European Underground Research Infrastructure for Disposal of nuclear waste in Clay Environment

Mol, Belgium

European Underground Research Infrastructure for Disposal of nuclear waste in Clay Environment

Mol, Belgium
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Salehnia F.,University of Liège | Sillen X.,Ondraf Niras | Li X.L.,European Underground Research Infrastructure for Disposal of nuclear waste in Clay Environment | Charlier R.,University of Liège
International Journal for Numerical and Analytical Methods in Geomechanics | Year: 2017

Deep excavation in some geological media needs lining of the gallery. This could limit the extent of the so-called excavation damaged zone and the resulting convergence of the material due to tunneling. Boom clay, the reference potential host rock in Belgium for disposal of high-level radioactive waste, is one of these media for which lining of the gallery walls is essential. A correct simulation of the lining behavior in the course of the excavation process, where the rock comes into contact with the lining, and in the long term, remains a significant challenge in analysis of the whole coupled phenomena of rock in interaction with the lining. This study aims to numerically model the lining behavior. The main objective is to develop a model that could realistically simulate the behavior of a discontinuous lining made of concrete segments. We propose to numerically analyze the response of the blocks in contact with each other and in interaction with rock, with the use of zero-thickness interface elements. To validate the developed model and a proposed approach, a particular analysis compares the obtained results with the available in situ measurements. This study then discusses the deficiency of the simplistic model that considers a continuous lining. In addition, regarding the contact mechanism on the interface between the rock and the lining, the obtained results demonstrate an interesting relation between the contact phenomena and the shear banding within the rock around the gallery. © 2017 John Wiley & Sons, Ltd.

Agency: European Commission | Branch: H2020 | Program: RIA | Phase: NFRP-06-2014 | Award Amount: 9.66M | Year: 2015

The Modern2020 project aims at providing the means for developing and implementing an effective and efficient repository operational monitoring programme, taking into account the requirements of specific national programmes. The work allows advanced national radioactive waste disposal programmes to design monitoring systems suitable for deployment when repositories start operating in the next decade and supports less developed programmes and other stakeholders by illustrating how the national context can be taken into account in designing dedicated monitoring programmes tailored to their national needs. The work is established to understand what should be monitored within the frame of the wider safety cases and to provide methodology on how monitoring information can be used to support decision making and to plan for responding to monitoring results. Research and development work aims to improve and develop innovative repository monitoring techniques (wireless data transmission, alternative power supply sources, new sensors, geophysical methods) from the proof of feasibility stage to the technology development and demonstration phase. Innovative technical solutions facilitate the integration and flexibility of required monitoring components to ease the final implementation and adaptation of the monitoring system. Full-scale in-situ demonstrations of innovative monitoring techniques will further enhance the knowledge on the operational implementation of specific disposal monitoring and will demonstrate the performance of the state-of-the-art, the innovative techniques and their comparison with conventional ones. Finally, Modern2020 has the ambition to effectively engage local citizen stakeholders in the R&D monitoring activity by involving them at an early stage in a repository development programme in order to integrate their concerns and expectations into monitoring programmes.

Yu H.D.,CAS Wuhan Institute of Rock and Soil Mechanics | Chen W.Z.,CAS Wuhan Institute of Rock and Soil Mechanics | Li X.L.,European Underground Research Infrastructure for Disposal of nuclear waste in Clay Environment | Sillen X.,Ondraf Niras
Rock Mechanics and Rock Engineering | Year: 2013

Boom clay can be considered as a transversely isotropic geomaterial. However, due to lack of experimental evidence and data base, it is still difficult to describe the transversely isotropic plastic behavior of this argillaceous rock. In this paper, we present first, by means of an experimental approach, the main features of the mechanical properties of Boom clay. Then, combining the transversely isotropic elastic model and the modified Mohr- Coulomb criterion, a suitable constitutive model is introduced so as to fully describe the mechanical behavior of the studied material, in which, an elastic damage law which takes into consideration, the transversely isotropic effect, a plastic hardening law and a plastic damage law were introduced to describe the nonlinear elastic, hardening and softening behavior of Boom clay. As a preliminary step, the evolution law of both elastic moduli and Poisson's ratio during the elastic stage was obtained by direct analysis of the test data. The synchronism of the elastic damage in both transversal and axial directions was proved by this method. Some of the parameters of the model in the elastic stage were also determined by direct analysis method and further verified by back analysis. Other unknown parameters in the model were determined by back analysis. © Springer-Verlag Wien 2013.

