Chemical analysis of simulated high level waste glasses to support stage III sulfate solubility modeling

Abstract

The U.S. Department of Energy (DOE), Office of Environmental Management is sponsoring an international, collaborative project to develop a fundamental model for sulfate solubility in nuclear waste glass. The solubility of sulfate has a significant impact on the achievable waste loading for nuclear waste forms within the DOE complex.A fundamental model of sulfate solubility in glass, under development at Sheffield Hallam University (SHU), could provide a solution to the issues of sulfate solubility in glass. The model uses the normalized cation field strength index as a function of glass composition to predict sulfate capacity, and has shown early success for some glass systems. The objective of the current scope at SHU is to mature the sulfate solubility model to the point where it can be used to guide glass composition development, allowing for enhanced waste loadings and waste throughput. A series of targeted glass compositions was selected to resolve data gaps in the model and is identified as Stage III. SHU fabricated these glasses and sent samples to SRNL for chemical composition analysis. SHU will use the resulting data to enhance the sulfate solubility model and resolve any deficiencies.Chemical composition analysis was performed on a representative sample of each of the Stage III study glasses. Three preparation techniques, sodium peroxide fusion, lithium metaborate fusion, and potassium hydroxide fusion, were used to prepare the glass samples for analysis. Each of the prepared samples was analyzed twice to obtain measurements for each element of interest. An average value was computed for each component on an oxide basis. The resulting measurements were compared with the targeted values. Some differences between the targeted and measured compositions were identified. It is therefore recommended that the measured compositions, rather than targeted compositions, be used to support the sulfate solubility modeling effort for these glasses.