Numerical investigation on melt freezing behavior in a tube by MPS method

Given the nuclear reactor severe accident, the instrument tubes of reactor vessel bottom head may fail and create paths through which melt could leak out of the reactor vessel wall. Thus, the melt freezing behavior in an instrument tube is a key factor that concerns the failure of the reactor pressure boundary. In this study, the moving particle semi-implicit (MPS) method was adopted to analyze the melt penetration and solidification behaviors in a tube. Both surface tension and viscosity variation with temperature were taken into account in the present MPS method. The numerical results had been compared with the downward and upward melt injection experiments, respectively. The comparative results showed that the melt leading edge position histories were in good agreement with the experimental results. The typical melt freezing behaviors were successfully reproduced by MPS method. The crust formed on the surface of the tube increased the melt flowing resistance, and would also increase the thermal resistance between the melt and the tube. Meanwhile, the melt velocity also decreased due to the increase of its viscosity. The present results indicate that MPS method is applicable to simulate the melt penetration behavior in an instrument tube.