Role of neoformed phases on the mechanisms controlling the resumption of SON68 glass alteration in alkaline media

Ribet, Solange; Gin, Stéṕhane

doi:10.1016/j.jnucmat.2003.09.010

Cited by 121 publications

(106 citation statements)

References 20 publications

(29 reference statements)

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“…10) show that the Na-P2 zeolite seeds do not significantly dissolve over the entire pH interval studied at 90 and 30°C. This result differs from that of Ribet and Gin 9 showing the dissolution of neoformed merlinoite crystals during SON68 glass leaching in KOH solution after a pH decrease from 11.5 to 9 due to HCl addition. The stability of zeolites in a solution with respect to solubility strongly varies, depending on the nature of the mineral and the composition of the solution.…”

Section: Effect Of Seedingcontrasting

confidence: 99%

“…[3][4][5][6][7] This phenomenon is associated with the precipitation of alumino-silicate minerals, mainly from the zeolite family. [8][9][10] Understanding the origin of a RA and evaluating its consequences are major issues to predict nuclear glass long-term behavior. Under high pH and temperature conditions, it is established that zeolite precipitation maintains glass alteration at a high rate.…”

Section: Introductionmentioning

confidence: 99%

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Contribution of zeolite-seeded experiments to the understanding of resumption of glass alteration

et al. 2017

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Understanding the origin and the consequences of glass alteration regimes is necessary for the prediction of nuclear glass durability. The so-called "stage 3" or "resumption of alteration regime" of glasses used to sequester nuclear waste by vitrification, is characterized by a sudden acceleration of glass alteration rate arising from the precipitation of secondary minerals, mainly zeolites. To study this process, a promising approach is developed, based on seeding by synthesized zeolite seeds. This study quantitatively links the alteration of a six-oxide reference borosilicate glass (ISG) and the precipitation of zeolites that affects concentrations of key species-in particular aluminum-and thus the glass dissolution rate. The characterization of stage 3-easier at alkaline pH-can now be extended to pH conditions more representative of those found in a geological repository thanks to seeding that reduces, or even eliminates, the latency period preceding a resumption of glass alteration. The resumption occurrence and glass dissolution rate are related with temperature and pH. This study shows that the detrimental effect of zeolite precipitation decreases with decreasing pH and temperature, until it is no longer detectable at a pH around 9 imposed by the dissolution of the ISG glass. Even for both high temperature and high pH, the resumption rate is lower than the initial alteration rate, which remains the fastest kinetic regime.npj Materials Degradation (2017) 1:17 ; doi:10.1038/s41529-017-0018-x INTRODUCTION Like the United Kingdom, Japan, Russia and India, France has chosen to reprocess spent nuclear fuel. Ultimate waste arising from this recycling process-consisting of fission products and minor actinides-are confined by vitrification. The reference solution for the management of these waste packages over geological time scales is their storage in a deep, low-permeability and stable geological formation.In contact with water, the vitrified product of waste, usually called "nuclear glass", undergoes both dissolution and irreversible transformation into more stable phases; the rate of this transformation strongly depends on geochemical conditions. Formation of a passivating layer (also called "gel") causes the reduction of the initial alteration rate r 0 -due to the hydrolysis of the vitreous network by nucleophilic substitution of hydroxide ions-until the persistence of a residual rate. For a glass, this gel can exhibit a great variability in composition-and thus in properties-depending on the environmental parameters, in particular pH, temperature and solution composition. Gel stability and its passivation properties allow-under the most favorable conditions-a glass package lifetime of hundreds of thousands to millions of years. However, a resumption of alteration (RA, also called "stage 3" in the literature)-i.e., a sudden acceleration of the glass alteration rate-can occur.1,2 Resumptions of alteration have been observed in specific experimental conditions, particularly in alkaline environments-as a conseque...

