produce a hydrogeological description is presented in Chapter 7. Hydrogeological characterisation will produce:

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• a fracture-specific database on the hydraulic and geological properties of hydraulically conductive fractures,

• an enhanced understanding of the coupled hydromechanical processes linking rock stress, rock fractures, excavation and hydraulic conductivity,

• an updated hydrogeological description (flow and permeability) of the volume of rock around ONKALO,

• a statistical description at a detailed scale of the hydrogeological properties of the first potential repository panel, and, in particular, of typical blocks of rock surrounding the deposition holes.

• an assessment of how the occurrence of gas in the groundwater influences flow.

• a detailed knowledge of the flow and transport properties of Olkiluoto rock mass to facilitate the development of a scientifically sound and adequate safety analysis.

In general, modelling will enhance confidence in the understanding of the flow and hydraulic properties of the rock mass at different scales and in different locations in the Olkiluoto area.

5.4 Hydrogeochemical conditions

5.4.1 Objectives

Hydrogeochemical characterisation involves both surface-based characterisation and characterisation during the construction and operation phase of ONKALO. The main objective of the hydrogeochemical characterisation of rock mass is to describe the distribution of groundwater composition in the potential disposal areas in sufficient detail and to explore the impact of ONKALO on its surrounding environment.

Hydrogeochemical characterisation will mainly focus on:

• Establishing spatial and temporal variations in the composition of surface waters and groundwaters,

• Determining the properties and composition of groundwater at a detailed scale (for individual panels in the repository) focusing on salinity distribution, redox and pH conditions in both the fractures and the rock matrix.

• Relating the hydrochemistry to the geochemistry of the rock and the fracture infilling minerals, in order to understand past and present rock-water interactions and the evolution of groundwater composition along the flowpaths and to facilitate prediction of future groundwater evolution

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• Examining redox and pH conditions and changes in them, determining whether the mixing process (such as occurs in groundwater flow) is sufficient to explain major groundwater compositional changes.

• Establishing hydrochemical system understanding, to be used to control and constrain hydrological models. Due to its open tunnel condition ONKALO acts as a large-scale pump test and the concentrations of many hydrogeochemical variables will probably change as a function of time during the construction and operation of ONKALO.

• Identifying variability in groundwater composition due to natural perturbations (e.g. recharge events) and human-induced activities (e.g. drilling, hydraulic testing) prior to and during excavation (including microbiological activity, potentially hazardous compounds etc., that might be deleterious to the performance of the repository; examples of these could be the presence of U, Ra, Rn, As, flammable gases, and sulphides or high U- and Th-bearing minerals in the rock, any of which could compromise these activities).

• Examining the potential influence of microbiological activity on the underground facilities and the surrounding rock mass by analysing microbial growths on tunnel walls and groundwater inlets, determining trace metals (e.g. Fe, Mn) taken up by these growths, and monitoring gas production, pH change and redox influence caused by the growths.

• Determining changes in groundwater composition and fractures (fracture mineralogy, porosity) due to the influence of construction and of the materials used during the construction and operating phases of ONKALO. This information will be used to evaluate the use of �foreign� materials at repository depths with respect to their impact on long-term safety.

• Deriving a reference groundwater composition, representative at the repository depth, for use in laboratory experiments and modelling.

• Deriving the sorption and retardation properties of the rock.

The above information will allow an assessment to be made of the composition of groundwater at the time the repository is closed down and will allow predictions to be made of long-term future changes in this composition. This information is crucial input in the safety assessment of the repository. It is important to recognise, however, that much of the present-day groundwater that will be characterised, will be removed due to drainage into the excavations during the construction and operation of first ONKALO and subsequently the repository. No tracking of every detail in the migration of groundwater bodies during the open phase of ONKALO will be attempted. However, these short-term changes are of interest as they help to further develop an understanding of the processes and the properties of the rock mass, which affect hydrogeochemical evolution.

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Many of these topics require calculations with geochemical modelling codes. Equilibrium and mass balance approaches (e.g. PHREEQC and NETPATH) are basic tools in understanding processes like mixing, pH-Eh evolution and salinity distribution. Furthermore, long-term evolution and predicitive problems related to hydrochemical evolution may require a more intimate coupling of hydrological and geochemical modelling approaches.

The activities listed above represent an ideal situation in which great resources are available and the data can be obtained over a long period of time. In reality, it is likely that efforts will concentrate on monitoring relevant parameters in selected groundwaters and inflows on a routine basis, with additional measurements (i.e. from the above list) dictated by situations that arise during excavation. This was found to be the case in the excavation and monitoring of the URL in Canada, where changing redox conditions in inflows, contamination of service water and groundwater by explosive residues and high salinity of matrix pore fluids were identified as potential problems requiring additional investigations (Gascoyne et al. 1995).


The main sources of hydrogeochemical and geochemical information for characterisation at ONKALO scale will be:

• Water samples taken from sections of surface-based boreholes isolated with multi- and double-packers, from sections of boreholes drilled in the access tunnel down to water-conducting sections isolated using double-packer, from inflows of groundwater into the tunnels and from boreholes drilled in underground openings for characterisation purposes. Only a few samples will be subjected to a comprehensively characterisation but major ion composition, pH, H and O isotopes, dissolved gas content (especially CH4 and H2) and electrical conductivity will be measured frequently and in a number of locations.

• In situ measurements of fracture specific EC of groundwater by flow loggings.

• Geophysical measurements for determination of salinity distribution.

• Detailed complete characterisation of the chemical parameters and isotopes when changes are observed at a monitoring point.

• Measurements of salinity, isotopes of H and O, dissolved oxygen, and carbon dioxide, Eh and pH, alkalinity and redox couples in groundwater in important major fracture zones during the construction and operational phase of ONKALO. These should make it possible to follow and evaluate the consumption of the buffering capacity of the rock and the fracture filling minerals as well as any changes in and movements of groundwater types.

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• Detailed characterisation of parameters that are easily disturbed in surface-based sampling, e.g. redox measurements and analysing of redox couples, C and S isotopes and organics.

• Determination of the content and type of organics (Humic acids (HA) and Fulvic acids (FA)) and colloids at a detailed scale on the research level of ONKALO and of individual panels in the repository

• Characterisation of the rock matrix, mineralogy and isotopic composition of selected minerals, e.g. S isotopes of sulphide minerals, fracture coatings, porosity, etc. in various borehole logs and on analyses of selected borehole cores.

• Detailed analyses of parameters that are related to construction and stray materials introduced into the facility, such as analyses of explosive residues, nitrogen compounds, microbes, pH-plumes etc.

Detailed instructions for sampling are presented in Posiva�s Field Instruction Manual for Groundwater Sampling (Ruotsalainen et al., 1998, Paaso et al., 2003).

Characterisation at a detailed scale of the repository panel may be performed on the cores obtained from boreholes drilled through the panel from the ONKALO tunnels. Matrix porosity may be measured of borehole cores in the laboratory, potentially supplemented by the results of geophysical logging. Special experiments may be conducted in the laboratory for extracting water from cores drilled into low permeability rock (unfractured matrix). Sampling of fluids from the matrix may be carried out in specially designed boreholes drilled in unfractured rock from ONKALO.

Some experiments and measurements will be carried out to verify to what extent the selected values of radionuclide sorption coefficient (Kd) used in safety assessment are representative of field values. However, it is likely that most Kd values will be selected from general databases. Examples of such measurements include laboratory tests performed on rock samples and in situ groundwater, complemented by �direct� in situ tests. The latter, however, are difficult to interpret and involve uncertainties that often are too large to allow a direct use of the determined values. The measurements may, nevertheless, still enhance confidence in the values that are finally selected.


Further interpretation and modelling of the hydrogeochemical data to produce a hydrogeochemical description is presented in Chapter 7. The expected results of the characterisation programme include:

• An updated and reliable characterisation of groundwater composition in the potential disposal areas, including a better understanding of redox and pH buffering capacity at disposal depths.

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• A better understanding of the buffering capacity of the rock and the fracture infilling minerals to limit the extent of O2 and CO2 penetration in the subsurface and the downward movement of the redox front.

• An understanding of potential groundwater compositions entering the repository in the future.

• An understanding of the effect of introduced foreign materials on the groundwater and the near-field rock.

• Improved capabilities for modelling the movement and origin of saline groundwaters and other types of groundwater, and their effects on repository materials and groundwater flow.

• An assessment of the impact on groundwater flow of the occurrence of high concentrations of dissolved gas in some groundwaters.

• A better understanding of groundwater movement (flow) and the properties of water-conductive structures (permeability and storativity) in the rock mass, and providing supporting evidence for groundwater movement.

• An assessment of the turnover time of groundwater bodies.

Ultimately these results should lead to an enhanced level of confidence in the flow model and safety assessment modelling.

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6 ASPECTS OF THE MONITORING PROGRAMME RELEVANT FOR CHARACTERISATION

The monitoring programme for ONKALO is described in a separate monitoring report. The aim of the monitoring is to follow the evolution of the site over time by studying the monitored changes of selected properties. According to the plans, monitoring will take place in surface-drilled boreholes, in boreholes drilled in ONKALO, and in ONKALO itself. This means that monitoring will provide important information for site characterisation. For this reason, this chapter presents an overview of monitoring aspects relevant to characterisation. Other aspects of the monitoring programme are discussed in the monitoring report. Furthermore, the monitoring program is to a large extent based on the characterisation activities described in earlier chapters, which means that this chapter will overlap with previous chapters on some points.

6.1 General Monitoring refers to a repeated series of long-term measurements of various defined properties. Depending on the nature of the property, monitoring may be continuous (on-line measurements) or restricted to discrete sampling, such as annual groundwater sampling. Miller et al., (2002) provide an overview.

The general objective of the monitoring programme is to observe and assess potential changes on the site over time. As far as ONKALO is concerned, the programme is focused on exploring the impact of the construction of ONKALO and of ONKALO itself on the state of the system. The evaluation of monitoring results may lead to enhanced confidence in the site description, with the actual evolution of the site compared with predictions made beforehand. An understanding of the present-day evolution of the site properties is also required to specify the initial conditions for site specific Safety Assessment.

These aims are in line with a recent IAEA publication on monitoring (IAEA 2001). It defines monitoring as �continuous or periodic observations and measurements of engineering, environmental or radiological parameters, to help evaluate the behaviour of the repository system, or the impacts of the repository and its operation on the environment�. Furthermore, it is noted that �the extent and nature of the monitoring will change throughout the various stages of repository development and monitoring plans drawn up at an early stage of a programme will need to reflect this�. Specifically this means that while monitoring prior to waste emplacement is a component of the overall Site Characterisation programme, monitoring alone does not comprise the entire programme. Special �one-time measurements� are needed to determine site properties and processes (see Chapter 5). Furthermore, the intent of the monitoring programme is not to carry out general geoscientific research.

Planning the characterisation monitoring programme is no different in character to planning the overall characterisation programme. Monitoring is carried out partly to

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check for unexpected changes, but the programme still needs to be focused on issues likely to be relevant to the future repository performance. The monitoring programme needs to include the parameters that are likely to be affected by the construction of ONKALO as well as parameters that can show that its construction will not result in too many detrimental changes.

The �optimisation� of the monitoring programme also needs to consider the practical aspects of monitoring, which are of particular interest when monitoring potential hydraulic impacts. A specific borehole may have many uses and, for example, the installation of a continuous pressure monitoring system may make groundwater sampling in the same hole difficult or even impossible.

6.2 Monitoring on the surface and in surface based boreholes Baseline conditions are established on the basis of a large number of observations on the Olkiluoto site and a subset of these observation locations will be selected for long-term monitoring. This selection is based on an assessment of where changes are likely to occur and will include locations that help demonstrate that ONKALO will not change natural conditions to an unacceptable extent.

6.2.1 Rock Mechanics and Tectonic Events

ONKALO is not expected to affect tectonic movements in the regional fracture zones surrounding the Olkiluoto site. Nevertheless, an assessment of any potential large-scale tectonic movements is considered important for the future Safety Assessment. Tectonic movements can be determined using GPS measurements (Ollikainen et al. 2002) and precise levelling, although their sensitivity is limited. In general, tectonic regional seismic events will be captured by the national seismic grid, which will also be supplemented by the local seismic station that will be installed on the site (see below).

Construction work will result in microseismic events, which may be recorded by the local micro-seismic network currently installed on the site (Saari 2003). The local station will also be part of the national seismic grid, the closest station of which is currently about 100 km from Olkiluoto.

The construction of ONKALO will affect stress distribution in its vicinity. Pre-ONKALO surface based stress measurements in existing boreholes located close to ONKALO's eventual location provide a rather detailed picture of the current state of stress (Johansson & Rautakorpi 2000, Malmlund & Johansson 2002). However, some reassessment of the existing stress measurements will be carried out using the anisotropic solution mentioned in section 5.2.2 and (one) new measurement will also be performed.

6.2.2 Hydrogeology

Even if actions are taken to seal the tunnels and the shafts, ONKALO will affect the groundwater flow pattern on the site, see e.g. the disturbance report by Vieno et al.

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(2003). The effects of stress or chemical changes may also alter the permeability of the rock close to the underground openings. The aim of the hydrogeological monitoring programme is to capture all these changes.

As most changes are expected to occur close to the underground openings, monitoring can focus on boreholes drilled close to ONKALO. In addition, hydraulic conditions will be monitored in boreholes where the impact of ONKALO is expected to be small. These boreholes will mainly be used for reference and can be used, for instance, to distinguish between changes caused by ONKALO and other natural variations.

The most straightforward parameter to monitor is groundwater pressure. Both flow and permeability changes will clearly manifest themselves as changes in the pressure. Pressure monitoring will also be complemented by direct measurement of flow and permeability, using the Posiva Flow Log (see e.g. Figure 5-3). The aim is to monitor flow changes in the vicinity of ONKALO and pressure changes at a distance from ONKALO. The main reasons for monitoring flow changes in the vicinity of ONKALO are:

• flow logging provides detailed (i.e. fracture-specific) information on changes in the flow and possibly also in hydraulic conductivity and

• flow logging covers the entire borehole.

