Long-term product consistency test of simulated 90-19/Nd HLW glass

Gan, Xueying; Zhang, Z.T.; Yuan, Weifeng; Wang, L.; Bai, Yunlong; Ma, Hassan

doi:10.1016/j.jnucmat.2010.11.020

Cited by 13 publications

(7 citation statements)

References 12 publications

(17 reference statements)

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“…52,53 These observations are consistent with the industrial synthesis of zeolites for which the rise in temperature reduces the latency period preceding crystal growth and accelerates the crystallization rate.…”

Section: Effect Of Temperaturesupporting

confidence: 79%

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 Temperaturesupporting

confidence: 79%

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

et al. 2017

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“…This stage is observed in some experiments [69], where the rate accelerates, apparently as the result of the formation of new crystalline phases(e.g. zeolites).…”

Section: Resumption Of Alteration(regime V)mentioning

confidence: 71%

“…(12) is because both reactions are controlled by water diffusion. As the retention in alteration layers can be negligible, B is more suitable than Na as the glass alteration tracer [69], especially in long-term conditions.…”

Section: 2 Model Equationsmentioning

confidence: 99%

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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“…In addition, the LR B of glass‐ceramics Nd‐2 and Nd‐6 is about 7.0 × 10 −3 g·m −2 ·d −1 after 42 days, which is the same order of magnitude as that of calcium aluminosilicate residual glass and zirconolite glass‐ceramics reported by Martin et al Since the reactive B element is easier to diffuse, the LR B is higher than both LR Ca and LR Nd . Furthermore, the sample Nd‐6 possesses a lower value of LR Nd (~4.4 × 10 −6 g·m −2 ·d −1 ) than that of 90–19/Nd borosilicate glass waste forms, which was developed to immobilize HLLW in China in the early 1990s . The sample Nd‐8 possesses the higher values of LR B and LR Nd , which might be due to its more friable structure and lower density of the samples.…”

Section: Resultsmentioning

confidence: 99%

Effects of Nd Content on Structure and Chemical Durability of Zirconolite–Barium Borosilicate Glass‐Ceramics

Wang

et al. 2016

J. Am. Ceram. Soc.

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The effects of Nd2O3 content (0–12 wt %) on crystalline phases, microstructure, and chemical durability of barium borosilicate glass‐ceramics belonging to SiO2–B2O3–Na2O–BaO–CaO–TiO2–ZrO2–Nd2O3 system were studied. The results show that the glass‐ceramics with 2–6 wt% of Nd2O3 possess mainly zirconolite and titanite phases along with a small amount baddeleyite phase in the bulk. Calcium titanate appears when the Nd2O3 content increases to 8 wt%, and the amount of quadrate calcium titanate crystals increases with further increasing content of Nd2O3. For the glass‐ceramics with 6 wt% Nd2O3 (Nd‐6), Nd elements homogeneously distribute in zirconolite, titanite, and residual glass phases. There is a strong enrichment of Nd in calcium titanate crystals for the sample with 10 wt% Nd2O3. The viscosity of Nd‐6 glass is about 49 dPa·s at 1150°C. Moreover, Nd‐6 glass‐ceramics show the lower normalized leaching rates of B (LRB), Ca (LRCa), and Nd (LRNd) when compared to that of the sample with 8 wt% Nd2O3. After 42 days, LRB, LRCa, and LRNd of the Nd‐6 glass‐ceramics are about 6.8 × 10−3, 1.6 × 10−3, and 4.4 × 10−6 g·m−2·d−1, respectively.

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Long-term product consistency test of simulated 90-19/Nd HLW glass

Cited by 13 publications

References 12 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

Effects of Nd Content on Structure and Chemical Durability of Zirconolite–Barium Borosilicate Glass‐Ceramics

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