Mass transport through defected bentonite plugs

Oscarson, D. W.; Dixon, David A.; Hume, Harold B.

doi:10.1016/s0169-1317(96)00021-x

Cited by 14 publications

(7 citation statements)

References 9 publications

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“…For a saturated density of 2.0 g/cm 3, hydraulic conductivities <10 -12 m/s and thus smaller than the required conductivity of 10 -1~ m/s were achieved. Oscarson et al (1996) examined the permeability and diffusivity of compacted bentonite plugs that were either slotted, to mimic fractures, parallel to the direction of mass flow or heated at 150 and 250~…”

Section: Hydraulic Conductivitymentioning

confidence: 99%

Clay mineralogical investigations related to nuclear waste disposal

Madsen

1998

Clay miner.

227

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Mineralogical and geotechnical investigations on the possible use of compacted bentonite as a buffer material in nuclear waste repositories are reported. The swelling capacity is highly dependent on the density of the compacted bentonite. Swelling pressures >30 MPa were measured for dry densities of ~2.0 g/cm3. Added iron or magnetite powder up to 20 wt% had no influence on the swelling capacity. Compacted mixtures of 20 wt% ground set cement and bentonite showed higher swelling pressures but lower swelling strain capability than compacted bentonite alone. Steam lowered the swelling pressure of compacted bentonite to ~60% of the original value. The influence was, however, reversible by ultrasonic treatment. The thermal conductivity of saturated compacted bentonite at a density of 2.0-2.1 g/cm3is ~1.35-1.45 W/m°K The volumetric heat capacity ranges from 3.1 x 106to 3.4 x 106j/m3°C The saturated hydraulic conductivity of the compacted bentonite is <10-12m/s. The apparent diffusion coefficients for various ions in compacted bentonite for water contents in the range of 20 to 25 wt% are: K+: 5 x 10-11, Cs+: 6 x 10-12, Sr2+: 3 x 10-11, UO22+: <10-13, Th4+: <10-13, Fe2+: 4 x 10-11, Fe3+: 4 x 10-11, Cl-: 1 x 10-10and I-: 1 x 10-10m2/s. The 'breakthrough time' for an apparent diffusion coefficient of 10-11m2/s in compacted bentonite 1 m thick was estimated to be ~3000 years. The mineralogical longevity was investigated on natural K-bentonites from Kinnekulle, Sweden, and Montana, USA. Although these materials have undergone considerable changes during diagenesis and contain various amounts of mixed-layer illite-smectite, they still have a substantial swelling and adsorption capacity. The investigations demonstrate that although the properties of bentonite are negatively influenced to a certain extent by heat, hot steam, iron and cement, compacted bentonite is still the best choice to act as a buffer material in a nuclear waste repository.

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Section: Hydraulic Conductivitymentioning

confidence: 99%

Clay mineralogical investigations related to nuclear waste disposal

Madsen

1998

Clay miner.

227

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“…A well-known characteristic of clay-rocks and engineered bentonite barriers is their very low hydraulic permeability k. The existing database indicates that k ranges from w10 À21 to 10 À17 m 2 with little sensitivity, at least in some cases, to the presence of fractures or faults (Neuzil, 1994;Oscarson et al, 1996;Bock et al, 2010;Barbour et al, 2012). In porous media with such low k values, at hydraulic pressure gradients representative of subsurface conditions, molecular diffusion is an important mass transfer mechanism on length scales up to hundreds of meters and millions of years, with implications in the isolation of landfills and contaminated sites (Johnson et al, 1989;Jo et al, 2006;Lange et al, 2009;De Soto et al, 2012), the persistence of dense nonaqueous-phase liquids (DNAPL) in contaminated aquifers (Parker et al, 2004;Chapman and Parker, 2005), the distribution of inert tracers in clay formations (Patriarche et al, 2004b;Lavastre et al, 2005;Mazurek et al, 2011), and the geologic storage of CO 2 (Ketzer et al, 2005;Gherardi et al, 2007) and high-level radioactive waste (HLRW) .…”

Section: Introductionmentioning

confidence: 99%

Self-Diffusion of Water and Ions in Clay Barriers

Bourg

Tournassat

2015

Developments in Clay Science

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“…At the conditions that would exist in proposed HLRW repositories, clay barriers display very low hydraulic conductivities, the ability to selfseal when fractured, and water and solute mass fluxes that are dominated by molecular diffusion as the primary transport mechanism on time-scales of millions of years (Neuzil, 1986(Neuzil, , 1994(Neuzil, , 2013Horseman and Volckaert, 1996;Oscarson et al, 1996;Bock et al, 2010;Mazurek et al, 2011).…”

Section: Introduction and Research Motivationmentioning

confidence: 99%

Laboratory Experiments on Bentonite Samples: FY15 Progress

Tinnacher¹,

Davis²

2015

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Mass transport through defected bentonite plugs

Cited by 14 publications

References 9 publications

Clay mineralogical investigations related to nuclear waste disposal

Clay mineralogical investigations related to nuclear waste disposal

Self-Diffusion of Water and Ions in Clay Barriers

Laboratory Experiments on Bentonite Samples: FY15 Progress

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