GLASS SELECTION STRATEGY: DEVELOPMENT OF US AND KRI TEST MATRICIES

Abstract

High-level radioactive wastes are stored as liquids in underground storage tanks at the Department of Energy's (DOE) Savannah River Site (SRS) and Hanford Reservation. These wastes are to be prepared for permanent disposition in a geologic repository by vitrification with glass forming additives (e.g., frit), creating a waste form with long-term durability. Wastes at SRS are being vitrified in the Defense Waste Processing Facility (DWPF). Vitrification of the wastes stored at Hanford is planned for the Waste Treatment and Immobilization Plant (WTP) when completed. Some of the wastes at SRS, and particularly those at Hanford, contain high concentrations of aluminum, chromium and sulfate. These elements make it more difficult to produce a waste glass with a high waste loading (WL) without crystallization occurring in the glass (either within the melter or upon cooling of the glass), potentially exceeding the solubility limit of critical components, having negative impacts on durability, and/or resulting in the formation of a sulfate salt layer on the molten glass surface. Although the overall scope of the task is focused on all three critical, chemical components, the current work will primarily address the potential for crystallization (e.g., nepheline and/or spinel) in high level waste (HLW) glasses. Recentmore » work at the Savannah River National Laboratory (SRNL) and by other groups has shown that nepheline (NaAlSiO{sub 4}), which is likely to crystallize in high-alumina glasses, has a detrimental effect on the durability of the glass. The objective of this task is to develop glass formulations for specific SRS and Hanford waste streams to avoid nepheline formation while meeting waste loading and waste throughput expectations, as well as satisfying critical process and product performance related constraints. Secondary objectives of this task are to assess the sulfate solubility limit for the DWPF composition and spinel settling for the WTP composition. SRNL has partnered with Pacific Northwest National Laboratory (PNNL) and the V.G. Khlopin Radium Institute (KRI) to complete this task.« less