Effect of homogenization on the microstructure and exclusion of chloride in compacted bentonite

Muurinen, Arto; Karnland, Ola; Lehikoinen, Jarmo

doi:10.1016/j.pce.2006.02.058

Cited by 29 publications

(36 citation statements)

References 6 publications

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“…Since neither the individual activity coefficient values nor the Donnan potential is accessible experimentally, y cannot be constrained independently. Similarly, macroscopic anion-exclusion data can be fitted with the MGC or MEP model by adjusting the pore-size distribution or the distance of closest approach of ions to the clay surface (Muurinen et al, 2007;Tournassat and Appelo, 2011;Tournassat et al, 2016). Independent information must, therefore, be sought that can be used to test these modeling approaches.…”

Section: Discussionmentioning

confidence: 99%

“…However, three recent studies that quantified anion exclusion in clay interlayers by MD simulation have yielded contradictory results: one concluded that interlayer water can be treated as having the same aqueous chemistry as bulk liquid water (Hedström and Karnland, 2012), whereas two others reached the opposite conclusion, that anion exclusion in clay interlayers is much greater than would be expected based on the aqueous chemistry of bulk liquid water (Rotenberg et al, 2007b;Hsiao and Hedströ m, 2015). Consequently, the correct way in which to account for anion exclusion in macroscopic models of ion migration in clay formations and engineered clay barriers remains uncertain (Muurinen et al, 2007;Birgersson and Karnland, 2009;Appelo et al, 2010;Tournassat and Appelo, 2011). The present study aimed to resolve the differences among previous MD simulations.…”

Section: Introductionmentioning

confidence: 97%

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Molecular Dynamics Simulations of Anion Exclusion in Clay Interlayer Nanopores

Tournassat

Bourg

Holmboe

et al. 2016

Clays and clay miner.

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Abstract-The aqueous chemistry of water films confined between clay mineral surfaces remains an important unknown in predictions of radioelement migration from radioactive waste repositories. This issue is particularly important in the case of long-lived anionic radioisotopes ( 129 I À , 99 TcO 4 À , 36 Cl À ) which interact with clay minerals primarily by anion exclusion. For example, models of ion migration in clayey media do not agree as to whether anions are completely or partially excluded from clay interlayer nanopores. In the present study, this key issue was addressed for Cl À using MD simulations for a range of nanopore widths (6 to 15 Å ) overlapping the range of average pore widths that exists in engineered clay barriers. The MD simulation results were compared with the predictions of a thermodynamic model (Donnan Equilibrium model) and two pore-scale models based on the Poisson-Boltzmann equation under the assumption that interlayer water behaves as bulk liquid water. The simulations confirmed that anion exclusion from clay interlayers is greater than predicted by the pore-scale models, particularly at the smallest pore size examined. This greater anion exclusion stems from Cl À being more weakly solvated in nano-confined water than it is in bulk liquid water. Anion exclusion predictions based on the PoissonBoltzmann equation were consistent with the MD simulation results, however, if the predictions included an ion closest approach distance to the clay mineral surface on the order of 2.0 Ô 0.8 Å . These findings suggest that clay interlayers approach a state of complete anion exclusion (hence, ideal semi-permeable membrane properties) at a pore width of 4.2 Ô 1.5 Å .

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Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 97%

Molecular Dynamics Simulations of Anion Exclusion in Clay Interlayer Nanopores

Tournassat

Bourg

Holmboe

et al. 2016

Clays and clay miner.

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“…The excess of cations in the DDL gives an increase of the concentration gradient in the free (uncharged) pores and thus, diffusion of cations is enhanced (Van Schaik et al, 1966;Kemper and Quirk, 1972;Ochs et al, 1998Ochs et al, , 2001Lehikoinen et al, 1999;Leroy and Revil, 2004;Leroy et al, 2006;Appelo and Wersin, 2007;Jougnot et al, 2009). Also, the deficit of anions in the DDL explains why anions diffuse more slowly (Lehikoinen et al, 1999;Ochs et al, 2001;Leroy et al, 2006;Jougnot et al, 2009), and why the accessible porosity is smaller for anions than for cations (Bolt and De Haan, 1982;Muurinen et al, 2004Muurinen et al, , 2007Van Loon et al, 2007).…”

Section: Introductionmentioning

confidence: 99%

Multicomponent diffusion of a suite of tracers (HTO, Cl, Br, I, Na, Sr, Cs) in a single sample of Opalinus Clay

