synthesis of final disposal related nuclides · 2014-06-02 · synthesis of final disposal related...
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Apri l 2014
Working Reports contain information on work in progress
or pending completion.
Tuire Haavisto
Teol l isuuden Voima Oyj
Working Report 2014-15
Synthesis of Final Disposal Related Nuclides
Synthesis of Final Disposal Related Nuclides ABSTRACT Posiva Oy manages the disposal of spent nuclear fuel from the Loviisa and Olkiluoto nuclear power plants (NPP). When the spent nuclear fuel is removed from the reactor it is stored in the cooling pools at the NPP units for approximately five years. After the first cooling period the spent nuclear fuel is transported to the interim storage (KPA) at the NPP's to cool down in water pools at least for 20-30 years. Generic radionuclide inventory calculations have been made for the spent nuclear fuel with a cooling period of 30 years. These calculations are the basis for Posiva's operational safety, safety case and decay heat power and criticality calculations. Validating the calculated radionuclide inventories with radiochemical analyses is advisable. The most important nuclides, both radioactive and stable, from the radiation and operational safety, long-term safety, decay heat power and criticality calculations point of view are listed. Also the nuclides possible to be assessed by Studsvik are listed. The conclusion is that the nuclides proposed by Studsvik in 2011 are recommended for radiochemical analyses of spent nuclear fuel. Keywords: Spent nuclear fuel, nuclide, radiochemical analyses, long-term safety, decay heat power, criticality calculations.
Synteesi käytetyn polttoaineen loppusijoittamiseen liittyvistä nuklideista TIIVISTELMÄ Posiva Oy huolehtii omistajiensa puolesta Loviisan ja Olkiluodon ydinvoimalaitoksissa syntyneen käytetyn polttoaineen loppusijoittamisesta. Kun käytetty polttoaine pois-tetaan reaktorista, säilytetään polttoainetta voimalaitosten polttoainealtaissa noin viisi vuotta. Tämän jälkeen käytetty polttoaine siirretään laitosalueilla sijaitseviin käytetyn polttoaineen varastoihin (KPA-varasto) jäähtymään vähintään 20-30 vuodeksi. Käytetty polttoaine siirretään välivarastoinnin jälkeen Posivan kapselointi- ja loppusijoitus-laitokselle kapselointia ja loppusijoittamista varten. Käytetylle polttoaineelle on tehty nuklidi-inventaarilaskut 30 vuoden jäähtymisajalla. Nämä laskut ovat Posivan käytönaikaisen turvallisuuden, pitkäaikaisturvallisuuteen liittyvän turvallisuusperustelun, sekä jälkilämpö- ja kriittisyyslaskujen perusta. Lasket-tujen nuklidi-inventaarien validointi radiokemiallisilla analyyseillä on kuitenkin suosi-teltavaa. Tärkeimmät radioaktiiviset ja stabiilit nuklidit säteilyturvallisuuden, pitkäaikaistur-vallisuuden, jälkilämmön ja kriittisyyslaskujen näkökulmasta on luetteloitu tässä syn-teesissä. Myös ne nuklidit, jotka on mahdollista radiokemiallisesti analysoida Studs-vikissa, on lueteltu. Johtopäätöksenä voidaan suositella Studsvikin vuonna 2011 ehdot-tamien nuklidien määrittämistä kemiallisesti käytetystä polttoaineesta. Avainsanat: Käytetty polttoaine, nuklidi, radiokemialliset analyysit, pitkäaikaisturval-lisuus, jälkilämpö, krittiisyyslaskut.
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TABLE OF CONTENTS ABSTRACT TIIVISTELMÄ FOREWORD .................................................................................................................. 2
1 INTRODUCTION ..................................................................................................... 3
2 SPENT NUCLEAR FUEL ........................................................................................ 4
3 NUCLIDES ............................................................................................................ 10
3.1 Safety case for geological disposal ................................................................ 10
3.2 Criticality safety .............................................................................................. 12
3.3 Nuclides contributing to the decay heat power ............................................... 14
3.4 Nuclides important for NPP operation and maintenance ............................... 14
4 ISOTOPE ANALYSIS METHODS AT STUDSVIK ................................................ 16
5 RADIOCHEMICAL NUCLIDE ANALYSES ............................................................ 18
6 CONCLUSIONS .................................................................................................... 20
REFERENCES ............................................................................................................. 21
Appendix A. The nuclides of importance for long-term safety, criticality, decay heat power, the nuclides mentioned in the YVL D.5 and the nuclides possible to be analysed at Studsvik.............................................................................................. 23
Appendix B. (LA)-ICP-MS analyses on spent nuclear fuel ........................................... 29
Appendix C. Important nuclides contibuting to decay heat power as a function of time.30
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FOREWORD
This report was compiled by Tuire Haavisto (Teollisuuden Voima Oyj). The following authors have contributed to the technical contents of the report: Anna-Maija Hahl (Posiva Oy), Aapo Tanskanen (Fortum Power and Heat Oy), Anssu Ranta-aho (Teollisuuden Voima Oyj), Linda Kumpula (Posiva Oy), Maria Palomäki (Teollisuuden Voima Oyj), Mari Lahti (Posiva Oy), Barbara Pastina (Saanio & Riekkola Oy), Peter Askeljung (Studsvik AB) and Michael Granfors (Studsvik AB).
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1 INTRODUCTION
Posiva Oy (Posiva) manages the disposal of spent nuclear fuel from the Loviisa and Olkiluoto nuclear power plants (NPP). Two pressurised water reactors (VVER-440) are in operation (LO1 and LO2) at Loviisa. At Olkiluoto two boiling water reactors are in operation (OL1 and OL2) and one pressurised water reactor (EPR) is under construction. The parliament of Finland endorsed a Decision in Principle (DiP) in 2010 to build a fourth reactor at Olkiluoto (OL4). According to the Finnish regulatory guide YVL D.5 Posiva's safety case "shall include... a functional description of the disposal system by means of conceptual and mathematical modelling and the determination of the input data needed in these models...". For the moment, the majority of the input data for the mathematical models are based on calculations. Experimental data on spent nuclear fuel composition are needed for the validation of these models. The guide YVL B.4 defines the constraints for the criticality calculations: In criticality safety analyses, all fissile nuclides significantly affecting the reactivity shall be taken into account... As regards unstable nuclides, the reactivity effect of daughter nuclides may be taken into account.... Also the importance of validating the calculations is defined in the guides. YVL D.5 ratifies the need for experimental analyses: "The safety case comprises a numerical analysis based on experimental studies and complementary considerations insofar as quantitative analyses are not feasible or involve considerable uncertainties". Some radiochemical analyses have been performed on spent nuclear fuel but there is still a need for more extensive analyses. Both the power companies and Posiva would benefit from nuclide analyses on spent nuclear fuel. In Posiva the results can be used for defining the operational safety of the encapsulation plant and for the final disposal facility in the long-term safety assessment, and decay heat power and criticality calculations for the disposal of spent nuclear fuel. In the power companies the results can be used when planning the radiation and operational safety. Also the implementation of safeguards might benefit of the results as Posiva is required to report the inventories of the nuclear material in the spent nuclear fuel in accordance with YVL D.1. This synthesis report presents the most important nuclides from the long-term safety, criticality and decay heat power point of view. Posiva can decide, on the basis of this synthesis, which nuclides to analyse from the spent fuel pellets stored at the Studsvik Hot Cell Laboratory (Studsvik).
