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As potential waste forms for immobilizing actinide‐rich radioactive wastes, Eu2Ti2O7 (Eu as a surrogate for minor actinides) pyrochlore glass‐ceramics were fabricated via hot isostatic pressing (HIPing) at 1200°C. The structure and microstructure at the reaction interface between the glass‐ceramic waste form and the stainless steel (SS) canister under HIPing conditions were carefully investigated with scanning electron microscopy (SEM), transmission electron microscopy (TEM), and synchrotron single crystal X‐ray diffraction (SC‐XRD). The interactions at the reaction interface led to the formations of a ~10‐µm‐thick Cr2O3 layer as the oxidation front of the SS and a layer of a mixed oxide phase (Eu1.25SiCr0.8Ti1.2O7.5) on the glass‐ceramic side of the reaction interface. The crystal structure of such a unique mixed oxide phase was revealed indubitably with a combination of synchrotron SC‐XRD and TEM assisted with a focused ion beam (FIB) SEM system. The improved structural understanding of the reaction interface will help to support the utilization of HIPing as a versatile hot consolidation process for the treatment of radioactive wastes. [ABSTRACT FROM AUTHOR]

Zirconolite glass-ceramic samples doped with plutonium have been prepared via hot isostatic pressing. The effects of processing redox and plutonium loadings on plutonium valences, the presence of cation vacancies, zirconolite phase compositions, microstructures and durability have been investigated. Either tetravalent or trivalent plutonium ions may be incorporated on the Ca-site of CaZrTi 2 O 7 zirconolite with the Ca-site cation vacancies and the incorporation of Al 3+ ions on the Ti-site for charge compensation. Plutonium and gadolinium (as a neutron absorber) are predominantly partitioned in zirconolite phases leading to the formation of chemically durable glass-ceramics suitable for the immobilization of impure plutonium wastes arising from the nuclear fuel cycle. [ABSTRACT FROM AUTHOR]