Knowledge From Recent Investigation on Local Fuel-Coolant Interaction in a Liquid Fuel Pool

Studies on local Fuel-Coolant Interactions (FCI) in a liquid pool are of crucial importance for the improved evaluation of severe accidents for Sodium-cooled Fast Reactors (SFR). To clarify the mechanisms underlying this interaction, several years ago a series of experiments was performed by Cheng et al. (2014) at the Japan Atomic Energy Agency (JAEA) through delivering a given quantity of water into a simulated molten fuel pool which is formed by a low-melting-point alloy. In order to acquire more evidence, numerical analysis using the SIMMER-III, an advanced fast reactor safety analysis code, was also conducted. However, through those analyses, many limitations of the experiments (esp. the uncertain initial geometry of water lump) which would impair the reliability of experimental observations and prevent the direct comparisons with calculations were realized. Focusing on those aspects, further investigations from both experimental and numerical aspects were continued at the Sun Yat-sen University in China. In this study, the effect of injection mode (namely the coolant-injection mode and fuel-injection mode) on local FCIs is studied using the FLUENT code along with its Volume of Fluid Model (VOF). It is seen that the interaction mode does have some influence on the transient behaviors, in particular the formation of steam bubbles, and time variation of temperature and pressure values. In addition, the difference on heat exchange rate due to the steam bubble formation is also confirmable. Knowledge and evidence from this study might be utilized for future development and analyses of SFR severe accident analysis codes in China.