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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]

A comprehensive review of the current advances on titanate glass-ceramic composite materials as waste forms for actinide immobilization is given. Apart from providing a comprehensive summary of earlier works in the field, some technical analysis and perspectives are provided pointing to the potential future studies. [Display omitted] • A comprehensive review on titanate glass-ceramic waste forms for actinide immobilization is provided. • Current advances on the titanate glass-ceramic composite materials are summarised. As the emerging versatile waste forms for immobilizing actinide-rich radioactive wastes, glass-ceramic composite materials based on some durable ceramic phases are being developed. They have apparent advantages over the conventional borosilicate glasses and multi- or single- phase ceramics as they essentially combine the chemical and processing flexibilities of glasses to accommodate processing impurities and excellent chemical durability of ceramic phases to host actinides. More recently, some new advances have been made on scientific and technological aspects including new glass-ceramic systems; improved understanding of ceramic phase evolution in glass; actinide validation studies and simplified processing techniques. This review is intended to cover the current advances on the development of glass-ceramic composite waste forms focusing on titanate ceramic phases (zirconolite, pyrochlore and brannerite) for immobilizing various actinide-rich radioactive wastes arising from the nuclear fuel cycle. [ABSTRACT FROM AUTHOR]

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]

[Display omitted] Pyrochlore glass ceramics have been fabricated via in-situ crystallization under reducing conditions by both sintering and hot isostatic pressing (HIPing) as candidate wasteforms for the acidic waste biproduct of Mo-99 radiopharmaceutical production. The tailored wasteform demonstrates flexibility in the wasteform design to receive the required waste variability, it also suitably passes high-level waste performance requirement, and successfully scales to 1 kg scale with 45 wt.% waste loading. U-rich pyrochlore as the major phase was confirmed by X-ray diffraction, scanning electron microscopy and energy dispersive X-ray spectroscopy, with residual glass and minor secondary phases. The presence of both U4+ and U5+ valences in the wasteforms was revealed by diffuse reflectance spectroscopy. Addition of glass content had little influence on the pyrochlore composition but facilitated minor perovskite formation. The up-scaled dense, HIPed sample showed elemental releases of < 2 g/L for all elements in durability experiments. [ABSTRACT FROM AUTHOR]

Graphical abstract Both Y 2 Ti 2 O 7 and Gd 2 Ti 2 O 7 pyrochlore glass-ceramics have been prepared with a typical oxide route and consolidated via hot isostatic pressing, and characterized as potential waste forms for the immobilization of actinide-rich radioactive wastes. Abstract Both Y 2 Ti 2 O 7 and Gd 2 Ti 2 O 7 pyrochlore glass-ceramics (GCs) have been prepared with an oxide route and consolidated via hot isostatic pressing (HIPing) as waste forms for actinide immobilization. The crystallization of Y 2 Ti 2 O 7 /Gd 2 Ti 2 O 7 pyrochlore as the major actinide host phase in the residue glass has been confirmed with XRD, SEM-EDS and Raman spectroscopy. The static leaching tests confirmed that both GCs are chemically durable with normalized Y/Gd and Ti leach rates ∼10−4–10-5 g m-2 d-1 after 28 days. In addition, the interactions between the 316L stainless steel (SS) HIP-can and the GCs have been investigated. Interactions occur at the interface with a layer of mixed Cr/Ti oxide and CrTi 2 O 5 crystals observed for the Y 2 Ti 2 O 7 GC and a layer (∼10 μm) of Cr 2 O 3 observed for the Gd 2 Ti 2 O 7 GC as the reaction fronts from the SS cans. Furthermore, a layer (∼10 μm) of Gd-(Si/Ti)-oxide phase formed on the GC side of the interface. [ABSTRACT FROM AUTHOR]