Radiophase Development in Hot-Pressed Alkoxide-Derived Titanate Ceramics for Nuclear Waste Stabilization

Phase development as a function of hot‐pressing temperature was studied in alkoxide‐derived titanate‐based ceramics doped with a 10 wt% loading of a sodium‐rich (NAR) and a sodiumpoor (NAP) simulated high‐level waste. Pyrochlore was found to be the most abundant phase in both calcine powders. A pseudobrookite phase existed metastably at hot‐pressing temperatures between 890° and 920°C. After hot‐pressing at 1100°C, the final phase assemblage for the NAP material consisted of zirconolite, hollandite‐type, perovskite, alloy, and reduced rutile (Magnéli phases). In addition, NAR samples contained hibonite, freudenbergite, and loveringite. Phase development was driven to completion over a very narrow temperature range (50°C), beginning at 870° and 850°C for NAP and NAR, respectively, although full densification was not achieved below 1100°C. Both waste forms exhibited comparable microstructure and aqueous durability.