Compositional Effects on the Long-Term Durability of Nuclear Waste Glasses: A Statistical Approach
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Compositional Effects on the Long-Term Durability of Nuclear Waste Glasses: A Statistical Approach Solange Ribet1, Isabelle S. Muller1, Ian L. Pegg1, Stéphane Gin2 and Pierre Frugier2 1 Vitreous State Laboratory, The Catholic University of America, Washington, D.C. 20064, USA [email protected] 2 CEAValRho DTCD/SECM/LCLT BP17171 30207 Bagnols-sur-Cèze, France ABSTRACT As a result of the development of a reference glass formulation for the immobilization of West-Valley nuclear waste, a large number of glass compositions have been tested under a variety of leaching conditions for extended durations. In this work, data from the standard PCT leaching procedure (deionized water, 90°C, S/V = 2000 m-1) are evaluated for a subset of 98 of these glasses, for which the alteration times extend up to fifteen years. Analysis of the leachate data over this extended period has led to a classification of the glass compositions according to their PCT behavior, as characterized by the boron release in solution, the decrease in the rate of alteration, or the occurrence of a resumption of alteration. Three types of behavior are associated with a normalized mass loss of boron after 100 days of around 1, 2, or 5 g m-2 respectively, and a ratio of the rate of alteration at 7 days to the rate at 1000 days of about 30. A fourth type is characterized by a much larger decrease between the rates at 7 and 1000 days with a ratio exceeding 120. Four further categories are associated with late-stage resumption of glass alteration. A statistical analysis of the data has been used to model the leachate data as a function of glass composition. The effects of seven major elements (Si, B, Al, Li, Na, K, Fe) on the longterm glass durability have been studied. As a result of this analysis, the different types of leaching behaviors can be predicted with a good reliability from the composition of the pristine glass.
INTRODUCTION During research performed to support the vitrification of West-Valley high-level nuclear waste, numerous glass compositions have been tested at the Vitreous State Laboratory (VSL) at The Catholic University of America. Many types of composition variations were investigated, including simple one- or two-component variations, to support the selection of a West-Valley reference glass composition and the determination of suitable limits around it. That work led directly to the selection of the glass that was produced at the West-Valley site; vitrification has now been successfully completed and the facility is being decommissioned. The large amount of leaching data that has been collected at VSL allows a more global interpretation of the compositional effects. The leach tests on the 98 glasses studied herein were started between 1989 and 1994 and are still in progress, giving 10 to 15 years of alteration. For the data set considered here, the same (standard) test conditions were employed and therefore the differences in the results reflect only the compositional effects. The principal objective of the present work was to i
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