All boreholes have been and new ones will be logged systematically using difference flow logging of the Posiva Flow Log. The frequency of repeated logging in the selected or in all boreholes in the vicinity of ONKALO will be determined later. According to the plans, some measurements will also be carried out before the start of the construction activities to see if there are any �natural� changes in the flow and to study in more detail the general repeatability of this type of logging. Several and repeated tests during the past two years in borehole KR6 have proved that such logging functions properly, i.e. the differences in fracture specific flow results have been minor (Pöllänen & Rouhiainen, 2002).

In summary, the surface-based hydrogeological monitoring programme consists of:

• continuous (automatic) monitoring of groundwater pressures (using piezometers) in selected packed-off sections of some 10 to 15 deep boreholes located mainly at a distance from ONKALO,

• continuous (manual) monitoring of groundwater pressures in permanent multilevel piezometers (EP1-EP7),

• re-logging of a few boreholes with the difference flowmeter in order to determine the extent of any changes in flow, pressures or hydraulic conductivity caused by the construction of ONKALO,

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• repeated measurements of cross-flow in selected boreholes and at selected depths, with the possibility of installing online tools to measure cross-flow in the most interesting sections to be considered on the basis of the results of the repeated tests.

Surface hydrology is discussed in section 6.2.4.

6.2.3 Hydrogeochemistry

The current groundwater composition around the ONKALO site consists of chemically distinct bodies of groundwater and mixtures of waters. Remnants of meteoric water, glacial melt water, brackish Baltic Sea water, Litorina Sea water and deep saline brines have been found in the bedrock (Pitkänen et al. 1999). The locations of these water bodies and the degrees of mixing keep changing due to the natural flow of groundwater caused by infiltration of surface water and changes caused by continuing post-glacial isostatic rebound.

The drainage pattern round the ONKALO site may experience significant additional changes in the future, at least in the vicinity of the underground construction works. Some of the groundwater types, such as glacial meltwater or Litorina Sea water, may almost disappear as they are drained along transmissive fractures into the tunnels. In addition, the highly saline, deep groundwater may temporally migrate upward, toward the tunnels, but will start to migrate back toward its original position after the repository is sealed and tunnel drainage ceases.

It is questionable whether precise mapping of all the details of different groundwater types� migration is necessary and no exact prediction of the movements of each type using, for example, coupled chemical and transport models, is readily attainable. The fact that the location of past boundary conditions and flow regimes are subject to great uncertainty also means that there are limits as to which extent the current chemical composition can be correlated with the current groundwater flow regime. However, it is important to map the changes in groundwater type and model the changes in proportions of end-members in selected locations during the construction and operating phases of ONKALO. This is because the start of excavation is a new zero point for the hydrogeological system and, in principle, the boundary conditions for a disturbed open-tunnel condition are well defined.

Monitoring the changes in groundwater composition is likely to help improve the details of the hydrogeological model and to increase consistency between hydrochemistry, groundwater flow and the structural model (see Chapter 7). Furthermore, from the safety assessment perspective, there are also other important aspects of groundwater composition. These include the presence of dissolved oxygen, high TDS, and the pH, Eh and redox parameters of the groundwater. In summary, the hydrogeochemical monitoring should aim to:

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• follow changes in groundwater composition during the excavation of ONKALO in order to provide further insight into the extent of the mixing and advection processes,

• track the migration of selected parameters relevant to safety assessment, (e.g. O2, CO2 , NH4

+, SO4/S2- , Cl- and TDS, and pH and redox buffering capacity of the rock).

Special efforts will be devoted to tracking the potential migration of the redox front and the changes in pH. Monitoring will start in shallow holes where the position of the current redox front is known and will then try to follow the potential migration paths through the rock (see Figure 6-1). Proper evaluation and selection of sampling points would thus require input from updated structural and geological models, see the Baseline report (Posiva, 2003a). Groundwater analyses will look for evidence of dissolved oxygen as well as for changes in pH and alkalinity. This work will be complemented by analyses of the microbiological activity and the organic matter (especially in near-surface locations) as these constituents may be major consumers of oxygen. Mineral samples will also be taken in order to track the current and past oxidation and acidification of the water-rock interface.

In summary, the surface-based hydrogeochemical monitoring programme consists of:

• Analyses of water samples from selected borehole zones close to ONKALO, including analyses of SO4, NH4

+, Br/Cl, sulphur isotopes etc. to monitor the potential migration of seawater and potential risk of sulphate reduction to sulphide.

• Monitoring of electrical conductivity in a number of locations in order to trace the migration of saline water.

• Sampling of shallow groundwater from groundwater tubes and shallow wells, and possibly in lysimeter installations.

• Monitoring of the migration of the redox front and the change in pH by analysing the content of dissolved oxygen, dissolved CO2 and dissolved inorganic carbon (DIC), as well as pH, redox parameters (Fe2+/Fetot, S2-), organic matter and microbial activity. Monitoring of drainage from excavated rock piles and the possible recharge of this water to the groundwater flow system.

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Figure 6-1 The movement of the redox front is expected to follow the main flow paths toward ONKALO. The selection of sampling points should acknowledge this.

6.2.4 Surface hydrology

ONKALO is not expected to influence the circulation of surface water or affect the ecosystem to any great extent, except possibly in the vicinity of the shaft and the access ramp, and obviously inside and in the vicinity of the construction areas. Monitoring of surface hydrology consists of sampling and observing a set of parameters at regular intervals on some pre-selected locations.

Meteorological observations

Common meteorological parameters are monitored on an hourly basis in the western part of Olkiluoto by the nuclear power plant, at several different elevations: The data are sent to Posiva quarterly (Ikonen ed. 2002b). The most important parameters include temperature, precipitation, snow cover and relative humidity.

At the nuclear power plant continuous monitoring is carried out on the radionuclide composition in aerosols (dry) with a cumulative sampling period of two weeks, and on radionuclides in precipitation (wet) with a cumulative sampling period of one to three months (Ikonen 2002a).

Surface hydrology

Surface hydrology monitoring will comprise:

• Continued monitoring of a subset of the parameters collected as input to the baseline description, i.e. regular monitoring of groundwater levels (the �groundwater table�)

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in shallow boreholes and groundwater observation tubes in the overburden. In total more than 40 observation points are in use today.

• Measurement of surface runoff in four weirs and possible analysis of the water. The discharge will be measured continuously with a pressure transducer at the weirs or weekly with a measuring stage, using the relationship between the water level at the weirs and the discharge curves.

• Regular monitoring of sea level in the Rauma harbour, implemented by the Finnish Institute of Marine Research.

• Recording of the water balance in the Korvensuo reservoir.

The sampling sites should be located in areas already investigated during the programme of groundwater and surface water sampling, the results of which have been used as input to the Monitoring Report.

6.3 Monitoring in ONKALO As the underground work starts it will be possible to characterise and then also monitor the state of the rock underground. Observations will be made both in the tunnel and in the boreholes drilled from the tunnel.

A subset of the measurements and observations that are planned to take place during underground construction will be included in a longer term monitoring programme. This programme needs to be based on the results of the first assessments of the actual underground construction work and the plans for further monitoring will be re-assessed at this point. The sections below outline some potential monitoring inside ONKALO and the measurements are described in more detail in Chapter 5.

6.3.1 Monitoring the construction process

The progress of the construction work will be carefully monitored. Essentially this concerns all data assembled for the construction process as identified in Chapter 4, combined with activity logging, i.e. time records of excavation, drilling and grouting activities in various parts of the tunnel.

6.3.2 Rock Mechanics

Possible stress-induced damage in the tunnel walls and roof will be visually monitored during the construction and characterisation work, see also section 5.2.2. If significant fracture zones are penetrated, they will be instrumented with extensometers to monitor their displacement behaviour. If necessary and possible, stress measurements and monitoring can also be conducted in the vicinity of the fracture zone.

The rock response (displacements) to construction will be measured and monitored in a few cross-sections in the access ramp and on the main level of ONKALO in specific test tunnels that are to be constructed for rock mechanics studies, see section 5.2.2.

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The change in the stresses caused by the excavation will be measured in a few deep sections of the tunnel. In some of the most critical locations of the tunnels, extensometers will be installed to monitor rock displacements, stress cells to monitor stress changes, load cells to perform load measurements in rock support and acoustic emission (AE) cells to study rock damages. Monitoring will continue during the construction and operating phases of the repository. A specific monitoring programme will be prepared for the repository level.

Large-scale rock movements are to be monitored in ONKALO, using both microseismic (MS) measurements and convergence measurements (i.e. a method which allows the relative changes in length to be determined between fixed measuring pins using a special steel measuring tape) on a fracture zone that cuts the tunnel. The microseismic network will be expanded to include the ONKALO as soon as is feasible, and a sufficient number of underground monitoring stations will be located so that their separation is no greater than 150 m. The results will be used as input to the bedrock structure model of the site and incorporated in the rock mechanics description.

Most of the changes are expected to take place during the construction phases. After construction work is completed, visual monitoring will be limited to the inspection of the tunnel walls and roof. Instruments installed during the construction phase will be further monitored during the operating phase.

6.3.3 Hydrogeology

Hydrogeological monitoring inside ONKALO itself will use the same devices, methods and boreholes that are used in the characterisation programme (see 5.3.2) and in monitoring implemented in the surface-based boreholes (see 6.2.2). Monitoring will consist of:

• Continuous (automatic) monitoring of groundwater pressure in selected packed-off sections.

• Re-logging a few boreholes using the difference flowmeter in order to establish whether ONKALO has any effects on the flow of groundwater, on hydraulic pressures or on hydraulic conductivity.

• Monitoring of inflows into different sections of the tunnels and into individual fractures intersecting the tunnels in chosen locations, using dams and specific collectors (combined with a grouting record).

• Monitoring of groundwater flow in connection with groundwater sampling (composition and gas content, see section 6.3.4).

• Monitoring of water balance in ONKALO (natural inflow, artificial outflow (hydraulic tests, washing of walls etc), content of water abstracted by the ventilation system).

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6.3.4 Hydrogeochemistry

The monitoring of the composition of groundwaters entering ONKALO as direct inflows or with access through boreholes, will be an important part of the monitoring activities. Much of the experience gained in monitoring chemical changes in the Äspö HRL will be of use here, in establishing a monitoring programme for ONKALO.

Hydrogeochemical monitoring during the construction of ONKALO should include at least on-line electrical conductivity, pH, redox and dissolved oxygen measurements in the boreholes drilled in the tunnel on specific points, e.g. in fracture zones, where changes in groundwater chemistry are expected. Major cations and anions (Ca, Na, Mg, K, Cl, Br, SO4, HCO3), NH4, dissolved organics and isotopes of H and O should be analysed on specified sampling points and especially where significant changes in the electrical conductivity can be seen. Also, the amount of, and composition of (CH4 and H2) of dissolved gases will be measured frequently during construction, because flammable gases and Rn-222 may exsolve into the air. During the construction phase hydrogeochemical monitoring inside ONKALO itself will consist of:

• Sampling and analysis of groundwater flowing into the tunnel on a selection of inflow points in the tunnel and in conjunction with hydraulic tests performed in boreholes drilled from the tunnel. The number of samples should be large enough to give a good overview of the main changes occurring in the hydraulic and chemical conditions during construction. The exact number of samples must be determined during the progress of the work.

• Sampling and analysis of groundwater accessed by boreholes from the ONKALO. These samples will be of a higher quality than those taken from direct inflows to the underground facility because it will be possible to maintain the ambient pressure on the sample, thus preventing out-gassing or contamination by oxygen.

• Special efforts for measuring redox and pH in selected boreholes drilled in the tunnel. The strategy and technique used will be a continuation of the sampling carried out in the surface-based boreholes (see section 6.2.3 above).

• Monitoring the amount (see 6.3.3) and composition of water flowing into the tunnel before it is pumped out to sea. Parameters to be measured and defined include pH, electrical conductivity and the TDS of the water.

• Analyses of fracture minerals and detailed petrological analyses of fracture zones encountered during excavation or observed in boreholes.

• Analyses of microbes on rock surfaces and fracture infillings as well as in groundwater, e.g., sulphate reducing bacteria, iron reducing bacteria, methanogens.

• Analyses of the impact of construction, e.g. pH-plume effect on nearby bedrock groundwater and fractures, such as range of pH-plume, clogging of fractures,

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secondary mineral formations caused by the use of stray materials, such as cement grout.

• Analyses of chemical imprints in the underground facilities (blasting gases, carbon dioxide, carbonates, organics, microbes, oxygen, iron and sulphur compounds)

The evaluation of the hydrogeochemical impact of construction is discussed in section 7.5.2.

6.4 Monitoring during repository construction and operation A monitoring programme will later be established in order to follow the evolution of the site during repository construction and operation.. The monitoring programme will be based on the monitoring network, which is already in place for the construction of ONKALO, but will be revised and complemented with additional underground monitoring points. The lessons learned in the monitoring of ONKALO will be considered. This network will be in place during the construction and operation of the repository.

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7 EVALUATION MODELLING The information collected through characterisation and monitoring will all be assessed in an integrated modelling effort, based on modelling within the individual disciplines, i.e. geology, rock mechanics, hydrogeology and hydrogeochemistry. The aim of the modelling is both to successively enhance the description and understanding of the rock volume round ONKALO and to assess the potential impacts of ONKALO's construction and operation.

