Numerical simulation on aerosol pool scrubbing

Abstract

In the event of severe accident for nuclear power plant (NPP), radioactive aerosols may be released into spent fuel pool (SFP) through filtered-containment-venting-system (FCVS), which are entrained by mixing gas from containment, in order to prevent the overpressure of containment. The efficiency of aerosol pool scrubbing determines the radioactive threats of spent fuel compartment induced by containment venting, and the probable amount of radioactive substance during atmospheric dispersion later on. Therefore, it is necessary to study the typical flow phenomena during the process of aerosol pool scrubbing in the SFP of PWR nuclear power plants, and figure out the important regularities and mechanisms, which can provide reference for evaluations of radioactive threats of spent fuel compartment and provide technical supports for new type of designs for SFP and venting system. In this paper, Fluent is used to establish two kinds of numerical models of SFP, including horizontal injection and vertically downward injection configurations, according to the geometrical dimensions of Qinshan 2 NPP’s SFP. TiO2 is used as the substitute of radioactive substance and coupled numerical models of VOF and DPM are introduced for qualitative and quantitative studies on the effects of diameter of aerosol particle, injection velocity, initial water depth and injection direction. The decontamination factor (DF) is determined by quantifying the mass concentration of aerosol particles which escape and are traced from the SFP under different conditions, respectively. Based on the simulation results, it can be seen that with the increase of particle diameter, DF is going to decrease at first and then increase. There should be a negative correlation between injection velocity and DF. By contrast, there is a positive association between initial water depth and DF. Besides, DFs under vertically downward injection conditions are much lower than that under horizontal injection, due to the appearance of contra-vortex flow adjacent to the free water surface.