<p>Accurate evaluation of the aerosol decontamination effect in pool scrubbing is important for countermeasures against severe accident (SA) in nuclear power plants. Pool scrubbing is a method to prevent the release of Fission Products (FPs) into the surroundings. The SA analysis codes currently in use, such as MELCOR, assume simple models and have been found to deviate from actual scale experiments. In the existing MELCOR model, the DF in swarm region, where bubbles rise as a group and occupy a large area in pool scrubbing, is evaluated by using only the decontamination effect in single bubbles. However, very few studies have evaluated the effects of the bubbles interaction and the flow field formed by swarm bubbles on the decontamination effect in swarm bubbles. Therefore, in this study, we focus on the effect of rising bubbles as a group on the aerosol decontamination effect, and the objective of the study is to evaluate the effect of the flow field and bubbles interaction in swarm bubbles on the aerosol removal behavior. First, we measured flow characteristics and DF in a group of small bubbles and compared them with the existing model, MELCOR. As a result, although the bubble diameter and shape were roughly in agreement with those of MELCOR, there was a discrepancy between the MELCOR results and the experimental results, indicating that MELCOR underestimated the experimental results. This indicate that it is not sufficient to consider the decontamination effect in swarm bubbles by using only the DF in single bubbles, and that it is necessary to consider the effects of the interactions between bubbles and the flow field on the aerosol decontamination effect.</p>