Geologic Disposal of High-Level Radioactive Waste: Status, Key Issues, and Trends

Birkhölzer, Jens; Houseworth, James; Tsang, Chin‐Fu

doi:10.1146/annurev-environ-090611-143314

Cited by 102 publications

(37 citation statements)

References 39 publications

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“…Neretnieks [] summarized the issues of importance for nuclear waste repositories in crystalline rocks as seen at that time, and the approaches to obtain data and to increase understanding. Most of the issues presented are still valid, but additional needs have been identified since then [ Birkholzer et al ., ].…”

Section: General Introductionmentioning

confidence: 99%

Hydrologic issues associated with nuclear waste repositories

2015

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Significant progress in hydrology, especially in subsurface flow and solute transport, has been made over the last 35 years because of sustained interest in underground nuclear waste repositories. The present paper provides an overview of the key hydrologic issues involved, and to highlight advances in their understanding and treatment because of these efforts. The focus is not on the development of radioactive waste repositories and their safety assessment, but instead on the advances in hydrologic science that have emerged from such studies. Work and results associated with three rock types, which are being considered to host the repositories, are reviewed, with a different emphasis for each rock type. The first rock type is fractured crystalline rock, for which the discussion will be mainly on flow and transport in saturated fractured rock. The second rock type is unsaturated tuff, for which the emphasis will be on flow from the shallow subsurface through the unsaturated zone to the repository. The third rock type is clay-rich formations, whose permeability is very low in an undisturbed state. In this case, the emphasis will be on hydrologic issues that arise from mechanical and thermal disturbances; i.e., on the relevant coupled thermo-hydromechanical processes. The extensive research results, especially those from multiyear large-scale underground research laboratory investigations, represent a rich body of information and data that can form the basis for further development in the related areas of hydrologic research. General IntroductionSignificant progress in hydrology, especially in subsurface flow and solute transport, has been made over the last 35 years because of sustained interest in the performance assessment of proposed underground nuclear waste repositories. The present paper attempts to provide an overview of the key hydrologic issues involved and to highlight the advances in their understanding and treatment because of these efforts. This paper is not focused on the development of high-level nuclear waste repositories and their safety assessment; it focuses instead on the advances in hydrologic science which have emerged from such studies. These advances may find applications in other hydrology-related problems of current importance at the national and international levels, such as environmental contamination remediation, carbon dioxide geosequestration, and natural gas production through fracking.In the next section, we present, in a general way, the context for the hydrologic framework related to performance and safety assessment of underground nuclear waste repositories that are proposed to be constructed in three particular rock formations-crystalline rock, unsaturated tuffs, and clays. Then, we discuss some particularly challenging factors concerning the research common to these three formations. This discussion will be followed by three sections devoted to each of these three rock types, respectively, to present a review of hydrologic research in these areas.

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Section: General Introductionmentioning

confidence: 99%

Hydrologic issues associated with nuclear waste repositories

2015

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“…While such time frames may not be of interest for some applications, we present results to the display entire arrival curves from an instantaneous point source for completeness. Time frames of this magnitude are not unusual for problems involving nuclear waste disposal, and safety assessments of disposal systems typically encompass 10 5 −10 6 years [ Birkholzer et al ., ].…”

Section: Solution Behavior Without Longitudinal Diffusion/dispersionmentioning

confidence: 99%

An analytical model for solute transport through a water-saturated single fracture and permeable rock matrix

2013

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[1] The problem of solute transport through a water-saturated single fracture in a permeable rock matrix is examined using an analytical modeling approach. A closed-form analytical solution is obtained that accounts for transverse and longitudinal advective transport in the fracture and matrix and transverse diffusion in the matrix. The solution also accounts for both diffusive and advective solute exchange between the fracture and matrix and a general solute source position in either the fracture or matrix. The novel features are the incorporation of advective transport in the matrix and a general source position into a closed-form solution for the solute-transport problem. Examples of the solution behavior are presented, which demonstrate the effects of matrix advection in combination with advection along the fracture, transverse diffusion in the matrix for solute release in the fracture and matrix. A semianalytical solution in the form of a superposition integral is also derived that includes these transport features, plus independent levels of longitudinal diffusion and dispersion in the matrix and fracture, respectively. Examples are presented that include advective transport in the fracture and matrix, longitudinal and transverse diffusion in the matrix, longitudinal dispersion in the fracture, as well as solute release from the fracture and matrix. An approximate criterion is proposed to evaluate the significance of longitudinal diffusion and dispersion relative to longitudinal spreading caused by fracturematrix interaction.

