Development of Containment Spray Removal Model for Integrated Severe Accident Analysis Code ISAA

The fission products released from the core fuel in severe accidents are mainly transported in the form of aerosols and exist in the gas phase in the containment. Once the containment fails, it will cause radioactive leakage. As an important mitigation measure for severe accidents, containment spray can effectively reduce the containment pressure and aerosol concentration, as well as the release of radioactivity to the environment. In order to analyze the thermal-hydraulic and aerosol behavior in the containment after accidents, a containment spray removal model was added to the integrated severe accident analysis code ISAA. The removal mechanism considers spray droplets washing aerosols by inertial impaction, interception collection, diffusion, thermophoresis, and diffusiophoresis. The containment spray removal model was coupled with the containment thermal-hydraulic module in ISAA to calculate the rate constant for spray removal. Benchmark experiments were selected for assessment of the improved code. The comparison shows that the results of the thermal-hydraulic response and aerosol mass distribution simulated by ISAA are consistent with the experimental data trends. The improved code can accurately simulate the thermal-hydraulic response and aerosol mass distribution during aerosol removal by spray droplets. Implementation of the containment spray removal model in ISAA satisfies the analysis of aerosol behavior in the containment.