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2 SPENT NUCLEAR FUEL
The spent nuclear fuel produced by the reactors in operation at Loviisa and Olkiluoto, the OL3 unit under construction and the planned OL4 unit all have different types of fuel, Figure 2-1. The design of the fuel assemblies varies depending on the reactor type. Since the OL4 reactor type has not been decided yet it is assumed to correspond to OL3 in Posiva's safety case (Posiva 2012-12).
Figure 2-1. Representative illustrations of fuel assemblies for the following reactor types (from left) LO1-2, OL1-2 and OL3. LO1-2 and OL1-2 fuel elements are partly cut open to show the internal structures. The pictures are not to scale (Posiva 2013-01). The spent nuclear fuel assemblies are composed of fuel pellets, metallic tubes and other metal parts, Figure 2-2.
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Figure 2-2. The structure of a BWR GE-14 type fuel assembly (OL1 and OL2). The materials of the different fuel assembly parts are the same regardless of reactor type. (TVO brochure)
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The fuel pellets are made of sintered UO2. The 235U enrichment and amount of burnable poison (e.g. Gd2O3) as well as possible chemical additives (oxides of Al and Cr) vary depending of the fuel type. The bundle average 235U enrichment in the fuel varies normally between 3-5%. The enrichment has risen during the years enabling higher burn-ups. The current licensed maximum bundle average burnup for LO1-2 is 57 MWd/kgU whereas it is 50 MWd/kgU for OL1-2 and 45 MWd/kgU for OL3. TVO is planning to increase the maximum average burnup to 55 MWd/kgU for all three units. The structural materials of the fuels of different reactor types are in many ways similar to each other. The claddings are made of different types of zirconium alloys and the other components of the fuel assemblies are made of stainless steels or nickel based alloys. (Posiva 2012-12) The fuel assembly type, total amount of uranium (tU) and number of canisters to be disposed of for LO1-2 and OL1-4 are shown in Table 2-1. When the average amount of uranium per canister is two tonnes and the total amount of uranium is 9000 tonnes, a total of 4500 canisters are to be disposed of in the repository. Table 2-2 shows the 235U enrichment, discharge burn-up and the void fraction (only for BWR) for the spent nuclear fuel taken into account in the reference inventory. When the spent nuclear fuel is removed from the reactor it is stored in the cooling pools at the NPP units, in reactor hall pools, for approximately five years. After the first cooling period the spent nuclear fuel is transported to the interim storage pools (KPA) at the NPP's for further cooling lasting for 20-30 years.
Table 2-1. The fuel assembly types contributing to the inventory (Posiva 2012).
Reactor Fuel assembly type Total amount of uranium (tU)
Number of canisters
Loviisa 1‐2 VVER‐440 (manufacturers TVEL and BNFL)
1050 750
Olkiluoto 1‐2 BWR Atrium 2950 1400
Olkiluoto 3‐4 PWR 1) 5000 2350
Total 9000 4500 1) The reactor type of Olkiluoto 4 has not been chosen, but OL3 is applied as the reference for the inventory.
Table 2-2. The fuel parameter variants taken into account in the reference inventory (Posiva 2012-09).
Parameter Unit Values 235U enrichment (%) 3.6 (PWR)
3.7 (VVER‐BNFL) 3.8 (BWR) 4.0 (PWR and VVER‐TVEL) 4.2 (BWR) 4.4 (VVER)
Discharge burnup
(MWd/kgU) 40, 50, 60
Void fraction (%) 0, 40, 80
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Currently the spent nuclear fuel is not planned to be encapsulated before 20 years of cooling after operation in storage pools. Even after 20 years of cooling, spent nuclear fuel is highly radioactive and radiation protection is essential. Generic radionuclide inventory calculations have been made for the spent nuclear fuel with a cooling period of 30 years (Posiva 2012-09). In addition to the total inventory it is essential to know where the nuclides are distributed within the fuel assemblies and how quickly the nuclides are released in case of canister leakage. The material composition of the fuel assemblies affects the location of the nuclides. The conceptual model for the radionuclide source term is illustrated in Figure 2-3. The radionuclide inventory that constitutes the source term is divided into four components: (Posiva 2013-01) - the fuel matrix, in which most of the radionuclides are present, - void spaces in the fuel rod (i.e. plenum the upper and lower part of the fuel rod,
gap between the pellet and cladding, grain boundaries in the fuel, cracks within the pellet, pores accessible to water) in which concentrations of certain radionuclides is enriched (referred as to IRF in Figure 2-3),
- zirconium alloys (fuel channels, guide tubes), and - other metallic parts (e.g. tie-plates, end plugs, spacer grids, nozzles and transition
pieces). The overall inventory and its partitioning will vary according to the type of spent nuclear fuel, its burn-up and its enrichment. For Posiva's safety case (Posiva 2012-09), a reference inventory of radionuclides and stable isotopes has been compiled to encompass the inventories of the different fuel types at different burnup and enrichment. To use different source terms for each fuel element would be unreasonable and highly complex. (Posiva 2013-01)
Figure 2-3. Conceptualisation of the source term as inventory components used in the assessment of radionuclide release scenarios. The relative size of the compartments in this figure does not reflect the actual partitioning of the radionuclides within a fuel assembly. (Posiva 2013-01)
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Table 2-3 shows potential safety-relevant long-lived radionuclides according to the inventory calculations. The radioactive inventory shown in Table 2-3 is the reference inventory of radionuclides used in the analysis of radionuclide release scenarios within Posiva's safety case. Table 2-3. The reference inventory of the potentially safety-relevant radionuclides in one tonne of uranium (tU) at 30 years after discharge from the reactor (Posiva 2013-01).