7.1 Modelling Strategy The modelling strategy is outlined by Saksa et al., (2003) and is similar to the strategy now being employed by SKB (see e.g. SKB, 1999 or Andersson, 2003). Basically all geoscientific disciplines � geology, hydrogeology, hydrogeochemistry and rock mechanics � follow the same work-flow, as depicted in Figure 7-1. Data are collected (see Chapters 4-6), processed and interpreted. The processed data, in turn, are used to compile/construct descriptive models of the site (site descriptive modelling) with the aim of providing estimates in three dimensions of geological, rock mechanics, hydrogeological and hydrogeochemical properties. Integration between modelling in different disciplines is essential since all the models describe the same rock volumes. Modelling often leads to iteration as questions and uncertainties may rise and supplementary processing and interpretation is necessary. Also, new ideas may lead to re-evaluation of interpretations and supplementary data may become available. The descriptive models will be used in turn for different types of analyses and assessments and later as input to civil engineering design and Safety Analysis. As part of characterisation modelling, the descriptive models will be used to predict and assess the impact that ONKALO itself has on the rock mass.

Figure 7-1: Work phases of subsurface modelling (from Saksa et al., 2003).

The underground characterisation of ONKALO involves a clear learning aspect. The whole chain from data collection to analysis provides feedback to the data acquisition practise and future surveying needs. The cycles of modelling aim at successive improvements. Prediction-outcome studies will also be used to test the ability to

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estimate the rock mass properties and to evaluate modelling capabilities and the achievable accuracy.

7.1.1 Data processing and interpretation

Subsurface data collected in the investigation and monitoring activities require processing and interpretation before they can be used further. The main purpose of data processing and interpretation is to assess the quality of the data and to convert the large amount of raw measurement data into a manageable and meaningful form for use in, for example, interpretation of local conditions in one borehole or in three-dimensional descriptive modelling. The information level of processed data is higher and understanding is enhanced.

Data processing normally includes arrangement, calibration, level adjustment, noise reduction and plotting. Interpretation covers qualitative and quantitative assessment of results. Typical means include compilation of maps and images, delineation of anomalies, classification of results as well as the use of interpretational models. Together with petrophysical and geological background data the possible origins of anomalous features can be estimated and their geometrical extensions and alternatives can also be evaluated.

From a strategic point of view it is important that enough time is reserved for data processing and interpretation. However, the required resources and time may vary considerably from one investigation method to another. Direct observations, like results of mappings, represent the simplest type of data in this sense, as only location information may need to be attached to them. On the other hand, geophysical soundings to explore larger volumes normally require a sequence of processing and interpretation steps before the user can fully take advantage of the results. It is also necessary that the processing and interpretation steps are conducted and the results are made available before modelling is started.

7.1.2 Discipline integrated descriptive modelling

A specific modelling task force will be set up for integration of the results and of the modelling work in different disciplines. Within this framework the geological model plays a central role, as illustrated in Figure 7-2. The other models, i.e. rock mechanics, hydrogeological and hydrogeochemical models, use the geometrical framework (structures, lithological boundaries etc.) of the geological model at least as background information together with additional data. Even if a discipline model itself can be compiled independent of the geological model, as is the case with the hydrogeochemical model, analysing the result with regard to the geological model will be beneficial for the development of both models.

The models and the attached descriptions are central to further analysis, to safety assessment, and in the planning of continued underground construction work. In order to meet performance and safety assessment needs, it is essential that the interpretation

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and modelling procedure be objective (i.e. the result should be essentially independent of the person doing the work), traceable, transparent and to the greatest extent possible, quantitative (Olsson Ed. 1992).

Figure 7-2 The individual discipline models are all integrated. The geometrical framework of the geological description is the key to this integration.

Mutual dependence between different discipline models calls for the establishment of an integrated modelling strategy and a modelling task force (see above) to execute this strategy. The strategy should ensure that:

• the investigations are focused on those conditions in the bedrock that are important for the safety case,

• consistency between models is assessed and reasons for apparent inconsistencies are explained,

• alternatives in model descriptions are documented and tested, taking uncertainties and the supportive data related to the different alternatives into consideration,

• explanations may be found for observed processes, properties or behaviour,

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• interpolation and extrapolation will be enhanced with the help of other models or parametric constraints,

• the quality of the modelling work and the models is improved and the learning process is enhanced.

Discipline integration

The understanding of the site conditions can be tested on the basis of:

• the capacity to predict various properties in the bedrock over larger scales from the information obtained in measurement scales,

• the capacity to predict various processes in controlled experiments,

• the mutual consistency between models built on independent pieces of information.

In practice all these means require the integration of the information derived by different methods and interpretation systems. The starting point of such integration efforts is the identification of knowledge-related dependencies between different investigations activities. The dependencies can be recognised by determining the essential input requirements and their theoretical bases in different work activities and putting the connections under common conceptual models.

The search for integration will be a systematic phase in the modelling. Models covering the same volumes, developed in similar scales are natural counterparts in integration. Integration includes crosschecking and co-interpreting the information, transfer of direct or indirect information between disciplines, checks of consistency, consideration of constraints and questions raised by other data sets. Consistency between the different discipline descriptions (geological, rock mechanics, hydrogeological and geochemical) should be reached and differences explained if not fully understood at the point. This will result in quality improvement of the models and could possibly also lead to decrease in investigations and direct observations than otherwise. Also the requirements set for a model, especially for the geological model by the other modelling activities can be considered.

There are obvious links, and thus direct integration needs, between the geological and the rock mechanics model, the geological and the hydrogeological model and the hydrogeological and the hydrogeochemical model. Even if all the discipline descriptions are indirectly related, integration may focus on these links. Integration needs to work in both directions. For example, the geometric framework, i.e. fracture zones and main lithological units, of the geological model is used in the rock mechanics and hydrogeological descriptions, and on the other hand, the mechanical and hydrogeological observations, e.g. stress distribution or sections of high transmissivity, may have consequences for, and lead to modification of the geological model. The

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salinity distribution assessed in the hydrogeochemical description needs to be consistent with the simulated salinity evolution used in the hydrogeological model.

Site-specific data will always be sparse, and for ONKALO there is also a need to limit the amount of boreholes that may potentially disturb the rock mass. This makes it a modelling challenge to interpolate and extrapolate sparse data into a reliable three-dimensional description. Furthermore, the models used in the different disciplines share a common geometric framework. Integration of data, interpretations and models is important:

• to achieve a broader understanding that cannot be achieved within individual disciplines ,

• to achieve reliable descriptions,

• to ensure an optimal use of site data and to avoid oversampling (e.g. an excessive amount of boreholes) and,

• to better evaluate variability and the remaining uncertainty.

Software

Several different types of software will be used. The data management system currently under development, see Chapter 10, will be utilised in the handling of data and other information. Currently available geological modelling software packages, such as SURPAC, are able to cope with the required modelling tasks. CAD-software such as normal 3-D and 2-D design-drawing platforms as well as GIS systems with 3-D extensions are also used frequently.

Three-dimensional visualisation tools will be essential for the development of geometrical structure models, for sharing model development within the integrating modelling team and for exploring the models, the descriptions as well as the simulation results. Presentations such as animations, fly-through, and half-slicing as well as easy navigation of all the ONKALO components and the geological model should be possible.

While all descriptions share a common geometrical framework, different discipline applications will use different software in their analyses. Different software packages handle the geometry of the objects in varying ways. For instance, some representations need to be translated to for purposes of numerical computations, for instance.

For example, in the past hydrogeological modelling has mainly applied the porous medium approach, but now fracture network modelling and hybrid approaches will now be required. Software such as VTT�s FETRA, GMS and discrete fracture network codes (FracMan, FRAC3DVS etc.) will be used. Codes for evaluation and fitting of individual hydraulic tests will also be applied.

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Uncertainties are to be analysed in a more quantitative manner and presented also in a visually understandable format. The minimum requirement is that areas and volumes, which are better covered by data and interpretation results are differentiated from areas and volumes that are very sparsely covered.

7.1.3 Modelling scales and stages

Scales

Models will be constructed at various scales, including regional scale, site scale and local scales. The different scale models needs to be consistent, even if there is less detail in the geometrical resolution of the larger scale models.

Regional scale models present the geoscientific conditions of the general region of Olkiluoto (e.g. of southern Satakunta), or, at a larger scale (semiregional), of the Olkiluoto island and its immediate surroundings. The areas covered range from the order of 100 km2 to the order of 10 000 km2. Data coverage is typically very heterogeneous and usually not collected in connection with the site investigations. Although regional and semiregional models are mostly two-dimensional map presentations, they can include considerable depth data derived from geophysical modelling (e.g. depth profile of igneous intrusions, crustal structure and depth to Moho). More importantly, regional models often place important genetic constraints on the site model (e.g. geological evolution, modes of formation), which cannot be obtained for the investigation of the site alone. Hence, targeted regional and semiregional investigations will be an essential complement to detailed site investigations.

The site-scale geological model covers the area of the investigation site at the surface and the volume of rock immediately below that area, down to the depth of the deepest drillholes. The area of the investigation site at Olkiluoto is 3-4 km2 and the deepest drillholes about 1000 m, so the rock volume below the investigation site, which contains ONKALO and the future repository at its centre, is 3-4 km3. Geohydrological and hydrogeochemical models will be centred on the site scale, but will necessarily also include semiregional-scale models of the immediate surroundings of the site. The site model acts as a boundary condition and starting point for modelling of smaller volumes, i.e. for local-scale models.

Local-scale models will be developed representing different sub-volumes within the rock volume represented by the site-scale model. The lay-out of ONKALO underground research facility and planned experiments will subdivide the investigated volume into smaller sub-volumes. The local-scale models will be embedded, nested, in the site-scale model and will aim at a more detailed description of selected sub-volumes. The local-scale models may also cover different aspects and may also have differences in detail and accuracy.

The following sub-volumes for ONKALO may be modelled in varying detail:

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• The upper access tunnel volume near the surface at a depth range of ca. 0 - 300 m.

• The shaft site with its immediate rock rooms, depth range 0 - 500 m, up to 100 m around the shaft(s).

• The access tunnel line as a whole and its environs - this sub-volume resembles a free-form tube in 3D.

• The main level characterisation tunnel area, basically on one level at a depth of about 420 m, the rock mass within the characterisation tunnel area (some 300 x 400 m) and its surroundings.

• The lower level area rock rooms and possible tunnel(s), essentially on one level at a depth of ca. 520 m and assumed to occupy a small area round the shaft. The area can also be part of the shaft site model.

Natural boundaries, such as major fracture zones, or lithological and hydrogeological boundaries, or engineered objects may also outline the sub-volumes.

As an example of a local-scale, the upper ramp volume down to c. -300 m is likely to allow a comprehensive, detailed geological model to be developed. The model can probably be extrapolated down to -400 � -500 m level to some extent, at least for larger rock units and structures dipping favourably, but this extrapolation will evidently need further updating after the actual characterisation of the levels below � 300 m has been carried out. The same may apply to the shaft site with its immediate surroundings. In both volumes large amounts of multidisciplinary pre-investigations are to be conducted, and the volumes will contain tunnels and underground rock rooms with varying orientations. Figure 7-3 shows an example of the access tunnel modelling activities.

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Figure 7-3 Example of local-scale models which may be developed on the basis of tunnel mapping data from the upper part of the ONKALO access tunnel.

Modelling stages - revisions and updates

Modelling will be updated several times; first during the selection of the access tunnel volume, then during construction site investigations and finally when the tunnels and the investigation drillings are completed within a particular volume. The construction schedule will affect the interpretation and modelling activities. A faster �on-line� type method needs to be created to run parallel with the current type of a longer-term data processing and interpretation scheme. This means that the drilling results and the inferred geological estimates are processed as they are received. The same applies to geophysical loggings, soundings and hydrogeological measurements. Modelling must support supplementary planning and changes in construction when these are expected. The planning and preparation of construction requires that the results are assessed within a week or a month. Longer-term research and characterisation runs in a month - year span. However, it is possible that conclusions based on the first, fast modelling round will sometimes change, as more comprehensive interpretations become available. Review and iterative updating mechanisms are required.

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Model updating and the role of prediction � outcome studies

Repeated prediction and outcome studies, see Figure 7-4, will be conducted to estimate the outcome of new exploration activities and to compare the estimations with the observed results. This procedure will start already in the access tunnel.

In general, the difference between the estimate and the result indicates the level of knowledge and the prevailing uncertainties. The differences should decrease as a result of more comprehensive input data sets, better conceptualisations (e.g. more precisely defined processes), as well as improved and more detailed models. The improvements are based on learning and the development of skills during the process. System descriptions should converge to the conditions and properties prevailing in the nature. Testing and forecasting can also help recognise when investigations have reached a mature state, i.e. when adding of new data does not seem to reduce uncertainties or improve understanding significantly. Repetition is an essential component of prediction-outcome studies at varying scales to ensure that the results are measurable.

However, the main object of the prediction-outcome studies is to contribute to the updating and revision of the descriptive models. The �prediction� should focus on the descriptive models and not on forecasting every possible disturbance of a local or transient nature to be encountered during the excavation work.

Themes for prediction-outcome studies include ranges of:

• Deterministic location, orientation and properties of major fracture zones.

• Occurrence of minor fracture zones (deterministically or statistically: frequency, properties) and statistical properties of individual fractures in the rock between the major fracture zones.

• Rock type distribution, major veins and lithology related engineering parameters.

• Main groundwater types, saline water boundary, salinity, Eh and pH.

• Hydrogeological conditions such as the frequency of hydraulic conduits and the distribution of hydraulic head.

• Distribution and variability of rock stress state.

Prediction-outcome studies are also essential for the development and application of the coordinated investigation, design and construction activities, see Chapter 3. The idea of this approach in construction is to recognise most probable, favourable and unfavourable conditions in advance and pre-established design alternatives based on these conditions. So far it has not been applied to full extent by organisations involved in nuclear waste management (Bäckblom & Öhberg 2002).

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Figure 7-4 Prediction-outcome process.

7.1.4 Modelling impacts of ONKALO and its construction

As noted by Posiva (2000) the construction of ONKALO will result in changes in the natural environment, mainly due to groundwater inflow into the excavations. The changes will be reflected in the local rock stress and the mechanical state of the rock mass, in hydraulic head distribution and in the level of the groundwater table, as well as in hydrogeochemical conditions.

