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Tsang C.F.,Lawrence Berkeley National Laboratory | Tsang C.F.,Uppsala University | Barnichon J.D.,Institute for Radiological Protection and Nuclear Safety | Birkholzer J.,Lawrence Berkeley National Laboratory | And 3 more authors.
International Journal of Rock Mechanics and Mining Sciences | Year: 2012

The present paper provides an overview of key coupled thermo-hydro-mechanical (THM) processes in clay formations that would result from the development of a high-level radioactive waste repository. Here, in this paper, clay formations include plastic clay such as the Boom Clay of Belgium, as well as more indurated clay such as the Callovo-Oxfordian and Upper Toarcian of France and Opalinus Clay of Switzerland. First, we briefly introduce and describe four major Underground Research Laboratories (URLs) that have been devoted to clay repository research over the last few decades. Much of the research results in this area have been gained through investigations in these URLs and their supporting laboratory and modeling research activities. Then, the basic elements in the development of a waste repository in clays are presented in terms of four distinct stages in repository development. For each of these four stages, key processes and outstanding issues are discussed. A summary of the important areas of research needs and some general remarks then conclude this paper. © 2011 Elsevier Ltd.


Gens A.,Polytechnic University of Catalonia | Vallejan B.,Polytechnic University of Catalonia | Sanchez M.,Texas A&M University | Imbert C.,CEA Saclay Nuclear Research Center | And 2 more authors.
Geotechnique | Year: 2011

The paper describes a theoretical and experimental study of the coupled hydromechanical behaviour of a compacted mixture of bentonite powder and bentonite pellets intended as sealing material in underground repositories for nuclear waste. One of the main advantages of the use of powder/pellets mixtures is the reduction of the compaction effort required to achieve the value of average dry density necessary to attain the required swelling potential. However, the heterogeneous fabric of the material requires special approaches in order to describe adequately its behaviour during hydration. A double porosity formulation is presented to account for the presence of two distinct structural levels in the material. Hydraulic equilibrium between the two porosities is not assumed; instead a water exchange term between them is postulated. The formulation is applied to the modelling of a number of one-dimensional swelling pressure tests performed in the CEA (Commisariat à l' Énergie Atomique, France) and CIEMAT (Spain) laboratories. A very satisfactory quantitative description of the experimental observations is obtained that includes a number of complex behaviour features such as size effects and nonmonotonic development of swelling pressures. Some microfabric observations using X-ray tomography and mercury intrusion porosimetry lend support to the conceptual approach adopted. The formulation is then applied to the analysis of a long-term large-scale sealing test performed at the Hades underground facility in Belgium, using the same set of hydraulic and mechanical parameters employed in the modelling of the laboratory tests. Although the field observations exhibit a much higher degree of scatter, the basic behaviour of the field sealing test is satisfactorily simulated. A formulation that incorporates basic features of the microfabric of the mixture is thus able to span successfully over a large range of space and time scales.


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 | Cui Y.J.,ParisTech National School of Bridges and Roads | Tang A.M.,ParisTech National School of Bridges and Roads | And 2 more authors.
Applied Clay Science | Year: 2012

Boom clay formation, a deposit of slightly over-consolidated marine clay that belongs to the Oligocene series in the north east of Belgium, has been studied as a possible host material of nuclear waste disposal. In this context, the long-term deformation behavior of Boom clay is of crucial importance in the performance assessment of the whole storage system. In this study, low and high pressure oedometer tests are carried out; the e-log σ'v (void ratio-logarithm of vertical effective stress) and e-log t (void ratio-logarithm of time) curves obtained are used to determine the compression index Cc*, swelling index Cs* and secondary deformation coefficient Cα during both loading and unloading. The relationship between Cα and the effective stress ratio (σ'v/σ'c, vertical effective stress to pre-consolidation stress) is analyzed, and it is observed that Cα increases linearly with log σ'v/σ'c. Examination of the ratio of Cα/Cc* for various soils shows that the secondary deformation behavior of Boom clay is similar to that of shale and mudstone. The relation between Cα and Cc* is linear; but the relation between Cα and Cs* is bi-linear. The bi-linearity observed is related to two different mechanisms: the mechanically dominated rebounding and the physico-chemically dominated swelling. © 2012 Elsevier B.V.


Ragoussi M.-E.,Oecd Nuclear Energy Agency | Brassinnes S.,Ondraf Niras
Radiochimica Acta | Year: 2015

The NEA Thermochemical Database (TDB) Project (www.oecd-nea.org/dbtdb/) provides a database of chemical thermodynamic values treating the most significant elements related to nuclear waste management. The work carried out since the initiation of TDB in 1984 has resulted in the publication of thirteen major reviews and a large set of selected values that have become an international reference in the field, as they are characterized for their accuracy, consistency and high quality. Herein, we describe the basis, scientific principles and organization of the TDB project, together with its evolution from its inception to the present organization as a joint undertaking under Article 5(b) of the Statute of the OECD Nuclear Energy Agency (NEA). © 2015 Walter de Gruyter Berlin/Boston.