Radionuclide T1/2 [a] Total inventory at 30 years cooling time [GBq/tU]
Partitioning of activity [%]
Fuel matrix [%]
IRF 1) of all
components [%] Zirconium alloy [%]
Other metal parts [%]
108mAg 4,38E+02 2,50E+04 100
241Am 4,32E+02 1,93E+05 100
243Am 7,37E+03 3,42E+03 100
10Be 1,51E+06 1,26E‐02 95 5
14C 5,70E+03 1,61E+02 22,4 5,5 12,1 60
36Cl 3,01E+05 2,63E+00 73,6 8,2 18,2
245Cm 8,42E+03 1,03E+02 100
246Cm 4,71E+03 3,57E+01 100
135Cs 2,30E+06 3,43E+01 95 5
137Cs 3,01E+01 3,46E+06 95 5
129I 1,57E+07 1,91E+00 95 5
93Mo 4,00E+03 2,26E+01 1,33 0,07 0,2 98,3
91Nb 6,80E+02 2,86E‐04 88,8 11,2
92Nb 3,47E+07 2,35E‐04 1,2 98,8
93mNb 1,61E+01 5,08E+03 1,7 98,3
94Nb 2,03E+04 7,52E+02 42,8 57,2
59Ni 7,60E+04 2,21E+02 0,3 2,9 96,8
63Ni 1,01E+02 2,47E+04 0,3 3,3 96,4
237Np 2,14E+06 2,37E+01 100
231Pa 3,28E+04 1,39E‐03 100
107Pd 6,50E+06 9,72E+00 99 1
238Pu 8,77E+01 2,64E+05 100
239Pu 2,41E+04 1,42E+04 100
240Pu 6,56E+03 3,12E+04 100
241Pu 1,43E+01 1,75E+06 100
242Pu 3,75E+05 2,17E+02 100
226Ra 1,60E+03
79Se 3,27E+05 4,67E+00 99,6 0,4
151Sm 9,00E+01 1,74E+04 100
126Sn 2,30E+05 3,92E+01 99,99 0,01
90Sr 2,88E+01 2,23E+06 99 1
99Tc 2,11E+05 8,48E+02 99 1
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Radionuclide T1/2 [a] Total inventory at 30 years cooling time [GBq/tU]
Partitioning of activity [%]
Fuel matrix [%]
IRF 1) of all
components [%] Zirconium alloy [%]
Other metal parts [%]
229Th 7,34E+03
230Th 7,54E+04 1,32E‐02 100
232Th 1,40E+10 2,06E‐08 100
233U 1,59E+05 3,86E‐03 100
234U 2,46E+05 5,53E+01 100
235U 7,04E+08 8,15E‐01 100
236U 2,34E+07 1,46E+01 100
238U 4,47E+09 1,17E+01 100
93Zr 1,61E+06 1,27E+02 87,9 12,1
1) IRF: Instant Release Fraction. The percentages are calculated as a ratio of the IRF activity and the total activity.
Fortum and TVO have transported some spent nuclear fuel rods to Studsvik in Sweden for Post Irradiation Examinations (PIE). In 2009, TVO sent two spent nuclear fuel rods to Studsvik to be analysed in the hot cell laboratory. These fuel rods have been irradiated in OL1 NPP for five cycles to reach an average burn-up of over 50 MWd/kgU. The measurements consisted of puncturing and fission gas analysis, visual inspection, gamma-scanning and examination in optical microscope. The IRF (instantaneous release) has been studied for the TVO fuel rods at Studsvik in the EU FIRST-Nuclides project 2012-2013 (www.firstnuclides.eu). In the IRF leaching experiments the samples consisted of both the fuel and the cladding. In 2003 four spent nuclear fuel rods from a bundle with an average burn-up of 55 MWd/kgU were transported from Loviisa NPP to Studsvik. The analyses included, among others, fission gas release analysis and gamma scanning. Substantial amount of spent fuel material is still left in Studsvik. No IRF analyses have been performed on Fortum spent nuclear fuel. There is an interest from different perspectives to measure the nuclide composition of the spent nuclear fuel. A limited number of radionuclides are of importance in the long-term safety analyses of the Posiva's disposal system. The nuclides that have no plausible long-term safety or criticality relevance have been excluded (Posiva 2013-01).
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3 NUCLIDES
The nuclides in the spent nuclear fuel are located in the fuel matrix, the cladding, the grain boundaries, cracks and gaps and in the structural materials, as shown in Figure 2-3. Different analysis methods are used at Studsvik for assessing the isotopes, for example HPLC (High Performance Liquid Chromatography), DRC (Dynamic Reaction Cell), ICP-MS (Inductively Couples Plasma Mass Spectrometry) and laser ablation. Yet for some nuclides there is no established method for screening; Studsvik has been unable to assess the isotopes 14C, 36Cl and 79Se. Lately Studsvik has been developing a method for analysing 14C but the preparation work and analyses are still very difficult (Daqing 2013). The important nuclides from the long-term safety point of view differ to some extent from the nuclides important for the criticality calculations (burnup credit). In Appendix A the nuclides of interest are presented. The Finnish Guide YVL D.1 and D.5 specifies some nuclide-specific constraints that have to be taken into account in the Posiva's safety case. The Guide YVL B.4 defines the constraints for criticality and validation calculations. The nuclides of interest are both radioactive and stable. The long-term safety relevant nuclides are those isotopes that might contribute to the doses to the biosphere in scenarios leading to a premature release from the canister. The chemistry, half-life, radiotoxicity, mobility and high inventory of the isotopes are features that affect the importance of the nuclides. The capability to absorb neutrons is one important feature of the isotopes that affect the reactivity in the repository conditions.
3.1 Safety case for geological disposal
To fulfil the long-term safety requirements, the repository needs to isolate the spent nuclear fuel from the biosphere as long as it can cause significant harm to the normal habitat for humans, plants and animals. Internationally, most safety assessments for spent nuclear fuel disposal, as well as the present safety case of Posiva, focus on the period up to one million years into the future, referred to as the assessment time frame. (Posiva 2012-09) The Finnish regulator has set nuclide specific constraints for the radioactive releases to the environment in Guide YVL D.5, Table 3-1. In Table 3-2 the long-term safety relevant nuclides in Posiva's safety case are listed. The five nuclides assessed to cause the highest doses to a representative member of the most exposed group are 14C, 36Cl, 93Mo, 108mAg and 129I (Posiva 2012-10).
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Table 3-1. The nuclide-specific constraints for the radioactive releases to the environment, as set out in the regulatory guide YVL D.5. The constraint applies to each individual radionuclide. (Posiva 2012-09)
Radionuclide Constraints [GBq/a]
Long‐lived alpha‐emitting Ra, Th, Pa, Pu, Am and Cm isotopes 0.03 79Se, 94Nb, 129I, 237Np 0.1 14C, 36Cl, 135Cs, long‐lived uranium isotopes 0.3 126Sn 1 99Tc, 93Mo *) 3 93Zr 10 59Ni 30 107Pd 100 *) 93Mo is not mentioned in YVL D.5. However, based on a preliminary evaluation by STUK (personal communication May 9, 2012) that takes into account the inventory and the dose conversion factors for ingestion, it has been recommended that the same nuclide‐specific constraint as for 99Tc is used. (Posiva 2012‐09)
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Table 3-2. The long-term safety relevant nuclides (Posiva 2013-01).
