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Brussels, Belgium

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. Source

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. Source

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. Source

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. Source

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. Source

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