Multiphysics Coupling Analysis of an FCM-Fueled Gas-Cooled Microreactor

Abstract The micro high-temperature gas-cooled reactor (mHTGR) is a compact, efficient, and safe nuclear reactor using fully ceramic microencapsulated (FCM) fuel. This study focuses on the core design and multi-physics analysis of a 15MWt mHTGR, which uses helium as the coolant, graphite as the moderator and reflector, and control rods for reactivity control. The reactor is designed to operate continuously for 20 years without refueling. A model coupling multiple physics of a typical fuel assembly was developed using OpenMC and ABAQUS software. The model is simplified by dividing it into 3D solid heat transfer with 2D fluid-solid interface conduction and 1D fluid heat transport. Coupled multi-physics simulations are then performed under steady-state and two typical accident conditions. During steady-state operation, the core coolant flow rate is 9.0 kg/s, and the outlet temperature is 904.6 K. The maximum temperature of 1149 K occurs at a distance of 100 cm from the outlet. In transient simulations, the peak fuel temperature reaches 1204 K during a 200 pcm reactivity insertion and remains almost unchanged during a loss of flow accident. The results show that the core exhibited good transient response characteristics and inherent safety.