Improvement And Application Of The MPS Method To Simulation Of Melting Behavior

In case of a severe accident in the nuclear reactor, the fuel element may melt and drop into the lower head of reactor pressure vessel. The migration and relocation of corium have great impact on the progress and mitigation of severe accident. In this dissertation, the original MPS(Moving Particle Semi-implicit) method is further developed to enable the detailed simulation of the melting process of fuel rods. The improvements for the original MPS include: 1) The additional energy equation is solved to simulate the heat transfer process; 2) Several surface tension models are compared to determine the most appropriate one for melting simulation; 3) The enthalpy-based transition profile of viscosity near the melting temperature is implemented in order to reproduce more realistic melting behavior. 4) The implicit calculation scheme is utilized for the viscosity term in place of the original explicit one, which augments the time step size and hence improves the computing efficiency; 5) The Passively Moving Solid(PMS) model is adopted for the coupling calculation of the motion of fluid and solid.The one-dimensional unsteady heat transfer and square droplet oscillation are respectively used to verify the implementation of the heat transfer model and surface tension model. Furthermore, the modified 3D MPS method is validated by comparing the experiment results of Wood's metal melting with the numerical result. In order to demonstrate the capability of the improved MPS algorithm and code, a preliminary simulation is carried out for the melting process of 4-rod bundle.