While it is important that ONKALO will not significantly affect the suitability of the rock for a repository, the larger scale disturbance caused by underground construction in fact offers a unique opportunity to explore the site at a much larger scale than is possible with individual boreholes. Underground construction itself can thus be viewed as a large-scale experiment. The evaluation of this experiment, including a comparison between the predicted changes and the actual changes, offers considerable possibilities to enhance confidence in the understanding of the rock mass in the vicinity of the

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facility. The evaluation may also lead to updates/revisions in the description of the rock mass models, but these updates need to be incorporated into the specific characterisation programme for ONKALO (see Chapter 5). Here, an overview of these issues is provided, while the separate report on assessment of disturbances discusses them in more detail.

Evaluation will focus on the region close to ONKALO and will concern potential changes in:

• rock stress and mechanical state around the tunnels,

• groundwater pressures at depth, flow distribution and groundwater table, and

• salinity distribution and other major changes in groundwater composition.

The evaluation is based on predictions made on the likely impact of construction to be discussed in the disturbance report. Information on the changes caused by construction will be obtained through the monitoring activities described in Chapter 7 and through the underground characterisation programme. In order to provide suitable opportunities for comparisons to be made between predictions and outcomes a well thought through strategy is required.

7.2 Geological modelling As shown in Figure 7-2, the geological model is the central element in site descriptive modelling, since it provides the geometrical framework for all other types of modelling. The geological model is a 3D synthesis of primary geoscientific data in a form which is appropriate for numerical computations, whilst still retaining the essential first-order features of the site.

7.2.1 Model components

At Olkiluoto, the geological model consists of two parts, a bedrock model and an overburden model, which interface along the bedrock surface (Figure 7-5). The overburden model, which consists of a synthesis of thickness variations and facies distributions within the thin cover of Quaternary deposits, has not yet been prepared, although it may have significance for some aspects of hydrogeochemical modelling (see below). It will not be discussed further here. The bedrock model, which is a 3D representation of the spatial distribution of lithological and structural features in the bedrock of the site, in the volume of rock enclosing ONKALO and a future repository, forms the basis for all rock mechanics, hydrogeological and hydrogeochemical modelling.

As indicated in Figure 7-2 and Figure 7-5, the input to geological modelling consists of two types of data. Firstly, there is the body of quantitative data from the surface, drillhole and tunnel investigations, as detailed in Chapters 4-6 of this report. This provides the basic input to the numerical computations. Secondly, there conceptual

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models which summarises the present genetic understanding of the features being modelled, i.e. their mode of formation, geological significance, relation to other features, etc.. Experience shows that a properly argued geological model cannot be constructed without some basic understanding of what the modelled features represent and how they usually behave in association, including, of course, the general geological evolution of the site.

For convenience of description and handling, the bedrock model has been subdivided into a series of subsidiary descriptions, as shown in Figure 7-5. A distinction is made between the lithological description, the fracture zone description, the fracture network description and the rock mass description, as outlined below. This subdivision is for convenience of handling different types of data and should not be regarded as of fundamental significance. For instance, the fracture zone model and fracture system model both represent the effects of brittle deformation at the site, describing deterministic large-scale features and stochastic small-scale features, respectively. However, this is clearly an artificial subdivision, geologically, since these features are closely related with regard to mode of formation. Similarly, the lithological model may have considerable significance for the distribution of fracturing in space, and the rock mass model is a means of representing the overall properties of fractured rock in a way which is meaningful for engineering geological purposes.

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Figure 7-5 Components of the geologic modelling.

7.2.2 Evolutionary aspects

The geological evolutionary model describes deformation history events, the processes involved, the folding, trends, age relationships, continuity, faulting and extensions of the geological units. Tectonic features such as fracture populations and domains, fold axis orientations, fold profile form and scale, faulting and shear zones are to be described. The evolution model is essentially illustrative in the sense that it does not

Lithology

Fracture zones

Fracture network

Rock mass

Bedrock model

Characterisationdatabase

Processunderstanding

Interpretations,evaluation

Lithology

Fracture zones

Fracture network

Rock mass

Bedrock model

Characterisationdatabase

Processunderstanding

Interpretations,evaluation

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depict the processes and geometries of exact locations. The evolution model is refined with new information on a regular basis and the knowledge is transferred to the development of a lithological model. Occurrence of lithological bodies and mineralogy encountered are tied to geological processes and deformation phases.

The evolution model can benefit of new numerical analysis methods by applying the known folding stages and events to laminated sediment beds. Evolution modelling can also utilise forward modelling with geophysical parameters (magnetic, density) and thus allows comparison with geophysical maps. The evolution model supports lithological and structural modelling. It provides trends and supports the selection of probable geometries. The modelling approach fills the gap between direct observations and an appropriate spatial solution.

7.2.3 Lithological description

The lithological description includes all rock matrix properties, i.e. not just rock types and contacts (lithology) but also structural aspects, such as foliation and lineation. It is based on a conceptual model of the tectonic and deformation history of the site, as deduced from surface observations (outcrops, investigation trenches), drill core logging, mapping of tunnel and shaft walls, etc., as well as on detailed quantitative information, such as rock composition (mineralogy) , layer thickness data (heterogeneity), degree of alteration or weathering, and structural information (foliation, etc.). As with the other models, discussed below, what data is described deterministically (i.e. by defining the position, orientation, etc., of the lithological unit within the rock volume simulated by the model) and what is described statistically (e.g. small-scale heterogeneities in terms of bulk lithological parameters), depends of the scale of the model and the degree of detail in the data.

A particular aspect of the lithological model, especially important at Olkiluoto, is the anisotropy of the rock units, i.e. the degree of development of a pervasive foliation. "Foliation" is a general term for a planar arrangement of textural or structural features in any type of rock, e.g. cleavage in slates, and schistosity or gneissic structure in metamorphic rocks. It imparts on the rock matrix what in geology is referred to as a "planar anisotropy", and in rock mechanics as a �transverse isotropy�. Foliation is a pervasive structure, i.e. a feature, which does not occur as an individual element (like fractures or bedding planes) but affects the whole of the rock matrix, usually as a preferred shape and/or crystallographic orientation of every mineral grain.

Its main effect is that it makes bulk properties of the rock matrix, like strength, thermal conductivity, resistivity, etc., also anisotropic, which in turn affects the way in which numerical modelling is carried out. Also, another important characteristic of the Olkiluoto site is clearly dependent on the foliation. This is the feature, described qualitatively in many reports, that the foliation in the rock matrix seems to pre-determine the orientation of one of the dominant fracture sets, thus imparting on the rock mass (not only the rock matrix) a bulk anisotropy which can have important rock engineering and hydrogeological effects.

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7.2.4 Fracture zone description

Fractures and fracture zones form the main pathways for groundwater flow and possible radionuclide transport. The fracture zone model summarises information on the large-scale features of the site, and is deterministic, i.e. it aims to describe the 3D arrangement (thickness, orientation, continuity, etc.) of the modelled structures at their respective positions within the model volume. Consideration and avoidance of fracture zones is one of the main factors in the ONKALO and repository design, and the fracture zone model will improve in accuracy and reliability continuously during the construction of ONKALO and the characterisation project. Especially the internal properties of these zones, and their extensions, orientation and relationship with others will become better known.

The identification of fracture zones builds on the identification of intersections in drillholes, at the bedrock surface and in tunnels and shafts. These form "fixed points" or "fixed lines" within or at the boundaries of the bedrock model of the site. Based on a conceptual model derived from the characterisation of these intersections and other fracture data, inferred correlations between the various measurements, mapping and observation points are made. Such correlations are also based on an analysis of the geometrical data (measured orientations at a point or indirectly observed in space), planar or trend surfaces, and features of geological similarity. Also, indications of connectivity between distinct observations (hydraulic, electrical, elastic and chemical properties) may be used, and the correctness of correlations can sometimes be checked against VSP or borehole radar data. Electrical correlation with galvanic measurements may also indicate cross-hole or cross-tunnel connections.. During underground characterisation, correlations will be tested, and either rejected or confirmed, as the density of observations increases. At the same time, new challenges will evolve because more realistic models will require new objects to be considered in the bedrock models (e.g. faulting and continuity, folding). In addition, if smaller scale structural features are to be included deterministically in the models, the number of objects will increase considerably. As the model develops, the uncertainty regarding the larger and major fracture zones will decrease. Downscaling will, however, bring a new set and scale of structures to model.

Because of the scaling problem, an important aspect is to understand the relation between the deterministic fracture zones and the fracturing in the rock mass between them, which is modelled separately using stochastic methods (see below). These are not two fundamental different things, but are instead two related aspects of the same phenomenon. What is regarded as a deterministic fracture zone and what is included in the statistical fracture network model is a matter of scale.

7.2.5 Fracture network model

The possibilities of fixing the geometry and properties of individual fractures in a large-scale model deterministically are extremely limited. Hence, a statistical treatment is used to describe fracture systems in rock bodies. The fracturing is modelled with the

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help of so-called DFN (discrete fracture network) parameters, which define the geometries, directions and spatial distribution of the fractures, as well as other characteristics, such as mineralogy or transmissivity.

Information from outcrops, boreholes and underground excavations provide the basic data for defining the DFN parameters. These data, however, must go through an extensive processing before they can, in a correct way, simulate the properties of natural fracture network. In order to create a fracture network model, the following minimum amount of geometry-related information is required:

• orientation of the fractures

• size of the fractures

• fracture intensity

• fracture termination

• the spatial distribution of the fractures

This information is preferably given as different distribution functions with features, which can vary within one and the same model. Other parameters of interest, such as mineralogy, water-conducting properties, rock mechanical properties, etc., come into play when this basic geometrical-statistical model is used as a basis for dynamic hydrogeological or rock mechanical modelling (see below).

7.2.6 Rock mass model

The rock mass3 model describes rock mass properties between identified structures. It describes lithology, fracturing and detailed scale structures. Rock mass models are either deterministic or stochastic. Descriptions of relatively small volumes investigated in detail can be compiled in a deterministic way. Examples can be developed in the access tunnel or on the main ONKALO level rock rooms. Another type of rock mass model is generic, describing the average rock mass conditions in a certain volume or type of rock.

The majority of the rock mass is sparsely fractured. The description of fracturing concerns:

• variation by rock type,

• depth variation,

• spatial variation: domains of fracturing (implicit method), block analysis (explicit method),

3 In some past Posiva publications the rock mass model was denoted the �intact rock�. However, this vocabulary was potentially misleading and is not in accordance with international standard. In fact,

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• fracture populations (orientations, type, mineralogy),

• mineralogical, hydraulic and mechanical properties of fracturing.

The distribution of other rock mass properties, such as rock type, weathering and alteration, is estimated through interpolation, extrapolation or application of geostatistics. Arguably, geostatistical methods are not meaningful until more balanced 3-D sets of data points are available and statistical correlation distances are valid. Similar methods may be applied in the estimation of rock mass parameters in other disciplines; e.g. rock mass mechanics parameters, temperature distribution, pressure field and groundwater salinity etc.

It is assumed, that the rock mass can be divided into blocks with characteristic properties, differing from the surrounding rock. When such a division is not necessary, the whole rock mass may be a single block. The blocks may be bounded by major fracture zones or the bounding factor can be lithology, a tectonic boundary, large scale folding etc. Blocks defined by major fracture zones have been used previously in the Olkiluoto site analysis on engineering geological properties (Äikäs et al. 2000). When a single parameter varies strongly or is uncertain, several can be grouped together. This approach was applied in, for example, the SKB Laxemar modelling exercise (Andersson et al., 2002b) , using a combination of lithological variation, alteration and fracturing to identify rock domains with statistically similar properties.

7.3 Rock mechanics modelling The updated information database will form the basis for the updating of a rock mechanics model for the volume of rock around ONKALO. The modelling (Figure 7-6) will be based on:

• The updated geological structure model (see 7.2).

• An assessment of the thermo-mechanical properties of the rock mass and the boundary conditions of the volume of rock around ONKALO, using the mechanical and thermal data presented in section 5.3.

The modelling will be carried out to assess the mechanical state (e.g. the potential damage to the rock) of excavated rooms to assist in the design and layout of the repository (e.g. depth, tunnel orientation with respect to principal stress directions, room geometry, respect distance from fracture zone, need for support) and to predict the displacement behaviour of the rock, in order to allow comparisons with the displacements measured during construction.

�intact rock� is a concept used in rock mechanics and refers to rock without visible fractures. The rock mass model may indeed contain both fractures and smaller scale fracture zones.

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Figure 7-6 Rock mechanics modelling scheme

7.3.1 Descriptive modelling

Assessing the data

The data collected should represent the three-dimensional property distribution of the rock mass. Some data need to be assessed and evaluated due to limitations of measurements and sampling. The quality and reliability of the rock mechanics data also need to be evaluated before they can be used to predict rock mass properties.

Measurement results from the different parts of ONKALO will be analysed, and some will be numerically modelled and compared with earlier estimates and calculations. The most representative and meaningful results in 3D will most probably be acquired on the main level and on the lower characterisation level. On the main level varying geological properties and features (like fractures, zones, veins, contacts, schistose parts and faults) as well as spatial variability in parameters or in the degrees of anisotropy will be of interest in modelling. In addition to the results of rock mechanics measurements (stresses displacements etc) information on fracturing will also be important for modelling.

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Engineering classifications of the rock mass, such as Q and RMR, and their variation along the boreholes and the tunnels are commonly applied. However, the determination of the rock mass rating or quality using these systems is sensitive to the techniques chosen to define homogeneous sections of a borehole or a tunnel and the selection of Q and RMR components involves elements of arbitrariness, even when the rock properties are rather well known. A considerable portion of the host rock classification system, being developed for use in ONKALO and in the construction of the repository (McEwen 2002, Hagros et al. 2003), is related to the rock mechanics properties of the rock mass.

Detailed data on fracturing and fracture zones in 3D will be obtained from ONKALO by means of engineering geological mappings and this will also be beneficial to rock mechanics analyses. It is likely that at least some minor fracture zones will be intersected by the tunnels. The most applicable information related to fracture zones is likely to be acquired from the depth range 300 � 500 m. On the basis of these results a model for these zones and the rock mass will be constructed and used in rock mechanics analyses.

