Glass - Back to the Future!

Presenting Author:
Dr James Neeway

article posted 01 June 2016

Dr Neeway is a research scientist at Pacific Northwest National Laboratory. He specializes in the understanding of the long-term behavior of nuclear waste forms in geological environments. His studies have focused on secondary phase formation effects on the stability of glasses, the effect of repository near-field engineered barriers on glass durability, the diffusion of alkali metals in the glass matrix, and the relative stability of various minerals in multiphase waste forms. He has utilized several solution analytical techniques, such as in situ μ-Raman and MC-ICP-, and solids analytical techniques, such as APT and ToF-SIMS, to elucidate processes responsible for glass alteration in various environmental conditions

Recent Advances in the Understanding of Nuclear Waste Glass Durability through the Use of Stable Isotopes

Dr James Neeway
Pacific Northwest National Laboratory

Glass corrosion upon contact with an aqueous fluid is a result of many coupled processes including ion exchange, hydrolysis, matrix dissolution, condensation reactions, transport through alteration layers, and the formation of secondary phases with increased reaction progress. However, because these processes occur simultaneously, it is often difficult to identify which process or processes is/are responsible for controlling the glass corrosion rate. To this end, we have designed and performed several sets of experiments where various corrosion processes have been isolated and identified through the use of isotope tagging. In particular, the experiments have aided in 1) identification of alteration layers that form as a result of the glass alteration process, 2) parameterizing the alkali ion exchange/interdiffusion process (Fig. 1), and 3) allowed for the determination of Si partitioning between the glass alteration layer and solution in a flow-through system as a function of both time and pH (Fig. 2). In this paper, we give an overview of the results that have been obtained as a result of these experiments and we discuss how these results may be used in mathematical models that are used to calculate the glass dissolution rate at extended time periods in a geological disposal environment.

Fig. 1. Diffusion profile of Li in a glass exposed to 6LiCl/DMSO solution. Results from these experiments have been used to parameterized the alkali-alkali ion exchange process in simulant nuclear waste glasses.

Fig. 2. Evolution of 29Si/28Si as a function of time for the ISG and SON68 glasses. Results from these experiments enable the understanding of Si partitioning between the aqueous and solid phases during glass corrosion.