Experimental and analytical investigations on aerosol washout in a large vessel with high spray coverage ratio simulating PWR containment spray

In severe accident scenarios of a PWR, containment spray can be employed to washout the aerosol of radioactive materials, retaining them in the containment. Therefore, it is crucial to correctly predict the aerosol washout efficiency for safety assessment. For a PWR containment, a high spray coverage ratio (>84%-95%) is required. However, experimental studies focusing on the washout efficiency with such a high coverage ratio in a large vessel are quite limited. To understand such a washout phenomenon toward model development, specifically for PWR, aerosol washout experiments are performed in a large vessel with not only aerosol measurements but also spray droplet characterizations. Significant droplet impaction on the vessel sidewall is observed, and the spray coverage ratios are experimentally confirmed to be compatible with a real PWR. The washout features are investigated in terms of individual particle diameters and the entire one. The model in the safety analysis code, MELCOR, is examined using the experimentally obtained aerosol removal rate, showing the removal rate tendency against particle diameters being reproduced. Although a significant underestimation occurs for large particles, a satisfactory agreement is obtained for smaller ones (