Deng Y.-F.,Nanjing Southeast University | Deng Y.-F.,ParisTech National School of Bridges and Roads | Tang A.-M.,ParisTech National School of Bridges and Roads | Cui Y.-J.,ParisTech National School of Bridges and Roads | Li X.-L.,European Underground Research Infrastructure for Disposal of nuclear waste in Clay Environment
Canadian Geotechnical Journal | Year: 2011

The hydraulic conductivity is a parameter in geotechnical engineering practice that is key in seepage and consolidation analysis. Experimental results show that the hydraulic conductivity is mainly governed by the soil porosity, and correlations with void ratio are usually proposed. The validity of these correlations has been verified for soft clays and sands; however, few studies have included stiff clays. In this work, the hydraulic conductivity of Boom clay, a stiff clay taken from the Essen site in Belgium, was determined from both consolidation and constant-head percolation tests. The data obtained was then analyzed to evaluate the existing correlations to predict the hydraulic conductivity. In addition, as these correlations usually require a referred hydraulic conductivity at a known void ratio, the existing methods are often difficult to use in practice. Thus, a new method was developed allowing the prediction of hydraulic conductivity without the referred value, which was based on two existing correlations and involved the void ratio and the liquid limit. The proposed correlation was verified using the experimental results obtained from Boom clay samples that were collected from various locations in Belgium.

Agency: European Commission | 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.

Verstricht J.,European Underground Research Infrastructure for Disposal of nuclear waste in Clay Environment
Proceedings of the International Conference on Radioactive Waste Management and Environmental Remediation, ICEM | Year: 2013

In the frame of its radwaste disposal research programme, SCKCEN started the construction of the HADES underground research facility in 1980. Including several extensions and a comprehensive experimental programme, it has provided a lot of experience on monitoring. Monitoring is performed for many reasons: construction follow-up, field characterisation, investigation of phenomena, and model validations - in which the underground lab offers the opportunity for upscaling conventional laboratory set-ups. Construction monitoring has allowed to develop and optimise the underground construction techniques in a previously poorly known environment, resulting in a well-mastered application of mechanised methods for gallery construction with minimal damage to the host formation. Access to this formation also allows its characterisation, both geotechnical, geological and geochemical, and the detailed investigation of phenomena such as fracturing and oxidation. Finally, instrumented set-ups allow to test various numerical models by comparing the observations with the predicted behaviour. The specific conditions of the underground laboratory put particular requirements to the sensors. These conditions include the long-term nature of many set-ups - Typically several years to decades, the inaccessibility of many sensors after installation, high mechanical and water pressures, and corrosion. Combined with the fact that many sensors are custom made, obtaining and maintaining a fully functional instrumented set-up can be challenging. A lot of experience has therefore been gained which is very valuable when designing the monitoring of radwaste repositories - And it has allowed us to determine the critical success factors for monitoring. Engineers tend to look at this first from a technical viewpoint - And there are many technical aspects indeed that determine the reliability of monitoring. A first one is the combination of different observations ("redundancy") which can be implemented by the use of several sensors, different sensor principles, different (coupled) parameters, and the combination of point measurements with geophysical techniques. Cabling is also a critical issue as it is often considered as the primary enemy of barrier integrity. Minimal cabling techniques, such as distributed fibre optic monitoring and wireless signal transmission, therefore get increasing attention. Also the interpretation of the monitoring data - in particular those that are perceived as "wrong" or "unexpected", needs sufficient attention. The long-term experience has however also shown that the design of a monitoring programme must look beyond the technical part. In particular for long-term applications, issues such as data management and record keeping are vital to guarantee success in this. Copyright © 2013 by ASME.

Cui Y.J.,ParisTech National School of Bridges and Roads | Nguyen X.P.,ParisTech National School of Bridges and Roads | Tang A.M.,ParisTech National School of Bridges and Roads | Li X.L.,European Underground Research Infrastructure for Disposal of nuclear waste in Clay Environment
Applied Clay Science | Year: 2013

Oedometer tests were carried out with loading/unloading/reloading on natural stiff clays, Ypresian clays (YPClay), taken from several depths. Common unloading/reloading loops were identified. Further examination of the unloading or reloading curves shows that each path can be satisfactorily considered as bi-linear with a small and a larger slope separated by a threshold vertical stress. This threshold stress can be considered as the swelling pressure corresponding to the void ratio just before the unloading or reloading. Indeed, upon unloading, when the applied stress is higher than the threshold stress or swelling pressure, the mechanical effect is dominant and only small mechanical rebound is observed, corresponding to a small microstructure change; by contrast, when the applied stress is lower than the swelling pressure, physico-chemical effect becomes prevailing and soil swelling occurs with a larger microstructure change. Upon reloading, when the applied stress is lower than the swelling pressure, the microstructure is not significantly affected thanks to the contribution of the physico-chemical repulsive force, leading to a small volume change; on the contrary, beyond the swelling pressure, the mechanical effect becomes dominant giving rise to larger volume changes corresponding to the microstructure collapse. Like unsaturated expansive soils, it is found that there is a good relationship between the swelling pressure (threshold stress) and the void ratio just before the unloading or reloading. This is confirmed by the results from the data reported in the literature about other stiff clays such as Boom and London clays. It can be then deduced that the unloading/reloading loop is rather due to the competition between the mechanical and physico-chemical effects on the microstructure changes than the viscosity effect as commonly admitted. © 2013 Elsevier B.V.