Appelo¹,

Loon²,

Wersin³

2010

Geochimica et Cosmochimica Acta

194

176

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“…The volume of interlayer water has been measured as a function of the degree of compaction as reflected in the dry density (Muurinen, 2007). Strictly speaking, these results apply to montmorillonite with a large number of montmorillonite unit cells stacked on top of each other, since the interlayer porosity goes to zero as the grains become disperse.…”

Section: Formulation For Montmorillonite Interlayer Watermentioning

confidence: 99%

“…It was noted by Kosaki (1998) that a transition from 3 to 2 layer hydrates (corresponding to d001 spacing of 1.88 and 1.56 nm) occurred as the dry density increased from 1300 to 1600 kg/m 3 . This led Muurinen et al (2007) to propose an increase in interlayer spacing (in units of meters): where 2  is the tortuosity and D free is the diffusion coefficient in pure water. This suggested that free water disappeared from a compacted bentonite once the dry density reached a value of about 1800 kg/m 3 , in good agreement with the results of Kim et al (1993).…”

Section: Formulation For Montmorillonite Interlayer Watermentioning

confidence: 99%

Disposal systems evaluations and tool development : Engineered Barrier System (EBS) evaluation.

Rutqvist¹,

Liu²,

Steefel³

et al. 2011

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Eric Sonnenthal (LBNL) Engineered Barrier System (EBS) Evaluation This page is intentionally left blank Engineered Barrier System (EBS) Evaluation 5 Executive SummaryKey components of the nuclear fuel cycle are short-term storage and long-term disposal of nuclear waste. The latter encompasses the immobilization of used nuclear fuel (UNF) and radioactive waste streams generated by various phases of the nuclear fuel cycle, and the safe and permanent disposition of these waste forms in geological repository environments. The engineered barrier system (EBS) plays a very important role in the long-term isolation of nuclear waste in geological repository environments. EBS concepts and their interactions with the natural barrier are inherently important to the long-term performance assessment of the safety case where nuclear waste disposition needs to be evaluated for time periods of up to one million years. Making the safety case needed in the decision-making process for the recommendation and the eventual embracement of a disposal system concept requires a multi-faceted integration of knowledge and evidence-gathering to demonstrate the required confidence level in a deep geological disposal site and to evaluate longterm repository performance.The focus of this report is the following:• Evaluation of EBS in long-term disposal systems in deep geologic environments with emphasis on the multi-barrier concept;• Evaluation of key parameters in the characterization of EBS performance;• Identification of key knowledge gaps and uncertainties;• Evaluation of tools and modeling approaches for EBS processes and performance.The above topics will be evaluated through the analysis of the following:• Overview of EBS concepts for various NW disposal systems;• Natural and man-made analogs, room chemistry, hydrochemistry of deep subsurface environments, and EBS material stability in near-field environments;• Reactive Transport and Coupled Thermal-Hydrological-Mechanical-Chemical (THMC) processes in EBS;• Thermal analysis toolkit, metallic barrier degradation mode survey, and development of a Disposal Systems Evaluation Framework (DSEF).This report will focus on the multi-barrier concept of EBS and variants of this type which in essence is the most adopted concept by various repository programs. Empasis is given mainly to the evaluation of EBS materials and processes through the analysis of published studies in the scientific literature of past and existing repository research programs. Tool evaluations are also emphasized, particularly on THCM processes and chemical equilibria. Although being an increasingly important aspect of NW disposition, short-term or interim storage of NW will be briefly discussed but not to the extent of the EBS issues relevant to disposal systems in deep geologic environments. Interim storage will be discussed in the report Evaluation of Storage Concepts FY10 Final Report (Weiner et al. 2010). Engineered Barrier System (EBS) Evaluation 6This page is intentionally left blank Engineered Barrier System (EBS) Eva...

show abstract

Effect of homogenization on the microstructure and exclusion of chloride in compacted bentonite

Cited by 29 publications

References 6 publications

Molecular Dynamics Simulations of Anion Exclusion in Clay Interlayer Nanopores

Molecular Dynamics Simulations of Anion Exclusion in Clay Interlayer Nanopores

Multicomponent diffusion of a suite of tracers (HTO, Cl, Br, I, Na, Sr, Cs) in a single sample of Opalinus Clay

Disposal systems evaluations and tool development : Engineered Barrier System (EBS) evaluation.

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