Neutronic performances of small modular thorium-based molten salt reactor starting with TRUs

[Background] Transuranic isotopes (TRUs) in the spent fuel of pressurized water reactor (PWR) contain more than 50% of fissile fuels and can be used as a starting fissile fuel for thorium fuel cycle. [Purpose] This study aims to analyze the neutronic performances of a small modular thorium-based molten salt reactor (SM-TMSR) core with TRUs as fissile fuel and Th as fertile fuel. [Methods] Considering the batch reprocessing period and the limit value of the inherent safety, proper scenarios for thorium utilization in the SM-TMSR initiated by TRUs were proposed for the evaluation of the neutronic characteristics. Reactor analysis software SCALE6.1 was employed to analyze the influences of two important parameters(fuel volume fraction and initial heavy metal mole fraction)on the characteristics of neutron spectrum, ²³³U production, graphite life, temperature coefficient, TRUs consumption, etc. [Results and Conclusions] The calculation results show that TRUs are an ideal fuel for starting Th-U fuel cycle of the SM-TMSR. Considering the constraints of the graphite's five-year life and the intrinsic safety (-5 ∼ -8 pcm ∼ K^-1), the core with 6% heavy metal mole fraction and 25% fuel volume fraction can obtain a preferable fuel utilization efficiency. With the thermal power of 150 MW for 5- year full-power operation, the uranium production is about 16.0 kg ∼ a^-1 and the transmutation rate of TRUs can achieve about 36.1 kg ∼ a^-1, which can effectively reduce the spent fuel containing TRUs. (authors)