Preliminary safety analysis for heavy-water-moderated molten-salt reactor

The heavy-water-moderated molten-salt reactor (HWMSR) is a newly proposed reactor concept, in which heavy water is adopted as the moderator and molten salt dissolved with fissile and fertile elements is used as the fuel. Issues arising from graphite in traditional molten-salt reactors, including the positive temperature coefficient and management of highly radioactive spent graphite waste, can be addressed using the HWMSR. Until now, research on the HWMSR has been centered on the core design and nuclear-fuel cycle to explore the viability of the HWMSR and its advantages in fuel utilization. However, the core safety of the HWMSR has not been extensively studied. Therefore, we evaluate typical accidents in a small modular HWMSR, including fuel-salt inlet temperature-overcooling and -overheating accidents, fuel-salt inlet flow-rate decrease, heavy-water inlet temperature-overcooling accidents, and heavy-water inlet mass flow-rate decrease accidents, based on a neutronics and thermal-hydraulics coupled code. The results demonstrated that the core maintained safety during the investigated accidents.