Neutronics and thermal-hydraulics coupled analysis on dimensional change and lifespan of graphite components in small modular molten salt reactor

•An enhanced method has been developed to precisely evaluate the dimensional changes and lifespan of graphite components in an SM-MSR.•A novel solid hexagonal prism assembly (HPA) has been introduced, and an HPA with a pitch size of 18 cm and a fuel volume fraction of 10 % has been chosen for extensive analysis.•Coupling analysis of neutronics and thermal-hydraulics on graphite dimensional change and lifespan is conducted, and a more precise simulation compared to the uncoupled method is obtained. In recent decades, there has been a significant increase in attention towards small modular reactors (SMRs) from both nuclear system designers and prospective consumers. Therein, the small modular molten salt reactor (SM-MSR) stands out due to its special advantages, such as the flexible core design, deep burnup, high thorium breeding capability, etc. However, the lifespan of the moderator graphite is one of the limiting factors in the SM-MSR design, which has a high correlation with dimensional changes in graphite. In this work, a method coupling neutronics and thermal-hydraulics was developed to accurately evaluate the dimensional change and lifespan of graphite components in an SM-MSR. The neutronics and thermal-hydraulics properties coupled with the graphite dimensional change were analyzed. The results indicate that the coupled method employed in this work provides a more accurate simulation of the dimensional change of graphite as compared to the uncoupled method. A novel solid hexagonal prism assembly (HPA) was introduced, and an HPA with an 18 cm pitch size and 10 % fuel volume fraction was selected for analysis. Considering the ability of graphite components to maintain structural integrity during long-term reactor operation, it is noteworthy that there are two critical time periods, which are 6 years and 9 years, respectively. In this case, the HPA graphite has a lifespan of approximately 17.5 years.