Experimental Investigation on Aerosol Scavenging by Electrically Charged Spray with Preinjected Water Mist for Fukushima Daiichi Decommissioning

Abstract

Retrieving the resolidified debris in both aerial and submerged conditions is crucial in the context of Fukushima Daiichi (1F) decommissioning. This involves segmenting the debris into manageable pieces through assorted techniques, such as laser cutting. During these operations, radioactive aerosols, mostly submicron-sized, may generated, necessitating a containment spray system for removal. The challenge is the aerosols within the Greenfield gap (0.1-1 μm) are hard to remove with conventional sprays. Hence, a new method using water mist to enlarge aerosol sizes before removal with water sprays was proposed. Further, spray droplet changing is a useful technique to improve the aerosol scavenging efficiency through the additional electrostatic interactions for facilitating the aerosol capture. In this study, experiments are conducted in our UTARTS facility to improve the aerosol removal efficiency by developing an electrostatic-charged spray system with water mist. A ring brass electrode near the spray nozzle's outlet, charged by a high-voltage power supply, induces charges on the droplets. Prior to spray activation, water mist is injected to agglomerate aerosol particles for their size enlargement. Results indicate accelerated aerosol removal with electrically charged sprays, especially as voltage increases. However, the benefit plateaus at higher voltages (e.g., higher than 15 kV) due to droplet charge saturation. Pre-injected water mist also enhances removal efficiency under current electro-spraying conditions. The findings obtained from the current study will be beneficial to the optimization of spray system design for effective aerosol scavenging during the 1F decommissioning.