Evaluation of novel leaching assessment of nuclear waste glasses
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Evaluation of novel leaching assessment of nuclear waste glasses Clare L. Thorpe1, Russell J. Hand1, Neil C. Hyatt1, Albert A. Kruger2, David S. Kosson3, Michael J. Schweiger4, Brian J. Riley4, Claire L. Corkhill1 1Immobilisation
Science Laboratory, Department of Materials Science and Engineering, University of Sheffield, S1 3JD, U.K. 2U.S. Department of Energy, Office of River Protection, Richland, WA 99352 3Vanderbilt University, School of Engineering, 2301 Vanderbilt Place, Nashville, TN, US 37235 4Pacific Northwest National Laboratory, Richland, WA 99354 ABSTRACT This study investigates the use of ‘simple’ glasses, comprising six components, to represent the structure of complex LAW glasses proposed for Immobilized Low Activity Wastes from the Hanford site in the USA. The 18 elements present in ILAW glasses LAW A44, ORP LB2, and LAW A23 were represented by Al2O3, B2O3, CaO, Na2O, SiO2, and ZrO2 according to their coordination chemistry and their roles as network formers and modifiers. The dissolution behavior of each ‘simple’ glass was compared to its corresponding candidate “complex” LAW glass through PCT-B tests. Significant differences were observed; the durability of complex glasses was concluded to be LAW A44 > ORP LB2 ≥ LAW A23 whereas in their simplified versions the order was LAW A44 > LAW A23 > ORP LB2. These results are discussed in relation to compositional differences and highlight the importance of minor glass components in controlling glass durability. The implications of these results for the use of simplified glass compositions are discussed. INTRODUCTION At the Hanford site in the USA, low activity tank wastes will be immobilized by vitrification to create > 160,000 m3 of Immobilized Low Activity Waste (ILAW) destined for disposal in a shallow subsurface Integrated Disposal Facility (IDF) [1]. During waste reprocessing, tank wastes have a separable low activity waste fraction that will be sent to the LAW facility for treatment by vitrification. Radionuclides of concern in LAW glasses will include 154Eu, 99Tc and 90Sr alongside toxic metal contaminants. Conditions in the IDF are expected to differ from those within a deep geological disposal facility for high-level waste (HLW) with temperatures expected to be ~ 15o C, an arid climate with low infiltration rates (e.g., < 10 mm/y), variable pH and groundwater flow rates. The GLAD (Glass Leaching Assessment for Disposability) project is aimed to investigate newly developed leaching technologies for assessing the durability of ILAW glasses. New methodologies developed by the U.S. Environmental Protection Agency as the Leaching Environmental Assessment Framework (LEAF) Methods 1313 and 1315 are being considered for application [2,3,4]. ILAW glasses are compared to established leaching tests accepted for evaluation of HLW glasses (planned for deep geological repositories), including Product Consistency Test (PCT) and Materials Characterization Centre Static Leech Test (MCC-1) protocols. The GLAD project studies the process of glass dissolution and con
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