First Application of SIMMER-III to Local Fuel-Coolant Interactions in a Simulated Molten Fuel Pool

Studies on local fuel-coolant interactions (FCI) in a molten pool are important for the analyses of severe accidents that could occur for sodium-cooled fast reactors (SFRs). To clarify the mechanisms underlying this interaction, a series of simulated experiments was conducted at the Japan Atomic Energy Agency by delivering a given quantity of water into a molten pool formed with a low-melting-point alloy. From the preliminary experimental analyses, it was recognized that for a given melt and water temperature within the non-film boiling range, with the increasing of water volume, a limited pressure buildup can be observed for both the melt and cover gas regions. In this study, to further understand this interaction, SIMMER-III, an advanced fast reactor safety analysis code, is utilized for analyses. It is found that the SIMMER-III code can reasonably simulate the transient pressure and temperature tendencies during local FCIs as understood from experiments. In addition, from the comparative analyses between different cases, the observed limited pressurization characteristics from experiments can be confirmed as well. To achieve a deeper and more systematic understanding on local FCIs, with the ongoing of experimental analyses, more numerical analyses over various situations, such as much difference in water subcooling, melt temperature as well as the water release site, have been also planned