PNNL

Abstract

Recent tank retrieval and blending strategies at both the Savannah River Site (SRS) and Hanford have identified increased amounts of high-Al2O3 waste streams that are scheduled to be processed through their respective high-level waste (HLW) vitrification facilities. It is well known that the addition of small amounts of Al2O3 to borosilicate glasses generally enhances the durability of the waste glasses. However, at higher Al2O3 concentrations nepheline (NaAlSiO4) formation can result in a severe deterioration of the chemical durability of the slowly cooled glass near the center of the canister. Additionally, higher concentrations of Al2O3 generally increase the liquidus temperature of the melt and decrease the processing rate and thus result in a decreased waste loading in glass. Because of these effects, the maximum concentrations of Al2O3 in glasses have been restricted to the range of 17 wt% or lower. Pacific Northwest National Laboratory (PNNL), Savannah River National Laboratory (SRNL), and Khlopin Radium Institute (KRI) are jointly performing laboratory and scaled melter tests, through US Department of Energy, EM-21 Office of Waste Processing program, to develop glass formulations with increased Al2O3 concentrations. These glasses are formulated for specific DOE waste compositions at Hanford and SRS. The objectives are to avoid nepheline formation while maintaining or meeting waste loading and/or waste throughput expectations as well as satisfying critical process and product performance related constraints. This paper reports the results of recent tests of simulated Hanford HLW glasses containing up to 26 wt% Al2O3 in glass.