Crystal spatial distribution controls the electrical response of nuclear waste glasses containing RuO ₂ crystals

Abstract The content of platinum group metals (PGM, including Ru, Rh, and Pd) in high‐level liquid waste (HLLW) significantly exceeds their solubility in borosilicate glass, causing them to remain as crystalline phases. During the long‐term performance of the HLLW vitrification, crystals containing PGM tend to aggregate and settle at the bottom of the melter, forming a sludge layer that has a high electrical conductivity. This layer can cause short‐circuiting of the bottom electrodes, disrupting the melting process. Here, we study the effects of nanosized RuO 2 crystals and their spatial distribution on the electrical conduction mechanism of glasses and melts that contain RuO 2 crystals. We showed the remarkably low percolation threshold of RuO 2 crystals and connected these low values with the spatial distribution of these solid particles. These findings were correlated with the transition of conduction mechanisms of glass melts from ionic to electronic at different temperatures. This work provides insights into the electrical conduction mechanism in nuclear waste glasses containing RuO 2 crystals, highlighting their correlation with the spatial distribution of precipitated RuO 2 . The findings have implications for the vitrification of nuclear wastes containing suspending RuO 2 phases.