Analysis of xenon gas inclusions in nuclear fuel using laser ablation ICP-MS

Abstract

Analysis of fluid and gaseous inclusions in solids have been a major interest in various fields and have been carried out at different pressures, temperatures, and phase conditions. In nuclear fuel, approximately 20% of the fission products (FPs) are gaseous with isotopes of Xe contributing up to 90% to the product gases. However, previous to this work quantitative analysis of Xe inclusions in nuclear fuel samples have not been performed systematically. The method used must incorporate simple sample handling procedures in a shielded environment. This study is the development of a method for the direct determination of the fission gas (FG) products in micro inclusions contained in nuclear fuels using LA-ICP-MS. To determine the concentration of Xe in nuclear fuel, two calibration strategies were investigated. The first strategy was based on the direct injection of a known quantity of a reference gas into the LA-ICP-MS carrier gas system. Further, the ablation of a ‘matrix-matched’ standard of a non-irradiated UO₂ sample, implanted with a known amount of ¹²⁹Xe was also applied. Using these quantification methods, quantitative LA-ICP-MS measurements were performed on high burnup nuclear fuel. This study demonstrates that direct gas injection is most suitable for the quantification of fission gas in micron-sized inclusions. The direct gas addition is simple and linear calibration curves were obtained. Good reproducibility was obtained and matrix effects were within the uncertainty of the measurements. For the quantification of fission gases in nuclear fuel, aerosol particles were filtered before entering the ICP to remove interferences on the Xe isotopes from the solid FP matrix. The first quantitative determinations of the amount of gas in nuclear fuel using the direct injection method for calibration led to sample pressure calculations which were in good agreement with pressures estimated from computer simulations.