An optimized current-controlled electrostatic charging water system for enhanced aerosol removal in Fukushima decommissioning

Abstract

The decommissioning of Fukushima Daiichi nuclear reactors generates submicron radioactive aerosol particles (0.1–1 μm) during fuel debris cutting, necessitating efficient removal to ensure safety. Previous studies show that conventional aerosol removal systems relying on short-range van der Waals forces are less efficient than charged sprays. In these systems, droplets carry net charges (typically 0.1–1 mC/kg) whose polarity can attract neutral or oppositely charged particles via long-range Coulombic forces. Removal efficiency depends on droplet charge magnitude and polarity, as well as particle properties such as size, conductivity, and pre-existing charge. Submicron particles (<1 μm) are influenced by induced-dipole interactions, while larger particles (>1 μm) undergo Coulombic acceleration toward highly charged droplets. Building on these advancements, this study introduces a novel constant current charging system, integrated with the Jacob's Ladder concept, to improve aerosol scavenging performance. Experiments conducted in the UTARTS (University of Tokyo Aerosol Removal Test with Sprays) facility systematically evaluate the efficacy of the constant current setup compared to previous constant voltage systems, alongside the effects of water properties, such as conductivity, pH, and salinity, on removal efficiency. Additionally, the impact of optimized electrode placement within the spray system on enhancing the electric field and particle capture was investigated. Results demonstrate that the constant current system provides superior aerosol removal efficiency, attributed to stable particle charging and intensified electrostatic interactions. Notably, the placement of two copper wires within the water spray direction further enhanced removal efficiency by intensifying the electric field around the aerosol particles. Furthermore, increasing salinity while maintaining constant pH decreases removal efficiency by lowering system resistance, resulting in faster electron movement and inadequate droplet charging. The novel constant current charging spray system demonstrates improved aerosol removal efficiency, offering a significant advancement in aerosol removal strategies for nuclear decommissioning.