Scavenging of laser-generated aerosols with electrostatic-charged spray droplets

Abstract

At the Fukushima Daiichi nuclear power station, high radiation hot spots were found at the concrete shield plugs above the Primary Containment Vessel (PCV), indicating that radioactive material may have flowed into narrow gaps at the upper part of the reactor building. High-power fiber lasers can be the preferred choice for cutting fuel debris and cleaning high radiation hot spots due to their advantages over conventional mechanical removal methods. However, laser decontamination generates submicron radioactive particles that pose a risk of internal dose to workers if dispersed. Effective confinement and scavenging are critical to reducing the risk of radiation exposure during decommissioning processes at the Fukushima Daiichi nuclear power station. Various other industries such as coal, mining, and chemical produce flue gases that contain particles smaller than a micron in size, which are harmful to both the environment and human health. To understand the feasibility of implementing an electrostatically charged spray to capture the aerosol particles in decommissioning applications and other industries, laser cleaning experiments were conducted inside UTARTS (University of Tokyo Aerosol Removal Test with Sprays) facility with a class-4 laser having maximum irradiation power of 1.5 kW. Various test samples made of carbon steel (CS), stainless steel (SS), and concrete were coated with CeO2 and cleaned using the laser. The aerosol particles generated during laser decontamination were confined inside the UTARTS and captured using a spray and electrostatic droplet charging system. The study proposes the use of a charged spray, which proves highly efficient for scavenging aerosols generated through laser irradiation. This technique can be used to efficiently decontaminate radiation hotspots adhering to shield plugs, PCV walls, and structures to ensure the safety of operators in high-dose environments and extend the operating time of electronic devices.