A Preliminary Steady Neutronics and Thermal-Hydraulics Coupling Analysis of Molten Salt Infiltration

Molten salt reactors (MSR) utilize molten salt dissolved with fissile elements as fuel, enabling online refueling and reprocessing. The unique design allows the liquid fuel to flow directly through nuclear graphite, greatly simplifying the core structure. However, nuclear graphite is a porous material with an open porosity of approximately 10%. Driven by a pressure gradient, liquid fuel salt would infiltrate into these open pores and fission reactions in the infiltrated fuel induce a local power increase in graphite, subsequently driving a temperature elevation. To accurately assess this phenomenon, this study proposes a steady-state infiltration-neutronics-thermal-hydraulics coupling method based on OpenMC and MOOSE (Multiphysics Object-Oriented Simulation Environment). The coupled method simulates the infiltration of FLiBe fuel salt into IG-110 graphite within RCA (Round Channel Assemblies) under operating pressures (200–300 kPa) and analyzes its effects on the system’s power and temperature. Results indicate that the infiltration for an assembly strongly depends on the flow channel pressure. At 300 kPa, the maximum saturation can achieve 0.73 and thus significantly increases the power share in the graphite. This leads to a notable rise in the overall temperature of the assembly, with a peak temperature increase of 821 K over the non-infiltration case. Although infiltration is relatively limited at 250 and 200 kPa, the assembly’s k∞ (Effective Multiplication Factor) and temperature remain highly sensitive to this process.