Categorisation of Active Material from PPCS Model Power Plants

Transcription

1 SESE-IV Categorisation of Active Material from PPCS Model Power Plants Robin Forrest, Neill Taylor and Raul Pampin Euratom/UKAEA Fusion Association Culham Science Centre This work was funded jointly by the United Kingdom Engineering and Physical Sciences Research Council and by EURATOM

2 Outline Active material from fusion power plants PPCS models Neutronics and activation modelling Categorisation of active material Results: Materials from five PPCS plant models Comparison of radiotoxicity of materials from fusion power plants with those from fission reactors and coal-fired power stations Conclusions

3 Introduction Rather large volume of material in a fusion power plant will be exposed to some level of neutron flux Most of it at very low level Materials that are activated decay relatively quickly Strong motivation for clearance and recycling of material European studies since SEAFP have categorised material according to radiological criteria related to ability to handle material for recycling procedures Earlier studies (SEAFP, SEAL, etc.) concluded that there is very little material, if any, requiring permanent disposal after 100 years The Power Plant Conceptual Study (PPCS) re-examined this conclusion For the updated power plant designs Using improved computational models

4 Power Plant Conceptual Study (PPCS) European study of four concepts (Plant Models A, B, C, D) for 1.5 GWe (nominal) fusion power plant designs Ranging from near-term, with little assumed advances in physics or technology to advanced, with optimistic assumptions throughout. Fifth power plant concept added in follow-on study, Plant Model AB All five models assessed for safety, environmental and economic performance.

5 PPCS Plant Models Model A Model AB Model B Model C Model D Fusion Power (GW) Net electrical output (GWe) Average neutron wall load Major Radius (m) Blanket structure Eurofer Eurofer Eurofer Eurofer (ODS) SiC/SiC Blanket coolant Water He He LiPb + He LiPb Blanket LiPb LiPb Li 4 SiO 4 + Be pebbles LiPb LiPb Divertor CuCrZr W alloy W alloy W alloy SiC/SiC Coolant water He He He LiPb

6 Neutronics and activation modelling 3-D models with multiple layers in poloidal sectors MCNP4C3 Monte Carlo calculations of neutron fluxes In every cell of the models out to the cryostat 175-group energy spectra obtained FISPACT activation calculations (EASY-2003) For every material (with assumed impurities) In every cell of the model Computed inventories, activation and derived quantities (dose rates, decay heat, clearance indices ) Results at decay times from 1 s to 10,000 years Simplified, homogeneous representation of divertor regions HERCULES in-house code system sets up geometric model, materials specifications, etc., and links MCNP and FISPACT codes

7 HERCULES Geometry: Plant Model B 187 o 165 o 143 o 209 o 121 o 231 o 253 o 99 o 275 o 77 o 297 o 319 o 55 o 341 o o 11 o

8 Categorisation of active material at end of life Activation properties of materials of each component depends on: Position in the device: level and energy spectrum of neutron flux Irradiation history: duration of exposure to flux (e.g. vacuum vessel for full life of plant, divertors for 2.5 years) Materials composition, including impurities Disposition of active material will depend on Radiological properties (activation, dose rates, decay heat, etc.) Regulations Viability of recycling, including social and economic factors Currently we categorise based only on radiological parameters

9 Waste Categories adopted since SEAFP Non-active Waste (NAW) Material whose activity has fallen below Clearance Level Clearance Levels defined on nuclide-by-nuclide basis In this work, IAEA 1996 proposals used (New guidelines were issued by IAEA, 2004) Clearance Index computed for mixtures of nuclides, must be <1 Simple Recycle Material (SRM) Material that could be recycled by hands-on or simple remote handling techniques Complex Recycle Material (CRM) Material that could be recycled using more advanced remote handling, probably at higher cost Permanent Disposal Waste (PDW) Material that would need long-term disposal, probably in deep geological repository

10 Categorisation of active material Active material classifications Contact gamma dose rate (msv.hr -1 ) Decay heat per unit volume (W.m -3 ) Clearance index Permanent Disposal Waste (PDW) > 20 >10 Complex Recycle Material (CRM)* Simple Recycle Material (SRM) < 2 < 1 Hands-on if contact dose < 10 µsv.hr -1 Non Active Waste (NAW) < 1 * The CRM limits are probably too conservative, and are to be reviewed.