The main challenge to understanding rock properties at a larger scale is the requirement to extrapolate the information measured on discrete points and at different scales and to upscale this information to the scale required. This upscaling will be achieved using the geological model and by expert judgement on where rock blocks are grouped into rock domains. Essential steps include:

• understanding and evaluating the geological model,

• visualisation and geostatistical analyses to support 3D modelling,

• direct description of stress field,

• selection of blocks or domains to be used.

Larger domains incorporate more data and, while a greater amount of data will be associated with a lower level of uncertainty, the accuracy of the resulting description of the rock mass may be inadequate. In contrast, smaller domains will be associated with greater levels of uncertainty and a less amount of data (Andersson et al. 2002a).

Rock mechanics analyses with models

The rock mechanics analyses of ONKALO will contribute to the selection of the final design of the tunnels and other underground excavations. These analyses may concern a specific part of the underground construction or be generic (related to tunnel profiles, deposition holes - both vertical or horizontal, i.e. for the KBS-3V or KBS-3H disposal concepts). Eventually, analyses will be carried out as part of the application for the construction licence and there is also an obvious need to increase co-operation with the other disciplines for this to be done efficiently.

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The majority of rock mechanics analyses need to provide results at the tunnel scale, approximately some tens of meters, to capture the mechanical processes that are expected around the tunnels and the excavated rooms of ONKALO. Some modelling of rock mass domains at a scale of tens to a hundred meters of rock is also needed.

Understanding the geological history and the structural setting at the site scale (see section 7.2) is useful for establishing the evolution of the stress regime. Numerical modelling may be used to investigate the mechanisms that could be responsible for a particular stress regime on the site. The main characterisation level (dimensions in hundreds of meters) and the lower characterisation level (dimensions in some tens of a meter but expected to be an important area for rock mechanics) could be the targets of such modelling, as they are expected to produce a large amount of supporting geological data and reliable geological model descriptions. Modelling can assist in interpolation between boreholes and tunnels where stress measurements have been made.

Alternative structural models (e.g. different in geometry, properties and loading conditions) may also be analysed and compared. Simple stress estimators � such as linear functions of stress versus depth � should be used if the underlying reason for the depth variation in stress is not known, if data are sparse or if the assessment considers volumes of rock mass remote from any measurements. Stress estimation should, as a matter of course, include a quantitative estimate of uncertainty and variability.

Possibly the best approach to rock mechanics modelling is to apply different methods (empirical and theoretical) in the estimation of the rock mass mechanics properties and to devise a procedure for making an overall judgement. The planned prediction-outcome studies, see section 7.1.3, which are integrated with geological modelling activities, could be used and analysed to prove competence and site knowledge. At the Äspö HRL the rock mechanics test cases carried out showed that the application of more than one modelling method was important (Andersson et al. 2002a).

7.3.2 Evaluating the rock mechanics impacts of ONKALO

Underground construction will affect the in situ stress conditions in the vicinity of the excavated spaces. The mechanical properties (i.e. mainly strength and deformation properties) of intact rock and rock mass are not expected to change to any significant extent, but the impact may be greater on the hydraulic conductivity of the rock due to fracturing and rock damage, which is likely to be limited to the EDZ. The excavation process will also cause micro-seismic events.

Potential impacts and their observation

The predicted rock mechanics changes presented in the Baseline Report (Posiva, 2003a) suggest that the changes in the stress conditions of the rock mass due to construction will be restricted to the near vicinity of the excavated spaces (Figure 7-7). The mechanical impact of these stress changes will essentially be controlled through

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inspection/monitoring of the tunnel walls, complemented by stress measurements in the tunnels. The mechanical state of the tunnel walls and the new stress data will be compared with the predictions made.

The mechanical properties (i.e. strength, fracturing, deformation properties) of intact rock or rock mass outside the Excavation Damaged Zone, EDZ, are not expected to change at all, or possibly only to a small extent due to some reactivation of pre-existing fractures. An assessment of the rock mechanics properties will be made by evaluating fracture statistics, fracture zones, lithology along the tunnels and by carrying out specific rock mechanics tests on cores obtained from boreholes drilled in the tunnels.

The excavation process will, however, cause some damage in the peripheral zone of the excavation. The excavation technique (e.g. blasting) and the redistributed stresses reaching the rock strength will result in damages in a limited zone around the tunnel. The stress redistribution zone outside this limited damaged zone will show stress changes but no damages (the recoverable elastic region), see Figure 7-7. The studies show that the thickness of the damaged zone defined in terms of increased porosity is about few centimetres around the half barrel of the blast hole due to the blasting (Siitari-Kauppi & Autio 1997, Autio et al. 2003). However, some tens of centimetres long fractures, which do not affect the porosity significantly are also induced by the blasting. The EDZ in the floor section in both the Research Tunnel at Olkiluoto and ZEDEX-tunnel at Äspö is clearly larger and the fracturing more connected than in the walls and roof. The floor section can be, however, excavated to produce EDZ similar to that in the wall and roof sections, if necessary. Only minor changes in the properties of the zone are expected due to relaxation of tunnel boundaries, rock damages caused by high stress concentration and increased porosity caused by blasting. The thickness of damaged zone could be more than few centimetres if we consider not just the solid rock, but also the dilatation of fractures.

The extent of the damaged zone will be studied during ONKALO's construction using existing, well established investigations such as the 14C-PMMA method (Siitari-Kauppi and Autio 1997) as well as visual and colour penetrant mapping of the tunnel walls. Development work on using the 14C-PMMA technique for in-situ rock matrix characterisation as well as on the visualisation of the connective pore space under stress conditions is also under way and is a possible alternative to be used in ONKALO EDZ investigations (Autio et al. 1999).

In the comparison of predictions and observations, due consideration will be given to

• measurement inaccuracies,

• scale effects (e.g. differences between measurement scale, modelling scales and actual tunnel scale).

Comparisons made between predictions and eventual observations will be documented and then used in evaluation modelling (see below).

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Figure 7-7: Schematic illustration of redistribution zone (full line) and damaged zone (dashed line) around a disposal tunnel and a deposition hole.

Evaluation modelling

Where the comparison of predictions with later observations (see above) shows significant differences between measured and predicted stresses or between the measured and the predicted mechanical state round the tunnel, modified numerical rock stress and deformation modelling will be carried out. Modelling will consist of the following steps:

• sensitivity analysis to explore to what extent uncertainty in rock mechanics properties may explain the differences between predicted and measured properties, and

• re-analysis of the data, incorporating the updated rock mechanics description based on the results of the detailed characterisation programme (see section 5.2) and possibly a revision of the geometry and the stiffness/strength of the fractures.

Evaluation modelling may suggest what changes should be made in the description of the rock mechanics properties of the rock mass and to what extent changes are needed with respect to the different effects described above.

7.4 Hydrogeological modelling The descriptive hydrogeological model of the site will be refined, re-evaluated and re-calibrated on the basis of the results of characterisation and monitoring carried out both in the tunnel and in the surface-based boreholes. The descriptive model developed will, in turn, be used as input in the modelling of the hydraulic impact of excavation.

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Due to its open tunnel condition ONKALO will act as a large-scale pump test. The pressure and flow responses as well as the geochemical changes (TDS as well as the impact of surface waters) to be monitored in ONKALO and the surrounding boreholes will provide a unique opportunity to estimate how well the different types of features, including EDZ and the skin of the open tunnel, have been modelled.


Figure 7-8 illustrates the components of the descriptive hydrogeological model. Its geometrical framework is based on the geological model. The modelling aims to produce reliable hydrogeological models for groundwater flow analysis. Descriptive modelling will be carried out using the stochastic discrete fracture network approach (DFN) at a detailed scale and the combined DFN � porous medium approach at a larger scale. The DFN description will also provide upscaling relations for larger scale model descriptions. Modelling at a larger scale, and possibly also at a detailed scale will require consideration of density-dependent effects.

Figure 7-8 Development of hydrogeological model.

Modelling will build on:

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• The updated geological structure model (see section 7.2), with due consideration to the fact that hydraulic conductivity has been used as a parameter in the determination and classification of structures. However, hydraulic features not meeting the criteria of structures but considered important for intended groundwater flow modelling, can be conceptualised and described as additional objects in the hydrogeological model.

• An assessment of all hydraulic tests and monitoring results (see Chapter 5 and 6).

• An analysis of the correlation between geological and hydrological properties, and rock mass and rock stress at different scales.

• New fracture trace mapping carried out in the main level characterisation tunnels to enable a much more relevant DFN-model to be developed.

• A re-assessment of salinity distribution (see section 7.5).

• An assessment of the effects of skin and degassing on inflow into the tunnels.

• An assessment of the hydraulic connections between fracture zones and the surrounding rock.

• The knowledge of the fracture network geometry and the distribution of hydraulic conductivity (or rather fracture transmissivity distribution). These will be used extensively in the hydrogeological characterisation of blocks of rock surrounding each deposition hole in the first disposal panel. The characterisation will be based on modelling of the flow field corresponding to pressure and pumping response measurements.

Experience shows that compiling the hydrogeological model in parallel with the development of the structural model is an effective method. It also supports integration from the beginning. However, some analyses and assessments can be carried out separately, since the relationship between groundwater flow and the structural models is not known exactly. In the future, rock mass volumes bounded by important structures or containing special fracturing or hydraulic properties can delimit/define the analysed units.

The geological models will possibly be updated more frequently than the hydrogeological models. The hydrogeological descriptive model finds a major use as input to the numerical groundwater flow analysis. Modifications may be needed in the model geometry. Complex geometrical structures may be simplified, structural features that have no hydraulic significance may be left out according to expert judgment and additional connectivity between structures ending near each other may be added.

7.4.2 Evaluating the hydrogeological impacts of ONKALO

The hydrogeological system at Olkiluoto that consists of superficial water circulation and a groundwater regime affected by numerous natural factors, is very complex. The

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construction of ONKALO will disturb this system and this disturbance offers a unique opportunity to increase the level of knowledge of host rock conditions in general and of the hydraulic system in particular. Besides site characterisation, measurements of the impact of the tunnels are linked to the estimation of the hydraulic significance of EDZ as well as other coupled �skin effects�, (see also section 5.3.2).

Potential impacts and their observation

Atmospheric pressure in the tunnels will result in some inflow of groundwater into the tunnels. This will have a significant effect on the nearby flow pattern and may give rise to up-coning of more saline water at depths as well as to lowering of the groundwater table above ONKALO. The created flows will affect the naturally evolved distribution of deep groundwater types.

In addition, there are large surface water reservoirs (e.g., Liiklansuo, Olkiluodonjärvi) in the vicinity of the tunnels. It is possible that these surface water deposits will provide sufficient recharge, through rainfall, to maintain their water levels practically unchanged. If this occurs, the response of the groundwater system to the tunnel excavations will not be detected as a change in groundwater levels but possibly as a reduction in surface runoff. Similarly, the water level in the artificial water reservoir located about 200 m west of borehole KR14 (known as the �Korvensuo-reservoir�) will be kept at its present level through artificial recharge, since the reservoir is needed for the power plant operation. In this case the pertinent monitoring parameter for the reservoir is the flow rate needed to keep the water level in the reservoir unchanged.

The parameters of groundwater flow regime that will respond immediately to the excavations include the hydraulic head and the flow rates in deep boreholes. The chemical composition of groundwater samples taken in the boreholes are expected to evolve with time, but more slowly. These responses are to be evaluated, together with the observations of groundwater inflow rates into the tunnels and their spatial distribution and chemical compositions.

The following factors need to be taken into account:

• Monitored quantities that are expected to evolve in response to tunnel excavation and the induced ingress of groundwater into the ONKALO tunnels. These include hydraulic head, flow rates and TDS in monitoring boreholes.

• Parameters to be measured and monitored but not affected by the underground tunnels (e.g. precipitation, snow thickness, temperature, air pressure, chemical composition of seawater).

• Effectiveness of grouting and its impact on inflow into the tunnel.

• Monitoring measurements in the tunnels. These measurements yield basic data on the rate of groundwater inflow and its spatial distribution, the chemical

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composition of inflowing groundwater (especially its salinity) and an evaluation of the skin. Unlike measurements made on the surface and in the boreholes, the measurements made in the excavated and in some cases also grouted tunnels will inevitably take place under constantly changing conditions.

These parameters are also included in the monitoring programme (see sections 6.2.2 and 6.2.3).

Analysis of the impact with numerical flow modelling

Numerical flow modelling of ONKALO�s impact at site scale will be carried out in three dimensions. Tunnel excavations will clearly give rise to a transient disturbance, whereby numerical modelling also needs to be time-dependent. Modelling will be based on several items of input data:

• Horizontal extent of the model. The vertical boundaries will be located at a sufficient distance from the area of interest to make the modelling results insensitive to boundary conditions. In principle, the deeper the excavations the further their impact will extend.

• Vertical depth of the model. The model will be deep enough to make its results insensitive to the boundary condition applied to its base. Previously, Löfman (1999, 2000) has set the depth at 1500 m, but it may be necessary to make the model deeper.

• Flow conditions on the top of the model. A prescribed hydraulic head top surface boundary condition may be sufficient for long-term predictions. However, since the excavations are expected to affect the groundwater table, at least part of the top of the model has to be treated as a freely moving surface, although in the parts of the ground surface that are covered by large water reservoirs, a fixed hydraulic head boundary condition is still valid.

• Structures of the bedrock. These will be provided by the geological structure model, see section 7.2.4.

• Transmissivity of bedrock structures. The transmissivity of bedrock structures exhibits high levels of spatial variability and knowledge of their hydraulic properties is subject to large uncertainties. Their hydraulic properties may vary by several orders of magnitude. Descriptive modelling, see section 7.4.1, needs to focus on this.

