Preprint of paper to be published in the proceedings of the symposium on High Temperature Corrosion and Materials Chemistry, The Electrochemical Society, 10 South Main St., Pennington, NJ (Fall 1998). THERMOCHEMICAL MODELING OF NUCLEAR WASTE GLASS*

The development of assessed and consistent phase equilibria and thermodynamic data for major glass constituents used to incorporate high-level nuclear waste is discussed in this paper. The initial research has included the binary Na2O-SiO2, Na2O-Al2O3, and SiO2-Al2O3 systems. The nuclear waste glass is assumed to be a supercooled liquid containing the constituents in the glass at temperatures of interest for nuclear waste storage. Thermodynamic data for the liquid solutions were derived from mathematical comparisons of phase diagram information and the thermodynamic data available for crystalline solid phases. An associate model is used to describe the liquid solution phases. Utilizing phase diagram information provides very stringent limits on the relative thermodynamic stabilities of all phases which exist in a given system.