Improvement of aerosol spray scavenging efficiency with water mist

Abstract

The resolidified fuel debris from the damaged Fukushima Daiichi reactors must be cut into small pieces prior to removing it from reactor buildings. Submicron radioactive aerosol particles are likely to be generated and dispersed into the primary containment vessel (PCV) atmosphere during this cutting process. However, traditional sprays cannot effectively scavenge aerosol particles with diameters in the range of 0.1–1 μm from gas environments. In this paper, a new aerosol agglomeration method is accordingly proposed employing water mist as a pretreatment to enlarge the aerosol particles prior to removing them using water sprays. First, the water mist is injected into a vessel in which aerosol particles are primarily dispersed. Following a short waiting time, subsequent spray injection is then able to more effectively remove the enlarged aerosol particles. The application of water mist was found to improve the aerosol spray scavenging efficiency by coalescing with aerosol particles under both diffusiophoresis and different coagulation mechanisms to form large-sized agglomerated mist–aerosol particles that can subsequently be removed by the water spray. The efficiency of removal is increased due to the enhanced collection mechanisms of inertial impaction and improved particle surface hydrophilicity. The optimized spray system evaluated in this study will be used to effectively control radioactive aerosol suspension inside the Fukushima Daiichi PCVs and protect workers and the public from any unknown consequences of internal radiation exposure during reactor decommissioning. The proposed method can also be applied throughout the nuclear industry to reduce the risk posed by small-sized aerosol particles during maintenance.