Effect of Dry Density on Diffusion of Some Radionuclides in Compacted Sodium Bentonite

Sato, Haruo; Ashida, Takashi; Kohara, Y.; Yui, Mikazu; Sasaki, Noriaki

doi:10.1080/18811248.1992.9731607

Cited by 115 publications

(28 citation statements)

References 4 publications

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“…To determine the ratio Γ of Re (VII) in experiment, we need to predict the D e of HTO in the same clays. At the compacted dry density of 1,600 kg/m 3 , D e of HTO was reported around 1.1 × 10 −10 m 2 /s in GMZ bentonite (Wu, Dai, et al, 2012) and around 0.95 × 10 −10 m 2 /s in Na‐bentonite (Sato et al, 1992). It was 1.0 × 10 −10 to 1.8 × 10 −10 m 2 /s in compacted clay at dry density of 1,550 kg/m 3 (Tachi et al, 2011).…”

Section: Resultsmentioning

confidence: 99%

“…Since the pore size is very small, many studies have shown that the diffusion process dominates the transportation of radionuclides in bentonite buffer (Idiart & Pękala, 2016; Tournassat & Appelo, 2011; Van Loon et al, 2007). Radionuclides diffusion is influenced by many factors, such as dry densities of bentonite (Sato et al, 1992; Wu et al, 2018), salinities and compositions of pore solution (Glaus et al, 2020; Tachi & Yotsuji, 2014; Wigger & Van Loon, 2018), and sizes and shapes of clay particles (Tertre et al, 2018).…”

Section: Introductionmentioning

confidence: 99%

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Anion Diffusion in Compacted Clays by Pore‐Scale Simulation and Experiments

Yang

Wang

et al. 2020

Water Resources Research

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Accurate understanding of diffusion of anionic radionuclides in different clays is significant to predict long-term performance of high-level radioactive waste (HLW) repositories. The importance of electrical double layer (EDL) on anionic tracer diffusion in different clays has been studied by both through-diffusion experiments and pore-scale simulations in this work. The through-diffusion experiments measured the effective diffusion coefficient and the accessible porosity of Re (VII) in compacted montmorillonite, Na-bentonite, and illite/smectite mixed layer (I/S) at different salinities. The results showed that the accessible porosity and the effective diffusion coefficient of Re (VII) in montmorillonite and Na-bentonite were similar but lower than those in I/S under the same conditions. For mechanism analysis and predictions, a pore-scale modeling was implemented to simulate the diffusion of anions in compacted clays. In the simulations, the characteristics (porosity, density, and total surface area) of microstructures of montmorillonite and I/S were used to regenerate three-dimensional pore structures numerically by a Quartet Structure Generation Set method. The Re (VII) diffusion was then simulated by directly solving coupled Poisson-Nernst-Planck equations via the lattice Boltzmann method. The diminished effect of EDL was therefore calculated and compared with Donnan and multiporosity models. As EDLs overlap in compacted clays, the Donnan model overestimates the influence of EDL on Re (VII) diffusion, while the multiporosity model underestimates it. The pore-scale modeling, which captures the structure of overlapping EDLs automatically, can simulate the diffusion of anionic radionuclides in compacted clays without any fitting parameters.

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Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Anion Diffusion in Compacted Clays by Pore‐Scale Simulation and Experiments

Yang

Wang

et al. 2020

Water Resources Research

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“…In all of the approaches to characterizing the porosity of bentonite, the most important factor controlling the material microstructure is density (Sato et al , 1992; Marcial et al , 2006; Muurinen et al , 2013). It is expected that the degree of compaction affects the pore structure, but the following results show the finer influence of purification and chemical conditions observed with various methods.…”

Section: Resultsmentioning

confidence: 99%

Comparison of microstructural features of three compacted and water-saturated swelling clays: MX-80 bentonite and Na- and Ca-purified bentonite

Matusewicz

Olin

2019

Clay miner.

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The planned final disposal repositories of spent nuclear fuel in several countries, including Finland, pose significant scientific challenges due to their extremely long lifespan. One of the key materials proposed for use in Posiva Oy's repository in Finland is MX-80 bentonite in a compacted, water-saturated state. Border cases of calcium and sodium forms of purified bentonite were included in this study. The MX-80 in the repository is expected to undergo cation exchange due to the composition of the groundwater. The clays were studied at different dry densities between 0.7 and 1.6 g cm -3 . The microstructure of the water-saturated, compacted clays was investigated using small-angle X-ray scattering, nuclear magnetic resonance and transmission electron microscopy. Additionally, atomic force microscopy was used to characterize the shape and size of the fine-fraction clay platelets. As expected, the average shape of the fine fractions was smaller than the bulk material, but a more elongated shape was present in the purified material. Mainly due to sample density, the pore structure was noticeably different for the Na form of purified bentonite at 0.7 g cm -3 density, but at higher degrees of compaction, no significant differences were noted between the samples. The laboratory results obtained in this study could be useful for safety and performance analysis of this high-level waste repository where sodium bentonite is used and is expected to change its charge-compensating cation composition during the repository's lifetime. Microstructural data may be used in modelling of diffusion and sorption by surface complexation modelling, for example, or as a basis for mechanical and water transport models.

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“…[67] This affirmation is reinforced by measurements of effective iodide diffusion coefficients. In high-density materials, chloride and iodide have very similar behavior with respect to diffusion [Kozaki et al, 1998;Sato et al, 1992]. Iodide D e measurements performed using diffusion-permeation experiments [Pocachard et al, 1998] range between 1.4 and 2.4 Â 10 À13 m 2 s À1 , and reflect the extremely slow diffusion properties for chemical species in Tournemire argillites and marls.…”

Section: Reliability Of Method: Comparison With Results On Other Claymentioning

confidence: 99%

Diffusion as the main process for mass transport in very low water content argillites: 1. Chloride as a natural tracer for mass transport—Diffusion coefficient and concentration measurements in interstitial water

Patriarche

Michelot

Ledoux

et al. 2004

Water Resources Research

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[1] Argillites are one of the rock types studied by French authorities for their confining properties for the isolation of radioactive wastes. One of the main objectives of such study is the better understanding of water transport through rocks with very low water content and hydraulic conductivity, using modeling of tracer profiles. This article presents the protocol developed and applied for acquiring data on chloride in interstitial water of the Toarcian argillites in Tournemire (southern France). This protocol is based on laboratory experiments involving diffusion process and on modeling. Experimental data obtained during transient and steady parts of diffusion allow for the assessment of the diffusion coefficient and initial concentration in pore water, respectively. Profiles for both have been acquired along the geological sequence; they are used in part 2 of this article for proposing a hydrogeological model where diffusion appears to be the main process for mass transport through the argillites and for comparing deuterium and chloride transport.

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Effect of Dry Density on Diffusion of Some Radionuclides in Compacted Sodium Bentonite

Cited by 115 publications

References 4 publications

Anion Diffusion in Compacted Clays by Pore‐Scale Simulation and Experiments

Anion Diffusion in Compacted Clays by Pore‐Scale Simulation and Experiments

Comparison of microstructural features of three compacted and water-saturated swelling clays: MX-80 bentonite and Na- and Ca-purified bentonite

Diffusion as the main process for mass transport in very low water content argillites: 1. Chloride as a natural tracer for mass transport—Diffusion coefficient and concentration measurements in interstitial water

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