Chen G.J.,European Underground Research Infrastructure for Disposal of nuclear waste in Clay Environment | Sillen X.,Belgian Nuclear Research Center | Verstricht J.,European Underground Research Infrastructure for Disposal of nuclear waste in Clay Environment | Li X.L.,European Underground Research Infrastructure for Disposal of nuclear waste in Clay Environment
Computers and Geotechnics | Year: 2011

The ATLAS III small scale in situ heating test aimed at assessing the thermo-hydro-mechanical (THM) effects on the Boom clay of the significant temperature gradients generated in this host rock as a consequence of the geological disposal of radioactive, heat-emitting wastes. This paper presents data on temperature, pore water pressure and total stress measured during the experiment and highlights several interesting observations regarding the thermal anisotropy and THM coupling in the Boom clay. The test has a simple geometry and well defined boundary conditions, which facilitates the comparison between measurement and numerical modeling studies. These studies included three dimensional coupled THM modeling of the test. The good agreement between measurement and numerical modeling of temperature and pore water pressure yields a set of THM parameters and confirms the thermo-mechanical anisotropy of the Boom clay. © 2011 Elsevier Ltd.

Li X.,European Underground Research Infrastructure for Disposal of nuclear waste in Clay Environment
Journal of Rock Mechanics and Geotechnical Engineering | Year: 2013

Disposal of spent nuclear fuel and long lived radioactive waste in deep clay geological formations is one of the promising options worldwide. In this concept of the geological disposal system, the host clay formation is considered as a principal barrier on which the fulfillment of key safety functions rests. Between 2006 and 2010, the European Commission project TIMODAZ, which gathered 15 partners from 8 countries, has investigated the coupled thermo-hydro-mechanical (THM) effects on clay formations for geological disposal of radioactive waste, and specific attention was paid to investigating the thermal effect on the evolution of the damaged zone (DZ). Three types of potential host clay formations were investigated: the Boom Clay (Belgium), the Opalinus Clay (Switzerland) and the Callovo-Oxfordian argillite (France). Intensive experimental (laboratory and in situ in underground research laboratories) and numerical studies have been performed. Multi-scale approach was used in the course of the project. High degree of similarities between the failure modes, sealing process, stress paths, deformation, etc., observed in laboratories and in situ has been obtained, which increased the confidence in the applicability of laboratory test results and up-scaling perspective. The results of the laboratory and in situ tests obtained allowed the parameters for numerical models at various scales to be derived and provided the basis for the simplified performance assessment models that are used to assess the long-term safety of a repository. The good cooperation between the numerical modeler and experimenters has allowed an in-depth analysis of the experimental results and thus better understanding the underlying processes, and consequently increased the capabilities to model the THM effects in claystones. This paper presents the main achievements obtained by TIMODAZ project and shows how a European scientific community investigates a problem of concern in a collaborative way and how the obtained main results are applied to the performance assessment of a geological repository. © 2013 Institute of Rock and Soil Mechanics, Chinese Academy of Sciences.

Chen G.,European Underground Research Infrastructure for Disposal of nuclear waste in Clay Environment | Yu L.,Belgian Nuclear Research Center
Computers and Geotechnics | Year: 2015

In this study, a solution for the response of a poroelastic medium around a deeply excavated circular tunnel is analytically formulated based on Biot's consolidation theory. The proposed solution considers the initial anisotropic stress in the medium around lined or unlined tunnels and is an improvement over previous solutions (Carter and Booker, 1982, 1984) because it considers Biot's coefficient, the combined compressibility of liquid and solid phases in the porous medium, and a thick-walled liner. The solution is expressed using the Laplace transform domain, and numerical inversion techniques are used to obtain real time domain results. The new solution is verified by comparing it with previous analytical solutions and numerical results obtained using the commercial finite element software COMSOL Multiphysics (COMSOL AB, Stockholm, Sweden). Parametric studies are performed to determine the influences of Biot's coefficient and the combined compressibility and liner properties during the consolidation process. © 2015 Elsevier Ltd.

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