Impacts of Cr(III) and Cr(VI) concentrations on key high-level waste glass properties

This study investigates the effects of chromium concentration and redox on simulated high-level waste (HLW) borosilicate glass properties for high-chromium Hanford wastes. Thirty glasses with target 1 ≤ Cr₂O₃ ≤ 2.5 wt% were fabricated and analyzed. The Cr redox ratios were measured using K-edge X-ray absorption near edge structure along with properties of interest to vitrification of Hanford HLW: crystal formation after centerline canister cooling, crystallinity as a function of temperature, viscosity, electrical conductivity, toxic characteristic leaching procedure and product consistency test (PCT) responses, and SO₃ solubility. Only Cr(III) and Cr(VI) were identified in the test glasses, and their ratio was found to be largely correlated to optical basicity. Cr redox appeared to have a significant impact on most of the properties, except for PCT. Most properties were affected differently by Cr(III) than by Cr(VI). These effects were quantified and rationalized based on the previously studied bonding nature of the two primary oxidation states.