Partitioning & Transmutation Combined with Molten Salt Fast Reactor B. Merk

1. Partitioning & Transmutation Combined with Molten Salt Fast Reactor B. Merk Department Reactor Safety at Institute of Resource Ecology Helmholtz-Zentrum Dresden-Rossendorf EVOL Winter Scholl, Orsay 2013

3. Partitioning & Transmutation

4. Chances of P&T (Dreams) • transmutation goals are to eliminate 99.9% of the TRU and up to 95% of the long-lived fission fragments 99-Tc and 129-I • massive reduction radio toxicity • no final disposal required • solution of all waste problems • 500-year final disposal • TRUs could disappear from the world • Volume reduction of the waste to 5%

5. The General Idea The major contribution to the long term activity and RTI is created by Pu and the minor actinides (Am & Cm) and their decay chains The long term activity and radio toxicity can be reduced significantly when it is possible to separate these elements from the waste and to transmute them

6. The Potential of P&T More Realistic • Volume reduction to ~30% mostly due to separation of Uranium • Over all activity in final disposal after 1 000 years with P&T~activity after 1 000 000 without P&T  reduced hazard potential  observation time is fixed by law • Elimination of the risk of misuse of Pu from final disposal on the long term • Possibility for improved conditioning after partitioning  no early release of mobile fission products • reduced heat production after 70 to 100 years due to separation of Am • Elimination of decay chain products from actinides • P&T is a matter of inter-generational fairness

7. Requirements for Efficient P&T • efficient separation/reprocessing technology • acceptable solution for the fuel production • fast neutron spectrum for efficient transmutation Pu-242 Am-243 radiative capture and fission XS

8. Requirements for Efficient P&T • efficient reprocessing technology • acceptable solution for the fuel production • fast neutron spectrum for efficient transmutation

9. Risks of P&T • fast reactor technology is required • multi recycling of minor actinides is needed • radiation risk and technological challenges in solid fuel production • fuel behavior of material with high Pu and minor actinide loading • challenges of fertile free solid fuel – production and reactor operation • safety of fast system cores with high minor actinide load • success depends on very efficient lanthanide ↔ actinide separation • short term proliferation risk due to Pu separation

10. Comments on Current Status of P&T • A major part is already demonstrated  Pu separation and MOX use is industrial technology for LWR • the already performed Pu recycling reduces the required final disposal site dimension by ~30% • Am separation and fuel production has been demonstrated on lab scale • transmutation of Am has been demonstrated in PHENIX • currently 1970ies technology is foreseen for transmutation (e. g. sodium cooled fast reactors) •  special systems for transmutation could offer better performance (e. g. molten salt reactor) • current proliferation risk can and has to be controlled by safeguarding (IAEA)

11. The Fuel Cycle for P&T

12. Desired Characteristic for Efficient Transmutation • a high TRU content is required for efficient transmutation • no breeding is desired to avoid the built up of new TRU isotopes • long cycle time is required for efficient transmutation • long cycle time requires a small reactivity loss over cycle as design target for the core or a core design with high excess reactivity • small reactivity loss over cycle requires breeding of new fissile material, thus fertile material is essential • high excess reactivity has negative safety consequences, therefore a strong control system is needed • a high burnup is required for an efficient transmutation • very high Pu content tends to degrade the Pu – remember CAPRA • short out of core period and long in core residence time of the TRU fuel is required

13. Molten Salt Reactor in the View of Transmutation

14. Advantages of MSFR • fertile free fuel is no problem due to online re-fuelling • no challenging solid fuel production with high Am load and its irradiation in the reactor is required • no multi-recycling due to online salt cleanup • excellent safety due to strong negative feedback effects • possibility for the elimination of last transmuter problem

15. Fertile Free Fuel • very step burnup curve of fertile free fuel caused by rapid burning of fissile material • U-238: • less absorption in U-238 • lower BOL Pu content • fertile free: • no absorption in fertile • significantly less BOL Pu content • significantly lower HM content

16. Fertile Free Fuel • very step burnup curve of fertile free fuel caused by rapid burning of fissile material • high excess reactivity would be required in solid fuel reactors to reach acceptable cycle time • high excess reactivity requires a strong control system •  strong initiator for transient over power accidents caused by malfunction of control system • high Pu content tends to degrade Pu quality • breeding of higher Pu and MA isotopes • unknown reprocessing strategies for different inert matrix fuel types Solutions: • fast power reactors – isobreeder core, breeding compensates burnup and allows long cycle times, weak control assemblies, and breeding of fresh Pu • online re-fuelling compensates reactivity loss continuously

17. Pellets with High Am Content • Dust free production process is required • reduced losses • reduced contamination • Swelling of the fuel pellets, which decreases the pellet-cladding gap • Helium release into the plenum and high He production • Degradation of the thermal conductivity of the pellets, due to the presence of fission products and additional porosity • unknown reprocessing strategies for different inert matrix fuel types Solution: • avoid solid fuel production completely

18. The Cm Problem • Cm is always produced by breeding processes • Current strategy, wait and see • let the Cm decay to Pu • Cm is one of the major carriersof radiotoxicity • Fuel production is fairly unknown • Cm is highly complicated to handle due to the neutron production cause by spontaneous fission Solution: • avoid solid fuel production completely • don’t separate • don’t take it out of the reactor

19. Multi-Recycling • only a share of the TRUs is burnt (10-30%) in a cycle • long cooling time for MOX fuel assemblies • unknown reprocessingof transmutation fuel • repeated separation of Pu  possible proliferation risk • production of new transmutation fuel assemblies • repeated irradiation in the reactor Solution: • avoid multi-recycling at all

20. Safety of Fast Transmutation Systems • insertion of TRUs degrades the inherent feedback effects of fast reactors • limited amount of TRUs in critical reactors Solutions: • low TRU and especially Am content in critical reactors • critical fast reactors with enhanced feedback effects

21. Optimization of Fast Reactor Safety • feedback effects are an inherent safety mechanism in all nuclear reactors • Insertion of fine distributed moderating material • enhances the negative Doppler effect • reduces the positive sodium void effect • reduces the positive coolant effect • insertion of transmutation materials damps the feedback effects • compensation of effects caused by insertion oftransmutation materials (Americium) • improved transmutation efficiency due to higher possible loading

22. Safety of Fast Transmutation Systems • insertion of TRUs degrades the inherent feedback effects of fast reactors • limited amount of TRUs in critical reactors Solutions: • low TRU and especially Am content in critical reactors • critical fast reactors with enhanced feedback effects • use of accelerator driven systems • use of fluid fuelled reactor • coincidence of fuel and coolant • any temperature increase leads to reduction of fuel amount in the core •  very strong temperature feedback, comparable to LWR

23. Last Transmuter Problem Problem in the view of a phase out: • EOL configuration of the last loading is left over • when fuel is replaced assembly by assembly, there is always a not burnt leftover of TRUs Possible solution: • twofold lifecycle • successive replacement of fissile material in a MSFR • TRUs are burnt and Uranium can be feed into • solution of the proliferation problem

24. Challenges

25. Challenges of MSFR • lack of maturity of the general concept • missing transmutation optimized design • experience is only available for thermal MSRE system • missing safety approach for system with liquid fuel • safety concept for reactor wit co-located ‚reprocessing‘ facility • material damage of the inner structures due to irradiation • highly reactive salt requires special materials – nickel based alloys • nickel based alloys are very sensitive to Helium embrittlement caused by irradiation with thermal neutrons