EFFECT OF AEROSOL PARTICLES ON DEFORMED BUBBLES BEHAVIOR DURING POOL SCRUBBING

<p>In severe accidents at nuclear power plants such as heat transfer tube failure accidents at pressurized water reactors (PWRs) and venting accidents from wet wells at boiling water reactors (BWRs), aerosols containing large amounts of fission products (FP) are generated. In order to avoid these accidents especially like the Fukushima Daiichi nuclear power plant, pool scrubbing, which steam containing aerosols is injected into a pool water of the reactor vessel and aerosols are captured in the water to reduce the amount of aerosol released to the atmosphere, is proposed.</p><p>The evaluation of FP release is important for the analysis of the effects of countermeasures against SA at nuclear power plants, and a SA code including higher reliability and precise physical models is strongly required because the migration behavior of FP is a complex flow phenomenon.</p><p>The MELCOR code, which is one of the SA codes, is designed to analyze pool scrubbing and defines two models: 1) a bubble swarm model that focuses on the formation, breakup, and rise of bubbles caused by gas phase entering a pool, and 2) a single-bubble model that focuses on the movement of aerosol particles inside each bubble. In the bubble swarm model, the entire DF is evaluated by integrating the DF of a single bubble using single-bubble model. Although it is well known that the existing of contamination on the bubble surface is affected on bubble behavior, the effect of aerosol particle in bubbles on the bubble behavior and deformation is not much discussed in this model.</p><p>The aim of this study is to elucidate the effect of existence of aerosol particle in bubbles on the bubble deformation and behavior which is related to the transport phenomena of aerosol particle in bubbles. In this study, we compared the equivalent diameter, aspect ratio, and rising speed of bubbles containing and not containing aerosols, respectively. Solubility of aerosol particle is as parameter. Two high-speed cameras and LED backlights were used for the measurements; the interface of the bubbles illuminated by the LEDs is colored dark due to scattering. The images obtained are used to construct the shape of the bubble interface through a 3D-dimensional reconstruction process. As a result, the experimentally measured aspect ratios at z=0 mm were found to tend to be similar to those of Fujiwara et al[12]. This may be due to the fact that the height of the analytical domain in the Fujiwara et al[12]. simulations is small, less than 30 mm, and the simulations are consistent with the experimental results. This result also confirms that the simulation results of Fujiwara et al. can adequately account for the initial inertia at nozzle ejection[13].</p>