Partial Loss-of-Flow Transient in SMART’s Hottest Fuel Element: A CFD and System-Code Comparison

Abstract

A loss-of-flow transient featuring a fifty percent reduction in coolant mass flow was simulated for the highest-power fuel element of the 330 MW SMART small modular reactor. Two complementary thermal-hydraulic tools were employed: the lumped-parameter system code STHIRP and a three-dimensional conjugate-heat-transfer model in OpenFOAM. The domain exploits one-eighth symmetry of the 17×17 fuel assembly and includes fuel, cladding (as thermal resistance) and coolant. Steady-state baseline simulations under nominal flow conditions were first validated against theoretical predictions of temperature variation. Subsequently, the transient flow reduction was imposed, and the temporal evolutions of the coolant outlet temperature, fuel-clad maximum temperature, and pressure drop were predicted. OpenFOAM predicted a 38 K rise in outlet temperature and a peak fuel temperature of 1305 K. The good agreement in trends between the two codes demonstrates both the viability of high-fidelity CFD for detailed local analysis and the efficiency of lumped-parameter codes for rapid safety assessments.