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“…The requirement for long-term geological sequestration of CO 2 [1,2] and nuclear waste management [3][4][5] has prompted increased interest in low-permeability, clay-rich sedimentary rocks [6][7][8][9][10][11][12]. These rocks are characterized by low hydraulic conductivity (<10 −11 m/s) and, as a consequence, solute transport is dominated by diffusion [4,[13][14][15][16][17]. Characterization of natural tracers, such as Cl − and Br − in the porewaters of low-permeability rocks is critical in establishing the provenance of salinity, whether marine or otherwise, as well as solute transport mechanisms and residence times [8,10,[18][19][20][21][22][23].…”

Section: Introductionmentioning

confidence: 99%

Measurement of Cl⁻ : Br⁻Ratios in the Porewater of Clay-Rich Rocks—A Comparison of the Crush-and-Leach and the Paper-Absorption Methods

Celejewski

Barton

2018

Geofluids

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Characterization of porewater chemistry in low-permeability, clay-rich rocks provides insights into solute transport mechanisms and the origin and residence time of porewater. Extraction of porewater for chemical quantification is challenging, and several methods have been applied including squeezing, advective displacement, crush and leach, and a relatively new technique that extracts porewater by absorption into a cellulosic paper by capillary action. Here we compare porewater Cl − and Br − mass ratios from samples using the paper-absorption and crush-and-leach techniques. Samples were obtained from Upper Ordovician shales in the Michigan Basin in Ontario, the Opalinus Clay at the Mont Terri Rock Laboratory in Switzerland, and the Upper Ordovician Lorraine Group shale in southern Quebec. The data display consistent and reproducible differences among methods for Cl − and Br − mass ratios, with the paper-absorption method producing systematically lower Cl − : Br − ratios. The observed differences in Cl − : Br − ratios are attributed primarily to anion exclusion effects which are stronger for Br − than for Cl − , resulting in higher Br − concentrations in the largest pores that are preferentially sampled by the paper-absorption technique. In addition, calculations suggest that Cl − is more effective than Br − in forming ion pairs and clusters with neutral or positive charge which can enter the diffuse double layer. This causes a further decrease in the Cl − : Br − ratios for the mobile water. One important message from this work is that different extraction methods should not be expected to converge on a unique porewater Cl − : Br − ratio because each method reflects different proportions of the interlayer, diffuse double layer, and mobile fractions of porewater.in the Opalinus Clay at Mont Terri, Switzerland, the Boom Clay at Essen, Belgium, and the Couche Silteuse at Marcoule, France, by plotting spatial profiles of tracers across these formations. The data allowed for determination of transport processes and porewater residence times.Sampling porewater from low-permeability, clay-rich formations for chemical quantification is a challenging endeavor. This is in part due to the small volumes available for extraction and because of the complexity of waterclay interactions [24]. Negatively charged clay surfaces are balanced by cation-rich water in direct contact with the surface [25,26]. This cation-rich water is "bound water" and occupies the interlayer positions in clay minerals or the diffuse double layer (DDL) that surrounds mineral surfaces,

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Geologic Disposal of High-Level Radioactive Waste: Status, Key Issues, and Trends

Cited by 102 publications

References 39 publications

Hydrologic issues associated with nuclear waste repositories

Hydrologic issues associated with nuclear waste repositories

An analytical model for solute transport through a water-saturated single fracture and permeable rock matrix

Measurement of Cl⁻ : Br⁻Ratios in the Porewater of Clay-Rich Rocks—A Comparison of the Crush-and-Leach and the Paper-Absorption Methods

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Geologic Disposal of High-Level Radioactive Waste: Status, Key Issues, and Trends

Cited by 102 publications

References 39 publications

Hydrologic issues associated with nuclear waste repositories

Hydrologic issues associated with nuclear waste repositories

An analytical model for solute transport through a water-saturated single fracture and permeable rock matrix

Measurement of Cl− : Br−Ratios in the Porewater of Clay-Rich Rocks—A Comparison of the Crush-and-Leach and the Paper-Absorption Methods

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Measurement of Cl⁻ : Br⁻Ratios in the Porewater of Clay-Rich Rocks—A Comparison of the Crush-and-Leach and the Paper-Absorption Methods