Th-U and U-Pu cycling performances of molten chloride salt fast reactor under LEU start-up mode

[Background] Compared with molten fluoride salt fast reactor, molten chloride fast reactor (MCFR) has higher solubility of heavy metals, harder neutron energy spectrum, and better breeding performance, hence an ideal type of reactor for realizing closed fuel cycle. [Purpose] This study aims to analyze and compare Th-U and U-Pu cycle performances of MCFR. [Methods] Based on the 2500 MW molten chloride salt fast reactor, the TMCBurnup and MESA codes were used to analyze the transition and equilibrium states of Th-U and U-Pu cycles with Low Enriched Uranium (LEU) as the starting fuel. Two different transition modes were analyzed from the perspectives of nuclide evolution, proliferation, safety and radioactivity. [Results] The results show that U-Pu cycle has better breeding performance than Th-U cycle. In breeding and burning (B and B) mode, the breeding ratios of the U-Pu and Th-U cycle are 1.56 and 1.24, respectively. The corresponding doubling time (DT) of the U-Pu and Th-U cycle is 13.5 years and 16.5 years, while in pre-breeding and burning (PB and B) mode, the replacement ratios are 1.58 and 1.08, and the doubling time is 12.8 years and 13 years, respectively. However, Th-U cycle has better safety performance, lower transuranic nuclides (TRU) accumulation and lower radiotoxicity. [Conclusions] Both Th-U and U-Pu cycle have good breeding performance in MCFR, and they can keep safety under all cycle modes. However, the U-Pu cycle has better breeding performance and the Th-U cycle has lower radiotoxicity and TRU accumulation, which reduces the difficulty of post-processing. (authors)