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The controversial role of inter-diffusion in glass alteration: Implications for Current Long-Term Modeling

Abstract : 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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S. Gin, L. Neill, M. Fournier, P. Frugier, T. Ducasse, et al.. The controversial role of inter-diffusion in glass alteration: Implications for Current Long-Term Modeling. Chemical Geology, Elsevier, 2016, 440, pp.115-123. ⟨10.1016/j.chemgeo.2016.07.014⟩. ⟨cea-02381000⟩

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