Waste Loading and Durability of Calcium Aluminosilicate Glasses for Immobilization of Plutonium‐Contaminated Material

ABSTRACT 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 (CaAl 2 Si 2 O 8 ) crystals. Redox conditions were such that 5–7 mol % Fe, from the melted steel drums, was incorporated in the glass phase, predominantly as Fe 2+ 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 Ce 3+ / 4+ valence state up to waste loadings of > 3.66 mol % CeO 2 , while Hf 4+ 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 Cr 2 O 3 was reached between 0.5 and 1 mol %. Laboratory glasses were melted in air, so the majority of Fe was incorporated as Fe 3+ 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.