Radionuclide T1/2 [a] 1) Studsvik 2)
14C 5 700 3) 36Cl 3,01E+05 3) 59Ni 7,60E+04 ‐ 79Se 2,95E+05 3) 90Sr 28,9 x 91Nb 6,80E+02 ‐ 92Nb 3,47E+07 ‐ 93mNb 16,12 ‐ 94Nb 2,03E+04 ‐ 93Mo 4,00E+03 x 99Tc 2,11E+05 x 107Pd 6,5E+6 ‐ 108mAg 438 ‐ 126Sn 2,30E+05 ‐ 129
I 1,57E+07 x 135Cs 2,30E+06 x 226Ra 1600 ‐ 229Th 7932 ‐ 237Np 2,14E+06 x 238Pu 87,7 x 239Pu 24110 x 240Pu 6561 x 242Pu 3,75E+05 x 241Am 432,6 x 243Am 7370 x 245Cm 8423 ‐
1) National Nuclear Data Center (NNDC), Brookhaven National Laboratory, http://nndc.gov/chart/chartNuc.jsp, 17.10.2013 2) Nuclides possible to assess at Studsvik, Presentation: Isotope analysis at Studsvik (HPLC, DRC, ICP‐MS, Laser ablation), Michael Granfors, Screening of isotopes, 25.5.2012 3) No established method or below detection limit
3.2 Criticality safety
The Guide YVL B.4 (Nuclear fuel and reactor) does not specify any nuclide-specific constraints for criticality calculations that have to be taken into consideration in the Posiva's safety case. In the calculations all fissile nuclides with significant impact on reactivity have to be taken into account. Credit can also be given to neutron absorbing neutrons. The reactivity effect of daughter nuclides may be taken into account in such a way that the combined reactivity effect of nuclides in a decay chain starting from an unstable nucleus is conservative (Finnish guide YVL B.4). Table 3-3 lists nuclides typically considered in burnup credit criticality safety analysis. Table 3-4 shows additional fission products that could be credited in the criticality calculations. (Ranta-aho 2011)
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In addition to the spent nuclear fuel, the control rods from OL3 contain nuclides that may be of importance for the criticality calculations. The control rods contain 109Ag and
113Cd among others, which are burnup credit-relevant nuclides.
Table 3-3. Nuclides typically considered in burnup credit criticality safety analysis calculations.
Radionuclide T1/2 [a] 1) Studsvik 2)
95Mo STABLE x 99Tc 2,11E+05 x 101Ru STABLE x 103Rh STABLE x 109Ag STABLE x 133Cs STABLE x 143Nd STABLE x 145
Nd STABLE x 147Sm 1,06E+11 x 149
Sm STABLE x 150Sm STABLE x 151Sm 90 x 152Sm STABLE x 153Eu STABLE x 155Gd STABLE 3) 234U 2,46E+05 x 235U 7,04E+08 x 236U 2,34E+07 x 238U 4,47E+09 x 238Pu 87,7 x 239Pu 24110 x 240Pu 6561 x 241
Pu 14,325 x 242Pu 3,75E+05 x 237Np 2,14E+06 x 241Am 432,6 x 242mAm 141 4) 243Am 7370 x 243Cm 29,1 ‐ 245Cm 8423 ‐
1) National Nuclear Data Center (NNDC), Brookhaven National Laboratory, http://nndc.gov/chart/chartNuc.jsp, 17.10.2013
2) Nuclides possible to assess at Studsvik, Presentation: Isotope analysis at Studsvik (HPLC, DRC, ICP‐MS, Laser ablation), Michael Granfors, Screening of isotopes, 25.5.2012 3) 155Gd normally as daughter of 155Eu only, Studsvik presentation 4) Might be below detection limit, Studsvik presentation
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Table 3-4. Additional fission products to those in Table 3-3 that could be credited in the criticality calculations.
Radionuclide T1/2 [a] 1) Studsvik 2)
83Kr 10,752 4) 90Sr 28,9 x 93Zr 1,61E+06 3) 97Mo STABLE ‐ 105Pd STABLE ‐ 107Pd 6,5E+06 ‐ 108Pd STABLE ‐ 113Cd 8,00E+15 5) 129I 1,57E+07 x
131Xe STABLE 4) 135Cs 2,30E+06 x 139La STABLE x 141
Pr STABLE x 144Nd 2,29E+15 x 147Pm 2,6234 x 148Nd STABLE x 155Eu 4,753 x 157Gd STABLE 3)
1) National Nuclear Data Center (NNDC), Brookhaven National Laboratory, http://nndc.gov/chart/chartNuc.jsp, 17.10.2013 2) Nuclides possible to assess at Studsvik, Presentation: Isotope analysis at Studsvik (HPLC, DRC, ICP‐MS, Laser ablation), Michael Granfors, Screening of isotopes, 25.5.2012 3) No established measurement method or below detection limit 4) Lost during sample dissolution, modeling might be more reliable than analysis 5) Not analysed so far, but 111, 112 and 114. Separately determined response might be an option, if no In‐113 in the sample
3.3 Nuclides contributing to the decay heat power
Nuclides contributing to the decay heat power have to be taken into account when disposing the spent nuclear fuel because they affect the temperature of the canister, of the buffer and of the rock, and therefore the final layout of the repository. Figure C-1 shows that the isotopes 90Y and 137mBa, along with 239Pu, 240Pu, 241Am and 244Cm, are important nuclides contributing to the decay heat power in the long term. The isotope 137mBa is daughter of 137Cs and 90Y is a daughter of 90Sr.
