Thermal performance evaluation of passive safety systems adopting phase change material applicable for passive molten salt fast reactor

Phase Change Materials (PCMs) have been widely applied across industries involving thermal energy management. In this study, we propose a decay heat removal system concept using PCMs. The thermal performance of the passive safety system (PSS) incorporating PCMs is evaluated for a target reactor. The reference design is the Passive Molten salt Fast Reactor (PMFR), a prolonged long-life core design that deliberately excludes online fuel purification systems. However, the accumulation of fission products in such systems introduces significant challenges for decay heat removal, which this work aims to address. The PCM-based PSS proposed in this paper is expected to resolve these challenges by providing both effective insulation during normal operation and effective decay heat removal during off-normal conditions. To investigate its feasibility, a lumped-parametric analysis is conducted to evaluate the thermal performance of the PCM-based PSS, focusing on heat loss reduction and residual heat removal capacity. The analysis results suggest that a significant reduction of heat loss from 0.42% to 0.114% of nominal power is achievable, while decay heat can be removed effectively during off-normal conditions. We perform parametric studies to assess the effect of PCM properties and system geometry on thermal performance, highlighting the significance of selecting appropriate PCM materials and its optimized geometrical design. The findings suggest that PCM-based PSS can enhance both safety and efficiency of PMFR.