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Peine, Germany

Jobmann M.,DBE Technology GmbH | Wilsnack Th.,IBeWa Ingenieurpartnerschaft | Voigt H.-D.,TU Bergakademie Freiberg
International Journal of Rock Mechanics and Mining Sciences | Year: 2010

An excavation damaged zone (EDZ) around emplacement boreholes for radioactive waste represents a potential pathway for radionuclides due to its increased porosity and crack permeability. As clay is one of the potential host rocks for radioactive waste disposal, Opalinus clay samples from the underground rock laboratory at Mont Terri were investigated regarding their hydraulic properties - and related crack occurrence - after excavation and during stress-dependent crack closure. After determination of their hydraulic properties in untreated conditions, the samples were artificially cracked by tensile strength tests. The cracked samples were put into a triaxial pressure cell and the permeability and effective porosity were measured during stepwise increase and decrease of confining pressure. When the pressure was increased, a continuous decrease of permeability was found, which was similar for all test samples, and a mathematical expression was identified. When the pressure was decreased, no increase of permeability was observed until the samples were completely depressurized, leading to the assumption that during pressurization some kind of sealing process took place resulting in a permanent crack closure. In addition to the dependence on pressure, a time-dependent permeability reduction and thus crack closure at constant pressure was found, indicating a creep compaction behaviour of the clay. By knowing the initial permeability immediately after excavation of an emplacement borehole, the permeability reduction due to time-dependent stress variation can be calculated for use in long-term safety analyses. © 2009 Elsevier Ltd. All rights reserved.

Jobmann M.,DBE Technology GmbH | Billaux D.,ITASCA Consultants S.A.
International Journal of Rock Mechanics and Mining Sciences | Year: 2010

An excavation damaged zone (EDZ) around emplacement boreholes for radioactive waste represents a potential pathway for radionuclides, due to its increased porosity and crack permeability. As clay is one of the potential host rocks for radioactive waste disposal, a methodical approach was developed for permeability calculation of damaged opalinus clay. The approach was based on a permeability-porosity relationship and on the theory of fractals, which allows the description of rock mass properties by fractal dimensions. It was calibrated against laboratory test data and provides the possibility to calculate the permeability from the pore size parameters "effective porosity" and "pore radius" as well as from the fractal dimension. An application of this relationship was given in terms of calculating the EDZ permeability around a vertical 50. m deep emplacement borehole in opalinus clay at a German generic repository site. The Particle Flow Code (PFC) was applied to simulate the fissure development in the EDZ. The results of the simulation provide the necessary pore size parameters. Considering the thermo-mechanical impact of adjacent, already filled, boreholes in an emplacement field for heat-generating radioactive waste, the crack occurrence and evolution over time in the EDZ of a newly drilled borehole was calculated on a 2D horizontal plane. A 3D calculation as well as a verification against in-situ data is still pending. © 2010 Elsevier Ltd.

Jobmann M.,DBE Technology GmbH | Meleshyn A.,GRS Society for plants and Reactor Safety
Mineralogical Magazine | Year: 2015

DBE TECHNOLOGY, BGR and GRS are developing a methodology to demonstrate the safety of a repository for high-level waste and spent fuel (HLW/SF) in clays according to the requirements of the German regulating body. In particular, these requirements prescribe that the barrier effect of host rocks must not be compromised by a thermal impact resulting from HLW/SF emplacement. To substantiate and quantify this requirement, we carried out a literature survey of research on thermally-induced changes on clay properties. Effects thus compiled can be divided into thermo-hydro-mechanical and chemical-biological-mineralogical effects and were analysed with regard to their relevance to the integrity of clay host rocks. This analysis identified one effect of major influence within each group: thermal expansion and compaction as well as results of microbial activities. Importantly, it further revealed that a moderate temperature increase above 100°C cannot be expected to compromise the integrity of the geological barrier according to the current knowledge state. Evidence is presented in this paper that temperature increases up to 150°C can actually contribute to an improved performance of a radioactive waste repository by increasing the consolidation of the clay and sterilizing the repository's near-field to depress the deteriorative microbial effects. A quantitative temperature criterion for thermal impact of HLW/SF on clay host rocks is accordingly proposed. © 2016 by Walter de Gruyter Berlin/Boston.

Keller L.M.,ZHAW Zurich University of Applied Sciences | Jobmann M.,DBE Technology GmbH | Schuetz P.,Center for X ray Analytics | Gasser P.,ETH Zurich
Transport in Porous Media | Year: 2014

Compacted crushed rock salt is considered as potential backfill material in repositories for nuclear waste. To evaluate the sealing properties of this material knowledge concerning the nature of the pore space is of eminent interest. Here, the pore microstructures of crushed rock salt samples with different compaction states were investigated by X-ray (XCT) computed tomography and Focused Ion Beam nanotomography (FIB-nt). Based on these methods the pore microstructures were reconstructed and quantitatively analyzed with respect to porosity, connectivity and percolation properties. Regarding pores with radii > 4 μm, porosity differs substantially in the two analyzed samples (Φ = 0.01 and 0.10). The pore microstructures are considered isotropic in connectivity and percolation threshold. Using two finite-scaling schemes we found percolation thresholds with critical porosities Φc 0.05. Based on statistical considerations, the millimeter size samples that can be analyzed by XCT are large enough to provide a meaningful picture of the pore geometry related to macroporosity. The samples contain also a small fraction (i.e. < 0.01) of pores with radii < 1 μ m, which were resolved by FIB-nt. Often these pores can be found along grain boundaries. These pores are granular shaped and are not connected to each other. Typical samples size that can be analyzed by FIB-nt is on the order of tens of microns, which turned out to be too small to provide representative geometric information unless an effort is made that involves several FIB-nt realizations per sample. © 2014 Springer Science+Business Media Dordrecht.

Agency: Cordis | Branch: FP7 | Program: CP-FP | Phase: Fission-2008-1.1.2 | Award Amount: 5.11M | Year: 2009

The MoDeRn project aims at providing a reference framework for the development and possible implementation of monitoring activities and associated stakeholder engagement during relevant phases of the radioactive waste disposal process, i.e. during site characterisation, construction, operation and staged closure, as well as a post-closure institutional control phase. Monitoring provides operators and other stakeholders with in-situ data on repository evolutions, to contribute to operational safety, to help manage construction, operation and/or closure activities, and may allow for a comparison with prior safety assessments. It thus provides information to inform necessary decisions. If, in addition, monitoring activities respond to stakeholder needs and provide them with understandable results, they will contribute to transparency and possibly to stakeholder confidence in the disposal process. The project is structured into six work packages (WPs). The first four WPs are dedicated to (i) analyze key objectives and propose viable strategies, based on both technical and stakeholder considerations; to (ii) establish the state of the art and provide technical developments to match specific repository requirements; to (iii) conduct in-situ monitoring demonstration experiments using innovative techniques; and to (iv) conduct a case study of monitoring and its integration into staged disposal, including specific scenarii analysis aimed at providing guidance on how to handle and communicate monitoring results, in particular when these provide unexpected information. In order to provide a shared international view on how monitoring can be developed within a given national context, WP5 regroups key dissemination activities and WP6 will provide a reference framework integrating project results and describing feasible monitoring activities, suggesting relevant stakeholder engagement activities, and illustrating possible uses of monitoring results for decision-making.

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