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Andra’s Safety Options of French underground facility Cigéo- a milestone towards the licensing application

S. Voinis1, M. Rabardy1, L. Griffault1 1 Andra, French National Radioactive Waste Management Agency, Parc de la Croix Blanche, 92298 Châtenay-Malabry, France.

E-mail contact of main author: sylvie.voinis@andra.fr

Abstract. Following the publishing of the Dossier 2005 Argile, the 28th June 2006 Act entitled “Programme National de Gestion des Matières et Déchets Radioactifs” (National program for radioactive waste and nuclear material management) [5] has set the deep geological repository in clay host rock as the selected solution for IL-LL and HL radioactive waste disposal in France. According to this 2006 Act, reversible waste disposal in a deep geological formation and corresponding studies and investigations shall be conducted with a view to selecting a suitable site and to designing a repository. Since 2011, the project has entered an industrial design development phase and has become the Industrial Center for Geological Disposal “Cigéo”.

In view of the licensing application, two main milestones for safety are identified for Cigéo: a Safety Options Dossier “DOS” early 2016 and the safety case to support Future License Application of Cigéo “RPs” in 2018. According to the 2007 French Act, the Safety Options is an opportunity for the operator to send in advance a first safety case to the French Safety Authority in order to stabilize the safety strategy, the safety requirements, the safety methods, key safety and design options, the list of safety scenario that are selected and a preliminary impact of a few margin scenarii. The Safety options don’t present the overall safety demonstration that needs to be presented in the safety case supporting the licensing application. The Cigeo geological disposal facility project is designed to cater for all the HLW and ILWLL that has been produced and will be produced by existing nuclear facilities.

Andra has conducted in the frame of the safety options a parallel and coordinated operation and post-closure safety analysis. Those safety options take into account the particularity of Cigéo: HLW and various types of IL-WLL waste; the step by step development of Cigeo and the balancing approach between safety, technology and economics. Considering the various families and nature of the ILWLL waste, the Safety Options consist in estab-lishing “dimensioning characteristics “for design and operational safety as well as “envelop inventory” to man-age the knowledge acquired at this stage. In addition, the classification of scenario and the safety approach are adapted to the operational and post-closure context. The safety options identify the links between the two phases.

Key Words: nuclear safety, disposal, waste management, safety options

1. Introduction

The purpose of the Cigeo geological disposal facility for HLW and ILW-LL is to allow the safe disposal of IL-HL LL radioactive waste in order to eliminate or reduce the burden to be borne by future generations, in accordance with Article L542-1 of the Environment Code. Since 1991, successive safety milestones were implemented, based on the acquisition of scientific and technical knowledge and the development of safety methods appropriate to deep geological disposal. Since 2011, Cigéo has entered an industrial design development phase. In view of the licensing application, as a key milestones for safety, the Andra Safety Options Dossier “DOS” early 2016 is submitted to a national review and an international review1. According to the 2007 French Act, the Safety Options is an opportunity for Andra to send in advance a first safety case and aims to stabilize the safety strategy, the waste inventory, safety requirements, the safety methods, key safety and design options, the list of safety scenarios and a preliminary impact of a few margin scenarios. The safety options apply to the disposal of high-level waste (HLW) and intermediate-level long-lived waste (ILW-LL). The Safety options don’t present the overall safety demonstration that will be presented in the

1 International review by expert from regulatory and IAEA on behalf of the French Safety Authority

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safety case to support Future License Application of Cigéo in 2018 according to the recent French Act of July 2016.

FIG. 1.: a step-by-step iterative process as regards safety since 1991

2. Safety options and the incremental development of Cigéo

The safety options consider the duration of operation for over a hundred years with successive phases (construction/operation); it has to be flexible enough to adapt to possible changes in France's energy policy. There are three main phases in the life of Cigeo: (i) an initial design and initial construction phase, (ii) an operation phase (including an industrial pilot phase) and (iii) a post-closure phase. Cigeo will be closed in stages and the post-closure phase will begin when the final closure of Cigeo has been authorised by a law.

FIG 2: Diagram showing the main phases in the life of Cigeo

Following final closure, the underground facility after its final closure, will be the facility as built. At the stage of the safety options, the underground layout is only an illustration of what Cigéo might be, based on the technical options chosen at this stage. According to the incremental development of Cigéo, if a new technological solution is suggested, it will be checked that the operational and post-closure safety functions are still fulfilled (safety indicator assessment) and the radiological impact remains as low as reasonably possible given economic and social factors.

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3. The disposal system (natural and engineered components) relies on both operational and post-closure safety principles and safety functions

Protecting people and the environment is primarily based on the performance of safety functions during operation comparable to those performed at all nuclear facilities, and on safety standards (national and international), safety requirements and safety options adapted to the specific underground environment of the Cigéo facility.

Andra has implemented, from the design stage (since the 90’s), a safety approach and process (including siting), which relies on the specific characteristics of a repository as such: (i) the choice of the Callovo-Oxfordian formation in which the underground facility of Cigeo is located that meets the site technical criteria of the 2008 ASN nuclear safety guide, (ii) an underground facility located at a depth of around 500 m, of reduced geometry and long connecting drifts, requiring specific operating, intervention and evacuation conditions; (iii) a disposal facility being developed in successive phases, implying a need to consider the risks related to performing underground construction work and nuclear operations in parallel; (iv) a coordinated approach encompassing operating safety and post-closure safety. The approach integrates the successive iterations of Cigéo milestones including design and scientific knowledge evolutions with the objective of ensuring post-closure safety throughout the entire development cycle of the Cigeo project.

