Size Distribution and Filtration Property of Particles Generated from Laser Ablation Decontamination Process

摘要

This study investigated the size distribution of particles generated from a laser ablation process applied for the decontamination of a hot cell contaminated with radionu-clides. To simulate the hot cell contamination conditions, a stainless steel 304 (STS 304) plate on which Co and Cs ions (water soluble radionuclides, WSRs) were deposited and STS 304 specimens coated with Eu_2O_3 and CeO_2 (water insoluble radionuclides, WIRs) were prepared. The particle size distribution and concentration for each contamination condition were then measured. In addition, the filtration characteristics of the particles produced from the laser ablation processes were examined using a high efficiency air (HEPA) filter to completely remove these particles. Under the same laser ablation conditions, the particle concentrations for the water insoluble-contaminated specimen were higher than those for the water soluble-contaminated specimen. The mobility diameter of particles showing the highest concentration ranged from 70 to 80 nm for all tests. For the specimens contaminated with Cs ion, when a potassium salt such as KNO_3 or KOH was added, the concentration of particles generated under the same fluence increased owing to a removal in the form of Cs oxide, such as Cs_2O. The overall collection efficiency of the tested HEPA filter for the particles generated from the laser ablation was over 99.4% regardless of the type of contaminated specimen. Consequently, it was confirmed that a high efficiency air filter is very effective as a means to capture particles produced from the hot cell decontamination process using laser ablation technique.