Experimental Study on Aerosol Collection by Spray Droplets: Application to Fission Products Removal in Containment

During a severe accident of a pressurized water reactor (PWR), fission products (FPs) may be released and transported to the containment. The containment spray can be utilized to remove the aerosols of FPs, which contributes to retaining the FPs in the sump. Therefore, it is important to develop an analytical model for predicting the aerosol removal efficiency by the containment spray for nuclear safety. The containment spray is required to have a very high spray coverage ratio where the droplets are expected to impact the containment side walls. In such condition, the gas flow induced by the droplets will behave differently from that in the other condition without the droplet impaction where a stable gas circulation is expected between the boundary of the spray and the side walls. Since the aerosol removal efficiency also depends on the gas flow behavior, to develop the aerosol removal model applicable for the containment spray from this viewpoint, several aerosol removal experiments were carried out in the TOSQAN IRSN facility. Based on the droplet mass flux measurements, it was confirmed that the spray coverage ratios were comparable to that of the containment spray and many droplets impacted the side wall. According to the aerosol measurement results, it was found the aerosol removal was more effective in higher spray water flow rates. Since larger particles were removed more quickly, the mean particle diameter was decreasing during the spray operation and approached to a value. Based on a CFD simulation for the experiment, gas velocity field was investigated. The measured and calculated particle number concentration decays agreed well.