Yuanzineng kexue jishu (Feb 2023)
Experimental Study on Influencing Factor of Aerosol Pool Scrubbing under Different Flow Regimes
Abstract
During a severe accident in nuclear power plant, if passive containment cooling system fails and other pressure relief measures are also useless, the mixed gas in containment can be injected into the spent fuel pool via a injector to reduce the risk of containment overpressure failure and the release of radioactivity to the environment. A aerosol pool scrubbing facility was built to study the factors influencing the effect of aerosol pool scrubbing under the injector. This facility can perform a great variation of experiments using various measurement tools. The aerosol concentration and particle size were monitored by using the spectrometer with a 20% measurement error. TiO2 powder was used as a stimulant for the aerosols in containment, and the mass median diameter ranged from 0.5 to 1.5 μm, the geometric standard deviation ranged from 1.63 to 2.15. According to the different characteristics of gas-liquid hydrodynamic behavior, the pool scrubbing process can be divided into two regions, including injection and rise zones. In the injection zone, with the flow flux increase, the gas regime changed from bubble (We<105) to jet regime (We≥105). The effect of mass flux on the aerosol removal efficiency under these two different flow regimes was studied. The decontamination factor (DF) increases with mass flux in the case of jet regime. The high-speed gas interacts with the water and causes water entrainment in the form of droplets, and then the aerosol is removed by droplet interception and inertial collision. With the increase of the mass flux, the jet length and entrained droplet fraction increase, the droplet interception and inertial impact aerosol removal mechanism are enhanced, resulting in an increase in DF. DF decreases with the increase of mass flux in the case of bubble regime. With the increase of mass flux, the aerosol removal mechanism of rising zone dominates. Although the inertial collision effect in the injection zone is enhanced, the bubble swarm rises faster, the movement time of the bubbles in the water is reduced, which leads to a decrease in DF. In addition, in the presence of steam, the effect of aerosol scrubbing removal is significantly enhanced due to the steam condensation. The existing calculation formula of steam condensation underestimates the effect of steam condensation on aerosol removal. The reason is that at a high steam fraction, condensation droplets generated by steam condensation will also have an impact on aerosol retention and enhance the effect of steam condensation.
