Mechanism of aerosol decontamination from a bubble during pool scrubbing

In severe accidents (SAs) of nuclear power plants, release of gas containing fission products (FPs) from the reactor vessel is thought to be a major issue. As to reduce the leakage of FPs into the environment, gas containing FPs are generally discharged though the wet-well and decontaminated by the transfer effect of FPs from the gas-phase to the liquid phase. This effect is called pool scrubbing. In SA analysis codes such as MELCOR, it is predicted in the model that FP particle motion inside a single bubble, created by the bubbly flow inside the wet well as a major factor in decontamination. However, there are few experimental evidences to support the modeling of this phenomena. Therefore, in this paper, the experiment to observe particle decontamination in order to understand the relationship of particle motion and decontamination. In the decontamination behavior measurement, by using Maki-interferometer microscope, density distribution of particle decontaminated from an air bubble was observed. From the results, we succeed in visualizing the phase distribution around the air bubble due to optical path difference of decontaminated particle. From the results, strong occurrence of decontamination is observed in the major axis and the bottom of bubble. By comparing the results to the previously obtained particle motion, we confirmed that the decontamination in the major axis is related to the inner flow in terms of centrifugal force due to the peak of interface velocity, and the decontamination in the bottom of could be explained by the gravitational sedimentation. (author)