Influences of 7Li enrichment on Th-U fuel breeding for an Improved Molten Salt Fast Reactor (IMSFR)

The molten salt fast reactor (MSFR) shows great promise with high breeding ratio (BR), large negative temperature coefficient of reactivity, high thermal-electric conversion efficiency, inherent safety, and online reprocessing. Based on an improved MSFR optimized by adding axial fertile salt and a graphite reflector, the influences of Li-7 enrichment on Th-U breeding are investigated, aiming to provide a feasible selection for the molten salt with high fissile breeding and a relatively low technology requirement for Li-7 concentration. With the self-developed molten salt reactor reprocessing sequence based on SCALE6.1, the burn-up calculations with online reprocessing are carried out. Parameters are explored including BR, U-233 production, double time (DT), spectrum, Li-6 inventory, neutron absorption, and the tritium production. The results show that the Li-7 enrichment of 99.95% is appropriate in the fast fission reactor. In this case, BR above 1.10 can be achieved for a long time, corresponding to the U-233 production of 130 kg per year and DT of 36 years. After 80 years' operation, the tritium production for 99.5% is only about 7 kg, and there is no obvious increase compared to that for 99.9995%.