11 Calculation method Series of Excel spreadsheets detailing: Masses and volumes of material in each cell Activation quantities (dose rates, decay heat, clearance index) in each cell at a series of decay times Assignment of material in each cell to one of the categories at 50 and 100 years following shutdown Component replacement: TF coil, vacuum vessel and LT shield not replaced during 25 full power years Divertors, replaced every 2.5 full power years First wall and blanket, replaced every 5 full power years Proper account taken of decay time for each divertor and blanket since time of removal from the plant

12 Irradiation history based on PPCS maintenance scheme (1) 2.5 years at full power operation (2) Two months for divertor replacement (3) Further 2.5 years at full power (4) Ten months for divertor + blanket replacement Repeat five times results in planned availability of 85.7%.

13 Results for Model A 100,000 90,000 80,000 70,000 87,857 Total NAW Total SRM Total CRM Total PDW Mass (tonnes) 60,000 50,000 40,000 30,000 27,597 42,161 36,853 26,723 30,070 20,000 10, Decay time (y) 15,408 0

14 Results for Model AB Mass (tonnes) Decay time (y) total NAW total SRM total CRM total PDW 0

15 Results for Model B 40,000 35,000 30,000 30,417 Total NAW Total SRM Total CRM Total PDW Mass (tonnes) 25,000 20,000 15,000 10,000 9,640 14,265 11,303 13,753 10,801 7,743 5, Decay time (y) 0

16 Results for Model C 60,000 50,000 52,277 Total NAW Total SRM Total CRM Mass (tonnes) 40,000 30,000 20,000 10,000 29,168 25,352 12,780 9,862 9,862 15,023 Total PDW Decay time (y) 0

17 Results for Model D 40,000 35,000 30,000 36,595 Total NAW Total SRM Total CRM Total PDW Mass (tonnes) 25,000 20,000 15,000 22,135 17,384 11,981 10,000 9,057 5, ,740 3, Decay time (y) 0

18 Origin of material as categorised at 100 years Plant Models A and AB A AB CRM SRM SRM - hands on NAW

19 Origin of material as categorised at 100 years Plant Models B and C B C CRM SRM SRM - hands on NAW

20 Origin of material as categorised at 100 years Plant Model D D CRM SRM SRM - hands on NAW

21 Comparison of biological hazard potential with other power sources Comparison of the total potential radiotoxicity index of all active materials from entire power plant Five PPCS plant models Fission power plants (typical PWR and two fast reactor variants) Coal-fired power plant (Radiotoxicity from naturally-occurring actinides in ash) Normalised to 1 GWe Index: ingestion dose (relative units) Values for fission and coal from environmental impact study (1990) These results update those previously obtained in SEAFP and SEAFP-2 (as in the SEIF report, 2001)

22 Potential Radiotoxicity Index (ingestion dose) 1.0E E+00 Radiotoxicity Index (Ingestion) 1.0E E E-03 Coal PWR 1.0E-04 EFR A EFR B Model A 1.0E-05 Model B Model C 1.0E-06 Model D Model AB 1.0E Time after final shutdown (y)

23 Summary and Conclusions Analyses of active material from power plant concepts of PPCS has updated earlier assessments Current power plant concepts Improved 3-D models (SEAFP used 1-D) By 100 years, in all models, no material needs permanent disposal Viability of recycling to be assessed Comparison of total potential radiotoxicity shows that dose from fusion waste falls to same level as coal within a few hundred years