Shale, mudstone, and claystone as potential host rocks for underground emplacement of waste

Characterizing mineralogy and redox reactivity in potential host rocks for a UK geological disposal facility

Mineralogical Magazine ◽

10.1180/minmag.2015.079.6.11 ◽

2015 ◽

Vol 79 (6) ◽

pp. 1353-1367 ◽

Cited By ~ 5

Author(s):

J. Quirke ◽

C. M. B. Henderson ◽

R. A. D. Pattrick ◽

K. M. Rosso ◽

A. Dent ◽

...

Keyword(s):

Iron Content ◽

Host Rock ◽

Azo Dye ◽

Total Iron ◽

Geological Disposal ◽

Potential Host ◽

Fine Grained ◽

Reducing Conditions ◽

Redox Reactivity ◽

Host Rocks

AbstractGeological disposal facilities (GDF) are intended to isolate and contain radioactive waste within multiple protective barriers, deep underground, to ensure that no harmful quantities of radioactivity reach the surface environment. The last line of defense in a multi-barrier GDF is the geosphere, where iron is present in the host rock mineralogy as either Fe(II) or Fe(III), and in groundwater as Fe(II) under reducing conditions. The mobility of risk-driving radionuclides, including uranium and technetium, in the environment is affected significantly by their valence state. Due to its low redox potential, Fe(II) can mediate reduction of these radionuclides from their oxidized, highly mobile, soluble state to their reduced, insoluble state, preventing them from reaching the biosphere. Here a study of five types of potential host rocks, two granitoids, an andesite, a mudstone and a clay-rich carbonate, is reported. The bulk rocks and their minerals were analysed for iron content, Fe(II/III) ratio, and for the speciation and fine-grained nature of alteration product minerals that might have important controls on groundwater interaction. Total iron content varies between 0.9% in clays to 5.6% in the andesite. X-ray absorption spectroscopy reveals that Fe in the granitoids and andesite is predominantly Fe(II), and in mudstones, argillaceous limestone and terrestrial sandstone is predominantly Fe(III). The redox reactivity of the potential host rocks both in the presence and absence of Fe(II)-containing 'model' groundwater was investigated using an azo dye as a probe molecule. Reduction rates as determined by reactivity with the azo dye were correlated with the ability of the rocks to uptake Fe(II) from groundwater rather than with initial Fe(II) content. Potential GDF host rocks must be characterized in terms of mineralogy, texture, grain size and bulk geochemistry to assess how they might interact with groundwater. This study highlights the importance of redox reactivity, not just total iron and Fe(II)/(III) ratio, when considering the host rock performance as a barrier material to limit transport of radionuclides from the GDF.

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Fracture-fluid relationships: implications for the sealing capacity of clay layers – Insights from field study of the Blue Clay formation, Maltese islands

BSGF - Earth Sciences Bulletin ◽

10.2113/gssgfbull.185.1.51 ◽

2014 ◽

Vol 185 (1) ◽

pp. 51-63 ◽

Cited By ~ 3

Author(s):

Yves Missenard ◽

Audrey Bertrand ◽

Pierre Vergély ◽

Antonio Benedicto ◽

Marc-Edward Cushing ◽

...

Keyword(s):

Fluid Flow ◽

Co2 Storage ◽

Complex Deformation ◽

Potential Host ◽

Maltese Islands ◽

Sealing Capacity ◽

Fracture Fluid ◽

Clay Layers ◽

Clay Formation ◽

Host Rocks

Abstract Sealing capacity of clay layers is a key parameter in many fields of geoscience, such as CO2 storage, hydrocarbons trapping, and waste disposal. In the context of deep geological disposal of radioactive waste, clayey formations are studied as potential host rocks. This work deals with tectonic fracturing, fluid flow, and the sealing capacity of clay layers in an outcropping formation sharing similarities to these potential host rocks. The Blue Clay formation (Maltese islands) outcrops between two limestones affected by slight extensional tectonics. Zones of oxidation around fractures are interpreted as evidence of palaeofluid circulation, and are used to assess the role of joints and faults in controlling the hydrological communication between adjacent layers. Joints and small faults (displacement < 5 m) seem to die out quickly up-section within the Blue Clays, and appear to have played an insignificant role in the palaeohydrology of the area. In contrast, large faults (displacement > 50 m) display clay smear structures, and the lack of oxidized zones around them suggests they served as barriers to fluid flow. Intermediate-sized faults die out up-section into complex deformation zones comprised of irregular joints that are filled with gypsum and surrounded by oxidation zones. These observations indicate that these intermediate-sized faults, usually considered as sealed by classical predictive methods such as “Shale Smear Factor”, may have played a significant role in the local palaeohydrology.

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Hydro-mechanical Response to Gas Transfer of Deep Argillaceous Host Rocks for Radioactive Waste Disposal

Rock Mechanics and Rock Engineering ◽

10.1007/s00603-021-02717-3 ◽

2021 ◽

Author(s):

Laura Gonzalez-Blanco ◽

Enrique Romero ◽

Paul Marschall ◽

Séverine Levasseur

Keyword(s):

Radioactive Waste ◽

Gas Flow ◽

Mechanical Response ◽

Radioactive Waste Disposal ◽

Opalinus Clay ◽

Gas Transfer ◽

Potential Host ◽

Bedding Planes ◽

Host Rocks ◽

Differential Properties

AbstractDuring recent decades, argillaceous sedimentary formations have been studied as potential host formations for the geological disposal of long-living and heat-emitting radioactive waste—Boom Clay in Belgium and Opalinus Clay and Brown Dogger in Switzerland. A significant issue in the long-term performance of these potential host rocks concerns the generation and transport of gases. The pressure resulting from the generation of gas in an almost impermeable geological medium in the near field of a repository will increase. Under high gas pressures, the mechanical and hydraulic properties of the host rock are expected to change significantly. Preferential gas pathways may develop which exploit material heterogeneity, anisotropy (bedding planes), rock discontinuities, or interfaces between the different components of the repository, and may eventually lead to the release of the produced gases. Gas flow through these clayey rocks is investigated on the basis of laboratory work. Priority has been given to studying the volume change response of these initially water-saturated materials through relatively fast and controlled volume-rate gas injections. The effect of the gas injection rate, the confining pressure and the bedding orientation on the gas transport properties have been studied with particular attention paid to the coupling with strain behaviour. The results have shown features common to the three formations concerning the gas transfer process through preferential pathways, despite their initially differential properties.

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