Compositional Effects on the Long-Term Durability of Nuclear Waste Glasses: A Statistical Approach

Abstract

AbstractAs 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 long-term 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.