3.4 Nuclides important for NPP operation and maintenance
During reactor operation, radiation levels, fuel performance and water chemistry are monitored. The nuclides that contribute the most to the doses at NPP's are (Lundgren 2011): - 60Co (T1/2=1925,28 d),
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- 58Co (T1/2=70,8 d), - 54Mn (T1/2=312,12 d), - 124Sb (T1/2=60,2 d), - 110mAg (T1/2=249,76 d), and - 63Ni (T1/2=101,2 y). Of these nuclides only 63Ni (contributing to the dose at Loviisa NPP's along with 110mAg) is in Table 2-3 where the potentially safety relevant nuclides at 30 years after discharge from the reactors are listed. Some of the nuclides that cause high doses at NPP's are left outside the scope of this synthesis. These nuclides have very short half-times which is why they are not considered important from the long-term safety point of view. The radionuclides that affect the reactivity of the fuel during operation at the NPP's and at the disposal facility are shown in Table 3-3 and Table 3-4. Other important nuclides during operation are for example plutonium and caesium and their isotopes. The activated corrosion products (crud), mostly 60Co, 59Ni and 63Ni, are important from the radiation safety point of view and are therefore monitored during operation. Even though these nuclides have relatively short half-times, they can also affect the operational safety at the encapsulation plant and the nuclear waste facility. Although these nuclides are relevant to operational safety, they are not relevant in the long time scales considered in the final disposal of spent nuclear fuel; hence, they are not taken into account in this synthesis report. Radiation and activity measurements are planned to be used at the encapsulation plant and in the final disposal facility to assure the operational safety and for securing that no significant amounts of radioactive materials are released to the environment (Posiva 2012-91). The planning of operational safety is based on the same activity calculations that are used in the long-term safety, decay heat power and criticality calculations. Nuclides of significance for radiation and operational safety at the encapsulation and nuclear waste disposal facility are listed in Appendix A.
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4 ISOTOPE ANALYSIS METHODS AT STUDSVIK
Studsvik has several methods for nuclide analyses on spent nuclear fuel. First, cut out sections of spent nuclear fuel rods have to be dissolved and filtrated for analyses. The equipment used at Stusdvik for isotope analyses on spent nuclear fuel are HPLC, DRC, ICP-MS and laser ablation. Figure 4-1 shows the dissolution process of the fuel samples. After cutting and weighing, the samples are boiled in 8M HNO3 for six hours (step 1). After this the samples are boiled in a second dissolution (7M HCl) for four hours (step 2). If iodine is assessed, instead of boiling the sample in a second dissolution, the nuclide is collected in washing bottles from the off-gas during dissolution (step 1). The portion of iodine is determined by comparing the amount of natural iodine carrier added to the fuel sample before dissolution and the amount found in the washing bottles (N-211134). Iodine is analysed by ICP-MS in combination with a dynamic reaction cell (DRC), in order to eliminate mass overlap with 129Xe. For other nuclides, after the second dissolution (step 2), the main solution is filtered and analysed. The filtrated residue is dissolved in high pressure in 1 vol. HNO2 + 2 vol. HCl + 0.5 vol. HF for four hours at 180°C. The residue solution is also analysed. (Granfors 2012) The HPLC and DRC are used for separation of isobaric overlap. In DRC isotopes with the same mass are separated by a reaction gas which reacts with one of the elements but not with the other. With HPLC isotope dilution analysis is used. (Granfors, 2012) Studsvik can also offer laser ablation (LA)-ICP-MS analyses on fuel pellets, the method is described in Appendix B. The analysis methods have always uncertainties, which are dependent on the method chosen and on the sample quality and content. For external calibration the uncertainty is estimated to be 5-10% and for special analysis methods ~10%. The determination of 129I depends strongly on the yield during dissolution and the uncertainty is estimated to be higher than 10%. (Granfors 2012)
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Figure 4-1. Sample dissolution methods at Studsvik on spent nuclear fuel. (Granfors 2012)
18
5 RADIOCHEMICAL NUCLIDE ANALYSES
Most of the nuclides of interest from the long-term safety, criticality and decay heat power point of view, can be assessed by Studsvik. Only for a few of the essential nuclides for long-term safety, i.e. 14C, 36Cl and 79Se, there is no established method for screening. In November 2013, Daqing Cui from Studsvik presented at the FIRST-Nuclides 2nd Annual Workshop improvements in assessing 14C from spent nuclear fuel (Daqing 2013). If the method for assessing 14C will be validated it is highly recommended. For some of the long-term safety relevant nuclides there are specific constraints for the radioactive releases to the environment set out in the Guide YVL D.5 (Table 3-1). Also one of the major grounds for assessing a set of nuclides is the calculated release rates from the near-field to the geosphere and from the geosphere to the surface, Figure 5-1. Five nuclides make the greatest contribution to the total releases; 14C, 36Cl, 129I, 135Cs and 59Ni (Posiva 2012-09). Validating these calculated release rates by radiochemical nuclide analyses is advisable.
Figure 6-1. Evolution of the total radionuclide release rate from the geosphere to the surface and the evolution of release rates of 14C, 36Cl, 129I, 135Cs and 59Ni, which are the five nuclides making the greatest contributions to the total. (Posiva 2012-09)
After all, Posiva is disposing heat in the nuclear waste facility. The maximum temperature allowed on the outer surface of the copper canister is set to 100°C which in turn defines the maximum total decay heat power of the fuel bundles positioned in a disposal canister. For LO1-2 the maximum decay heat power for the canister is 1370 W, for OL1-2 1700 W and for OL3 the maximum decay heat power is 1830 W (Posiva 2012-65). Calorimeter measurements are one way to specify the decay heat power of the
19
fuel assemblies. These measurements could be supported by the radiochemical nuclide analyses. The important nuclides contributing to decay heat power as a function of time are shown in Appendix C. Most of these nuclides can be assessed at Studsvik.
20
6 CONCLUSIONS
In Appendix A, a list of nuclides to be taken into account when disposing spent nuclear fuel is given. The list is based on the nuclides relevance with respect to long-term safety, criticality safety, decay heat power and regulatory constraints mentioned in the Finnish regulatory guides YVL D.1, D.5 and B.4. The nuclides of importance to SKB (Posiva's counterpart in Sweden) are also listed, for comparison. Finally, for each nuclide, the availability of radiochemical analyses by Studsvik is provided. It should be noticed that different isotopes of the same element may be of interest from different viewpoints. If all the isotopes of a nuclide are automatically included in the assessment, all isotopes should be reported. Assessing certain nuclides with radiochemical analyses at Studsvik is essential for validating the inventory calculations that Posiva's safety case relies on. Furthermore, the Finnish Guide YVL D.5 points out the need of experimental analyses. Currently, the safety case relies mostly on calculated inventories. The experimental data are expected to support the use of calculation methods for the determination of the nuclide composition of the spent nuclear fuel to be disposed of in a geologic repository.
