Hot isostatically pressed glass-ceramics for the immobilisation of sulphate‑bearing nuclear wastes

The treatment and remediation of sulphate-bearing nuclear wastes is challenging as the presence of sulphur limits available wasteform options for their stabilisation. This study is the first to demonstrate successful Hot-Isostatic Pressing (HIP) consolidation of wasteforms specifically designed for sulphur-rich nuclear wastes. Two optimised glass-ceramic formulations were produced with 10.3–11.5 wt.% of SO 3 (14–16 wt.% Li 2 SO 4 ) waste loading. Characterisation showed a targeted glass matrix containing dispersed BaSO 4 and minor secondary phases. HIPed samples exhibited up to 76% higher density and 92% lower porosity than sintered samples. NMR revealed predominantly amorphous, highly polymerised silicate-aluminate network, with durability primarily influenced by the balance between network formers and depolymerizing species. Chemical durability testing showed these candidate wasteforms met or exceeded performance criteria for similar Low Activity Waste wasteforms. The stainless-steel canister-wasteform interaction zone did not produce additional phases compared to the bulk wasteform nor had any detrimental impact on the HIP canister properties.