Decay Storage of Large Components from Decommissioning of Nuclear Power Plants

Transcription

1 Decay Storage of Large Components from Decommissioning of Nuclear Power Plants M. K. Hummelsheim, U. Hesse, M. Kirsch, M. Wehrfritz (GRS) T. S. Thierfeldt (Brenk Systemplanung) IAEA Workshop, Heringsdorf

2 Outline Introduction (Brief) Model description Results Comparison to measurements at Greifswald (VVER-440) Results for a generic western PWR (German Konvoi type) Results on radiological and economic aspects (Brenk Systemplanung) Summary and Outlook Markus Wagner - Decay Storage 2

3 Introduction Decommissioning strategies in Germany Immediate dismantling (Würgassen, Stade) Safe enclosure (Lingen) Alternative strategy: Decay storage of large components Remove large components in one piece (RPV, steam generators) Storage of large components Examples: NPP Greifswald, NPP Rheinsberg Aim: Use radioactive decay to Reduce radiation exposure of personnel Reduce material to be disposed in repository Markus Wagner - Decay Storage 3

4 Introduction Assessment of decay storage Questions to be answered: Reduction of dose and materials to be disposed of? Optimal storage time? Some important aspects Dose to personnel reduced due to lower dose rates Dismantling techniques (remote, by hand) Fraction of material to be disposed of, choice of container Basic Quantity: Nuclide inventory calculated by GRS Two models VVER-440 Greifswald Comparison to measurements Generic western PWR (German Konvoi type) Assessment Analysis regarding radiological and economic aspects: Brenk Systemplanung Markus Wagner - Decay Storage 4

5 (Brief) Model description How did we calculate the inventory? Material composition (including impurities) Neutron flux Power history steps Geometry Model Neutron flux calculation Activation Source term generation Calculate dose rates DORT (2D deterministic transport) GRS-ORIGENX NGSRC (GRS) DORT (, MCNP) Markus Wagner - Decay Storage 5

6 Model Description 2D R-Z-geometry PWR model VVER model Markus Wagner - Decay Storage 6

7 Results - VVER Backscattering Markus Wagner - Decay Storage 7

8 Results Comparison to measurements at Greifswald General remarks NO adjustment to measurements Partly sparse information Good agreement on Fe-55 and Co-60 (~ factor of 2) Co-60 deviation partly due to assumed Co concentration in material Larger deviation on Ni-63? Markus Wagner - Decay Storage 8

9 Results Comparison to measurements at Greifswald dose rate measurements in 50 cm and 2 m distance from pressure vessel (core internals removed, years after shutdown) Dose rate dominated by Co-60 Good agreement in core region Not so good agreement at coolant nozzle Some deviations at lower part (low activity) Markus Wagner - Decay Storage 9

10 Results - PWR Large backscattering effect Markus Wagner - Decay Storage 10

11 Results - PWR Calculation includes a few hundred isotopes Analysis carried out for: H-3, Be-10, C-14, Cl-36, Ca-41, Ca-45, Cr-51, Mn-54, Fe-55, Fe-59, Co-58, Co-60, Ni-59, Ni- 63, Zn-65, Se-74, Se-79, Sr-90, Ze-93, Nb- 93m, Nb-94, Mo-93, Mo-99, Ag-108m, Ag- 110m, Sb-125, Cs-134, Cs-137, Ba-137m, Ce- 144, Eu-152, Eu-154, Ta-182 And many more components have been analyzed. Markus Wagner - Decay Storage 11

12 Results - PWR 0,5a 5a 10a 20a 30a 50a 70a 100a 150a 200a Ratio of activity to clearance level for different isotopes (average activity for reactor pressure vessel) Co60 67% Ta182 15% Mn54 Co60 95% 3% Eu154 Co60 94% 4% Eu154 Co60 89% 9% Eu154 Co60 79% 17% Eu154 48% Co60 45% Eu154 76% Co60 14% Eu154 75% Nb94 16% Mo93 Nb Mo93 Nb94 76% Mo93 13% Ag108m 14% 2% 3% 4% 6% 5% 3% 10% 3% Mn54 Nb94 Nb94 Eu154 Ag108m 3% 2% 3% 2% Fe59 Mo93 Co60 Nb93m TL208 2% Eu154 Ag108m Ni59 Nb93m Fraction of nuclide gamma power to overall gamma power for one cell of reactor pressure vessel in core region Markus Wagner - Decay Storage 12

13 Results Analysis by Brenk Systemplanung What has been done with all the data? Based on the activation data and the resulting dose rates an extensive study has been performed to optimize Resulting individual and collective doses Material quantities to be cleared / to be treated as radioactive waste Costs Different data sets have been considered to account for uncertainties in impurities Following strategies have been taken into account Strategy 1: direct and complete dismantling of the pressure vessel and internals Strategy 2: decay storage of the pressure vessel with internals and subsequent dismantling Strategy 3: direct dismantling of the highly activated internals, decay storage of the pressure vessel and low activated internals Markus Wagner - Decay Storage 13

14 Results Standard case Rechenläufe DWR RDB-Unterteil - Standardfall Dose (turquoise) Clearance (pink) Costs (orange) as function of time Kollektivdosis [Pers.-mSv] Freigabe Sp. 5, 9, 10a [Mg] akk. Kollektivdosis Kosten Entsorgung [Mio. ] 50 Freigabe akk. Kosten Rechenläufe WWER RDG1-Unterteil - Standardfall Dauer der Entsorgung [a] Kollektivdosis [Pers.-mSv] Freigabe Sp. 5, 9, 10a [Mg] akk. Kollektivdosis Freigabe akk. Kosten Kosten Entsorgung [Mio. ] Optimum at about 50 to 80 years (corresponds to decay storage of about years) with respect to dose and cost Dauer der Entsorgung [a] Markus Wagner - Decay Storage 14

15 Results Disposal balance Clearance (pink) Repository (orange) Smelt (turquoise) Entsorgungsoptionen [Mg] Endlager [Mg] Einschmelzen [Mg] Freigabe [Mg] Rechenläufe DWR RDB-Unterteil (Standardfall) - Entsorgungsmassenbilanz - 50 Rechenläufe WWER RDG1 (Standardfall) - Entsorgungsmassenbilanz Dauer der Abklinglagerung [a] Entsorgungsoptionen [Mg] Endlager [Mg] Einschmelzen [Mg] Freigabe [Mg] Dauer der Abklinglagerung [a] Markus Wagner - Decay Storage 15

16 Summary Study of decay storage of large components Activation calculation VVER-440 Greifswald Generic western PWR (German Konvoi type) Analysis of activation data with respect to radiological and economic aspects Model calculations for standard case show an optimum at about years Clearly show reduction of doses Clearly show reduction of material to be disposed of Worst case scenarios taking into account uncertainties also have been considered Outlook Improvements in activation calculation 3D model Further comparison to measurements Markus Wagner - Decay Storage 16