Waste loading and durability of calcium aluminosilicate glasses for immobilization of plutonium‐contaminated material

Calcium aluminosilicate (CAS) glass was assessed for its ability to immobilize elements present in Plutonium-Contaminated Materials (PCM) including metals (Fe and Cr), polyvinyl chloride (PVC), and Pu (investigated using the nonradioactive surrogates Ce and Hf). Industrial-scale trial melts containing simulant inorganic and organic PCM were characterized to ascertain glass homogeneity, structure, and chemical durability. They were highly durable, comprising a glassy matrix with anorthite (CaAl2Si2O8) crystals. Redox conditions were such that 5–7 mol % Fe, from the melted steel drums, was incorporated in the glass phase, predominantly as Fe2+ in place of Ca, with no significant change to the glass structure. The solubility of Ce and Hf (as Pu surrogates), mixed metal, and PVC in CAS glass was investigated using a series of laboratory-scale melts and shown to exceed those measured in borosilicate glasses. Ce was incorporated in a mixed Ce3+/4+ valence state up to waste loadings of > 3.66 mol % CeO2, while Hf4+ was incorporated to the same extent with no significant change to the CAS structure. Fe was fully incorporated up to 3.43 mol %, but the solubility limit for Cr2O3 was reached between 0.5 and 1 mol %. Laboratory glasses were melted in air, so the majority of Fe was incorporated as Fe3+ in tetrahedral coordination, leading to structural differences between laboratory- and industrial-scale CAS. Chlorine incorporation was low in all systems, likely due to volatilization rather than approaching the solubility limit of Cl in CAS glass.