An appropriate level of monitoring and control will be also applied to Cigeo from its construction and during its operation, to ensure the protection and preservation of the passive post-closure safety features, as necessary, so that they can fulfil their safety functions once the repository is closed.

During operational phase, five safety functions are applicable to Cigeo throughout the operating phase and must be maintained in all incident or accident situations of internal or external origin or, at least, restored within time limits consistent with the objectives of protecting people and the environment defined for the Cigeo project. They are: (i) contain radioactive substances to protect against the risk of their dispersion; (ii) protect people from exposure to ionising radiation; (iii) manage safety with regard to the criticality risk; (iv) remove the heat produced by waste and (v) remove gases formed by radiolysis in order to manage explosion risks.

For the post-closure phase, the Cigéo aims to isolate the waste from humans and the biosphere and to confine it within a deep geological formation to prevent dissemination of the radionuclides contained in this waste (see table 1). The post-closure disposal system relies particularly on the Callovo-Oxfordian that plays the main role, and the closure structures of the surface-to-bottom connections (sealed shafts and ramps). The global approach to post-closure safety assessment is based on practical expression of the safety functions and associated requirements, analysis of component performance and analysis of the uncertainties related to the scientific and technological knowledge underpinning the design. To fulfil the post-closure safety functions, design principles for Cigeo and for the choice of site (see examples in table 1) are established.

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TABLE I: Example of Safety Principles for Cigéo

Post-closure safety functions General principles in terms of choice of site and design

Isolating waste from surface phenomena and human actions

Location of Cigeo at a depth and in an area of low, uniform geody-namic

Preventing the circulation of waterLow water flows in the Callovo-Oxfordian due to its low permeabil-ity and the low hydraulic head gradient;Consolidation and sealing of the surface-to-bottom connections

Restricting the release of radionuclides and toxic elements and immobilising them in the repository

Cells (particularly the materials used for them) designed to protect the waste and packages from a physicochemical point of view

Delaying and reducing radionuclide migration

Thickness of Callovo-Oxfordian (at least 130 m), high retention ca-pacity…Optimised geometries of the cells and drifts in the underground in-stallation, particularly in terms of length.

Whether the disposal system is functioning correctly and more specifically whether the safety functions are being fulfilled (operation normal functioning and post-closure normal evolution,) the design options relies also on the results of the risks analysis during operational phase adapted to Cigéo context (mainly transfer of waste package, co-activity of works and operation..) and the subsequent scenario (e.g. dimensioning waste characteristics and scenarios). It also relies on the scientific and technological uncertainties analysis after closure and the resulting normal evolution, altered evolution and what-if scenarios assessment. In the case of Cigéo, the safety options present a series of scenarios considering the dysfunction of sealing, the dysfunction of vitrified waste canister, as well the occurrence of inadvertent human intrusions (mostly borehole for Cigéo). Quantitative evaluations aimed at considering “envelop” situations of those scenarios.

FIG 3: Diagram showing the coordinated approach to operating safety and post-closure safety

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Appendix 1: References

[3] Act 91-1381 of 30 December 1991 on radioactive waste management research. (1992). Official Journal of the French Republic Acts and Decrees No. 1, 10 p.

[4] Act 2006-739 of 28 June 2006 on the sustainable management of radioactive material and waste. (2006). Official Journal of the French Republic. Acts and Decrees No. 93, 9,721 p.

[5] Délibération du conseil d'administration de l'Agence nationale pour la gestion des déchets radioactifs du 5 mai 2014 relative aux suites à donner au débat public sur le projet CIGEO. Ministère de l'écologie, du développement durable et de l'énergie (2014). Journal Officiel. Lois et décrets, n°108, pp.7851-7854.Safety Options Report – Post-Closure Part (DOS-AF). Andra. (2015). ° CGTEDNTEAMOASR20000150062.

[6] Safety Options Report – Operation Part (DOS-Expl). Andra. (2015). ° CGTEDNTEAMOASR20000150080.

[7] Act No. 2006-686 of 13 June 2006, as amended, on transparency and security in the nuclear field. Consolidated version dated 12 July 2014. (2006).

[8] Order of 7 February 2012 laying down the general rules on basic nuclear installations Consolidated version dated 05 July 2013. (2012).

[9] NEA IGSC Scenario Development Workshop, 1-3 June 2015, Issy-les-Moulineaux, France , to be published, OCDE.

[10] Radioactive Waste Disposal Facilities Safety Reference Levels v2.2. (Wgwd), W.G.O.W.a.D. Western European Nuclear Regulators Association (WENRA). (2014). 81 p.

[11] Fundamental safety principles. Safety fundamentals. IAEA. (2006). IAEA safety standards series n°SF-1. 37 p.

[12] Disposal of Radioactive Waste. Specific Safety Requirements. IAEA. (2011). IAEA Safety Standards Series n°SSR 5. 62 p.

[13] The management system for facilities and activities. Safety Requirements. IAEA. (2006). IAEA Safety Standards Series n°GS-R-3. 27 p.

[14] Monitoring and Surveillance of Radioactive Waste Disposal Facilities. Specific Safety Guide. IAEA. (2014). IAEA Safety Standards Series n°SSG-31. 96 p.

[15] The Safety Case and Safety Assessment for the Disposal of Radioactive Waste. Specific safety guide. IAEA. (2012). IAEA Safety Standards Series n°SSG-23. 140 p.

[16] Geological Disposal Facilities for Radioactive Waste. Specific Safety Guide. IAEA. (2011). IAEA Safety Standards Series n°SSG 14. 104 p.

[17] The management system for the disposal of radioactive waste. Safety guide. IAEA. (2008). IAEA safety standards series n°GS-G-3.4. 85 p.