21
REFERENCES
Posiva 2010-79, Radionuclide Transport and Dose Assessment Modelling in Biosphere Assessment 2009, November 2010, Posiva Oy, Eurajoki. Posiva 2012-09, Safety Case for the Disposal of Spent Nuclear Fuel at Olkiluoto Assessment of Radionuclide Release Scenarios for the Repository System 2012, December 2012, Posiva Oy, Eurajoki, ISBN 978-951-652-190-2. Posiva 2012-10, Safety Case for the Disposal of Spent Nuclear Fuel at Olkiluoto - Biosphere Assessment 2012, September 2012, Posiva Oy, Eurajoki, ISBN 978-951-652-191-9. Posiva 2012-12, Safety Case for the Disposal of Spent Nuclear Fuel at Olkiluoto - Synthesis 2012, December 2012, Posiva Oy, Eurajoki, ISBN 978-951-652-193-3. Posiva 2012-65, Laitoskuvaus 2012 - Kapselointi- ja loppusijoitussuunnitelmien yhteenvetoraportti, May 2013, Posiva Oy, Eurajoki. Posiva 2012-71, Oliluodon kapselointi- ja loppusijoituslaitoksen käyttöturvallisuus-analyysi, November 2012, Posiva Oy, Eurajoki. Posiva 2012-91, Kapselointi- ja loppusijoituslaitoksen säteily- ja aktiivisuusmittaukset, February 2013, Posiva Oy, Eurajoki. Posiva 2013-01, Safety Case for the Disposal of Spent Nuclear Fuel at Olkiluoto - Models and Data for the Repository System 2012, September 2013, Posiva Oy, Eurajoki, ISBN 978-951-652-233-6. Posiva 2013-01, Safety Case for the Disposal of Spent Nuclear Fuel at Olkiluoto - Models and Data for the Repository System 2012, Appendix C.4, September 2013, Posiva Oy, Eurajoki ISBN 978-951-652-233-6. Posiva 2012, Construction application license (Rakentamislupahakemus Olkiluodon kapselointi ja loppusijoituslaitoksen rakentamiseksi käytetyn ydinpolttoaineen loppusijoitusta varten), Posiva Oy, Eurajoki. Akseljung Peter, Granfors Mikael, personal e-mail, 13.12.2013. Daqing Cui, C-14 measurements, presentation at the FIRST-Nuclides 2nd Annual Workshop, November 2013, Studsvik Nuclear AB. Granfors Mikael, Isotope analysis at Studsvik (HPLC, DRC, IPC-MS, Laser ablation), presentation, May 25 2012, Studsvik. Lundgren Klas, Wikman Gunnar, OL1, OL2: Chemistry, radiation and fuel performance review 2010, Presentation, March 2011, Studsvik Nuclear AB.
22
Haavisto Tuire, Synthesis of final disposal related nuclides, Confidental TVO Memo 157272, February 2014, Teollisuden Voima Oyj, Eurajoki. National Nuclear Data Center (NNDC), Brookhaven National Laboratoty, http://www.nndc.gov/chart/chartNuc.jsp, 17.10.2013. NDS/IAEA Live Chart of Nuclides, nuclear structure and decay data (http://www-nds.iaea.org/relnsd/vcharthtml/VChartHTML.html). OL1/OL2, Nuclear power plant units Olkiluoto 1 and Olkiluoto 2 - brochure, Teollisuuden Voima Oyj, Eurajoki. Ranta-aho Anssu, List of typical burn-up credit nuclides, 2011. Ranta-aho Anssu, Criticality Safety Analysis of BWR, PWR and VVER-440. Disposal Canisters in the Final Disposal Facility 2012. Roth Olivia, Spent fuel leaching - preliminary results FIRST-Nuclides, presentation, May 2013, Studsvik Nuclear AB. Spent Nuclear Fuel Assay Data for Isotopic Validation, State-of-the-art Report, Nuclear Science Committee, Working Party on Nuclear Criticality Safety (WPNCS), NEA/NSC/WPNCS/DOC(2011)5, 2011. SKB TR-11-01, Long-term safety for the final repository of spent nuclear fuel at Forsmark, Volume I and III. SKB TR-10-13, Spent nuclear fuel for disposal in the KBS-3 repository.
23
AP
PE
ND
IX A
. T
HE
NU
CL
IDE
S O
F IM
PO
RT
AN
CE
FO
R L
ON
G-T
ER
M S
AF
ET
Y, C
RIT
ICA
LIT
Y, D
EC
AY
HE
AT
PO
WE
R, T
HE
NU
CL
IDE
S
ME
NT
ION
ED
IN T
HE
YV
L D
.5 A
ND
TH
E N
UC
LID
ES
PO
SS
IBL
E T
O B
E A
NA
LY
SE
D A
T S
TU
DS
VIK
.
Posiva
SKB
STUK
Research
RN
T 1/2 [a] 1)
Why this
radionuclide?
2) 3)
Dau
ghter
nuclide 4)
Criti‐
cality
3)
Burn‐up
credit
criticality
analyses 5)
Rad
ionuclide
release
assess‐
ment 6
)
Biosphere
assess‐
ment 7
)
Models
and
Data
8)
Rad
iation
safety 9)
Long‐term
safety
at Forsmark
10)
SKB
radionuclide
inventory 11)
YVL
D.1 12)
YVL D.5
13)
Studsvik
2011 14)
Screening
isotopes
15)
FIRST
Nuclides 16)
3H
12,32
‐
x
x x
10Be
1,39E+06
High inventory based
on
Serpent calculations
‐
x
x
14C
5 700
Long term
safety, non‐sorbing
‐
x
x x
x x
x
x
x 18)
x
36Cl
3,01E+05
Waste
managem
ent,
non‐sorbing
‐
x
x x
x x
x
x
x 18)
x
59Ni
7,60E+04
Sufficient inventory,
release rate 2MBq/y from
the NF, 4000 M
Bq/y from
far field, saline chem
istry
‐
x
x x
x
x
x
63Ni
101,2
The release rate like
for other m
etal parts
‐
x
x
x
x
60Co
5,3
Activation product
60Ni
x
79Se
2,95E+05
Waste
managem
ent, high
inventory
‐
x
x x
x x
x
x
x 18)
x
85Kr
10,752
85Rb
x
85Rb
STABLE
‐
x
90Sr
28,9
Decay heat, saline
chem
istry, high flow,
important if pen
etrating
canister
90Y
x x
x x
x x
x
x
93Zr
1,61E+06
BUC*
93Nb
x
x
x x
x
x
91Nb
6,80E+02
‐
x
x
92Nb
3,47E+07
‐
x
x
23
24
Posiva
SKB
STUK
Research
RN
T 1/2 [a] 1)
Why this
radionuclide?