Kermisch C.,Roosevelt University | Depaus C.,Ondraf Niras | Labeau P.-E.,Roosevelt University
Progress in Nuclear Energy | Year: 2016

Risk distribution is a core problem in the context of risk management. In this respect, the issue of equity with regard to the management of high-level radioactive waste is complex and has given rise to substantial literature, mainly related to the notions of consent, compensation or sustainable development. This paper aims at contributing to this debate by analysing one aspect often neglected in the ethical literature, namely the question of equity associated with the health impact of different management strategies. Therefore, we will assess qualitatively the potential exposure of individuals in the case of three management strategies – surface storage, non-retrievable geological disposal, and retrievable geological disposal –, and we will compare the results using a criterion of Rawlsian inspiration, which states that the fairest option is the one for which the least well-off groups are as well-off as possible. Our analysis shows that non-retrievable geological disposal is favoured in this regard for each vulnerable group, namely local communities, and on-site workers. © 2016 Elsevier Ltd


Aertsens M.,Belgian Nuclear Research Center | Maes N.,Belgian Nuclear Research Center | Van Ravestyn L.,Belgian Nuclear Research Center | Brassinnes S.,Ondraf Niras
Clay Minerals | Year: 2013

In situ migration experiments using different radiotracers have been performed in the HADES Underground Research Facility (URF), built at a depth of 225 m in the Boom Clay formation below the SCK CEN nuclear site at Mol (Belgium). Small-scale experiments, mimicking laboratory experiments, were carried out with strongly retarded tracers (strontium, caesium, europium, americium and technetium). Contrary to europium, americium and technetium which are subjected to colloid mediated transport, the transport of strontium and caesium can be described by the classic diffusion retardation formalism. For these last two tracers, the transport parameters derived from the in situ experiments can be compared with the laboratory-derived values. For both tracers, the apparent diffusion coefficients measured in the in situ experiments agree well with the laboratory-derived values. In the large-scale experiments (of the order of metres) performed in the URF, non-retarded or slightly retarded tracers (HTO, iodide and H14CO- 3) were used. The migration behaviour of these tracers was predicted based on models applied in performance assessment calculations (classic diffusion retardation) using migration parameter values measured in laboratory experiments. These blind predictions of large-scale experiments agree well in general with the experimental measurements. Fitting the experimental in situ data leads to apparent diffusion coefficients close to those determined by the laboratory experiments. The iodide and H14CO- 3 data were fitted with a simple analytical expression, and the HTO data were additionally fitted numerically with COMSOL multiphysics, leading to about the same optimal values. © 2013 Mineralogical Society.


Desbois G.,RWTH Aachen | Urai J.L.,RWTH Aachen | Hemes S.,RWTH Aachen | Brassinnes S.,Ondraf Niras | And 2 more authors.
Engineering Geology | Year: 2014

This contribution reports on the distribution of in situ pore-water in preserved clay cores from Belgium (Boom Clay at HADES URF level and clay from the Pittem Member of the Gent Formation) and identification of typical pore-scale damage induced by drying.BIB-cryo-SEM (Broad Ion beam-cryogenic-SEM) shows that the majority of pores visible at the resolution of SEM (>. 50. nm) does not contain water, suggesting that the water content measured by weight loss is located in clay aggregates, in pores. <. 50. nm.Because water-free pores are not expecting in situ clay formation, we conclude that the procedure used to preserve the original clay cores is not fully efficient. Observations of evolution of microstructures before and after drying by sublimation of water point to four types of drying-damages driven by the shrinkage of clay particles. On the one hand, quantification of pore size and pore morphologies before and after drying indicates no significant change in statistical pore characterization, suggesting that quantitative pore morphology studies on a large number of pores performed on dried samples are representative of the preserved core samples. On the other hand, the drying damage observed in this contribution is proposed to be responsible of the changes of fluid flow properties typically measured by other authors on preserved and dried specimens of clays. © 2014 Elsevier B.V.


Vandenberghe N.,Laboratory Applied Geology and Mineralogy | Mertens J.,Ondraf Niras
Newsletters on Stratigraphy | Year: 2013

The Rupelian Boom Clay in Belgium is a marine sedimentary deposit with an extensive data set. Astronomical control on high-frequency cyclicity has been proven before, and sedimentological analyses have shown climate-driven cycles caused by sea-level fluctuations. A long cycle in grain-size and bed thickness, involving the entire Boom Clay section, is related to tectonism. Shorter-duration low-frequency cycles, attributed in the past also to climate-driven eustasy, show a relationship with sediment supply expressed by bed thickness but related to tectonism. This apparent contradiction is studied by measuring the thickness differences of the individual Milankovitch-related (astronomical) beds in several wells with the thickness of the same bed in a reference well in the area. Such an approach eliminates eustasy as a controlling factor in the observed cyclicity patterns. Cumulative differential evolution maps of the basin are provided, and the evolution of the relative subsidence in all individual wells through time is visualised as cumulative-difference curves. Both approaches demonstrate that the levels considered in previous studies as controlled by eustasy in fact reflect tectonic history. © 2013 Gebrüder Borntraeger, Stuttgart, Germany.


Beerten K.,Belgian Nuclear Research Center | De Craen M.,Belgian Nuclear Research Center | Wouters L.,Ondraf Niras
Physics and Chemistry of the Earth | Year: 2013

We have compiled a dataset containing information on patterns of burial and erosion that occurred during the last ca. 30. Ma in the Campine area, north-eastern Belgium. This area coincides with the occurrence of the Rupelian Boom Clay which is considered as one of the potential host formations for radwaste disposal. Patterns and estimates of erosion and sedimentation, based on geological and geomorphological data, from several locations within the Boom Clay outcrop and subcrop zone, show increasing burial in northern and north-eastern direction over the last 30. Ma. More southern areas have experienced erosion and denudation during some geological stages, usually in the order of several 10. m, up to 100. m at most at two discrete locations. During the Quaternary, erosion is a widespread phenomenon in the Campine area, except in the Roer Valley Graben. The obtained estimates of erosion and burial are compared and discussed in the context of the overall geodynamic evolution of north-western Europe. © 2013 Elsevier Ltd.

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