In situ tracer tests to determine retention properties of a block scale fracture network in granitic rock at the Äspö Hard Rock Laboratory, Sweden

Andersson, Peter; Byegård, Johan; Tullborg, Eva‐Lena; Doe, T.; Hermanson, Jan; Winberg, Anders

doi:10.1016/j.jconhyd.2003.09.009

Cited by 53 publications

(40 citation statements)

References 8 publications

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“…Sorption along fracture walls is a surface process rather than a volumetric process, like sorption within matrix blocks. Similar to the discussion on molecular diffusion, the TRUE-1 and TRUE Block Scale tests conducted at Äspö Hard Rock Laboratory indicate that sorption in the unfractured rock matrix is a dominant process over adsorption onto fracture walls and fault gauge (Andersson et al, 2002a;b). This is because matrix blocks have a greater surface area and length scale, and hence, a greater number of available sorption sites than fracture walls and fault gauge.…”

Section: Radionuclide Adsorptionmentioning

confidence: 53%

“…The reason for this is simple: the time a radionuclide molecule spends trapped in an immobile zone is proportional to the size of that zone, and the scale of matrix blocks is typically on the order of centimeters to meters while within fracture stagnant zones and fault gauge are on the order of micrometers to millimeters. Diffusion into matrix blocks was found to be a major retention mechanism at the time scales of the Tracer Retention Understanding Experiments conducted at the Äspö underground laboratory at both single fracture (Winberg et al, 2000) and block scales (Andersson et al, 2002a;b). For these in-situ experiments, the prevalence of molecular diffusion as a retention mechanism is exhibited by late-time breakthroughs with slopes equal to -3/2 for both conservative and non-conservative radionuclides.…”

Section: Diffusional Mass Exchangementioning

confidence: 95%

“…Studies in highly characterized rock masses have shown that fracture K is extremely heterogeneous and may encompass 5 to 8 orders of magnitude (Andersson et al, 2002a;b; Guimerá & Carrera, 2000;Paillet, 1998). Often the distribution of K (and T) is thought to be lognormal:…”

Section: Hydraulic Conductivitymentioning

confidence: 99%

“…Values of log(σ K ) are typically around 1 for fractured media (Andersson et al, 2002a;b;Stigsson et al, 2001). However, other studies suggest power law distributions (Gustafson & Fransson, 2005;Kozubowski et al, 2008) and that these lognormal distributions, similar to length, could be caused by censoring flow data possibly due to instrument limitations.…”

Section: Hydraulic Conductivitymentioning

confidence: 99%

“…exchange within fracture stagnant zones and fault gauge (Andersson et al, 2002a;b;Grisak & Pickens, 1980;Neretnieks, 1980;Sudicky & Frind, 1982;Winberg et al, 2000). The reason for this is simple: the time a radionuclide molecule spends trapped in an immobile zone is proportional to the size of that zone, and the scale of matrix blocks is typically on the order of centimeters to meters while within fracture stagnant zones and fault gauge are on the order of micrometers to millimeters.…”

Section: Diffusional Mass Exchangementioning

confidence: 99%

See 4 more Smart Citations

Hydrogeologic Characterization of Fractured Rock Masses Intended for Disposal of Radioactive Waste

Reeves¹,

Parashar²,

Zhang³

2012

Radioactive Waste

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Section: Radionuclide Adsorptionmentioning

confidence: 53%

Section: Diffusional Mass Exchangementioning

confidence: 95%

Section: Hydraulic Conductivitymentioning

confidence: 99%

Section: Hydraulic Conductivitymentioning

confidence: 99%

Section: Diffusional Mass Exchangementioning

confidence: 99%

See 3 more Smart Citations

Hydrogeologic Characterization of Fractured Rock Masses Intended for Disposal of Radioactive Waste

