Dimensionless Analysis of Aerosol Dynamic Behaviors in the Light Water NPP Severe Accidents

Abstract The aerosols dispersed inside the containment space undergo a variety of complex dynamic behaviors such as convection, sedimentation, thermophoresis, diffusiophoresis, and Brownian coagulation after a severe accident in a modern light water nuclear power plant (NPP). These aerosol behaviors occur simultaneously and compete with each other. The relative significance of the aerosol behaviors varies greatly under different environmental conditions. In order to study the significance of convective transport, gravitational sedimentation, thermophoresis, diffusiophoresis, brownian coagulation under different environmental conditions after a severe accident, a population balance equation for aerosol dynamic behaviors after a severe accident was constructed in the present work. A dimensionless analysis was carried out on the population balance equation, and the Peclet number and the Damköhler number, were introduced to describe the relationship between the aerosol behaviors after a severe accident. The variation rules of the dimensionless parameters were obtained under various environmental conditions such as temperature, pressure, particle sizes, and particle number concentration. The results show that, under typical severe accident conditions, the changes of temperature and pressure have significant effects on the diffusiophoresis process. The change of aerosol number concentration mainly affects the aerosol diffusion and coagulation rate. While the aerosol particle size affects most aerosol dynamic processes, and the gravity sedimentation process has the highest sensitivity to the change of particle size. The results of this study are helpful to understand the dominant mechanisms of aerosol behavior after severe accidents and to understand the spatial-temporal evolution of aerosols after severe accidents.