Systematic investigation on neutronics and thermal-hydraulics model for multi-physics analysis of micro molten salt fast reactor with moderating reflector

A moderating reflector in Molten Salt Fast Reactors (MSFRs) enables dual‐spectrum core—combining advantages of both fast and thermal spectra—but introduces strong local power peaking and a positive reflector temperature coefficient (RTC), whose impacts in steady and transient states remain largely unexplored. To address the research gap, we systematically evaluated neutronics and thermal-hydraulics model effects on the multi-physics behavior of an MSFR with moderating reflector, using GeN-Foam and OpenMC. First, multi-group diffusion analysis with various multi-group cross section (MGXS) models was conducted, demonstrating that refined MGXS (30-group structure with multi-region spatial homogenization) model can provide reasonably accurate predictions for MSFR with moderating reflector. Next, the influences of different neutronics (N) and thermal-hydraulics (TH) models on steady-state multi-physics calculations were examined. The results show that explicit reflector region modeling in TH simulation, together with the refined MGXS model, is crucial for accurate multi-physics simulation. Finally, transient analysis of accident scenarios was performed to investigate the basic dynamic behavior of the system and to assess the impacts of the positive RTC and MGXS model. The results show that simple MGXS model exhibits delayed power response to negative temperature feedback, and that positive RTC effects are not significant over short-term periods. • A detailed neutronics analysis for molten salt fast reactor with moderating reflector was conducted using GeN-Foam, confirming that multi-group diffusion approach can be adopted to achieve reasonably accurate neutronics results if refined multi-group cross section is applied. • Key neutronics and thermal-hydraulics models for accurate multi-physics simulation were identified. In particular, explicit solid (reflector) region modeling in thermal-hydraulics simulation and the use of refined multi-group cross section model were shown to be crucial. • Basic transient responses as well as the effects of the positive reflector temperature coefficient and multi-group cross section model were investigated under unprotected loss of power and unprotected loss of flow scenarios.