Current kinetic models for nuclear waste glasses (e.g. GM2001, GRAAL) are based on a set of mechanisms that have been generally agreed upon within the international waste glass community. These mechanisms are: hydration of the glass, ion exchange reactions (the two processes are referred as inter-diffusion), hydrolysis of the silicate network, and condensation/precipitation of partly or completely hydrolyzed species that produces a gel layer and crystalline phases on surface of the altered glass. Recently, a new idea with origins in the mineral dissolution community has been proposed that excludes inter-diffusion process as a potential rate-limiting mechanism. To understand how the so-called interfacial dissolution/precipitation model can change the current understanding of glass behavior, an in-depth review of the current knowledge with a special focus on inter-diffusion processes is considered. Also discussed is how experimental conditions change the predominant mechanisms and how one model may not be sufficient to explain the glass dissolution behavior under a wide range of geochemical conditions. In addition to the review of the above subjects, a key experiment used to account for the interfacial dissolution/precipitation model was replicated to further revisit the interpretation. It is concluded that the selected experiment design may lead to ambiguous conclusions and that, under the conditions investigated (dilute conditions, deionized water), evidence of inter-diffusion exists.

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Understanding composition-structure-property relationships of high-alumina nuclear waste glasses are important for vitrification of nuclear waste at the Hanford Site. Two series of glasses were designed, one with varying Al:Si ratios and the other with (Al + Na):Si ratios based on the international simple glass (ISG, a simplified nuclear waste model glass), with Al 2 O 3 ranging from 0 to 23 mol% (0 to 32 wt%). The glasses were synthesized and characterized using electron probe microanalysis, X-ray photoelectron spectroscopy, small angle X-ray scattering, high-temperature oxide melt solution calorimetry, and infrared spectroscopy. Glasses were crystal free, and the lowest Na 2 O and Al 2 O 3 glass formed an immiscible glass phase. Evolution of various properties-glass-transition temperature, percentage of 4-coordinated B, enthalpy of glass formation-and infrared spectroscopy results indicate that structural effects differ based on the glass series.

High-alumina containing high-level waste (HLW) will be vitrified at the Waste Treatment Plant at the Hanford Site. The resulting glasses, high in alumina, will have distinct composition-structure-property (C-S-P) relationships compared to previously studied HLW glasses. These C-S-P relationships determine the processability and product durability of glasses and therefore must be understood. The main purpose of this study is to understand the detailed structural changes caused by Al:Si and (Al + Na):Si substitutions in a simplified nuclear waste model glass (ISG, international simple glass) by combining experimental structural characterizations and molecular dynamics (MD) simulations. The structures of these two series of glasses were characterized by neutron total scattering and 27 Al, 23 Na, 29 Si, and 11 B solid-state nuclear magnetic resonance (NMR) spectroscopy. Additionally, MD K E Y W O R D S aluminosilicates, borosilicate glass, international simple glass, molecular dynamics, nuclear magnetic resonance, scattering F I G U R E 1 Neutron total scattering structure factor spectra obtained from (A-B) experimental data and (C-D) MD simulation for (A, C) ISG-An and (B, D) ISG-AnN glasses.

Stage III glass dissolution, the occasionally observed tendency for accelerated aqueous corrosion after extensive time spent at low reaction rates, is a major area of technical uncertainty in long-term glass performance modeling for vitreous nuclear waste forms. Stage III dissolution behavior is thought to be caused by the precipitation of zeolite phases that lower the activity of the ratecontrolling 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 impact of temperature and pH conditions on Stage III behavior. Accurate analysis of this phenomenon is complicated by the typically very long (e.g., years), and variable length of the induction period preceding the onset of Stage III behavior. In this study of a high-sodium aluminoborosilicate glass, we demonstrate the ability to initiate the onset of Stage III behavior in a controllable fashion so as to both reduce the time delay of the incubation period, and to also be able to initiate Stage III dissolution in controlled conditions. In this case, we demonstrate that Stage III glass corrosion behavior is possible at 70°C, a lower temperature than previously observed (90°C), even in an unseeded experiment. We confirm, through a comparison study, 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 report further development of the use of in situ Raman spectroscopy monitoring of boron concentration and pH through simple and chemometric analysis methods.