Candidate wasteforms for the immobilisation of lithium sulphate-bearing nuclear wastes: A scoping study

In this study, the suitability of glass and glass–ceramic wasteforms for the immobilisation of nuclear waste streams containing high concentrations of lithium sulphate was explored. The aim of the study was to maximise sulphate incorporation while also achieving acceptable waste loadings and chemical durability. An immiscible layer rich in BaSO 4 and Na 2 SO 4 formed on the surface of the glass when the sample was consolidated at lower temperatures. This surface layer disappeared when consolidation temperature was increased to 1200 °C and sulphur loss was observed via volatilisation. The glass wasteform with the highest sulphate incorporation of 2.78 wt.% SO 3 (from waste loading of 11 wt.% as Li 2 SO 4 ) was achieved following melting at 1200 °C. Tailored glass–ceramic wasteforms were also investigated, produced at lower temperature and with higher waste loadings. Crystalline inclusions were observed within the glass matrix at 1000 °C with 14–16 wt.% waste loading for sintered samples. The synthesised wasteforms were studied via various analytical techniques. The chemical durability was assessed using the ASTM C1285 standard test method and evaluated relative to relevant nuclear waste glasses. Graphical abstract