• Permeability of rock between fracture zones Fractures at scales smaller than that of the fracture zones will give rise to permeability of the intervening rock mass. Although essential for describing radionuclide migration, the significance of this rock in modelling the impact of ONKALO is not very great. Typically a few percent of the total groundwater flow take place in this part of the rock.

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• Flow porosity of bedrock structures. In effect, flow porosity sets a timescale for all the evolution of the groundwater system that depends on flow velocity (e.g. the rate of movement of groundwater table, the interface between saltwater and freshwater, etc.). The ONKALO research plan aims at a better characterisation of the bedrock porosity, as described in Chapter 5.

• Density of groundwater. The density of groundwater is derived from measured values of TDS (salinity) in groundwater samples using relations found in the literature. The UCRP aims at obtaining a substantially improved understanding of TDS concentrations at depth, as already discussed in section 5.4.

• Diffusion porosity. Diffusion porosity is the part of total porosity that does not directly contribute to the active groundwater flow paths, but can affect groundwater composition via matrix diffusion. This is a very slow transport phenomenon, so it is likely that the effect of matrix diffusion will not be apparent in the monitoring measurements over the time period of ONKALO investigations. Different assumptions may be tried in modelling as was done by Löfman (1999, 2000). While investigations in ONKALO will significantly improve the understanding of diffusion porosity and (average) fracture spacing, the determination of corresponding model-dependent parameters on the basis of in situ observations is a challenging process.

• Land uplift. Due to post-glacial land uplift, groundwater circulation at Olkiluoto is in a state of natural but slow evolution and its significance was demonstrated by Löfman (1999). Due to the slow rate of change, it is not likely that land uplift will have to be taken into account when the only interest is the impact of tunnel excavations.

An analysis of the impact of the underground tunnels at site scale will be carried out in staged prediction-outcome studies, as generally outlined in section 7.1.3. The numerical value of every parameter at each stage of the analysis will always be based on the best estimate at the time. At these analysis stages due consideration will be given to the skin effect caused by grouting processes, to fracturing caused by blasting, de-gassing and stress changes, (i.e. the EDZ), and to the chemical composition of groundwater, especially salinity, in addition to the main site characterisation data.

An initial prediction will be an analysis based on all data that have been gathered prior to the commencement of tunnel excavations in 2004. This first prediction stage will differ from the other stages of numerical analysis while the latter stages can exploit the observed response of the groundwater table and the observations made in the tunnel itself, e.g., inflow of groundwater and observations on the tunnel walls, which is not possible at the first prediction stage.

When a sufficient body of measurement data and the corresponding predictions have been obtained, the initial prediction will be thoroughly reassessed. The degree of agreement between predictions and observations will be recorded, in addition to any

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unexpected results concerning grouting, gas content, skin effects or density distribution. This record will be passed on to the evaluation modelling stage. The reassessment will consist of the following steps:

• an analysis of parameter variations to establish to what extent the differences, if any, can be explained by existing uncertainties in permeability distribution and boundary condition,

• a re-analysis where different processes and aspects are introduced in a stepwise manner considering e.g.: grouting, degassing (based upon the measured gas content of inflowing water), skin effects (based on measured skin),

• a re-analysis using the hydrogeological model updated on the basis of the characterisation results (see section above), and the potentially altered salinity distribution.

It is expected that ONKALO will lead to a great increase in the amount and production rate of hydrogeologic information. In addition, the most recent geological and hydrogeochemical models need to be applied. To ensure this will be one of the main challenges of the integrated modelling task force (see section 7.1.2).

7.5 Hydrogeochemical modelling Hydrogeochemical data can be used in a number of ways to support site characterisation and safety assessment modelling. Hydrogeochemical modelling provides a description of the groundwater composition for use in e.g. safety assessment modelling. Furthermore, hydrogeochemical modelling is used in assessing the potential chemical impacts of ONKALO. Modelling also needs to assure consistency with the geological description (e.g. fracture minerals) and with the hydrogeological description (e.g. flow paths and predictions of salinity distributions).


The geochemical characterisation of the rock volume from ONKALO will produce data and a description of groundwater composition in the potential disposal areas. Figure 7-9 illustrates the steps of hydrogeochemical descriptive modelling. Major activities include thermodynamic speciation and geochemical mass transfer calculations, identification of natural/engineering geochemical processes, reaction quantities, and estimations of buffer capacity evolutions. In addition, the modelling task deals with the spatial occurrence of groundwater types and salinity in 3-D. The goal of modelling is to evaluate and integrate the results with geological and hydrological data.

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Figure 7-9 Hydrogeochemical modelling consists of additive steps aiming at an integration of geochemical results with other modelling disciplines.

Geochemical speciation and solubility calculations will first be performed on major ion data to determine the saturation state of various groundwater types with respect to low-temperature minerals such as calcite, gypsum, chalcedony and clays. Thermodynamic geochemical codes such as PHREEQC can be used in this process. Geochemical calculations are also useful in checking for potential inconsistencies in a single groundwater sample, which may occur particularly between concentrations of redox- and pH-related species and in the direct measurement of Eh and pH.

Additional geochemical mass transfer calculations will also be performed using net geochemical mass-balance codes such as NETPATH. Work carried out previously on the Olkiluoto site using the mass-balance approach (Pitkänen et al. 1999) can be tested and extended to include the new data obtained at this stage. Interpretation involves mass transfer in chemical reactions (i.e. identification of feasible processes and estimation of reaction quantities) and mixing of different groundwater types (meteoric, glacial, saline etc.) along a flow path. At a larger scale, the distribution of different types of groundwaters in the structural bedrock model and their mixing characteristics can be

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examined using an interpolation approach (c.f. Baseline Report, Posiva, 2003a). The spatial distribution of groundwater types in fracture zones, especially salinity distribution, as well as any changes in their distributions will be visualised with interpolation techniques.

The distribution of salinity and other water types resulting from hydrogeochemical modelling will also be compared with the updated groundwater flow model, see section 7.4. If major inconsistencies are found, one or both of these models may be updated. It is also important to compare salinity distribution with the salinity profiles determined on the basis of geophysical measurements (see the Baseline Report, Posiva 2003a). A further issue that may affect both mass-transfer calculations and flow-path modelling during excavations is the presence of N-compounds ((NO3, NO, N2O) and organic matter imported into the ONKALO environment as a result of blasting.

The redox measurement of groundwater should produce an improved understanding of redox conditions in the rock mass. It may be possible to determine the spatial distribution and depth of a redox front using a combination of electrode Eh and pH measurements, dissolved O2 and CO2 concentrations, and concentrations of redox-sensitive species, such as S2-, Fe, Mn, and U (Gascoyne 1997). The evaluation of the movement of the redox and pH front in response to excavation will require more direct migration modelling with regard to transport processes, in order to determine the time scale of migration and to select the migration paths from the groundwater flow model. The modelling of front movement will provide a good insight into the buffering capacity of O2 and CO2 by interaction with the fracture infilling minerals and the adjacent host rock.

The composition of the pore- and inclusion water of the unfractured rock can be determined by laboratory analyses of pore fluids in a selection of borehole cores. Modelling will focus on understanding the results and on exploring the potential importance of the chemistry of the unfractured rock, especially with respect to groundwater salinity. This would probably require detailed numerical migration modelling and several ideas can be tested.

For the evaluation of Kd measurements, a more detailed knowledge of certain groundwater characteristics, such as redox conditions and content of organics and colloids will aid in evaluating the role of these parameters in laboratory experiments. The main studies will be performed in the laboratory to improve the understanding of the fundamental mechanisms that control sorption.

The assessment of dissolved gas content in groundwater will be based on data obtained during the 1997-2002 sampling period and on additional results obtained by sampling during the ONKALO Stage 1 prior to starting of excavations of the access tunnel to ONKALO in 2004. New data should help confirm the presence of high concentrations of CH4 at depth in the saline groundwaters at Olkiluoto (Gascoyne 2000) and further modelling will be carried out to determine the extent of gas saturation at ambient hydrostatic pressure. Measurements and modelling of CH4 concentrations have also

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practical significance because of the potential hazard that CH4 presents during excavation.

The final modelling and evaluation of model results should include estimates of the effects of analytical uncertainties and natural fluctuations in the data. Measurement uncertainties and temporal or seasonal variations, etc. provide reliability estimates for geochemical modelling results that in turn are valuable in linking hydrogeology with geochemistry.

7.5.2 Evaluating the hydrogeochemical impacts of ONKALO

Changes in groundwater circulation may affect the location of different groundwater types (e.g. glacial melt water, meteoric water, seawater, brine etc.). The changes may be assessed with the help of the monitoring boreholes (section 6.2.3) and on the basis of the composition of the groundwater flowing into the facility (section 6.3.4).

Hydrogeochemical changes may also be due to the effects of construction, such as grouting or the degradation of other introduced materials. These changes, which will need to include effects on both groundwater chemistry and fracture infillings, will have to be monitored using specific boreholes.

Potential impacts

The hydrogeochemical impacts of ONKALO will mainly concern:

• Rock-water interactions. Large surface areas of rock will be exposed as a result of the excavation of the access tunnel, shafts and panels and these can potentially influence the composition of the groundwater flowing into ONKALO. The presence of significant concentrations of sulphide minerals in the host rock at Olkiluoto may result in the formation of sulphuric acid as these minerals oxidise, which will acidify the groundwater flowing into ONKALO and could result in strong microbial activity. The rock also contains quantities of soluble salts, which are released on fracturing, microcracking and pulverising caused by blasting and excavation. These salts will likely be Na-Ca-Cl in composition and will cause an increased salinity of inflowing groundwaters. This may result in problems in meeting the environmental requirements for water quality before discharge on the surface. In addition, increased salinity will accelerate processes such as corrosion of steel used underground in rock bolts, pipes, reinforcing structures, etc. Redox changes may also result in calcite precipitation in fractures close to ONKALO, which may reduce transmissivity in these fractures.

• Explosives residues. Blasting using conventional explosives causes emission of large amounts of nitrogen oxides (through decomposition of ammonium nitrate) and significant levels of organics (from fuel oil and other explosives). These compounds are largely removed as off-gases but some become dissolved in the service water used to wash down the rock faces after blasting. In this case, NO3 concentrations, in

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particular, will increase in the service water and may exceed the limits for discharge on the surface. Monitoring and mass balance calculations for NO3 concentrations in service water in the Canadian URL showed that 1.3 kg NO3 was dissolved in service water for every metre of excavated tunnel (Gascoyne et al. 1995).

• Cement/concrete interactions. The use of cement in e.g., tunnel seals, borehole grouting and shotcrete for rock mass stability is likely to cause chemical changes in the groundwater surrounding and entering ONKALO and subsequently also affect the surrounding rock fractures, e.g., by formation of secondary minerals or by dissolution of some fracture minerals (Gascoyne 2002). Conventional cement and grout are highly alkaline (pH >12) and can contribute significant amounts of dissolved ions (e.g. OH, SO4, K, Ca) to the groundwater. New cements are for this reason being developed that will cause a much lower pH shift and are believed to have negligible long-term effects on groundwater composition (see section 8.3 for further discussion).

Comparing predictions and observations

A procedure for predictive modelling, based on hydrogeochemically interpreted conservative water-type fractions and hydrogeologically simulated water-type fraction-estimates, has been presented in the Baseline report (Posiva 2003a). The predicted chemical composition (including salinity distribution) will be compared against the measured composition on monitored sampling points in boreholes and of the water flowing into ONKALO. In the view of the more advanced problems to be solved with coupled reactive transport codes these comparisons provide necessary boundary information. Special attention will be paid to coupled problems:

• Evidence of a faster than predicted movement of the redox front, i.e. is it possible for an inferred flow line on the surface of an ONKALO panel to lose its reducing capacity under open-tunnel conditions.

• Evidence of a faster than predicted movement of the pH-buffering front, i.e. is it possible that some of the studied/predicted flow lines will lose their pH-buffering capacity under open-tunnel conditions.

Both issues are related to the life-time of reactive fracture-filling minerals, recharging surficial water compositions, additional dissolved components (e.g. oxygen, organic matter), average groundwater flow velocity, etc.

A framework will be established to allow interdisciplinary modelling and prediction based on geological, hydrogeochemical and hydrogeological data, as well as models derived from these data. Comparison between the proportions of water types interpreted from hydrogeochemistry data and proportions simulated from hydrogeological modelling, will focus on:

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• substantial deviations between interpreted and simulated fractions of meteoric, sea water and saline water types,

• time-dependent removal of relict water-types (e.g. glacial water) and

• time-dependent diverging deviations between interpreted and simulated water-type fractions (the deviations are likely to increase as a function of time).

In comparing predictions and observations, due consideration will be given to:

• hydrogeological evaluation suggesting major deviations between predicted and actual groundwater flow patterns,

• evidence of organic matter affecting the migration of the redox front or the consumption of pH buffers.

The degree of agreement between predictions and observations will be recorded and observations will be made concerning groundwater flow, organic matter, etc. This record will be used in the evaluation modelling step (see below).

Evaluation modelling

Where the comparison step suggests that there are significant differences between measured and predicted groundwater compositions, the hydrogeochemical model needs to be updated in close connection with hydrogeological modelling.

Modelling will consist of the following steps:

• An assessment of whether observations lie within the large range of uncertainty in the existing distribution model of groundwater composition.

• An assessment of whether progressive distributions of type waters in fracture zones indicate that modifications need to be made to the geological structural model or to its hydraulic parameters.

• A re-analysis with a density-dependent groundwater flow model based on the updated hydrogeological and geophysical salinity models (see also 7.4.2). This would affect predictions of salinity distribution.

• An assessment of other sources (including organic matter and buffering minerals in near-surface boreholes) that may affect the predictions of groundwater composition.

Evaluation modelling may suggest that changes need to be made in the hydrogeochemical description and suggest to what extent these changes are needed in relation to the different effects described above. In general, modelling will enhance the consistency of the hydrogeochemical and hydrogeological models and the confidence in the description of the site.

