An integrated sorption–diffusion model for the calculation of consistent distribution and diffusion coefficients in compacted bentonite

Ochs, Michael F.; Lothenbach, Barbara; Wanner, Hans; Sato, Haruo; Yui, Mikazu

doi:10.1016/s0169-7722(00)00157-1

Cited by 88 publications

(59 citation statements)

References 20 publications

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“…Many researchers have developed mech-anistic diffusion models, such as the pore diffusion model that is most widely used, 11,12) the model based on the electric double layer theory, 6,13,14) and the model considering anion exclusion, 15,16) surface diffusion, [16][17][18] interlayer diffusion, [18][19][20] and Donnan equilibrium. 21) However, diffusion models for evaluation of the variable D e of anionic species depending on the montmorillonite content and porewater salinity are limited.…”

Section: Introductionmentioning

confidence: 99%

“…21) However, diffusion models for evaluation of the variable D e of anionic species depending on the montmorillonite content and porewater salinity are limited. 14,15,21) Van Loon et al 15) modeled the diffusion behavior of Cl À in compacted Volclay KWK bentonite as a function of the bulk dry density and the ionic strength of the external bulk solution. The effective diffusivity of Cl À , D e,Cl , is described as…”

Section: Introductionmentioning

confidence: 99%

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Experimental and Modeling Study on Diffusion of Selenium under Variable Bentonite Content and Porewater Salinity

Iida

Yamaguchi

Tanaka

2011

Journal of Nuclear Science and Technology

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Effective diffusion coefficients of selenium through bentonite/sand mixtures were obtained by the through-diffusion method under reducing conditions where selenium was dissolved as HSe À and Se 4 2À . Experiments were carried out under variable bentonite content and porewater salinity. Bentonite contents in bentonite/sand mixtures varied from 20 to 70 wt%. The salinities of experimental solutions varied from 0.05 to 0.5 mol dm À3 , simulating brackish groundwater and seawater. Effective diffusion coefficients were also obtained under anaerobic conditions where the dominant selenium species was determined to be SeO 3 2À . The effective diffusion coefficients of selenium species decreased with increasing bentonite content and with decreasing salinity. This tendency is primarily due to anion exclusion that was caused by the negative surface charge of montmorillonite. A diffusion model for anionic species was developed based on the electric double layer theory and the pore diffusion model, to evaluate the diffusion behaviors of HSe À , Se 4 2À , and SeO 3 2À in bentonite porewater. In this model, pores in bentonite/sand mixtures are assumed to consist of two types of space; one is the space between mineral particles and the other is the space between layers of montmorillonite. The scope of application of this model is limited to less than or equal to 1,600 kg m À3 in dry density. The effective diffusion coefficients of selenium species predicted using this model showed good agreement with experimentally measured ones.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Experimental and Modeling Study on Diffusion of Selenium under Variable Bentonite Content and Porewater Salinity

Iida

Yamaguchi

Tanaka

2011

Journal of Nuclear Science and Technology

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“…The unknown G // -value, considered to vary with 74 bentonite dry bulk density, is routinely estimated by fitting a diffusion model to experimental 75 data on the diffusion of water tracers in bentonite in the x // direction (5,14,(19)(20)(21)(22) …”

Section: Introductionmentioning

confidence: 99%

Modeling Cation Diffusion in Compacted Water-Saturated Sodium Bentonite at Low Ionic Strength

Bourg

Sposito

Bourg

2007

Environ. Sci. Technol.

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23Sodium bentonites are used as barrier materials for the isolation of landfills and are under 24 consideration for a similar use in the subsurface storage of high-level radioactive waste. The 25 performance of these barriers is determined in large part by molecular diffusion in the bentonite 26 pore space. We tested two current models of cation diffusion in bentonite against experimental 27 data on the relative apparent diffusion coefficients of two representative cations, sodium and 28 strontium. On the 'macropore/nanopore' model, solute molecules are divided into two categories, 29 with unequal pore-scale diffusion coefficients, based on location: in macropores or in interlayer 30 nanopores. On the 'surface diffusion' model, solute molecules are divided into categories based 31 on chemical speciation: dissolved or adsorbed. The macropore/nanopore model agrees with all 32 experimental data at partial montmorillonite dry densities ranging from 0.2 (a dilute bentonite 33 gel) to 1.7 kg dm -3 (a highly compacted bentonite with most of its pore space located in 34 interlayer nanopores), whereas the surface diffusion model fails at partial montmorillonite dry 35 densities greater than about 1.2 kg dm -3 . 36 37

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“…Compacted bentonite has been proposed as backfill material in many of the European repositories, because of its very low permeability (Kim et al, 1993;Muurinen, 1994;Pusch, 2001;Molera and Eriksen, 2002;Bourg et al, 2003) and its strong sorptive properties (Eriksen et al, 1999;Ochs et al, 2001), both of which will limit the release of radionuclides. The low permeability of bentonite is largely due to the fact that it contains a high percentage of Namontmorillonite, a clay that swells in water.…”

Section: Reactive-diffusive Transport In the Ebsmentioning

confidence: 99%

“…The low permeability of bentonite is largely due to the fact that it contains a high percentage of Namontmorillonite, a clay that swells in water. The very low permeability of the compacted bentonite implies that transport of radionuclides away from the waste forms will be almost exclusively by molecular diffusion, with effective diffusivities far below that in water (Madsen, 1998;Ochs et al, 2001;Bourg et al, 2007). (This of course may change in the presence of advective pathways in the bentonite, which may result from insufficient homogenization, THMC-related fracturing, erosion, long-term degradation, etc.…”

Section: Reactive-diffusive Transport In the Ebsmentioning

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...

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An integrated sorption–diffusion model for the calculation of consistent distribution and diffusion coefficients in compacted bentonite

Cited by 88 publications

References 20 publications

Experimental and Modeling Study on Diffusion of Selenium under Variable Bentonite Content and Porewater Salinity

Experimental and Modeling Study on Diffusion of Selenium under Variable Bentonite Content and Porewater Salinity

Modeling Cation Diffusion in Compacted Water-Saturated Sodium Bentonite at Low Ionic Strength

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

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