Neutronic Design of a Heat Pipe-Cooled Epithermal Molten Salt Reactor (HP-EMSR)

To address the demand for lightweight micro heat pipe-cooled molten salt reactors capable of operating on low-enriched fuel, this paper proposes a heat pipe-cooled epithermal molten salt reactor (HP-EMSR). Introducing an adequate quantity of moderator (YH1.8) into the core results in an epithermal neutron spectrum, which decreases the required fissile inventory and allows for long-term steady-state operation using low-enriched uranium. The core geometric parameters were optimized to minimize both the total core mass and nuclear fuel loading. The optimized design features a cylindrical core 73.0 cm in diameter and 77.5 cm in height, with a total mass of 1195.95 kg. The results show that the initial effective multiplication factor satisfies the criticality requirement, and the core sustains full-power operation for 1800 days. Furthermore, the temperature coefficient of reactivity remains negative throughout the entire life-cycle, while the control drums provide enough reactivity regulation and shutdown margin. This investigation validates the technical feasibility of the HP-EMSR design, which features a compact structure and low fuel enrichment requirements. The findings contribute valuable insights for the development of micro nuclear energy systems suitable for space exploration and off-grid applications.