Reeves¹,

Parashar²,

Zhang³

2012

Radioactive Waste

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Influence of porosity structures on mixing-induced reactivity at chemical equilibrium in mobile/immobile Multi-Rate Mass Transfer (MRMT) and Multiple INteracting Continua (MINC) models

et al. 2013

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[1] Trapping mechanisms and slow diffusion in poorly connected porosities are well modeled by several anomalous transport models including the Multi-Rate Mass Transfer framework (MRMT). In MRMT, solutes in fast mobile advective zones are slowed down by first-order exchanges with immobile zones. While MRMT models have been used essentially for conservative transport, we investigate their relevance to reactive transport.To this end, we analyze the influence of the structure of the diffusive porosity zone on the distribution of concentrations within the immobile zone and on the reactivity of simple precipitation/dissolution bimolecular reactions at equilibrium. We build Multi-Rate Mass Transfer (MRMT) and Multiple INteracting Continua (MINC) models with equivalent transport characteristics. Both models have the same mobile zone concentrations at any time. They, however, differ by the connectivity structure of their immobile zones. MRMT has a star-shaped connectivity structure with the mobile zone linked to all immobile zones and acting as the sole exchanger. MINC has a chained-type connectivity where immobile zones are mutually connected on a line. We show that both connectivity structures give the same concentration variance whatever the model parameters, dimensionality, and initial conditions. Reaction rates of bimolecular reaction at chemical equilibrium are also highly similar but not equal as long as concentration gradients within the diffusive zone remain low like in the uniform injection case, or at large times when high initial concentration gradients have been reduced. For high initial immobile concentration gradients in the diffusive zone, however, reaction rates are much lower in the star-shaped connectivity structure (MRMT), and consequently depend on the organization of the immobile porosity structure. Negative concentrations also occur in some of the immobile zones of the equivalent MRMT as a result of the direct connection of the mobile and immobile zones. While acceptable for conservative components, negative concentrations limit the relevance of MRMT to model reactivity at high immobile concentration gradients. The concept of immobile zone concentration should thus be taken with great care and systematically be assessed.

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From conservative to reactive transport under diffusion‐controlled conditions

Babey

Dreuzy

Ginn

2016

Water Resources Research

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International audienceWe assess the possibility to use conservative transport information, such as that contained in transit time distributions, breakthrough curves and tracer tests, to predict non-linear fluid-rock interactions in fracture/matrix or mobile/immobile conditions. Reference simulated data are given by conservative and reactive transport simulations in several diffusive porosity structures differing by their topological organization. Reactions includes non-linear kinetically-controlled dissolution and desorption. Effective Multi-Rate Mass Transfer models (MRMT) are calibrated solely on conservative transport information without pore topology information and provide concentration distributions on which effective reaction rates are estimated. Reference simulated reaction rates and effective reaction rates evaluated by MRMT are compared, as well as characteristic desorption and dissolution times. Although not exactly equal, these indicators remain very close whatever the porous structure, differing at most by 0.6% and 10% for desorption and dissolution. At shorter times, this close agreement arises from the fine characterization of the diffusive porosity close to the mobile zone that controls fast mobile-diffusive exchanges. At intermediate to larger times, concentration gradients are strongly reduced by diffusion, and reactivity can be captured by a very limited number of rates. We conclude that effective models calibrated solely on conservative transport information like MRMT can accurately estimate monocomponent kinetically-controlled non-linear fluid-rock interactions. Their relevance might extend to more advanced biogeochemical reactions because of the close representation of conservative concentration distributions, even by parsimonious models (e.g., MRMT with 3-5 rates). We propose a methodology to estimate reactive transport from conservative transport in mobile-immobile conditions

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In situ tracer tests to determine retention properties of a block scale fracture network in granitic rock at the Äspö Hard Rock Laboratory, Sweden

Cited by 53 publications

References 8 publications

Hydrogeologic Characterization of Fractured Rock Masses Intended for Disposal of Radioactive Waste

Hydrogeologic Characterization of Fractured Rock Masses Intended for Disposal of Radioactive Waste

Influence of porosity structures on mixing-induced reactivity at chemical equilibrium in mobile/immobile Multi-Rate Mass Transfer (MRMT) and Multiple INteracting Continua (MINC) models

From conservative to reactive transport under diffusion‐controlled conditions

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