Vitrification of High-Level Waste at the Savannah River Site
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Vitrification of High-Level Waste at the Savannah River Site Kevin M. Fox and David K. Peeler Environmental & Chemical Process Technology, Savannah River National Laboratory Aiken, SC 29808 U.S.A. ABSTRACT The objective of this study was to experimentally measure the properties and performance of a series of glasses with compositions that could represent high level waste Sludge Batch 5 (SB5) as vitrified at the Savannah River Site Defense Waste Processing Facility. These data were used to guide frit optimization efforts as the SB5 composition was finalized. Glass compositions for this study were developed by combining a series of SB5 composition projections with a group of candidate frits. The study glasses were fabricated using depleted uranium and their chemical compositions, crystalline contents and chemical durabilities were characterized. Trevorite was the only crystalline phase that was identified in a few of the study glasses after slow cooling, and is not of concern as spinels have been shown to have little impact on the durability of high level waste glasses. Chemical durability was quantified using the Product Consistency Test (PCT). All of the glasses had very acceptable durability performance. The results of this study indicate that a frit composition can be identified that will provide a processable and durable glass when combined with SB5. INTRODUCTION Cold War legacy, liquid, high level nuclear waste stored in underground tanks at the U.S. Department of Energy Savannah River Site is being vitrified into a glass waste form for safe immobilization and storage. The liquid (or sludge) waste is blended into batches to moderate its chemical composition prior to vitrification. The contents of Tank 51 have been blended with sludge from Tank 7 to constitute Sludge Batch 5 (SB5), the next batch to be vitrified at the Defense Waste Processing Facility (DWPF). The Savannah River Site (SRS) Liquid Waste Organization (LWO) performed low-temperature Al-dissolution in Tank 51 to reduce the total mass of sludge solids and Al being fed to the DWPF. A radioactive demonstration using a 3 L Tank 51 sludge slurry sample was performed to verify the Tank Farm processing parameters [1]. The aluminum dissolved sludge was used to determine potential downstream impacts so that technical issues could be identified before the start of SB5 processing. The potential downstream impacts assessed included the Tank Farm washing and concentration process and the DWPF Chemical Process Cell (CPC) and melter processing envelopes. The chemical composition of this 3 L Tank 51 sample was used to project potential compositions of SB5 as it will be processed by the DWPF. These projections were used by the Savannah River National Laboratory (SRNL) to develop frit compositions for SB5 that will produce glasses that will be acceptable for disposition to the federal repository. The objective of this study is to experimentally measure the properties and performance of a series of glasses with compositions that are anticipated to represent SB5 as proc
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