Zirconolite (CaZr_xTi_3-xO₇) has been widely studied as a candidate ceramic wasteform for immobilising actinide-rich wastes; this arises from its ability to accommodate actinides (U/Pu) in its crystal structure for long timeframes (~10⁶-10⁹ years) in geological environments. The addition of glass to zirconolite to fabricate glass-ceramics increases the flexibility to accommodate heterogeneous actinide-rich wastes while simplifying processing conditions; the latter was studied in this research. Cerium-bearing zirconolite glass-ceramics were fabricated by targeting zirconolite (Ca_0.8Ce_0.2ZrTi_1.6Al_0.4O₇; Ce as actinide surrogate) with varying amounts (0-100 vol.%) of glass (NaAl_1.5B_0.5Ca_0.7Ti_0.2Si₂O_8.6), followed by sintering at 1250℃-1450℃ / 6-24 h / air, to systematically investigate the effect of glass content on the phase assemblage (including composition) under various processing conditions. The calcined precursors possessed small particle sizes (< 25 μm) and this helped to minimise the influence of particle size on microstructural development during sintering for all samples. Thermogravimetric analysis and differential scanning calorimetry of the calcined precursors showed that glass addition (25-50 vol.%) lowered the zirconolite crystallisation temperature (1283℃ to 1250℃). X-ray diffraction, scanning electron microscopy, and X-ray energy dispersive spectroscopy analyses showed that glass addition lowered the sintering temperature (1320℃ to 1270℃) required to fabricate a near phase-pure glass-ceramic while minimising secondary phase formation (CeO₂/ZrO₂) with > 90% of cerium addition preferentially partitioned into zirconolite. These data showed that increasing the glass content (0-100 vol.%) and sintering temperature (1270°C to 1320°C) resulted in notable changes to zirconolite and glass compositions which was reflected in minor but systematic changes to zirconolite lattice parameters. X-ray photoelectron spectroscopy and X-ray absorption near edge spectroscopy analyses showed a predominance of Ce⁴⁺ incorporation as well as increasing amounts of Ce³⁺ due to auto-reduction at higher sintering temperatures (1270°C-1450°C). Overall, this research demonstrated that glass addition has the potential to simplify processing requirements of candidate glass-ceramic wasteforms for actinide immobilisation.

Aeschynite (ATiNbO₆, A = light rare earth elements) ceramics have been suggested as candidate wasteforms for high minor actinide content wastes. Whilst the possibility of high actinide loading and high aqueous durability of ceramic wasteforms, including the aeschynite structure, is attractive, they are often limited in chemical flexibility compared to glass wasteform materials. The use of glass-ceramics or glass-ceramic composite materials, where the actinides are preferentially partitioned into a specific ceramic phase and other elements are immobilised by the glass phase, can allow for immobilisation of the target radionuclides whilst also being able to safely manage the complex waste streams produced in reprocessing and clean-up operations.

This work examines the feasibility of forming aeschynite glass-ceramic composites, (Ce/Nd)TiNbO₆ in Na₂Al_2-xB_xSi₆O₁₆ glasses at varying glass:ceramic ratios, in a simple one-heat-treatment process. Preliminary work shows that, although aeschynite phases form well at 1200 °C in 50 wt.% Na₂AlBSi₆O₁₆ glass, secondary phases are also present in the produced materials. These include fergusonite (REENbO₄) and CeO₂, with no Ti-containing secondary phases observed. Given previous reports of the very poor resistance to amorphisation of the fergusonite structure, its presence in a wasteform is expected to be deleterious, particularly where amorphisation-induced swelling would lead to cracking of the glass phase in materials such as these.

Following studies performed on the impact of the glass composition (within the borated-albite glass system, Na₂Al_2-xB_xSi₆O₁₆) on the relative stability of zirconolite (CaZrTi₂O₇) formation against the formation of undesirable phases, glass-ceramic composites with varied glass composition have been produced. Similarly, the addition of an excess of TiO₂ has been shown to improve the final phase assemblage of brannerite (UTi₂O₆) glass-ceramic composites, so changes in ceramic-phase stoichiometry have also been examined, from ATiNbO₆ to ATi_1.3NbO₆. The produced materials have been characterised by X-ray diffraction, scanning electron microscopy, and Raman microscopy.

In some cases, nuclear wastes can be treated with ion-exchange materials to remove specific radionuclides from solution via cationic exchange. A promising inorganic ion exchanger, crystalline silico-titanate (CST) or IONSIV^®, has been employed within column systems to successfully remove Cs-137 from contaminated aqueous systems with high specificity. Once the Cs-137 has been incorporated within the IONSIV^® structure, the ion exchange material itself becomes radioactive waste and requires immobilisation within a nuclear wasteform for disposal. The current study investigated a series of advanced glass-ceramic wasteform design concepts for the immobilisation of Cs-loaded IONSIV^®. Key to the wasteform design strategy was to produce highly durable phases, a maximized waste loading and to provide a flexibility in the wasteform such that it can treat IONSIV^® wastes with various Cs-loadings. Non-radioactive Cs-loaded IONSIV^® was used to produce a flexible pollucite glass-ceramic wasteform following the addition of small quantities of glass formers and Fe. X-ray diffraction, scanning electron microscopy, and X-ray energy dispersive spectroscopic analyses showed successful formation of the pollucite glass-ceramic. Waste loadings of ~80 wt.% were achievable with Cs incorporated into the pollucite ceramic phase as targeted. The design also allowed for a wide variation in the Cs-loading of the IONSIV^® exchange material. The chemical durability of the pollucite glass-ceramic was assessed using the Product Consistency Test (PCT) ASTM C1285 standard protocol and evaluated in comparison to a glass wasteform designed for IONSIV^® immobilisation but with a relatively lower waste loading.