2) 3)
Dau
ghter
nuclide 4)
Criti‐
cality
3)
Burn‐up
credit
criticality
analyses 5)
Rad
ionuclide
release
assess‐
ment 6
)
Biosphere
assess‐
ment 7
)
Models
and
Data
8)
Rad
iation
safety 9)
Long‐term
safety
at Forsmark
10)
SKB
radionuclide
inventory 11)
YVL
D.1 12)
YVL D.5
13)
Studsvik
2011 14)
Screening
isotopes
15)
FIRST
Nuclides 16)
93mNb
16,12
Very high inventory,
the paren
t of 93Zr, it may
act as a source if short
ground‐
water travel tim
e
93Nb
x
x
x x
94Nb
2,03E+04
High inventory
‐
x
x x
x
x
x
93Mo
4,00E+03
93Nb
x x
x
x x
x
95Mo
STABLE
BUC
‐ x
x
x
x
97Mo
STABLE
BUC
100Mo
7,30E+18
‐
x x
x 99Tc
2,11E+05
BUC, large inventory
‐ x
x x
x
x x
x
x x
x x
101Ru
STABLE
BUC
‐ x
x
x
x
102Ru
STABLE
‐
x
104Ru
STABLE
‐
x
106Ru
371,8 d
‐
x
103Rh
STABLE
BUC
‐ x
x
x
x
105Pd
STABLE
BUC*
‐
x
x
107Pd
STABLE
High inventory
‐
x
x x
x x
x
x x
108Pd
STABLE
‐
x
110Pd
STABLE
‐
x
108mAg
438
Very low inventory
but in as "scoping"
radionuclide because it is
in the RCCA of PWR
canisters
108Pd
x
x
x x
109Ag
STABLE
BUC
‐ x
x
x
x
111Cd
STABLE
‐
x x
112Cd
STABLE
‐
x x
113Cd
8,00E+15
BUC*
‐
x
x
x
x
114Cd
2,10E+18
‐
x x
125Sb
2,75856
‐
x
121mSn
43,9
‐
x x
24
25
Posiva
SKB
STUK
Research
RN
T 1/2 [a] 1)
Why this
radionuclide?
2) 3)
Dau
ghter
nuclide 4)
Criti‐
cality
3)
Burn‐up
credit
criticality
analyses 5)
Rad
ionuclide
release
assess‐
ment 6
)
Biosphere
assess‐
ment 7
)
Models
and
Data
8)
Rad
iation
safety 9)
Long‐term
safety
at Forsmark
10)
SKB
radionuclide
inventory 11)
YVL
D.1 12)
YVL D.5
13)
Studsvik
2011 14)
Screening
isotopes
15)
FIRST
Nuclides 16)
126Sn
2,30E+05
High inventory
‐
x
x
x x
x
x
129I
1,57E+07
Waste
managem
ent, no
retention in
the near and
far field
‐
x
x x
x x
x
x x
x x
133Cs
STABLE
BUC
‐ x
x
x
x
134Cs
2,0652
Decay heat,
shielding
‐
x
x
x
135Cs
2,30E+06
BUC*, waste, very
high inventory
‐
x
x x
x x
x
x
x
137Cs
30,08
BU,
decay heat,
shielding, very high
inventory
137mBa
x x
x x
x x
x x
x
139La
STABLE
BUC*
‐
x
x
141Pr
STABLE
BUC*
‐
x
x
140Ce
STABLE
‐
x
144Ce
284,1 d
‐
x
142Ce
5,00E+16
‐
x
142Nd
STABLE
‐
x x
143Nd
STABLE
BUC
‐ x
x
x
x
144Nd
2,29E+15
BUC**
140Ce
x x
145Nd
STABLE
BUC
‐ x
x
x
x
146Nd
STABLE
BUC**
‐
x x
148Nd
STABLE
BUC**, B
U
‐
x
x
150Nd
9,70E+18
BUC**
‐
x x
147Pm
2,6234
147Sm
x
x
147Sm
1,06E+11
BUC
143Nd
x x
x x
148Sm
7,00E+15
144Nd
x x
149Sm
STABLE
BUC
‐ x
x
x
x
150Sm
STABLE
BUC
‐ x
x
x
x
151Sm
90
BUC
151Eu
x
x x
x x
x
x
x
x
152Sm
STABLE
BUC
‐ x
x
x
x
25
26
Posiva
SKB
STUK
Research
RN
T 1/2 [a] 1)
Why this
radionuclide?
2) 3)
Dau
ghter
nuclide 4)
Criti‐
cality
3)
Burn‐up
credit
criticality
analyses 5)
Rad
ionuclide
release
assess‐
ment 6
)
Biosphere
assess‐
ment 7
)
Models
and
Data
8)
Rad
iation
safety 9)
Long‐term
safety
at Forsmark
10)
SKB
radionuclide
inventory 11)
YVL
D.1 12)
YVL D.5
13)
Studsvik
2011 14)
Screening
isotopes
15)
FIRST
Nuclides 16)
154Sm
STABLE
‐
x x
151Eu
1,70E+18
‐
x
x
152Eu
13,528
152Sm
x
x
x
153Eu
STABLE
BUC
‐ x
x
x
x
154Eu
8,601
BUC**,
decay heat,
shielding
154Sm
x
x
155Eu
4,753
BUC*
155Gd
x x
154Gd
STABLE
‐
x
x x
155Gd
STABLE
BUC
‐ x
x
x
x
156Gd
STABLE
‐
x
x x
157Gd
STABLE
BUC
‐ x
x
x
158Gd
STABLE
‐
x
x x
160Gd
3,10E+19
‐
x x
166mHo
1,20E+03
‐
x x
210Pb
22,2
High radiotoxicity
‐
x
x
x
226Ra
1600
High radiotoxicity
‐
x
x x
x
x
x
228Ra
5,75
High radiotoxicity,
daughter of 228Th
‐
x
227Ac
21,772
Daughter of 231Pa,
high radiotoxicity, short
T 1/2
‐
x
x
229Th
29,5876
High inventory,
high radiotoxicity
‐
x
x
x
x
x
230Th
7,54E+04
High inventory,
high radiotoxicity
226Ra
x x
x
x x
x
232Th
1,40E+04
Ingrowth from 236U,
accounted for in the
solubility limits of Th
228Ra
x x
x
x x
x
234Th
24,10 d
‐
x
231Pa
3,28E+04
One of the highest
release rates in the long
time period, high
radiotoxicity
227Ac
x x
x
x x
x
26
27
Posiva
SKB
STUK
Research
RN
T 1/2 [a] 1)
Why this
radionuclide?