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8 R&D RELATED TO CONSTRUCTION AND CHARACTERISATION This chapter presents R&D plans related to construction and characterisation. This is a subset of the R&D to be conducted. The full R&D programme will be presented in Posiva�s coming 3-year RDD programme.

8.1 General According to Posiva's 2000 R&D programme (Posiva 2000), generic experiments of barrier functions will be carried out in suitable rock laboratories, such as the Äspö HRL, instead of ONKALO. However, some experiments are needed to test and explore the barrier functions of the rock mass under the conditions found at Olkiluoto, with its particular groundwater chemistry, hydrogeology and rock mechanics situation, i.e. in �prevailing in situ conditions�. Detailed plans for such experiments need not be developed until at a later date, as R&D will be performed at Stage 3.

Issues potentially worthy of studying are those that both have significant safety implications and are also potentially affected by the actual conditions on the site. Significant safety implications are associated with conditions that affect the long-term isolation and retention properties of the disposal system.

As far as the Olkiluoto site is concerned, the following conditions are potentially important with regard to safety implications:

• high salinity levels and their impact on buffer/backfill functions (and Cu corrosion),

• other chemical conditions (high sulphate, sulphide, ammonia, gas) which may affect canister performance,

• development of microbiological growth,

• rock mechanics properties.

In addition, there is also an element of demonstrating that the geological environment at the site is suitable. Some repository tests need to be carried out in ONKALO, even in cases where it would be possible to draw on results obtained from other sites, such as the Äspö HRL.

In the coming years the focus will be on construction and characterisation activities. R&D related to these is outlined below. The overall R&D programme, with plans and ideas for the experiments programme will be described in Posiva´s coming 3-year RDD programme.

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8.2 Mechanical and chemical impacts on the rock Various tests will be conducted to explore the mechanical and chemical impacts of the tunnel (the �disturbed zone�) and the operations in the tunnel on the rock.

Objective

The objective of the tests is to study the mechanical and chemical impacts on the rock caused by excavation and the operations in the tunnel. This will help establish the extent and significance of the Excavation Damaged and Disturbed Zone along the various tunnels.

Methods

Various methods could be applied. An acoustic emissions test is one way to study the extent of mechanical impact, but it would not provide additional information on the effect of the disturbance. The effect is potentially site-specific due to differences in mechanical parameters, such as rock stress and rock mass strength. Another possibility may be to explore the hydraulic pressure distribution in borehole sections round the tunnel. A statistical approach may be fruitful. For instance, is there a systematic difference in pressure in the vicinity of and at a distance from the tunnels?

The chemical impact may be assessed from water samples taken at different distances from the tunnel. The chemical imprints of the tunnel (blasting gases, carbon dioxide, carbonates, organics, microbes, oxygen, redox parameters, etc.) could then be assessed by migration modelling at tunnel scale.

Expected results

The varying extent of the chemical impact of the tunnel would be observed at scales of metres to centimetres from the tunnel wall depending on the extent of the hydraulic gradient toward the tunnel and the ability of the chemical species to diffuse against the flow gradient. For instance, the loss or gain of gases and gas-dependent parameters such as redox would probably migrate farther than dissolved chemical signatures such as a pH shift or microbial growth. It is possible that some components (e.g. blasting gases and residues) may migrate at a sufficient distance from the tunnel to form a plume that spreads outward from the tunnel. In addition, some parameters may be coupled, e.g. the microbial growth in fractures may be stimulated by migration of nitrogen-based gases contained in tunnel blasting residues.

8.3 Impact of grouting Groundwater inflow into the tunnels of ONKALO may cause disturbances including (Figure 8-1):

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• possible up-coning of deep saline waters,

• drawdown of groundwater level on the surface,

• migration of surficial and sea waters into the facilities,

• subsequent drifting of organic and oxidising material into the facilities,

• disturbances in the construction and operation of the facilities caused by major inflows.

The best way to control the foreseen impacts is to locate ONKALO in low conductivity bedrock and restrict the ingress of water by grouting. On the other hand, grouting may cause geochemical disturbances (e.g. pH-plume effects) in the nearby bedrock.

Figure 8-1 Foreseen site scale effects caused by groundwater ingress into the repository, judged to be important with respect to nuclear waste disposal (Riekkola et al. 2003).

Different types of grouting materials might be used in the construction of ONKALO and the repository. It is foreseen that cementitious grouts will be used in wider fractures, but in smaller fractures non-cementitious chemical grouts may need to be used to get the proper sealing effect. Cementitious grouts require the use of many additives (superplastisizers and accelerators). The additives are organic compounds, which are originally bound in the cement.

Seawaterintrusion

Upconing of deep saline

water

pH-plume

Drawdown ofgroundwater level

Drifting of organicand oxidizing

material

Migration ofsurficial waters into

disposal level

Disturbances forconstruction

and operation

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Standard construction cement pastes customarily used in rock grouting, such as Ordinary Portland Cements (OPC), may create pH pulses in the magnitude of 12-13. Such high pH values are detrimental (effecting both the fractures of the rock and the buffer material bentonite) and also unnecessarily complicate the safety analysis of the repository, see Figure 8-2. Thus, on the repository level at least, the use of OPC should be avoided. One possible alternative is to use low alkaline cementitious materials to minimise the pH plume effect.

SKB, Posiva and NUMO have started a joint project to define the activities necessary for qualifying a low-pH cement for practical use in deep repositories. On the basis of the feasibility study carried out in 2002, the new project focuses on the development of low pH (pH ≤ 11) injection grouts for wider and smaller fractures. A low-alkali cement can be based e.g. on the addition of silica to the cement paste to reduce the level of portlandite in the paste and to lower the Ca/Si ratio of the cement paste to produce a bulk paste with lower pH. The aim is to avoid the original high pH peak caused by leakage of alkali hydroxides and to lower the amount of portlandite in the cement to achieve a low pH porewater (pH ≤11).

Figure 8-2 A safety assessor�s view of the significance of pH and pH-evolution in standard cement.

Objectives

Hydrogeochemical measurements and the monitoring of the impact of stray materials, including grouting, were already discussed in Chapters 5 and 6. However, more work will be carried out to study the impact of grouting in ONKALO, with the aim to:

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• explore the potential impact of grouting on safety functions (including pH-plume, clogging of fractures, secondary mineral formations, long term durability of grouted zone)

• explore the long-term stability of grouting and to investigate whether the safety case can benefit from grouting, and

• determine the extent to which grouting could jeopardise the possibility of detailed rock characterisation.

Some studies are to be performed on different grout materials, e.g. the potential effects of high-pH plumes on the rock (fractures), and thereby on the migration of radionuclides, as well as on the interaction between cement and bentonite.

Methods

Detailed plans for the studies will be presented later. For example, Gascoyne (2002) compiled an evaluation of grouting tests and the results of studies performed in the URL in Canada.

The impact on groundwater chemistry, e.g. a pH-plume, will be explored by evaluating water samples taken from a pumped borehole section located outside, but close to the grouted zone. The planned analyses are discussed in Chapters 5 and 6. Some trial boreholes would be required for selection of a good location for this study.

Expected results

The studies discussed above will support the application of optimal grouting practices that will not jeopardise the safety functions of the repository.

8.4 Site specific tests on grouting technology A separate programme is under way for developing the construction and disposal technology required for the repository. Various underground construction tests (blasting, full face drilling, grouting, etc.) may be carried out in ONKALO. The UCRP needs to develop sufficient interaction with the technology programme on issues concerning the characterisation of volumes of rock and the host rock classification system in order to safeguard compatibility.

Posiva is at present running a project for the development and design of methods to control groundwater leakages in ONKALO and the repository. It is understood that normal cement grouting techniques cannot reach the tightness desirable for the repository. Pre-grouting of the rock using cement based materials, i.e. grouting the rock round the tunnel before excavation, has been identified as the main technical tool for reducing the amount of groundwater ingress into the underground rock tunnels. The

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sealing technology will be further developed and tested using field experiments in the access tunnel of ONKALO.

Objectives

The main objective of the development work for site specific grouting technology is to show that it is possible to achieve a high quality in investigations, design and implementation of sealing of rock fractures for the construction of a repository.

Methods

In order to achieve the main objective it is necessary to develop and test:

• methods to characterise the rock for grouting purposes,

• methods to predict leakages,

• grouting materials that are suitable for the fracture properties (both wider and smaller fractures) and meet the requirements specified for the sealing result,

• practical working methods,

• alternative methods with potential to reduce the costs without compromising quality or safety,

• methods to measure and evaluate the grouting result.

Grouting tests will contribute to the development of advanced and integrated sealing methods. Such methods consist of identifying and integrating the most suitable hydrogeological investigations, grouting materials and techniques and monitoring the obtained results. Testing of grouting techniques focuses on pre-grouting.

Expected results

The studies discussed above will support the application of optimal grouting practices that will not jeopardise the safety functions of the repository.

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9 INSTRUMENT DEVELOPMENT Most of the underground characterisation and research will be carried out using existing methodologies and instruments. However, in some areas additional instrument development is planned.

Instrument development will start prior to the construction of ONKALO. The first objective is to determine the methods and the equipment that may be used directly in ONKALO and the second objective is to develop the equipment needed at the early construction phase. As the programme in ONKALO involves both characterisation and research activities that take place in parallel, continuous instrument development and testing will be carried out during the entire construction phase. A separate instrument development programme will be set up after the investigation programme has been completed. Except instrument development there is also going on work relating to development of interpretation of the results.

9.1 Equipment in surface-based boreholes The need for further development of instruments for use in surface based boreholes is limited. Some development is under way for hydrogeochemical sampling and borehole seismics.

Groundwater sampling on the surface may be carried out using the same equipment that has been employed in the preliminary and detailed site investigations. However, on-line monitoring at depth, as well as in shallow boreholes and groundwater pipes will require new monitoring and pumping systems, which can be used in automatic mode over long periods of time. At a minimum, the new field monitoring system should be able to measure the electrical conductivity of water and possibly also pH, redox and O2. An automatic data storage system connected to a host computer is also needed.

The use of old field monitoring systems (Mäntynen & Tompuri 1999, Mäntynen 1999) can be continued with double packer, multi-packer and PAVE (pressurised water sampling system) equipment. Gas and microbe sampling can be carried out using PAVE equipment in open boreholes, but in shallow boreholes and groundwater tubes microbes have to be sampled using a separate technique. Gas samples can also be taken from the multi-packered boreholes but the sampling method needs to be improved. Representative microbe samples cannot be collected from multi-packer boreholes, because the hoses become contaminated with microbes and other particles during installation and all sampling hoses cannot be sterilised.

A method will also be developed for borehole seismic tomography purposes. Frequencies in the range of 1 � 2 kHz and above, up to 10 kHz, should be used in detailed scale studies. The measurements also require well controlled pulse sources with a high repetition rate and high emitting power in order to explore details over considerable (100 m) distances. Investigations at detailed scale call for an improvement

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in positioning and deviation measurements of drilled boreholes. Error deviation measurements along the borehole profile can be 1% at the highest and preferably a 0.1 % relative error should be attained (Albert et al. 1999). the tunnel layout with respect to boreholes may also help in improving borehole positioning. Seismic tomography at later investigation phases may also utilise the full waveform inversion (WFI) technique to improve the resolution of tomographic images

9.2 Equipment to be used underground Groundwater sampling in ONKALO can be performed in the same manner as in surface sampling, except for the sampling of gas and microbes. Field monitoring systems used on the surface can also been used in ONKALO and no pumping is needed in the holes drilled underground because water will flow from the holes due to the hydrostatic head difference at depth. Sampling and analysis procedures are under development for the measurement of gas content in groundwater samples to be drilled from the tunnels in ONKALO. Methods for microbe sampling in ONKALO (from rock surfaces, fracture fillings, boreholes and groundwater) need to be developed with assistance of relevant experts. There is also a need to plan and construct special equipment for colloid sampling, see Figure 9-1.

Figure 9-1 Development of methods and equipment for colloid sampling is under way. Field tests have been carried out in the VLJ Repository for low- and intermediate-level waste at Olkiluoto.

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Equipment for the continuous measurement of electrical conductivity, Eh, O2 and pH is also needed during construction on several sampling points, and the development work should begin in the near future, Figure 9-2. Automatic measuring systems also need to be developed for sampling and for the determination of the flow rate of groundwater inflows into ONKALO. All continuous measuring equipment need to be provided with automatic data storing systems.

Figure 9-2 Equipment for continuous measurement of electrical conductivity is also needed during construction of ONKALO. The data are automatically stored and can be transferred to a central computer if needed.

The two main pieces of equipment that have been used to measure hydraulic conductivity in deep boreholes include the Hydraulic Testing Unit (HTU) and the Posiva Flow Log (PFL). Double-packer injection tests with a constant head have been performed using HTU. PFL actually measures the flow into or out of the test section, without any pressure difference between the measuring section and the rest of the borehole (Öhberg and Rouhiainen 2000), and has been used successfully in the Äspö HRL (Rouhiainen & Heikkinen 1998), see Figure 9-3. This makes it suitable for measurements in ONKALO without any major modification. PFL can be moved in a borehole by rods, which allows it to be used in boreholes that dip upward and in some cases the flow in a borehole can be so high that it has to be limited in order to protect the thermistors in the tool (Rouhiainen & Pöllänen 1999).

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Figure 9-3 Posiva Flow Log (PFL) has already been used several times in deep underground conditions in the Äspö HRL.

A modification to PFL is being considered, to facilitate its use in carrying out rapid measurements of hydraulic conductivity to determine the need for grouting. The method would be used instead of the conventional Lugeon test, provided a feasibility study proves this would bring cost savings, e.g. more accurate hydraulic data in a shorter time.

HTU has been used for measurements in the Research Tunnel of the VLJ-Repository at Olkiluoto at a depth of 70 m. The difficulty of using this equipment in underground conditions combined with the size of the equipment makes HTU more suitable for measurements in surface-based boreholes.

