Quantitative and structural analysis of lanthanide elements in molten LiCl-KCl eutectic by laser spectroscopy

Abstract

This study has been performed to understand fundamental chemical behaviors of lanthanide elements in the pyroprocessing. The pyroprocessing is one of the promising techniques to reuse the spent nuclear fuel. The resources in spent nuclear fuel such as uranium, plutonium, and minor actinides are collectively separated in the pyrochemical process. The pyrochemical process is operated under the high temperature, highly radioactive, and argon atmosphere conditions. In view of that, in-situ monitoring and investigation of basic thermochemical behavior is challenging for the development of pyroprochemical process. In this study, the fundamental research about spectroscopic properties and chemical behaviors of lanthanide elements, such as in-situ investigations of qualitative and quantitative analysis, redox behaviors, and symmetry of chemical constitution of single and binary system, was carried out in molten LiCl-KCl eutectic salt by using spectroscopic techniques. Firstly, absorption and fluorescence spectroscopic properties of all series of lanthanide elements (La, Ce, … Yb, Lu) were analyzed in high temperature molten LiCl-KCl eutectic. Obvious absorption spectra and molar absorptivity were obtained and the absorption bands of each element were identified by comparing the literature studies in various media. On the other hand, the fluorescence study has not yet been vigorously investigated. For that reason, no spectroscopic evidence was reported in molten chloride salt prior to this work. In this study, fluoresce spectra and fluorescence lifetimes of all lanthanide elements were investigated at various concentrations, and this is the first to systematically present fluorescence spectroscopic properties of the whole lanthanide elements in molten LiCl-KCl salt. Secondly, the quantitative analysis and the investigation of chemical behaviors of lanthanide elements were performed by using spectroscopic techniques. The spectroscopic properties of europium, terbium, ...