PNNL

Abstract

The potential acceleration of the glass reaction rate after long times at low reaction rates that is termed Stage III dissolution represents a major uncertainty in long-term glass performance modeling for glass nuclear waste forms. Stage III dissolution behavior is thought to be caused by the precipitation of zeolite phases that lower the activity of the rate-controlling orthosilicic acid ion and cause the acceleration of glass dissolution. The uncertainty lies mainly in a poor understanding of the growth kinetics of these key crystalline phases. It is particularly important to understand the range of temperature and pH conditions in which Stage III behavior is possible. In this study of a high-sodium alumino-borosilicate glass, we demonstrate that Stage III glass corrosion behavior is possible at 70°C. We also, through a comparison study, confirm that seeded and unseeded Stage III corrosion rates are equivalent. This enables wide-scale testing of Stage III corrosion rates for many glass compositions in relatively short times through this technique. We also further develop the use of in-situ Raman spectroscopy monitoring of boron concentration and pH trough simple and chemometric analysis methods.