Lead-Cooled Fast Reactors with Th-based Fuels - Neutronics and Safety

In this paper, neutronic and safety performance of 600 MWe lead-cooled fast reactors (LFRs) employing Th-based fuels is studied. This includes investigation of both (self-) breeders fuelled by Th-233U and burner/breeder reactors incinerating Pu and transuranic elements (TRUs) from spent LWR fuel. Both systems use mixed oxide fuel. Neutronic and depletion characteristics were evaluated by the Monte Carlo code MCB. The European Accident Code-2 (EAC-2) and the Computational Fluid Dynamics code STAR-CD were used for safety analyses. The accidents studied were unprotected Loss-of-Flow, unprotected Loss-of-Heat Sink, and protected Total Loss-of-Power. Our calculations indicate that LFRs can be run in pure fast Th-233U mode. This is, however, at the expense of having large core actinide masses exceeding 100 tons at BOL.(Th,TRU)O2-fuelled LFRs can annually incinerate up to 320 kg of plutonium and about 80 kg of minor actinides. The latter corresponds to an annual MA production in about 1.6 EPR reactors. At the same time, approximately 225 kg of 233U are produced, which can be used to start-up new fast reactors in a pure Th-233U mode or fuel LWRs or advanced thermal PHWR or MSR breeders. A use of axial and radial Th blankets with 5% of MAs further increases the amount of 233U bred in (Th,TRU)O2 system to 285 kg/y. We confirm that requirements for 233U enrichments in fast systems employing Th-based fuels are lower than for LWR-Pu and LWR-TRU fuelled cores. Regarding the safety performance, in-core moderating pins (CaH2) are used to improve Doppler and coolant temperature reactivity coefficients. Finally, we also discuss the favorable behavior of our LFR core designs in postulated severe accidents.

TUCEK Kamil;  CARLSSON Johan;  WIDER Hartmut; 

2007-11-06

French Nuclear Energy Society (SFEN)

JRC36815