Study of the effect of seawater properties on the performance of molten fuel fragmentation

In this study, in order to explore the effects of seawater properties on the fragmentation behavior of melt jets during a severe core meltdown accident in the light water reactor, visualized fragmentation experiments are carried out by releasing superheated melt into subcooled water at different coolant salinities, melt temperatures, water temperatures, and melt penetration velocities using the VTMCI (Visualized Thermo-hydraulic characteristics in Melt Coolant Interaction) facility at Sun Yat-Sen University. It is found that under the current experimental conditions, as the coolant salinity increases, the size of the debris decreases, while the variation of debris sphericity and debris bed porosity is insignificant. When the water temperature or melt temperature increases, the sphericity of the debris is higher, and the porosity of the debris bed and the size of the debris decrease. When the penetration rate of the melt is higher, smaller particles can be generated, but it has no significant impact on the debris bed porosity and debris sphericity. The Weber number theory can be used to predict the median diameter of debris, while the Stephan number (St) can be used to predict the trends in debris bed porosity and debris sphericity. This study contributes to a deeper understanding of the actual fragmentation process mechanism of molten materials in severe accidents of light water reactors. The experimental data obtained will also contribute to the development, validation, and improvement of relevant physical models in China's pressurized water reactor severe accident analysis codes.