A NEW DESIGN OF EXPERIMENTAL SYSTEM AND PRELIMINARY NUMERICAL ANALYSIS OF LOCAL FUEL-COOLANT INTERACTIONS IN A SIMULATED MOLTEN FUEL POOL

摘要

Studies on local Fuel-Coolant Interactions (FCI) in a molten fuel pool are of crucial importance for the improved evaluation of severe accidents of 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 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 accurate quantitative 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. On one hand, to obtain a more reliable experimental database, a new experimental system has been developed and is being tested. On the other hand, noticing the fact that, with the rapid development of SFR in China, the requirement of a SFR severe accident code should become stronger and stronger in the future, currently systematic code investigations (including both commercial and open-source codes) and computer-model verifications have been initiated. In this study, the FLUENT code, along with its Evaporation/Condensation (E/C) model, is used for analyses. It is found that by adjusting the ratio between evaporation and condensation frequencies, the FLUENT code can successfully simulate the typical three boiling modes (namely the nucleate boiling, transition boiling and film boiling) involved in FCIs. In addition, as compared to previous SIMMER-III calculations, despite some differences, a reasonable transient variation of melt and water pressure history during FCIs seems to be obtainable as well. Knowledge and evidence from this work might be utilized for further improved analyses of local FCIs as well as future development and verifications of SFR severe accident codes in China.