Impact of Narrow Gaps on Graphite Component Lifespan in Small Modular Molten Salt Reactors

Abstract In molten salt thermal reactors, graphite serves as both the moderator and the support structure, while also forming the flow paths for fuel and coolant, as well as the channels for control rods. The molten salt narrow gap flow channel consists of several small gaps that exist between graphite assemblies in the reactor core. And the fuel in the narrow gap channel will cause several modifications to the properties of the graphite and the primary channel, which will affect the life of the graphite assembly. Therefore, thoroughly examining the performance variations of graphite caused by the narrow gap as the reactor operates is critical. In order to investigate the influence of the narrow gaps on the graphite assembly lifetime in small modular molten salt reactors (SM-MSR), a high-precision neutronics physics and thermal hydraulics coupling method for the analysis of the narrow gap is established in this study. The effect of the presence of the narrow gap on the lifetime of graphite components was investigated by comparing the changes in performance of RCA components with different narrow gap widths. The results indicate that the presence of the narrow gap increases the asymmetry of temperature distribution at both ends of the graphite, which in turn aggravates the inhomogeneity of graphite axial deformation distribution. In addition, when the narrow gap channel width is sufficiently small, the molten salt fails to cool the graphite as effectively as it theoretically should. Such a situation is alleviated by increasing the width of the narrow gap.