Spectroscopic properties and redox chemistry of uranium in borosilicate glass

Since borosilicate glass has been chosen as the primary matrix for the immobilization of radionuclide waste, study of the chemistry of actinides such as uranium in this glass network is essential for the design, construction, and optimization of advanced vitrification processes. In this work, the fluorescence and UV-vis properties of uranium doped in various glass matrices have been investigated. Results show that the fluorescence spectra as well as the lifetime distributions can be used to study the fundamental chemical properties of actinides in molten glasses such as the local structural heterogeneity. In addition, the fluorescence lifetime distribution of uranium can be used as an in situ optical sensor to determine its concentration in the immobilizing glass matrix. Study of the redox chemistry of uranium in the borosilicate glass suggests that the redox state of uranium is controlled by the basicity of the network as well as the imposed oxygen fugacity. The decomposition equations proposed in this paper can well explain the equilibria of uranium in molten glasses. These findings will have a broad impact on understanding the chemistry of uranium in glass melts and improving the current immobilization process.