Bentonite as a waste isolation pilot plant shaft sealing material

Daemen, J.J.K.; Ran, C.

doi:10.2172/434446

Cited by 6 publications

(3 citation statements)

References 51 publications

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“…The source term is modeled as a gaseous emission of 14 C with a release rate of 10% per year of the total activity; this highly conservative and unrealistic release rate has been intended to force the model to produce results that bring out the effects of different features of the sealing materials on the 14 C migration. In order to make a preliminary sensitivity analysis, the volume of bentonite has been selected as the focus of the sensitivity analysis, because of its very low permeability and its capacity to retard most radionuclides by sorption (Daeman and Ran 1997). Three case studies have been developed; in MR1 case, no bentonite is used to seal the underground facility; in MR2 case, a bentonite volume of 3657 m 3 is placed around the lower part of the monolith (underground shaft closure); in MR3 case, a bentonite volume of 9508 m 3 is distributed along the entrance of every disposal room and around the base of the monolith (Figure 3).…”

Section: Methodsmentioning

confidence: 99%

“…In these cases, generic features have been used for the sealing materials. According to Yim and Caron (2006), a K d value of 1.0E-5 m 3 /kg has been assumed for asphalt, waste form and concrete monolith, while K d = 0 for the crushed salt and intact salt; because of its sorption capacity, a high K d value (1 m 3 /kg) for bentonite has been assumed (Daeman and Ran 1997). The layout of shaft sealing materials has been maintained constant in all cases (Figure 4).…”

Section: Methodsmentioning

confidence: 99%

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Preliminary analysis of gaseous radiocarbon behavior in a geological repository hosted in salt rock

2018

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A preliminary evaluation of gaseous radiocarbon (14C) behavior under geological repository conditions for Italian radioactive high level waste-long-lived and intermediate level waste disposal has been performed. Although in Italy there is still no defined project for a geological disposal facility, current work may support future safety assessment studies for a hypothetical future repository in deep salt rock. In the Italian context of radioactive waste, the percentage of 14C bearing waste to be disposed in a possible geological repository is low; irradiated graphite is the most important radiological source. Data about the radiological inventory has been collected to simulate production and migration of gaseous 14C in a hypothetical geological repository. Three different conceptual models have been developed and simulated. The first model has considered a preliminary evaluation of the radiological impact referred to the whole inventory; the second and third model have evaluated the impact only due to the irradiated graphite. A preliminary sensitivity analysis has been carried out, highlighting the importance of geometry and of distribution coefficients (Kd) in materials used to seal the disposal underground facility. Results show the possibility to correlate the Kd values, the volume and the location of the sealing materials to the amount of 14C migrating toward the surface.

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Section: Methodsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Preliminary analysis of gaseous radiocarbon behavior in a geological repository hosted in salt rock

2018

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“…Because of this, the analysis of the thermo-hydro-mechanical properties of these materials has received considerable attention in recent years (e.g. Yong et al, 1986;Pusch, 1994;Börgesson et al, 1995;Daeman & Ran, 1996;Villar, 2002). One of the key parameters that must be determined for these compacted soils is the saturated hydraulic conductivity, in particular when analysing the long-term behaviour of the barriers.…”

Section: Introductionmentioning

confidence: 99%

Permeability of a bentonite–crushed granite rock mixture using different experimental techniques

Mata¹,

Ledesma²

2003

Géotechnique

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The use of bentonite-based mixtures as a sealing material for deep geologic repositories is common to many different concepts for isolating nuclear fuel waste. In this context, saturated hydraulic conductivity becomes a fundamental parameter when analysing the long-term behaviour of these facilities. Despite that, measurement of hydraulic conductivity is still far from being routine for very low-permeability materials. A mixture of 30% sodium bentonite and 70% crushed granite rock is being considered as a sealing material in a future repository in Sweden. This paper describes the experimental programme carried out to determine the permeability of this mixture. Constant-head tests, pulse tests and oedometer tests have been used for that purpose, but because of the characteristics of the material-large grain size and very low permeability-special test procedures and equipments had to be developed. The paper also presents the analysis of the results, including a numerical simulation of the pulse test by using finite elements. A comparison of all results established an average hydraulic conductivity of 6·5 3 10 À12 m/s for a dry specific weight of the mixture of 15·9 kN/m 3 . Darcy's law was also confirmed for this material over the range of gradients applied (4 to 100). Finally, the paper describes a methodology suitable for the measurement of hydraulic conductivity of lowpermeability laboratory samples based on the pulse test concept.

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Evaluation of Bentonite Application for the Abandonment of Deep Geo-energy Wells

Corina¹,

Wollenweber²,

Fischer³

et al. 2022

Rock Mech Rock Eng

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Hydrated bentonite is considered an alternative subsurface sealing/plugging material for deep geo-energy wells. However, the knowledge related to this application and the corresponding properties of bentonite is still lacking. This includes the mechanical properties at the interface of bentonite plugs with the adjacent materials (surrounding rock or casing steel) and the mechanical stability of plugs under downhole in-situ conditions. In this work, we performed experiments investigating the interface shear properties and shear strength of a bentonite plug under various settings for deep geo-energy applications, such as hydrocarbon and geothermal wells. The interface’s shear properties against various adjacent materials and fluid conditions were characterized. The influence of chemical exposure, the salinity of the curing fluid, fluid pH, pressure, and temperature on bentonite’s mechanical stability was evaluated in a small- and large-scale setting. The latter was performed using realistic casing sizes and placement methods, relevant for the field application. The experimental results show that the averaged shear strength of the bentonite plug interface is 13.3 kPa and 9.1 kPa when cured in freshwater and seawater, respectively. The increase in strength with increasing curing pressure, temperature, and fluid pH was characterized for the first time. The interfacial properties of cohesion and friction angle vary with different surrounding materials. They are also influenced by the saturating condition and salinity of the saturating fluid. Based on the experimental results, a bentonite plug with a minimum length of 15–43 m placed in casings of 7–5/8″ to 13–3/8″ would be sufficient to meet the necessary criteria of the Dutch regulators as an isolating material for well abandonment.

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Bentonite as a waste isolation pilot plant shaft sealing material

Cited by 6 publications

References 51 publications

Preliminary analysis of gaseous radiocarbon behavior in a geological repository hosted in salt rock

Preliminary analysis of gaseous radiocarbon behavior in a geological repository hosted in salt rock

Permeability of a bentonite–crushed granite rock mixture using different experimental techniques

Evaluation of Bentonite Application for the Abandonment of Deep Geo-energy Wells

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