Characterization of Particles Formed during Laser Cutting of Simulated Fuel-Containing Materials from the Fukushima Daiichi NPP and of SNF Samples

Fragmentation of massive debris of the fuel and fuel-containing materials (FCMs) is one of important steps in the final decommissioning of the Fukushima Daiichi NPP. The generation and dissemination of radioactive microparticles in the course of the fragmentation largely depend on the cutting technology used. A previous study [1] dealt with the experimental cutting of simulated FCM and spent nuclear fuel (SNF) samples to justify the optimum configuration and operation conditions of the gas treatment system. To understand the properties of particles generated in the course of cutting FCM and SNF samples and to justify the methods for their localization, it is necessary to study in more detail the size, shape, and composition of the structures formed. This study deals with the microparticles formed by laser cutting of simulated FCMs from the Fukushima Daiichi NPP and of SNF samples. The microparticles formed were examined with a laser particle size analyzer and with a scanning electron microscope equipped with wave- and energy-dispersive spectrometers. The formation of particles of different size and morphology was noted. The laser cutting generates separate particles of submicron size and different morphology, which form agglomerates. Up to 35 wt % of particles formed by laser cutting of the simulated FDM passed into the vapor–gas phase. For the WWER (water-cooled water-moderated energy reactor) SNF, this fraction was 25 wt %. The major components of all kinds of particles formed by laser cutting of SNF are uranium, oxygen, and zirconium; their total fraction is in the range from 97.9 to 98.4%. The plutonium content ranges from 0.7 to 1.3%.