Numerical simulation of melt jet breakup under non solidification conditions

Abstract

The nuclear reactor core melting accident can cause the leakage of radioactive materials, resulting serious harm to the surrounding environment and the safety of the public. For modern PWR, if the core structure was melted in a severe accident, the generated melt will move downward and interact with the remaining coolant at the lower head, resulting a series of physical phenomena. In this paper, the numerical model based on the VOF to DPM method is presented to analyze physical processes of the interaction between melt jet and coolant. The influence of coolant phase change on the jet breakup length, degree of fragmentation, and particle diameter of melt debris are analyzed under different conditions. This paper analyzes the impact of the incident velocity of melt, the incident diameter, the density ratio of melt and coolant on the jet breakup length based on Saito's empirical formula, and compares the simulation results with the empirical formula. The working condition of Yutaka experiment is simulated in this paper and the diameter distribution of the broken fragments is analyzed, as well as the influence of the incident temperature, incident mass and incident velocity of the melt on the average mass diameter of the generated particles. The numerical results reach a good agreement with the experimental data. This work provides a feasible numerical scheme for the analysis of melt jet entering the lower head coolant under accident conditions.