This study aims to improve the low accuracy of the aerosol model in the ISAA code by developing high-precision natural deposition model of aerosol in the containment.

Firstly, the aerosol dynamic shape factor was introduced to correct the natural deposition rate of non-spherical aerosols. Then, the gravity, Brownian diffusion, thermophoresis and diffusiophoresis deposition models were improved respectively. Finally, AHMED (Aerosol and Heat Transfer Measurement Device), ABCOVE (Aerosol Behavior Code Validation and Evaluation) and LACE (Light Water Reactor Aerosoal Containment Experiments) experiments were employed to validate and evaluate the improved ISAA code.

Calculation results show that the improved model is applicable to more accurate simulation of the peak aerosol mass and responding to the influence of the containment pressure and temperature on the natural deposition rate of aerosols, and the calculation accuracy of the residual mass of aerosols in the containment is significantly improved simultaneously.

The performance of improved ISAA with high-precision aerosol models of this study meets the requirements for analyzing the natural deposition behavior of aerosol in containment of advanced PWRs in severe accident. In the future, further optimization will be made to address the problems found in the current aerosol model.

Nuclear safety is the lifeline for the development and application of nuclear energy. In severe accidents of pressurized water reactor (PWR), aerosols, as the main carrier of fission products, are suspended in the containment vessel, posing a potential threat of radioactive contamination caused by leakage into the environment. The gas-phase aerosols suspended in the containment will settle to the wall or sump water through the natural deposition mechanism, thereby reducing atmospheric radioactivity.