In severe accidents (SAs) of nuclear power plants (NPPs), non-condensable gas including vapor and small particles of fission products (FPs) are released from the reactor vessel, pass through the wet well into the atmosphere. In these conditions, the suppression pool water traps the FPs before released to the atmosphere. This trapping effect is called pool scrubbing. Since pool scrubbing is assumed to have a great decontamination effect, research about the pool scrubbing is important from the viewpoints of NPPs safety. Therefore, it is necessary to understand the two-phase flow behavior. &nbsp;However, the mechanism of the FPs removal behavior by pool scrubbing is not clearly understood due to the complicated hydrodynamic phenomena. In addition, the evaluation of the validity of physical models used in pre-existing SA analysis codes aren't enough. Thus, a reliable model is highly regarded. &nbsp;Currently, decontamination factor (DF) of pool scrubbing is calculated by integrated SA analysis codes such as MELCOR, which is the target of our research. In the MELCOR code, some assumptions and empirical formula are used. DF is calculated by bubble diameter and rising velocity etc. But correlation DF and flow structure characteristics do not elucidate and, Detailed measurement of these correlation are not enough. Therefore, the aim of our study is the measurement of DF and flow structure characteristics and validate the code about flow characteristics in the bubbly flow including soluble particle, As to understand two phase flow characteristics during the pool scrubbing, we focus on bubble diameter and swarm rise velocity. Air-particle mixture flow injected into the experimental facility was measured by a wire mesh sensor (WMS) in several cross sections, also visualized by a high-speed camera. In addition, DF by pool scrubbing was derived from aerosol measurements using an aerosol spectrometer. From these results, we compared bubble diameter and swarm rise velocity with the code individually. When submergence increase, a mode of Bubble diameter and cross section average of swarm rise velocity is getting closer the code value. Finally, discussions for the correlation between DF and flow structure characteristics were done by comparing the result.


ICONE Competition - ICONE28-POWER2020-16216: Aerosol Decontamination Behavior in Two Phase Flow During Pool Scrubbing

Division / Sponsors: 
Power Division & Nuclear Engineering Division (NED)

Power Conference
Paper Proceedings: https://asmedigitalcollection.asme.org/POWER/POWER2020/volume/83747

International Conference on Nuclear Engineering
Paper Proceedings: https://asmedigitalcollection.asme.org/ICONE/ICONE2020/volume/83761

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