Geoenvironmental Application of Bentonites in Underground Disposal of Nuclear Waste: Characterization and Laboratory Tests

Tripathy, Snehasis; Thomas, Hywel Rhys; Bag, Ramakrishna

doi:10.1061/(asce)hz.2153-5515.0000272

Cited by 33 publications

(17 citation statements)

References 22 publications

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“…Several studies have been carried out in the past that focused in investigating the coupled thermo-hydro-mechanical behaviour of compacted bentonites and bentonite-sand mixtures when subjected to thermal, hydraulic, and thermo-hydraulic gradients [5][6][7][8][9][10][11][12][13][14][15][16][17][18]. The reported laboratory tests have been conducted at various temperatures (60 to 140 • C) and water injection pressures (5 kPa to 2 MPa).…”

Section: Introductionmentioning

confidence: 99%

“…Similarly, the changes in the dry density, the water content, the degree of saturation and the concentration of anions and cations were measured after the termination of the tests in various studies [9,15,16]. A variation of the axial stress during the tests was also monitored in some cases (see for example, [17,18]). This information is crucial in order to understand the coupled thermo-hydraulic-mechanical-chemical response of the engineered barriers, both under short and long-term in situ conditions involving anticipated temperatures and water pressures.…”

Section: Introductionmentioning

confidence: 99%

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Response of Compacted Bentonites to Thermal and Thermo-Hydraulic Loadings at High Temperatures

2017

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The final disposal of high-level nuclear waste in many countries is preferred to be in deep geological repositories. Compacted bentonites are proposed for use as the buffer surrounding the waste canisters which may be subjected to both thermal and hydraulic loadings. A significant increase in the temperature is anticipated within the buffer, particularly during the early phase of the repository lifetime. In this study, several non-isothermal and non-isothermal hydraulic tests were carried on compacted MX80 bentonite. Compacted bentonite specimens (water content = 15.2%, dry density = 1.65 Mg/m 3) were subjected to a temperature of either 85 or 150 • C at one end, whereas the temperature at the opposite end was maintained at 25 • C. During the non-isothermal hydraulic tests, water was supplied from the opposite end of the heat source. The temperature and relative humidity were monitored along predetermined depths of the specimens. The profiles of water content, dry density, and degree of saturation were established after termination of the tests. The test results showed that thermal gradients caused redistribution of the water content, whereas thermo-hydraulic gradients caused both redistribution and an increase in the water content within compacted bentonites, both leading to development of axial stress of various magnitudes. The applied water injection pressures (5 and 600 kPa) and temperature gradients appeared to have very minimal impact on the magnitude of axial stress developed. The thickness of thermal insulation layer surrounding the testing devices was found to influence the temperature and relative humidity profiles thereby impacting the redistribution of water content within compacted bentonites. Under the influence of both the applied thermal and thermo-hydraulic gradients, the dry density of the bentonite specimens increased near the heat source, whereas it decreased at the opposite end. The test results emphasized the influence of elevated temperatures (up to 150 • C) on the thermo-hydro-mechanical response of compacted bentonites in the nuclear waste repository settings.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Response of Compacted Bentonites to Thermal and Thermo-Hydraulic Loadings at High Temperatures

2017

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“…Column type experiment devices have been extensively used for such proto type tests [24][25][26][27][28][29][30]. In column experimental studies, the transient hydration process in compacted buffer is simulated under repository relevant loading paths and the material response is observed by monitoring the key THM parameters like temperature, relative humidity and swelling pressure etc.…”

Section: Column Experiments Setup At Rubmentioning

confidence: 99%

Transient boundary conditions in the frame of THM-processes at nuclear waste repositories

Schanz

2016

E3S Web Conf.

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Abstract. In nuclear waste repositories, initially unsaturated buffer is subjected to constant heat emitted by waste canister in conjunction with peripheral hydration through water from host rock. The transient hydration process can be potraied as transformation of initial heterogeneity towards homogeneity as final stage. In this context, this paper addresses the key issue of hydro mechanical behaviour of compacted buffer in context of clay microstructure and its evolution under repository relevant loading paths and material heterogeneity. This paper also introduces a unique column experiment facility available at Ruhr Universität Bochum, Germany. The facility has been designed as a forerunner of field scale testing program to simulate the transient hydration process of compacted buffer as per German reference disposal concept. The device is unique in terms of having proficiency to capture the transient material response under various possible repository relevant loading paths with higher precision level by monitor the key parameters like temperature, total suction, water content and axial & radial swelling pressure at three different sections along the length of compacted soil sample. In general, a larger spectrum of loading paths/scenarios, which may arise in the nuclear repository, can be covered precisely with existing device.

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“…Bentonite in various forms such as loose powder, compacted and slurry have been used in the construction of liners, engineered barriers, isolation walls and backfill material [1] [2]. Bentonites have been considered due to their unique containment properties (i.e.…”

Section: Introductionmentioning

confidence: 99%

An Evaluation of Osmotic Technique Under Ultraviolet Germicidal Irradiation Exposure

Tadza¹

2017

GEOMATE

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ABSTRACT:The osmotic technique, which uses polyethylene glycol (PEG) solutions of varying concentrations with semipermeable membranes of different molecular weight cutoffs (MWCO), is commonly used to apply suction in soils. Cellulose acetate membranes which are most commonly used, are susceptible to microbial attacks. This in turn will lead to the intrusion of PEG into soil specimens. Osmotic and vapour equilibrium techniques are often used to establish drying suction-water content soil-water characteristic curves (SWCC). In this study, suctions of 0.11 to 300 MPa were applied on Andrassy bentonite slurries. At higher applied suctions, the osmotic tests were carried under short length ultraviolet germicidal irradiation (UVGI). In addition, Atomic Force Microscopy (AFM) and Fourier Infrared (FTiR) were employed to evaluate the changes in the semipermeable membranes and PEG molecules, respectively. The water content of the clay obtained from the osmotic tests was found to be greater at the overlapping suction region. Interestingly, under UVGI exposure, the water content was found to be in good agreement with the water content determined using the osmotic technique at low suctions and the vapour equilibrium technique at higher suctions. FTiR spectrum and AFM results revealed that some changes had occurred on both the PEG and in the membrane pore sizes. However, these changes did not affect the final water content in the bentonite and therefore, more precise suction-water content SWCC for the clay could be established.

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Geoenvironmental Application of Bentonites in Underground Disposal of Nuclear Waste: Characterization and Laboratory Tests

Cited by 33 publications

References 22 publications

Response of Compacted Bentonites to Thermal and Thermo-Hydraulic Loadings at High Temperatures

Response of Compacted Bentonites to Thermal and Thermo-Hydraulic Loadings at High Temperatures

Transient boundary conditions in the frame of THM-processes at nuclear waste repositories

An Evaluation of Osmotic Technique Under Ultraviolet Germicidal Irradiation Exposure

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