Development and validation of an aerosol transport module in the primary circuit for evaluating the retention of fission product particles released during severe accidents in nuclear power plants

Nuclear safety is the lifeline for the development and utilization of nuclear energy. During severe accidents in nuclear power plants (NPPs), fission products (FPs) are mainly present in the form of aerosols. The aerosol retention in the primary circuit determines the amount of radiation released to the containment and the environment. To accurately assess the radiological consequences of severe accidents in NPPs, an Aerosol Transport (ATR) module has been developed and integrated into the Integrated Severe Accident Analysis (ISAA) code. This module considers the deposition of aerosols on the wall by dynamic mechanisms during transport. These mechanisms include gravitational settling, laminar/turbulent diffusion, thermophoresis, turbulent eddy impaction and inertial impaction caused by the pipeline geometry. Additionally, we selected the international standard problems FALCON, STORM and Phebus to evaluate the performance of the ATR module. By comparing the calculation results, ISAA-ATR can accurately simulate the retention of aerosols in the primary circuit and the mass of aerosols emitted into the containment. Furthermore, the ATR module has been employed to investigate the contribution of various mechanisms to aerosol deposition. In the primary circuit, thermophoresis is the most significant deposition mechanism, followed by diffusion and turbulent deposition. Gravitational settling and inertial impaction have relatively smaller effects. This work contributes to understanding the deposition mechanisms of radioactive aerosols in the primary circuit during severe accidents in NPPs. It provides valuable insights for the optimizing the design of the reactor coolant system (RCS) of NPPs and the management of radioactive source term after accidents.