For the US to realize a nuclear power renaissance will require closure of the nuclear fuel cycle. A key aspect to closing the nuclear fuel cycle is the storage and disposition of nuclear waste in geologic systems. The ability to accurately predict the behavior of sodalite-bearing multiphase ceramic waste forms over geological time scales requires an understanding of the thermodynamic stability of each mineral phase present in the multiphase matrix. In this study, we evaluated a sodalite-bearing multiphase ceramic waste form (i.e., fluidized-bed steam reform sodium aluminosilicate [FBSR NAS]) being considered for the immobilization of anion-bearing waste streams (e.g., Hanford low activity waste [LAW]). Numerous semi-volatile anions, Cl-, F-, SO42-, I-, and TcO4- present in the LAW stream are captured in the cage of feldsphathoid minerals, thus immobilizing them. The thermodynamic functions of the felspathoids were determined using low temperature heat capacity measurements and high temperature oxide melt solution calorimetry. The structure and thermochemistry of perrhenate sodalite as well as various other anion-bearing sodalites was measured and used to estimate the thermochemistry of pertechnetate sodalite. Results indicate that under oxidized conditions, the thermochemistry perrhenate sodalite represents a reasonable surrogate for the pertechnetate sodalite.

Structure and thermochemical studies of feldspathoid minerals used in nuclear waste management

247th National Meeting (2014)

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