Measurement of particle decontamination behavior using interferometer
Pool scrubbing is an important factor in the dischargement process of fission products during severe accidents in nuclear power plants. Therefore, a reliable model is required to analyze particle decontamination efficiency by pool scrubbing. However, the fundamental process of particle decontamination behavior during pool scrubbing remains unknown. In an experiment, an interferometer was built to measure particle decontamination behavior from interference fringe. From the interferometer, a bright field image and interference image around the bubble were obtained from high-speed cameras. However, it was difficult to apply existing interference fringe data processing method against our images, since the method requires to adjust the area of the phase extraction manually for each image. It was unrealistic to adjust the range of the extraction area manually for each image from high-speed camera measurement. As to overcome this problem, we developed a new data processing method to separate the phase information from qualitative criteria using data clustering, called the Gaussian mixture model method. From the data processing results, we measured the detailed particle decontamination behavior around a single bubble. From a series of experiments, we discovered that the particle distribution around the bubble tends to be unsteady, although existing models predict the decontamination phenomena to be steady. The results suggest that bubble deformation, which is not considered in existing pool scrubbing models, may be a dominant factor in particle decontamination. We also confirmed that the particle distribution in the lower part of the bubble is strongly affected by gravity.
This work was supported by the Nuclear Regulation Authority (NRA), Japan. The authors are thankful for their great support and discussions. The authors also thank Mr. Takao Maki, Mr. Kenji Kobayashi and Mr. Rintaro Fujikawa for their invaluable assistance.
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