Vapor hydration of a simulated borosilicate nuclear waste glass in unsaturated conditions at 50 °C and 90 °C

Chaou, Abdelouahed Ait; Abdelouas, Abdesselam; Mendili, Yassine El; Bouakkaz, Rachid; Utsunomiya, Satoshi; Martin, Christelle; Bourbon, Xavier

doi:10.1039/c5ra12384d

Cited by 24 publications

(22 citation statements)

References 53 publications

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“…One important step to determining their behavior in a variety of systems whether biological or environmental is to understand their interaction with water (Conradt, 2008;Filgueras et al, 1993;Morin et al, 2015). Glass is also being considered as a containment matrix for high, intermediate, and low level radioactive waste arising from the reprocessing of spent nuclear fuel by many countries (Chaou et al, 2015;Ojovan and Lee, 2011;Pierce et al, 2008). The geological storage of nuclear waste in general, and glass in particular, is under consideration worldwide and it is admitted that the fate of radionuclides and their impact on the biosphere is strongly tied to waste forms alteration by ground waters.…”

Section: Introductionmentioning

confidence: 99%

The controversial role of inter-diffusion in glass alteration

et al. 2016

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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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Section: Introductionmentioning

confidence: 99%

The controversial role of inter-diffusion in glass alteration

et al. 2016

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“…Recent studies carried out on nuclear glass in the presence of water vapor have highlighted the significant impact of vapor on glass alteration with substantial hydration depth and secondary phases precipitation. 13,15,[27][28][29] Nevertheless, it seems that there is no study assessing the role of the altered layer under these conditions. This question has also to be addressed in the case of stained-glass windows that are submitted to alternating saturated and unsaturated conditions for several centuries.…”

Section: +mentioning

confidence: 99%

“…In the unsaturated medium, hydration and interdiffusion are considered to be major glass-alteration mechanisms. [13][14][15] Many studies have focused on the formation of the glassalteration layer and its protective or passivating (hampering further alteration) character, in particular, for nuclear glasses, since highly radioactive wastes are vitrified and intended to be buried in geological storage. [15][16][17] Some of these works have highlighted a progressive pore closure and a change in the pore solution that decreases species diffusion within the alteration layer, and thus the alteration rate.…”

Section: +mentioning

confidence: 99%

“…[13][14][15] Many studies have focused on the formation of the glassalteration layer and its protective or passivating (hampering further alteration) character, in particular, for nuclear glasses, since highly radioactive wastes are vitrified and intended to be buried in geological storage. [15][16][17] Some of these works have highlighted a progressive pore closure and a change in the pore solution that decreases species diffusion within the alteration layer, and thus the alteration rate. 8,[18][19][20][21][22][23][24][25][26] This pore clogging is explained by the reorganization of the altered layer by hydrolysis and condensation of silicon.…”

Section: +mentioning

confidence: 99%

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Long-term weathering rate of stained-glass windows using H and O isotopes

et al. 2018

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The understanding of glass alteration is a biogeochemical, industrial, societal (radioactive waste confinement), and cultural heritage issue. Studies have been mainly performed in aqueous conditions. However, glass reactivity under hydraulically unsaturated conditions may be more important than previously recognized. In this context, we evaluate here the role of the alteration layer formed on medieval stained-glass windows on the ongoing alteration in unsaturated conditions. H 2 O adsorption isotherms were measured to study the relation between the vapor sorption and the relative humidity inside the alteration layer. From it, the average pore radius was calculated, yielding a water vapor diffusion coefficient of 7.8 × 10 -7 m² s -1 inside the pore network. Experiments using doped water vapor (D 2 18 O) confirm the vapor transport up to the alteration front via fractures and pore network. They also demonstrate that the alteration mainly progresses via an interdiffusion mechanism. The calculated interdiffusion coefficients at 20°C are 3.6 × 10 -20 m 2 s -1 at 70% RH and 4.9 × 10 -20 m 2 s -1 at 90% RH, which is similar to the values measured on model stained-glass samples altered in short durations (1-4 years). Therefore, this study highlights that, given its morphology, the alteration layer is not protective against vapor transport and interdiffusion.

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“…An evaluation of glass alteration under repository conditions has already been performed in contact with deionized water in unsaturated conditions, but alteration studies in cementitious media are scarce. [26][27][28] Countries such as Belgium, the United Kingdom and France are currently involved in such studies. [29][30][31] In Belgium, an engineering barrier system concept is designed to place vitried HLW in a super-container constituted of a carbon steel over-pack surrounded by a Portland cement concrete buffer, with the overall setup enveloped by an outer stainless-steel liner.…”

Section: Introductionmentioning

confidence: 99%