Obtaining the porewater composition of a clay rock by modeling the in- and out-diffusion of anions and cations from an in-situ experiment

Appelo, C.A.J.; Vinsot, Agnès; Mettler, S.; Wechner, Stefan

doi:10.1016/j.jconhyd.2008.07.009

Cited by 83 publications

(76 citation statements)

References 39 publications

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“…Using Equation 2, the derived I -1 concentration in pore water is between 24 and 38 µmol L -1 . This is in agreement with the value estimated by Appelo et al (2008) The main reservoir for iodine* is the carbonate fraction, in agreement with the findings obtained on size fractions of the reference sample (Figure 4) and on iodine* distribution at the formation scale ( Figure 5). This finding is potentially in conflict with the usual assumption that iodine* is mainly associated with the organic matter of rock or sediment (Schlegel et al 2006, Tournassat et al 2007.…”

Section: Chemical Sequential Extractionsupporting

confidence: 93%

“…In the following, when the redox state cannot be specified, the notation iodine* will be used. Soluble iodine* will probably exhibit its -1 valence state as the iodide anion (I -) in clayey formations such as Callovian-Oxfordian (COx, France), Opalinus Clay (OPA, Switzerland) or Boom Clay (Belgium), according to the near-neutral pH and low redox potential of these media (Pearson and Waber, 2001;Pearson et al, 2003;Gaucher et al, 2006;Appelo et al, 2008;Gaucher et al, accepted). Due to the inherent negative surface charge of clay rock minerals at near neutral and basic pH conditions, I -is repelled from their surface and most…”

Section: Underground Nuclear Waste Disposal In Clayey Formations Is Umentioning

confidence: 99%

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Natural iodine in a clay formation: Implications for iodine fate in geological disposals

Claret

Lerouge

Laurioux

et al. 2010

Geochimica et Cosmochimica Acta

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Iodine is one of the most problematic radioisotopes in the context of nuclear waste geological disposal due to its high mobility. Considerable effort has been dedicated to the measurement of its potential retardation during diffusive transport leading to conflicting results, from no retardation to significant retardation, leading in turn to considerable debate. The present study aims at providing new insights into this aspect of the iodine problem by careful quantification of iodine reservoirs in the Callovian-Oxfordian (COx) clay rock taken here as model material for these studies. The present study confirmed the ubiquitous presence of iodine at 1-5 mg kg -1 level in the COx clayey formation. The iodide concentration level in the porewater is also confirmed at a value in the range ~20-40 µmol L -1 , i.e. higher than the expected range of radio-iodine concentration in the far-field of the storage. Surprisingly, most of the iodine was found not to be associated with organic matter but rather in an inorganic form associated with carbonate minerals. This result has potentially significant implications for the fate of radio-iodine. In undisturbed far-field conditions, most natural iodine would not be accessible for isotopic exchange with radioactive iodine, reducing the effective Kd to negligible values. During laboratory experiments, good monitoring of the geochemical parameters (at least the Eh, pH, P CO2 , [Ca] and [Mg]) is mandatory to avoid iodine-bearing carbonate precipitation and to enable rigorous interpretation of the iodide diffusion/retention experiments.2

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Section: Chemical Sequential Extractionsupporting

confidence: 93%

Section: Underground Nuclear Waste Disposal In Clayey Formations Is Umentioning

confidence: 99%

Natural iodine in a clay formation: Implications for iodine fate in geological disposals

Claret

Lerouge

Laurioux

et al. 2010

Geochimica et Cosmochimica Acta

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“…Andra, 2005;Bradbury and Baeyens, 2003a;Yu and Neretnieks, 1997) and knowledge of the porosities accessible to the different contaminants is a prerequisite for the development of transport models. The contaminants behave differently according to their localisation (Appelo and Wersin, 2007;Appelo et al, 2008). In the bulk water, both cations and anions can be transported by diffusion and are not affected by the surface.…”

Section: Introductionmentioning

confidence: 99%

Porosities accessible to HTO and iodide on water-saturated compacted clay materials and relation with the forms of water: A low field proton NMR study

Montavon

Guo

Tournassat

et al. 2009

Geochimica et Cosmochimica Acta

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. Porosities accessible to HTO and iodide on water-saturated compacted clay materials and relation with the forms of water: A low field proton NMR study. Geochimica et Cosmochimica Acta, Elsevier, 2009, 73 (24) AbstractThe aim of the present work was to quantify accessible porosities for iodide and for a water tracer (HTO) on water-saturated compacted clay samples (illite, montmorillonite and MX-80 bentonite) and to relate these macroscopic values to the forms of water in these porosities (surface/bulk water, external/internal water). Low field proton NMR was used to characterize and quantify the forms of water. This enabled the three different populations (structural OH, external surface and internal surface water) to be differentiated on hydrated clays by considering the difference in proton mobility. An accurate description of the water forms within the different populations did not appear possible when water molecules of these populations were in contact because of the occurrence of rapid exchange reactions. For this 2 reason, it was not possible to use the low resolution NMR method to quantify external surface and bulk water in fully water-saturated compacted clay media at room temperature. This latter information could however be estimated when analyzing the samples at -25°C. At this temperature, a distinction based on the difference in mobility could be made since surface water remained in a semi-liquid state whereas bulk water froze. In parallel, accessible porosities for anions and HTO were determined by an isotopic dilution method using capillaries to confine the materials. HTO was shown to probe the whole pore volume (i.e. the space made of surface and bulk water). When the surface water volume was mainly composed of interlayer water (case of montmorillonite and bentonite), iodide was shown to be located in the pore space made of bulk water. When the interlayer water was not present (case of illite), the results showed that iodide could access a small fraction of the surface water volume localized at the external surface of the clay particles.

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“…Examples are the Callovo-Oxfordian (COX) formation considered as a host rock for the French high level waste repository (Leroy et al, 2007;Appelo et al, 2008;Jougnot et al, 2009), or the Opalinus Clay under investigation in Switzerland (Appelo and Wersin, 2007). In experimental studies, it is common to observe the effects of anion exclusion, which in a diffusive regime is reflected by a late arrival (or release) of the negatively charged ions relative to neutral species (Bazer-Bachi et al, Melkior et al, 2007.…”

Section: Reactive-diffusive Transport In the Ebsmentioning

confidence: 99%

“…Several treatments of an explicit diffuse layer calculation based on a Donnan Equilibrium assumption have been presented in the literature (Wersin et al, 2004;Appelo et al, 2007;Leroy et al, 2007;Appelo et al, 2008). Typically, this involves an assumption that a Donnan Equilibrium condition applies, which equates the chemical potentials of the species in the diffuse layer and the bulk solution.…”

Section: Donnan Equilibrium Modelmentioning

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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Obtaining the porewater composition of a clay rock by modeling the in- and out-diffusion of anions and cations from an in-situ experiment

Cited by 83 publications

References 39 publications

Natural iodine in a clay formation: Implications for iodine fate in geological disposals

Natural iodine in a clay formation: Implications for iodine fate in geological disposals

Porosities accessible to HTO and iodide on water-saturated compacted clay materials and relation with the forms of water: A low field proton NMR study

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

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