Preliminary analysis of fuel cycle performance for a small modular heavy water-moderated thorium molten salt reactor

Heavy water-moderated molten salt reactors (HWMSRs) are novel molten salt reactors that adopt heavy water rather than graphite as the moderator while employing liquid fuel. Owing to the high moderating ratio of the heavy water moderator and the utilization of liquid fuel, HWMSRs can achieve a high neutron economy. In this study, a large-scale small modular HWMSR with a thermal power of 500 MWth was proposed and studied. The criticality of the core was evaluated using an in-house critical search calculation code (CSCC), which was developed based on Standardized Computer Analyses for Licensing Evaluation, version 6.1. The preliminary fuel cycle performances (initial conversion ratio ( CR ), initial fissile fuel loading mass, and temperature coefficient) were investigated by varying the lattice pitch ( P ) and the molten salt volume fraction ( VF ). The results demonstrate that the temperature coefficient can be negative over the range of investigated P s and VF s for both 233 U-Th and LEU-Th fuels. A core with a P of 20 cm and a VF of 20% is recommended for 233 U-Th and LEU-Th fuels to achieve a high performance of initial CR and fuel loading. Regarding TRU-Th fuel, a core with a smaller P (~ 5 cm) and larger VF (~ 24%) is recommended to obtain a negative temperature coefficient.