Study on liquid phase separation phenomenon by constructing multi-physics field model

After the core meltdown in a severe accident, the molten pool (corium) formed at the lower head of the pressure vessel occurs liquid phase separation phenomenon at high temperature, Corium's morphologic evolution has a great influence on theIn-vessel retention technology. Therefore, the purpose of this study is to investigate the transient morphological evolution of the molten pool by coupling the thermodynamic properties of the corium, the flow and heat transfer characteristics. Firstly, considering the solidification effect, a multi-physics model with phase field - flow field - temperature field coupling is constructed to simulate the dynamic liquid phase separation phenomenon of the corium. Then it is verified that the phase-field model can be applied to macroscale simulation by using the U-O binary free energy for practical purposes. Also the morphological evolution and its kinetics of the U-O binary system, as well as the formation mechanism are discussed. The transient process of droplets nucleation, floating, fusion, and finally formation of stratified structure was observed, and the phenomenon of a ring of solid oxide wrapped around the liquid-phases was found. The results show that the constructed model can clearly capture the dynamic phenomenon in the process of liquid phase separation, and the model can be applied to the analysis of liquid phase separation of quaternary or multivariate systems, so as to provide a certain support for the safety analysis and design of reactors. It can also provide a reference for the analysis of liquid phase separation of complex materials.