The Posiva Flow Log family of flow measurement tools also includes a transverse flowmeter, which enables direct determination of groundwater flow (Rouhiainen 1993, Öhberg & Rouhiainen 2000). The borehole section to be measured is 2 m long and has inflatable packers at both ends as well as four longitudinal seals that separate the section into four sectors. The flow magnitude (ml/h) and the approximate direction of flow are measured with a heat pulse flow sensor. The equipment has also been tested in the Äspö HRL (Rouhiainen & Heikkinen 1998), but the result of the tests was not encouraging, as high groundwater pressure resulted in damage to the packers and the flow guide. A development project for constructing a new version of the transverse flowmeter, which will allow it to be used underground, was started in 2002.

It is important that the thermal transport properties of the bedrock, thermal conductivity and diffusivity in particular, are known when the distances between the deposition holes are determined. In situ thermal properties can be investigated using several methods, but

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Kukkonen & Suppala (1999) found the cylindrical heat source method for single-hole measurements to be the most promising. A project to develop a logging instrument for use in deep boreholes was launched in 2000 (Kukkonen et al. 2001), and a prototype probe (called TERO) is planned to be ready for tests in boreholes with a diameter of 56 mm at Olkiluoto in 2003. The maximum measuring depth will be 700 m. Since the diameter of the recent boreholes has been 76 mm (due to the use of triple tube drilling) another probe with a larger diameter will have to be developed later. It should be quite easy to adapt the instrument for underground measurements in ONKALO.

Posiva has developed multi-packer equipment for packing off of boreholes in co-operation with Lapela Oy. To date, this equipment has only been used in surface-based boreholes for hydraulic head monitoring and groundwater sampling. The mechanical properties of the rods and the packers will have to be checked before this equipment can be used underground where high hydrostatic pressures are present. In addition, installation procedures will have to be improved in cases where high rates of groundwater flow are present in boreholes.

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10 DATA MANAGEMENT During the site characterisation programme Posiva used the TUTKA data management system to archive field investigation data. The database is a Microsoft Access based database containing information on and reference to the actual data, which is stored separately. The abstracts of the Working reports and the POSIVA reports are also stored in the database. Most of the data are in ASCII-text files, although images and some binary files are also stored. The TUTKA system was originally designed only to store data, although in recent years it has served as a central database, from which data have been searched and delivered for further analysis.

As the construction of ONKALO starts, the requirements for the data management system increase and much faster data exchange between the different parties involved in the project will be needed. More interaction and better integration of the data storage and other applications is required. In addition, the amount and diversity of data, together with the long time span of the project, will be the major challenges to the data management system. The general objectives, requirements and features of the data management system are discussed below.

10.1 Objectives Data play a central role in the underground characterisation and research programme. All the construction and characterisation activities are based on the data and knowledge gained during the previous steps of the characterisation programme. The result of the programme is also data, which are needed for a better understanding of bedrock conditions as well as for layout design and an analysis of long-term safety.

The data management system should help in allowing both the construction and the characterisation programme operate efficiently. From the construction point of view, the two major data requirements are:

• efficient data acquisition and processing is needed to guide decision-making on technical measures to be taken in the next excavation round and

• the use that is to be made of the results of the characterisation programme in design work.

More or less the same data are used for construction and characterisation purposes. To integrate these activities, the progress of the construction work and future data needs have to be known. In addition to the results of the characterisation programme, links are therefore needed to construction schedules, technical design documents etc. as well as to different modelling applications.

This gives the data management system the following overall objectives:

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• to create a single location, central, digital data bank,where all the data can be accessed,

• to provide the best available data in a suitable format (�fit for purpose� � data) and on time to different users with a variety of needs, and

• to store the data in an accessible format and to document the data and its contents for future needs.

The link between measured data and the descriptive models (see Chapter 7) also needs to be transparent.

10.2 Features of the data management system The features of the data management system concern the diversity of data, its users, the accessibility of data and the integration and maintenance of the system.

10.2.1 Data

The data management system to be used for the construction of ONKALO and for underground characterisation programmes should be able to handle a diversity of data, including data in various formats and various versions. The co-ordinate system needs to be defined. Event logs are useful (see below). Given the various requirements, it is not evident that a single database will be used for all purposes.

A single database to store all the data will probably not be applicable, due to the variety and amount of data. Frequently used data could be stored in a (online) database that enables quick access and the use of database tools for data analysis. The storing of seldom-used large data sets (such as seismic measurement data) in an online database would be unreasonable. For these data a system similar to the currently used TUTKA system could be a practical alternative, as it entails virtually no limits as to the amount and types of data to be stored. The different databases should be integrated with each other and a single user interface should be provided to search all the data.

Data in various formats

In order to ensure long-term usability of data and to allow them to be used for analytical purposes, storage in text (ASCII) format is beneficial. In practice, text files are sometimes inappropriate and graphical formats are required � examples of this include digital images and maps. The use of graphical presentations of data should be encouraged, as they provide a method that allows a rapid overview to take place. The database should be linked to a visualisation application that permits both 2D- and 3D presentations.

Data table and file formats as well as the nomenclature and terms used should be defined and documented. Further use of data will be more efficient and less prone to errors, if the same type of data is saved in the same format and the terminology used is

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comparable. This will also make it easier to enter single pieces of data. A special issue will be time-dependent data that some monitoring activities can produce in vast amounts.

Versions of data

Various versions of the data need to be managed, such as:

• raw measurement data,

• processed data,

• interpreted data,

• predicted and observed data (e.g. bedrock properties for one excavation round or along the intersection of a tunnel and a fracture zone),

• data derived from planned and actual construction activities (e.g. the planned and the measured route of the access tunnel) as well as

• possibly different presentational formats of data (i.e. text/graphics and images).

The versions should be interlinked, even if different versions of related data are stored in different databases or modelling applications. It is important to save the data in a form that will enable their reprocessing in the future and in a form that is of practical use.

Models and model versions

The data management system should also be able to handle the descriptive models, see Chapter 7. Different model versions need to be distinguishable and the link to the underlying data needs to be transparent.

Co-ordinate system

An important aspect to consider is select the co-ordinate system to be used. It would be preferable to use the Finnish Co-ordinate System, which has been used so far . It will be essential to know the exact 3D co-ordinate (x, y, z) of any measurement point and the location of any activity.

Event logs

Event logs that tell the time and the place of all the activities will be needed not only for project management purposes, but also to help the scientists detect any disturbances and the reasons for outliers in their data. Documentation of any technical measures taken is

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of particular importance, such as the use of rock supports, grouting etc. and the time and the location of their application.

10.2.2 Users and accessibility

The users of the data management system can be divided into the following groups:

• Data providers, who submit data for storage in the system,

• Users with different needs, for example some need to obtain data for their own analysis, some just need to view data and

• Administrators, who maintain the system and control data and data flow.

A key requirement for the system is to make it accessible to users in geographically different locations. Remote access to the system can be arranged on different levels such as:

• browsing the data catalogue,

• browsing the data and

• using applications.

Possibilities include a web-based user interface and client-server applications.

It is important to create tools that will allow effective searches of available data. It should be possible to search data using both catalogues (as in the current TUTKA system, although more keywords should be included, e.g. time of the activity) and maps. Even if the data themselves are not just one mouse-click away, the knowledge of where to gain access to the data should be.

10.2.3 Integration

The integration of data with the applications used for interpretation and various types of modelling will be an important issue in creating an efficient working environment. Project management tools, documentation systems and layout design should also be integrated with the database(s) and modelling systems to provide a sound basis for decision-making at the different steps of the project.

As there will inevitably be several applications that use the data, storage of duplicate data sets and reformatting of data cannot be avoided. It is important, however, to create a central database, where researchers, designers, etc. can access the best available, most up-to-date data, although some modifications to the data are needed before it can be imported into the specific application in question. In these cases, well-defined data tables and proper documentation of the data content will be greatly appreciated.

The applications in question include databases, GIS-systems and CAD-systems to mention just the most obvious ones. So far, mainly primary measurement data have

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been systematically stored, while modelling applications have had their own databases and archiving systems with rather limited access. With the start of underground construction and research, these modelling applications will need to be integrated with the data management system.

10.2.4 Maintenance

There will be a constant data flow from construction-related activities, which should be stored in the system within hours of being obtained. It will be preferable to gather as much of the data as possible directly in digital format and to employ automated storage and control measures. Monitoring activities will produce data continuously. The results of the characterisation activities should also be stored as soon as possible, although there will be time for a more thorough quality check of the data. Data delivery from the databases should also be automated to as great an extent as possible and a log should be kept of data requests and deliveries.

For maintenance and data searching purposes, key information on the data should be provided and it should not be possible to store any data in the system without providing keywords that will enable data searches. Furthermore, proper documentation needs to be associated with all input data. This task will be easier, if predefined data, table and file formats are used. A status indicator can be added to the data as it will probably be necessary to store certain data in the system in raw draft format and the status of the data can then be changed accordingly after the data have been checked. The reliability of data will be determined by their quality.

10.3 Long time span of the project A special requirement for data management arises from the fact that ONKALO serves the design and may even become part of the future disposal facility. The data will, therefore, be used over and should be kept available and readable for a long period of time. Obviously computer systems and databases as well as the people and organisations involved will change during the long time span. The need to transfer data from one system to another will be facilitated by storing all the data in one location. It is also important that data is stored as soon as possible after the measurements are made, since a delay of a few years would make it extremely difficult to obtain the data from the contractors.

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11 MANAGEMENT, ORGANISATIONAL AND QA ASPECTS This chapter outlines the organisation, management and QA related to the ONKALO activities.

11.1 Organisation and management

11.1.1 Practical design and construction work

The practical design and construction work for the ONKALO falls under the responsibility of a Posiva project that carries the same name, �ONKALO�. This project will produce the final design of the facility, define the work packages for construction, prepare the time schedules and cost plans, select contractors, commission works, supervise the contractors and bear the overall responsibility for the implementation of ONKALO. A project group, headed by a project manager and including experts in design of underground facilities, actual rock construction, geologic investigations and project control, has the responsibility for the project implementation; a steering group consisting of members of Posiva�s top management supervises the implementation.

The �ONKALO� project is also responsible for carrying out the geologic investigations that are necessary for the construction purposes. This includes the interpretation of the geologic information from pilot and probe holes, tunnel mappings and the continuous updating of the local structural geologic model.

11.1.2 Underground characterisation

For the practical implementation of the underground characterisation programme principal coordinators will be attached to each main programme area, i.e.,

· general and structural geology

· geophysics

· rock mechanics

· hydrogeology

· hydrogeochemistry.

The Principal Coordinators are responsible for detailed work plans and programme updates, choice of contractors for practical investigation tasks, commission and supervision of the contracts and the overall control of progress in their programme area. The same Principal Coordinators will also be responsible for the surface-based site investigations at Olkiluoto. For effective planning and coordination all site characterisation activities at Olkiluoto are placed in a common programme structure. The programme has a Programme Coordination Group consisting of the Principal Coordinators, the area manager responsible for field support, investigations

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infrastructure and methodology, and the leader of the Task Force for Modelling (see section 7.1). The Task Force has the special responsibility for integration of the results from modelling and interpretations. The Programme Coordination Group is led by a Programme Coordinator, who has the overall responsibility for practical coordination of the programme planning and execution and also for coordination of the underground characterisation activities with other ONKALO activities (design, construction, monitoring, tests and demonstrations). The programme is supervised by the same Steering Group as the �ONKALO� project.

For efficient execution of specific time-bound tasks involving a large range of expertise the Programme Coordination Group may establish specific projects under the programme structure.

The organisation and management structure of the Olkiluoto site characterisation activities will be updated at the end of Stage 2, at the latest.

11.1.3 Tests, demonstrations and monitoring

The tests and demonstrations activities described in Chapter 8 may be organised into projects according to their particular needs.

The monitoring activities related to the ONKALO construction are kept as a separate programme. This ensures that the specific objectives of the monitoring system are fulfilled, in particular those related to controlling the potential disturbance caused to the characteristics of importance for the long-term safety. Of course, the information produced by the monitoring system will be fully utilized in the modelling and interpretation work..

11.1.4 Liaison

The coordination of everyday activities carried out in ONKALO is achieved by regular meetings between programme coordinators and project managers. These meetings are chaired during Stages 1 and 2 by the �ONKALO� project manager. In policy issues and issues of broader context and resource implications the responsibility for coordination and decisions is transferred to the Steering Group. The organisational structure of ONKALO activities is schematised in Figure 11-1.

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Figure 11-1 Organisation of ONKALO activities

11.2 Quality assurance All the activities are subject to Posiva�s quality assurance system implemented according to ISO 9001. The system is being updated to conform with the ISO 9001:2000 version, and at the same time it is extended to cover the ISO 14001 standard for environmental management. To enable the use of the ONKALO later as a part of the repository, IAEA�s recommendations for the quality assurance of nuclear facilities are also taken into account in the construction activities. For advisory and review functions an international reference group of experts is congregated.

STEERING GROUP FOR ONKALO

MONITORINGSYSTEM

OLKILUOTO SITE

CHARACTER-ISATION

MODELLINGTASK

FORCE

ONKALO DESIGN

ANDCONSTRUCTION

TESTSAND

EXPERIMENTS

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LIST OF REPORTS 1 (1) POSIVA-reports 2003, situation 9/2003 POSIVA 2003-01 Vertical and Horizontal Seismic Profiling Investigations at Olkiluoto,

2001 Calin Cosma, Nicoleta Enescu, Erick Adam, Lucian Balu

Vibrometric Oy March 2003 ISBN 951-652-115-0

POSIVA 2003-02 Baseline Conditions at Olkiluoto Posiva Oy September 2003 ISBN 951-652-116-9 POSIVA 2003-03 ONKALO Underground Characterisation and Research Programme

(UCRP) Posiva Oy September 2003 ISBN 951-652-117-7 POSIVA 2003-04 Thermal Analyses of Spent Nuclear Fuel Repository Kari Ikonen, VTT Processes June 2003 ISBN 951-652-118-5

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