Analysis of Th-U conversion and fission product characteristics in thorium-based molten salt reactor

Starting a thorium molten salt reactor (TMSR) with Pu or transuranic (TRU) nuclides can enable efficient thorium-uranium conversion while transmuting nuclear waste. Based on the LiF-BeF 2 -(Pu/TRU + Th)F 4 molten salt fuel system, this study systematically investigates the effects of fuel type (Pu + Th vs. TRU + Th, with heavy metal mole concentrations of 12 % and 15 %) and molten salt volume fraction V f (5 %-70 %) in the fuel assembly on the neutron spectrum, Th-U conversion performance, and fission product characteristics. The conversion ratio ( CR ) generally increases with V f . For the various fuel schemes, the annual production of 233 U normalized to 100 MWth ranges from 12.4 to 16.1 kg, with a 233 U isotopic abundance exceeding 97 % and a 232 U content below 0.015 %. This demonstrates the capability for industrial‑scale 233 U production from existing spent fuel, thereby addressing the long‑standing fuel availability challenge for thorium breeder reactors. Under normalized power conditions, the mass distribution of medium-mass fission products is insensitive to fuel composition, heavy metal concentration, and V f . This allows for the estimation of individual fission nuclide yields and radiological activity under different conditions, including neutron poisons, and radiotoxic products.