Reduction and Phase Transformation of Ce-Doped Zirconolites

Zirconolite is a wasteform that can immobilize Pu. Herein, zirconolites comprising Ce as a Pu simulant and Al as a charge compensator of Ce/Pu were synthesized by sintering raw CaO, ZrO2, TiO2, CeO2, and Al2O3 powder mixtures at 1400 °C in static air. The reduction behavior and phase transformation of zirconolites during their heat treatment in an Ar–H2 gas flow were investigated. In pure and Ce–Al co-doped zirconolite compositions, 2M-zirconolite and small amounts of perovskite were obtained after sintering. In contrast, 2M-, 4M-zirconolite and relatively large amounts of perovskite were obtained in Ce-doped zirconolite composition. All zirconolite compositions first underwent reduction at ~1050 °C by forming a small domain of perovskite phase. Ce–Al co-doped zirconolite showed a smaller fraction of phase transformation in perovskite than Ce-doped zirconolite, indicating the advantage of using a charge compensator to prevent perovskite formation.