Experimental study of single-bubble behavior containing aerosol during pool scrubbing

Abstract

During a severe accident (SA) in a nuclear power plant, the damaged core releases fission products (FPs). Pool scrubbing is a filtering process to avoid the release of radioactive aerosols into the environment, and its effects have already been modeled and implemented in some SA codes such as MELCOR. However, the effect of aerosols on bubble motion is not defined in this code's model. Therefore, in this study, we visualized the effect of aerosol on the bubble interface via the measurement of the bubble aspect ratio and rising velocity. High-speed videography enabled us to clearly record the effect of aerosol solubility on bubble shape. We found that the solubility of the aerosol inside the bubble – a factor not considered in the MELCOR code – affected the bubble shape and rising velocity. Moreover, soluble aerosols tended to affect bubbles in a manner similar to surfactants. The internal velocity of an oil droplet – a simulated air bubble – was measured using a PIV method. Using image processing, we obtained the interface velocity from the PIV data. The comparison of the experimentally obtained interface velocity and the theoretical value calculated from the equation in MELCOR suggests that MELCOR's internal flow can qualitatively predict the characteristics of internal bubble flow. Additionally, we combined the bubble visualization data and the MELCOR internal bubble flow model and calculated the decontamination factor (DF) for a single-bubble. The results show that the difference in the DF is due to solubility of aerosol, which is caused by the bubble shape and rising velocity.