Fluid Dynamics Exploration in Molten Salt Reactors: A Comprehensive Study of Draining Tank Using the Moving Particle Semi-Implicit Method

Abstract

Molten Salt Reactors (MSRs) represent a promising advancement in nuclear energy technology through the use of liquid fuels, offering inherent safety features and efficient thermal conversion. A critical safety mechanism in MSRs is the drain tank system, designed to passively remove molten salt fuel during emergency shutdowns. This study presents a comprehensive hydrodynamic analysis of the draining process in such tanks using the Moving Particle Semi-Implicit (MPS) method, a mesh-free Lagrangian computational fluid dynamics technique well-suited for simulating free-surface flows. The investigation focused on key parameters including discharge velocity, pressure distribution, discharge rate, discharge coefficient, and Reynolds number for three fluids: light water, FLiBe (LiF-BeF₂), and FLiNaK (LiF-NaF-KF). Simulations were performed under isothermal conditions, neglecting heat transfer to isolate pure fluid dynamic behavior. Results reveal a consistent discharge pattern across all fluids, characterized by an initial rapid flow phase followed by gradual stabilization. FLiBe and FLiNaK, due to their higher densities and viscosities, exhibited slightly greater initial velocities and pressures than light water, yet all fluids demonstrated similar discharge rates and coefficients over time. The Reynolds number analysis confirmed turbulent flow regimes throughout the drainage process for each fluid. Despite differences in physical properties, the overall draining behavior and temporal trends in velocity and pressure were remarkably similar. These findings validate the use of MPS in analyzing transient liquid dynamics in MSR safety systems and provide valuable insights into reactor design optimization. Future work incorporating thermal effects could further enhance understanding of coupled thermofluid behavior, supporting the development of MSRs as a reliable and sustainable energy solution.
Keywords: drainage, FLiBe, FLiNaK, liquid, MPS, MSR