Numerical investigation on the dissolution kinetics of ZrO₂ by molten zircaloy using MPS method

During the postulated core meltdown accident of the nuclear reactor which employs the dispersion plate-type fuel, the UO₂ microspheres would be dissolved by the molten zirconium, and the dissolution process is accelerated by the mass diffusion phenomenon. In this study, the dissolution model, based on the Fick's second law and the dissolution criteria, was developed and incorporated into the Moving Particle Semi-implicit (MPS) method. To validate the dissolution model, the one-dimensional mass diffusion problem was simulated by the improved MPS code. The study of numerical convergence was also performed based on the sensitivity analysis of the particle size. The distribution of the oxygen predicted by the improved MPS agreed well with the analytical solution for the particle size of 0.5 mm. Then the improved MPS was adopted to analyze the dissolution kinetics of the three-dimensional ZrO₂-Zr system in this study. The oxygen concentration and the interface displacement of the ZrO₂-Zr system were considered, and the simulation results indicate that the behavior of ZrO₂ dissolution caused by molten zircaloy follows the parabolic law. The improved MPS method is proved to be capable of simulating the dissolution process and the induced phase change.