Diffusion in a Variable Aperture Slot: Impact on Radionuclide Release from a Repository for Spent Fuel

Winberg-Wang, Helen

doi:10.1080/00295450.2018.1469348

Cited by 4 publications

(4 citation statements)

References 10 publications

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“…The experimental results were first compared to the simple Q-equivalent formula. Equation (2) gives an equivalent flow rate at steady state of 1.7 × 10 −12 m 3 /s, for a constant aperture 0.36 × 150 × 150-mm 3 slot with the pumping flow rate used. This is a factor 30 times larger than that obtained from the experiment.…”

Section: Simulations Of Flow and Solute Propagationmentioning

confidence: 99%

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Visualization of Mass Transfer Between Source and Seeping Water in a Variable Aperture Fracture—Impact of Tracer Density

Winberg-Wang

Neretnieks

2020

Nuclear Technology

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An experiment with a vertical slot with horizontally seeping water with a dye diffusing from below was performed to help validate and visualize the Q-equivalent model, which describes the mass transfer rate from a source into flowing water, such as that in a repository for nuclear waste. The Q-equivalent model is used for quantifying mass transport in geological repositories. However, the tracer propagated much slower and to a lesser extent than predicted by the model. It was found that the tracer gave rise to a small density gradient that induced buoyancy-driven flow, overwhelming that driven by the horizontal hydraulic gradient. This dramatically changed the mass transfer from the dye source into the water in the slot. For the release of contaminants, this can have detrimental as well as beneficial effects, depending on whether positive or negative buoyancy is induced. These observations led to an analysis of when and how density differences in a repository can influence the release and further fate of escaping radionuclides in waste repositories. This and other experiments also showed that laboratory experiments aimed at visualizing flow and mass transfer processes in fractures could be very sensitive to the heating of the dye tracers by the lighting in the laboratory.

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Section: Simulations Of Flow and Solute Propagationmentioning

confidence: 99%

“…The reason(s) for this large difference is sought next by some simulations in which buoyancy effects caused by the differences of water with dye and pure water were studied because considerable buoyancy-induced flow had been observed in some of our other experiments. 2…”

Section: Simulations Of Flow and Solute Propagationmentioning

confidence: 99%

Visualization of Mass Transfer Between Source and Seeping Water in a Variable Aperture Fracture—Impact of Tracer Density

Winberg-Wang

Neretnieks

2020

Nuclear Technology

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“…This was recently confirmed by experiments also for a variable aperture slot. 6 The penetration depth of solute is defined as the distance where the concentration of the solute into the water is 1% of ðc o À c w Þ and is obtained from Eq. (4):…”

Section: Iiib Regional Hydraulic Gradientmentioning

confidence: 99%

Density-Driven Mass Transfer in Repositories for Nuclear Waste

Neretnieks

Winberg-Wang

2018

Nuclear Technology

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In geologic repositories for nuclear waste located in crystalline rocks, the waste is surrounded by a bentonite buffer that in practice is not permeable to water flow. The nuclides must escape by molecular diffusion to enter the seeping water in the fractures of the rock. At high water-seepage rates, the nuclides can be carried away rapidly. The seepage rate of the water can be driven by the regional hydraulic gradient as well as by buoyancy-driven flow. The latter is induced by thermal circulation of the water by the heat produced by radionuclide decay. The circulation may also be induced by salt exchange between buffer and water in the fractures. The main aim of this paper is to explore how salt exchange between the backfill and mobile water in fractures, by buoyancy effects, can increase the escape rate of radionuclides from a repository.A simple analytical model has been developed to describe the mass transfer rate induced by buoyancy. Numerical simulations support the simple solution. A comparison is made with the regional gradient-driven flow model. It is shown that buoyancy-driven flow can noticeably increase the release rate.

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“…Instead, an indirect method was devised that visualized and demonstrated the diffusive transport to seeping water. 10 Recently, a flow pattern of another experiment, designed to study an effect of matrix diffusion on transport radioactive tracer pulse flowing in a narrow annulus between a concentric tube and a centered drill core, 11 was visualized using uranine. The outer tube was transparent to be able to observe the flow pattern.…”

Section: Introductionmentioning

confidence: 99%

A Note on the Use of Uranine Tracer to Visualize Radionuclide Migration Experiments: Some Observations and Problems

2019

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Uranine is a dye commonly used in tracer experiments; it is chosen for its high visibility even at low concentrations. Uranine solutions are slightly denser than water at the same temperature. However, in laboratory experiments uranine solutions have been known to occasionally show unpredictable flow behaviors. This paper investigates the possible effect of light-induced density change to explain some of these behaviors. Uranine has a wide light absorption spectrum for visible light, which can heat the dye solution and lower its density to below that of the surrounding water, which induces buoyancy-driven flow. Simulations are made in both one dimension and two dimensions to determine the extent of the effect. The results are then compared to different experiments with unanticipated flow patterns.

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Diffusion in a Variable Aperture Slot: Impact on Radionuclide Release from a Repository for Spent Fuel

Cited by 4 publications

References 10 publications

Visualization of Mass Transfer Between Source and Seeping Water in a Variable Aperture Fracture—Impact of Tracer Density

Visualization of Mass Transfer Between Source and Seeping Water in a Variable Aperture Fracture—Impact of Tracer Density

Density-Driven Mass Transfer in Repositories for Nuclear Waste

A Note on the Use of Uranine Tracer to Visualize Radionuclide Migration Experiments: Some Observations and Problems

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