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Section: Effect Of Seedingcontrasting

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Contribution of zeolite-seeded experiments to the understanding of resumption of glass alteration

et al. 2017

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“…There is no general agreement on the cause of this rate reduction. Two theories suggest that it is due to:(a) chemical affinity change [13,[42][43][44][45][46][47]; and(b) diffusion barrier effect [14,15,48,[51][52][53][54], or the combination of both [17,49,50].…”

Section: Rate Drop and Residual Ratementioning

confidence: 99%

“…When the concentrations of aluminium and silicon in solution high enough at high pH, nucleation and growth of zeolites at the gel/solution interface could occur, this reaction would consume dissolved aluminium and silicon in solution, result in the abstraction of Al from the protective alteration layer. Thus, the protective alteration layer would lose its passivating properties, and the rate of glass dissolution will be accelerated [48,71].…”

Section: Resumption Of Alteration(regime V)mentioning

confidence: 99%

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A mechanistic model for long-term nuclear waste glass dissolution integrating chemical affinity and interfacial diffusion barrier

Jivkov

et al. 2017

Journal of Nuclear Materials

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Abstract:Understanding the alteration of nuclear waste glass in geological repository conditions is critical element of the analysis of repository retention function. Experimental observations of glass alterations provide a general agreement on the following regimes: inter-diffusion, hydrolysis process, rate drop, residual rate and, under very particular conditions, resumption of alteration. Of these, the mechanisms controlling the rate drop and the residual rate remain a subject of dispute. This paper offers a critical review of the two most competitive models related to these regimes: affinity-limited dissolution and diffusion barrier. The limitations of these models are highlighted by comparison of their predictions with available experimental evidence. Based on the comprehensive discussion of the existing models, a new mechanistic model is proposed as a combination of the chemical affinity and diffusion barrier concepts. It is demonstrated how the model can explain experimental phenomena and data, for which the existing models are shown to be not fully adequate.Key words: nuclear waste glasses, long-term dissolution, mechanisms, modelling IntroductionRadioactivity wastes are generated at all stages of the nuclear fuel cycle, including the decommissioning of nuclear facilities, as well as from military applications. Of particular concern for the storage/disposal of radioactivity wastes are those containing long-lived radionuclides [1].The current plan ( countries such as Belgium, Finland , Sweden , France etc.)for long-term management of such wastes is to store them in deep, stable and lowpermeable geological formations [2].The storage design is based on the so-called multi-barrier concept, where several barriers prevent for a period of time, or slow down the release and migration of radionuclides through the geosphere [3,4].Within this concept, hazardous nuclides are immobilized into solidified bodies. The wasteform selection is difficult, since durability is not the sole criterion [5]. Currently, vitrification is regarded as the best solution for immobilizing radionuclides. This technology has been progressively developed over the last half-century, has matured and has become industrially robust.Data collected to date suggest that glass waste forms offer the advantages that they can accommodate a wide range of waste streams, are resistant to radiation damage, and are relatively inert to both chemical and thermal perturbations [6].The use of natural and archeological analogues supported further the durability argument of glass as waste forms [7][8][9][10][11]. Except for the alumino-phosphate glass used in Russia, the borosilicate glass has been universally selected by all other nations [12].In order to make scientifically-underpinned safety cases, the long-term behaviour of glassy wasteforms requires further understanding and assessment. Half-lives of some radionuclides extend to millions of years, requiring isolation for geological periods, while the period of investigation possible in the field and the la...

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Characterization of Alteration Phases on HLW Glasses After 15 Years of PCT Leaching

Muller

Ribet

Pegg

et al. 2006

Ceramic Transactions Series

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Role of neoformed phases on the mechanisms controlling the resumption of SON68 glass alteration in alkaline media

Cited by 121 publications

References 20 publications

Contribution of zeolite-seeded experiments to the understanding of resumption of glass alteration

Contribution of zeolite-seeded experiments to the understanding of resumption of glass alteration

A mechanistic model for long-term nuclear waste glass dissolution integrating chemical affinity and interfacial diffusion barrier

Characterization of Alteration Phases on HLW Glasses After 15 Years of PCT Leaching

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