Laboratory Radionuclide Migration Experiments at a Scale of 1 m

Vandergraaf, T. T.; Grondin, D.; Drew, D. J.

doi:10.1557/proc-112-159

Cited by 6 publications

(4 citation statements)

References 5 publications

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“…Although information is available on migration processes in porous systems [1 -3], there has been little work on the study of migration in fractured media [4][5][6][7][8][9]. Most of this deals with matrix diffusion tests and transport experiments of non-reactive tracers both in-situ and at laboratory scale.…”

Section: Introductionmentioning

confidence: 99%

Experimental Investigations of Radionuclide Transport Through Cored Granite Samples

et al. 1991

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Small scale infiltration experiments were conducted with granite cored samples of various degrees of alteration. Hydrodynamic characteristics of the granite columns were determined with nonsorbing tracers. The transport behavior of Np was investigated in the presence of natural organic matter. This was found to decrease the retardation factor of Np. Results from dynamic experiments were compared with static sorption tests. A preferential association of Pu with fracture-filling material was observed.

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Section: Introductionmentioning

confidence: 99%

Experimental Investigations of Radionuclide Transport Through Cored Granite Samples

et al. 1991

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“…Static sorption experiments indicate an increase in K a values as a function of the time allowed for partitioning [e.g., Vandergraaf and Drew, 1991 ]. As a result, the amount of retardation is often strongly affected by the residence time in the fracture [Vandergraaf et al, 1988]. We are currently investigating under which transport conditions the local equilibrium assumption can be invoked for surface sorption in a single fracture.…”

Section: Limitations Of This Studymentioning

confidence: 99%

Retardation of sorbing solutes in fractured media

Wels¹,

Smith²

1994

Water Resources Research

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Sorption of a reactive solute during transport in a fractured geologic medium is analyzed under the assumption that within each fracture, retardation varies in proportion to the product of a surface distribution coefficient and the specific surface area of the fracture (i.e., its surface area‐to‐volume ratio). This approach is analogous to the KD model commonly adopted for granular porous media. Numerical migration experiments in discrete fracture networks show that at the plume scale, retardation is both nonuniform and anisotropic. Different segments of the plume, or equivalently different breakthrough fractions at a downstream boundary, are retarded to a different degree. The degree to which various breakthrough fractions are retarded varies as a function of the orientation of the mean hydraulic gradient relative to the orientation of the fracture sets. This variation can be described in the form of a retardation ellipse. The mean arrival time is the only breakthrough fraction that is consistently described by a uniform, isotropic retardation factor. The degree of nonuniformity and anisotropy in the retardation factor is controlled largely by the difference in the mean apertures of each fracture set, the standard deviation in fracture aperture, and the orientation of the fracture sets relative to the mean hydraulic gradient. A larger variability in fracture aperture, or in the orientation of fractures within each set, promotes nonuniform retardation while reducing the degree of anisotropy in the retardation factor. Our results suggest that a transport model based on the conventional advection‐dispersion equation, using a uniform retardation factor, may be conceptually incorrect, even for a dense fracture network. While the effects of nonuniform retardation modify the dispersive flux in a way that could be described by “effective” dispersion coefficients, it is our opinion that a model formulation is needed that clearly separates chemical effects from those due to hydrodynamic dispersion.

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“…Dispersion of conservative and ideally sorbing solutes in a constant-aperture fracture has been described using analytical techniques [Kessler and Hunt, 1994], numerical simulations [Wels, 1995], and migration experiments [Vandergraaf et al, 1988;Fujikawa et al, 1993]. Vandergraaf et al [1988] noted that for a continuous injection of tracer into a sawed fracture in granite, dispersion of cesium was considerably greater than that for a conservative tracer. They suggested that deviations from the linearity and reversibility of the sorption process could have resulted in front sharpening or tailing of the elution profile.…”

Section: Introductionmentioning

confidence: 99%

“…A quantitative analysis of the breakthrough curves was not presented. Fujikawa et al [1993] performed migration experiments similar to those of Vandergraaf et al [1988], using pulse injections of cesium. They noted a strong dependence of the breakthrough curves, in particular peak height and tailing, on the fluid velocity in the fracture.…”

Section: Introductionmentioning

confidence: 99%

Influence of Specific Surface Area on Transport of Sorbing Solutes in Fractures: An Experimental Analysis

Wels¹,

Smith²,

Vandergraaf³

1996

Water Resources Research

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Experimental evidence is presented on the influence of specific surface area on the transport of the sorbing tracer strontium in fractures with uniform, but differing aperture. Specific surface area is defined as the ratio of the fracture surface area to the volume of mobile water in the fracture. Static sorption experiments on granite coupons suggest hysteresis in the sorption process, showing higher surface distribution coefficients for desorption than for sorption. Strontium was subject to significantly greater dispersion than the nonreactive tracer tritium. This enhanced dispersion is believed to be the result of chemical heterogeneity at the mineral grain scale, hysteresis in sorption, and limited transverse mixing across the fracture aperture. The influence of fracture aperture on retardation is much greater than predicted by the commonly used definition of the surface retardation factor. Strontium retardation was approximately an order of magnitude greater in a smaller‐aperture fracture (450 µm, Ra ∼ 45) than in a large‐aperture fracture (780 µm, Ra ∼ 3.5). We hypothesize that hysteresis in sorption, in conjunction with limited transverse mixing across the aperture, caused the apparent increase in sorption strength (Ka) with a decrease in fracture aperture.

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Laboratory Radionuclide Migration Experiments at a Scale of 1 m

Cited by 6 publications

References 5 publications

Experimental Investigations of Radionuclide Transport Through Cored Granite Samples

Experimental Investigations of Radionuclide Transport Through Cored Granite Samples

Retardation of sorbing solutes in fractured media

Influence of Specific Surface Area on Transport of Sorbing Solutes in Fractures: An Experimental Analysis

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