Investigation of Numerical Simulation Method on Mixing Characteristic in Lower Plenum of Reactor Pressure Vessel

When main steam line break accident occurs in the reactor coolant system, the convection and mixing characteristics of borated water have a great influence on the establishment of reactor safety analysis and mitigation strategies. In this paper, the mixing characteristics and diffusion process of coolant in the lower plenum were discussed based on experimental results. Several prediction models were compared with experimental data to verify the accuracy and reliability. The analytical results show that coolant mixing in the lower plenum tends to have the periphery diffusion process. The temperature gradient model and species transport model both have the ability to predict coolant mixing phenomena, but there shall be a further improvement and optimization in detail for both models.