2) 3)
Dau
ghter
nuclide 4)
Criti‐
cality
3)
Burn‐up
credit
criticality
analyses 5)
Rad
ionuclide
release
assess‐
ment 6
)
Biosphere
assess‐
ment 7
)
Models
and
Data
8)
Rad
iation
safety 9)
Long‐term
safety
at Forsmark
10)
SKB
radionuclide
inventory 11)
YVL
D.1 12)
YVL D.5
13)
Studsvik
2011 14)
Screening
isotopes
15)
FIRST
Nuclides 16)
233Pa
26,975 d
233U
x
237Np
2,14E+06
BUC, high inventory
233Pa
x x
x x
x
x x
x
x x
238Np
2,117 d
238Pu
x
239Np
2,356 d
239Pu
x
242Cm
162,8 d
238Pu
x
243Cm
29,1
239Pu
x
x
244Cm
18,1
Decay heat,
shielding
240Pu
x
x
x
245Cm
8423
High radiotoxicity
241Pu
x x
x
x x
x
246Cm
4706
High radiotoxicity
242Pu
x x
x
x x
x
x
233U
1,59E+05
229Th
x
x
x x
x
x x
x
x
234U
2,46E+05
BUC, high inventory
230Th
x
x x
x x
x
x
x x
x
235U
7,04E+08
BUC, high inventory
231Th
x
x x
x x
x
x x
x x
x
236U
2,34E+07
BUC, high inventory
232Th
x
x x
x x
x
x
x x
x
238U
4,47E+09
BUC, high inventory
238Th
x
x x
x x
x
x
x x
x x
238Pu
87,7
BUC, decay heat, very high
inventory, paren
t to 234U,
high radiotoxicity
234U
x x
x
x
x x
x
x x
239Pu
24110
BUC, decay heat, high
inventory, high
radiotoxicity
235U
x x
x x
x
x x
x x
x x
240Pu
6561
BUC, decay heat, high
inventory, high
radiotoxicity
236U
x x
x x
x
x x
x
x x
241Pu
14,325
BUC
241Am
x x
x
x
x x
x
x x
242Pu
3,75E+05
BUC, significant
inventory, high
radiotoxicity
238U
x x
x x
x
x x
x
x x
241Am
432,6
BUC, decay heat, high
radiotoxicity
237Np
x x
x x
x
x x
x
x x
242mAm
141
BUC**
high radiotoxicity, high
inventory
242Cm
x
x x
x x
17)
27
28
Posiva
SKB
STUK
Research
RN
T 1/2 [a] 1)
Why this
radionuclide?
2) 3)
Dau
ghter
nuclide 4)
Criti‐
cality
3)
Burn‐up
credit
criticality
analyses 5)
Rad
ionuclide
release
assess‐
ment 6
)
Biosphere
assess‐
ment 7
)
Models
and
Data
8)
Rad
iation
safety 9)
Long‐term
safety
at Forsmark
10)
SKB
radionuclide
inventory 11)
YVL
D.1 12)
YVL D.5
13)
Studsvik
2011 14)
Screening
isotopes
15)
FIRST
Nuclides 16)
243Am
7370
High radiotoxicity
239Np
x x
x x
x
x x
x
x x
1) National Nuclear Data Cen
ter (NNDC), Brookhaven
National Laboratory, http://w
ww.nndc.gov/chart/chartNuc.jsp, 17.10.2013
2) Safety Case ‐ M
odels and Data for the Rep
ository System 2012, A
ppen
dix C.4, Posiva 2013‐01
3) Criticality Safety Analysis of BWR, PWR and VVER
‐440 Disposal Canisters in
the Final Disposal Facility 2012 (A. R
anta‐aho 2012); Assessm
ent of
Radionuclide Release Scenarios for the Rep
ository System, Posiva 2012‐09
4) N
DS/IAEA
Live Chart of Nuclides, nuclear structure and decay data (https://www‐nds.iaea.org/relnsd/vcharthtm
l/VChartHTM
L.htm
l). D
aughter
nuclides m
arked only if present in the table.
5) List of nuclides commonly considered
in burn‐up credit criticality analyses, N
EA/N
SC/W
PNCS/DOC(2011)5
6) Potentially safety relevant radionuclides 30 years after discharge from the reactor, Posiva 2012‐09, Safety Case ‐Assessm
ent of Radionuclide Release
Scen
arios for the Rep
ository System
7) Full set of radionuclides included
in the screen
ing evaluation in
the biosphere assessmen
t, working report 2010‐79
8) Safety relevant radionuclides, Safety Case ‐ Models an
d Data for the Rep
ository System 2012, Posiva 2013‐01
9) Ympäristövaikutusten
kannalta m
erkittävät nuklidit, O
lkiluodon kapselointi ja loppusijoituslaitoksen
käyttöturvallisuusanalyysi, Posiva 2012‐71
10) A
selection of radionuclides based
on radiotoxicity, inventory, T(1/2) an
d shared
solubility, Long‐term
safety for the final rep
ository of spen
t nuclear
fuel at Forsmark, Volume I and III, SKB TR‐11‐01
11) Radionuclide inventory in
BWR II type canister, Table C‐8, Spen
t nuclear fuel for disposal in the KBS‐3 rep
ository, TR‐10‐13
12) YVL D.1
13) YVL D.5
14) N
uclide analyses on irradiated Atrium fuel at Studsvik, Cost estim
ate 13.6.2011, N
‐211134
15) N
uclides possible to assess at Studsvik, Presentation: Isotope analysis at Studsvik (HPLC, D
RC, ICP‐M
S, Laser ablation), M
ichael G
ranfors, Screening of
isotopes, 25.5.2012
16) Spen
t fuel leaching ‐ prelim
inary results FIRST Nuclides, Studsvik, O
livia Roth, M
ay 2013
17) Below detection limit?
18) N
o established
method in
2011
*) Potential burnup credit nuclide or daughter nuclide with m
oderate effect
**) Potential burnup credit nuclide with low effect
28
29
APPENDIX B. (LA)-ICP-MS ANALYSES ON SPENT NUCLEAR FUEL
Studsvik can also offer laser ablation (LA)-ICP-MS analyses on fuel pellets. A small laser beam ablates material from a small area on the surface. The ablated material is swept by a gas stream into the ICP-MS, where the isotopic compositions are measured. The LA results are presented as profiles plots for the radial and/or axial distribution for a pellet. These plots show the distributions of the analyzed isotopes in axial and radial directions in the pellets The LA result is also presented as pellet mean values and can be compared to dissolution chemical burn-up analyses. Laser ablation can offer radial and axial distribution for a pellet. LA is more cost effective than dissolution chemical burn-up analyses. The drawback for LA is higher uncertainty compared to dissolution chemical burn-up analyses. For this method it is not possible to separate overlapping isotopes. The analyses of isotopes with LA are divided into three different measurements and the isotopes which can be assessed are listed in (Haavisto 2014). (Askeljung 2013)
30
APPENDIX C. IMPORTANT NUCLIDES CONTIBUTING TO DECAY HEAT POWER AS A FUNCTION OF TIME.
Figure C-1. Important nuclides contributing to decay heat power as a function of time. (NEA/NSC/WPNCS/DOC(2011)5)