The ternary system palladium-rhodium-tellurium: A Study to understand phase formation in the vitrification process of high-level waste concentrates (HLWC)

We present the results of our investigation on the thermodynamics of the ternary system Pd-Rh-Te at temperatures of 1150, 1100, 1050, 1000, 950, 900, and 750 °C under inert conditions. The goal of these comprehensive studies was to determine the phase stability fields of the phases in the Pd-Rh-Te system under the aspects of vitrifying high-level waste concentrates from reprocessed spent nuclear fuels. Electron-probe microanalysis (EPMA), X-ray diffraction (XRD), and differential thermal analysis (DSC/TGA) were applied to quantify elemental phase composition, phase content and thermophysical properties. In the temperature range from 1150 to 1000 °C, the Pd-Rh-Te system (0-50 at.% tellurium) is dominated by the extensive three-phase space α1 + α2 + L, where α1, α2 denote the solid solution phases Rh(Pd,Te) and Pd(Rh,Te), respectively, and L (Liquid) denotes a tellurium-rich melt phase. This three-phase stability field describes the phase equilibrium conditions relevant for the process conditions to vitrify high-level waste concentrates from reprocessed spent oxide fuels.