Removal Characteristics of Ni-Ferrite Oxide Film Formed on the Stainless Steel Surface in Fiber Laser Decontamination

Abstract

Every nuclear facility has a limited operating life, at the end of which they must be shut down and decommissioned. For decommissioning, the removal of radioactive contaminants and demolition should be considered. Before nuclear power plants are decommissioned, the primary system, which is the most heavily contaminated, is decontaminated first, followed by decontamination of the surfaces of containment containers and buildings. This study examined the removal characteristics of Ni-ferrite coated on the stainless steel (STS304) specimen surface using an eco-friendly laser that generates little secondary waste, and derived the optimal efficiency conditions for laser decontamination. In this study, simulated oxide film specimens were fabricated by coating the STS304 substrate using non-radioactive Ni-ferrite. The experimental equipment for laser decontamination was a Q-switched fiber laser with an average power of 100 W. The laser beam was irradiated on the surface of the specimen according to the beam overlap rate. In addition, the characteristics of the decontaminated area and removal of the coating layer were checked using digital 3D microscopy, scanning electron microscope (SEM), and X-ray diffraction (XRD). The results of laser decontamination experiment indicated the possibility of coating layer removal with fewer scans as the x- or y-axis directions beam overlap rate increased. However, the surface was discolored when excessive overlaps occurred. This study provided basic data for laser decontamination applicable to the removal of Ni-ferrite oxide films on STS304.