Nuclear Waste Storage
Tools for the assessment of multi-barrier systems
Disposal in deep clay geological formation along with the confinement of the canisters containing the waste with proper buffer material is the most promising way for disposing of these high level wastes. Involved materials (host rock/clay and buffer) must be deeply analyzed in order to provide reliable prediction for the behaviour of storage facilities. Several interacting physical phenomena take place simultaneously during the waste disposal life, making any prediction for the reservoir behaviour a challenging subject. The involved materials are basically expected to undergo significant changes in temperature, stress state and water content. In this sense, the better understanding of the thermo-hydro-mechanical (THM) behaviour of these materials has to be addresses with reasonable accuracy.
Research Group for Nuclear Waste Storage:
International Research Projects
The Gas-Permeable Seal Test (GAST) was initiated in 2010 and conducted at the Grimsel Test Site (GTS, Switzerland) to demonstrate the effective functioning of gas-permeable seals at realistic scales and under realistic hydraulic conditions.
FEBEX: Full-scale Engineered Barriers Experiment
Modelling of the bentonite and the repository design. Partners are ENRESA and UPC (Spain), NAGRA (Switzerland), SKB (Sweden).
SHARC2: Shale Research Centre consortium
This consortium unites the state-of-the-art knowledge and research on shales of both oil industries and nuclear agencies. The Shale Research Centre’s objectives are the experimental and theoretical characterisation of gas shales properties and the analysis of problems related to reservoirs performance. Partners are CSIRO (Australia), NAGRA (Switzerland), BP (U-K), Total (France), SINOPEC (China).
Experimental investigation for the analysis of the hydro-mechanical behaviour of gas shales. Partner is CHEVRON (US).
FE-Experiment in Mont Terri
A full scale emplacement project of high level nuclear waste canisters in Mont Terri. The emplacement follows the Swiss concept involving compacted granular bentonite as a buffer material and Opalinus Clay as a host rock. the in-situ experiment is leaded by NAGRA (Switzerland).
Analysis of geomaterial behaviour in unsaturated conditions
In the concept of nuclear waste repository, both the natural and the engineered barriers are in unsaturated states. Understanding and characterising the behaviour of unsaturated geomaterials composing the multi-barrier system is therefore one of the main issues. Several advanced devices are available in our laboratory allowing to analyse experimentally swelling behaviour, mechanical response in unsaturated conditions, water retention behaviour and liquid and gas transfers.
Characterisation of the Thermo-Mechanical response of geomaterials
Heat from nuclear wastes induces temperature changes in the multi-barrier system and justifies our interest for the thermo-mechanical behaviour of geomaterials. The determination of model parameters in coupled thermo-mechanical models with consideration of partial saturation requires advanced lab testing. The behaviour of the geomaterial in such complex conditions has to be characterised in order to understand the in-situ governing physical processes and to feed numerical models with the necessary information.
|Non-iso Thermal Testing|
Thermo-hydro-mechanical constitutive modelling
A variety of phenomena occurs during wetting, drying, heating or mechanical loadings. The swelling behaviour, thermal collapse, wetting collapse, and the isothermal mechanical behaviour must all be included in a constitutive model. Based on concepts from the Cam-Clay model, our model, ACMEG, has been extended and tested to reproduce the key behaviours of unsaturated soils. It is currently expanded to other problems such as anisotropy or chemical couplings.
Numerical modelling – a key process in understanding the behaviour of the multi-barrier systems
The development of advanced elasto-plastic constitutive models for soils and their application to nuclear waste repository design in a finite element framework is a key competence in the Soil Mechanics group at EPFL.
The analysis of thermally and hydraulically induced plastic strains is performed in order to evaluate the long-term sealing capabilities of buffer materials.
Thermo-Hydro-Chemo-Mechanical behaviour of Shales
Shales are not only considered as a suitable soil for the storage of high-level nuclear waste. They also provide perfect cap rocks for oil and gas reservoirs. This makes their behaviour an exciting subject of research for the civil and environmental engineer. Hi-tech and advanced boring techniques are essential for the exploitation of the traditional and more recently discovered natural resources.
The mechanical issues occurring during a reduction of earth pressure form the basis for a challenging study of its effects on the surrounding material. Pressures of dozens of MPa have been recorded. Such in-situ stresses are not easy to assess in the laboratory. Nonetheless, LMS possesses adequate equipment. One example is the high-pressure oedometer cell, which can apply pressures up to 100 MPa. This kind of device allows for a mechanical characterization of the shales using methods similar to those applied to conventional soils.
A second aspect inspiring the research on shales and shale gas and/or oil exploitation, is the occurrence of high temperatures. At high depths and under high pressures, temperatures up to 100°C can be reached. LMS is equipped with an innovative device that can reproduce such temperatures, as well as extreme mechanical conditions, with an option for partial saturation. LMS’s thermo-hydro-mechanical (THM) triaxial cell is especially designed for this kind of situations.
Bore companies always search for efficient ways of exploitation. This affects also the engineers. One example of borehole improvement is the use of a drilling fluid, which is often water with dissolved salts. This fluid interacts with the soil with which it is in contact. In the case of partial saturation, the fluid can enter the pores of the material, for example. If saturated, a chemical gradient can result in osmotic pressures and flow of water, or diffusion of ions. All cases involve a change in the local chemistry of the pore fluid. LMS is currently researching the influence of salts on saturated soils and shales.
Previous studies in the field of shale characterization focussed mainly on (chemo-)poro-elasticity. LMS’s approach is developed in such a way that it provides the opportunity to consider irreversible strains as well.
The mentioned points alltogether form an advanced, unitary framework for the analysis of the thermo-hydro-chemo-mechanical behaviour of shales. LMS is convinced that its research adds valuable knowledge to the civil and environmental engineering community by profoundly researching the elasto-plasticity of this material.
- Anisotropic volumetric behaviour of Opalinus Clay shale upon suction variation, A. Minardi, E. Crisci, A. Ferrari and L. Laloui., Geotechnique Letters, vol. 6, p. 1-5, 2016
- Hydro-chemo-mechanical characterisation of sand/bentonite mixtures: with a focus on the water and gas transport properties, D. Manca, L. Laloui and A. Ferrari (Dirs.), Thèse EPFL, n° 6790, 2015
- Constitutive analysis of shale: a coupled damage plasticity approach, F. Parisio, S. Semat and L. Laloui. , International Journal of Solids and Structures, vol. 75-76, p. 88-98, 2015.
- Experimental analysis of the water retention behaviour of shales, A. Ferrari, V. Favero, P. Marschall and L. Laloui. , International Journal of Rock Mechanics and Mining Sciences, vol. 72, p. 61-70, 2014.
- Water retention behaviour and microstructural evolution of MX-80 granular bentonite during wetting and drying cycles, A. Seiphoori, A. Ferrari and L. Laloui., Geotechnique, vol. 64, num. 9, p. 721-734, 2014.
- Numerical Analysis of Canister Movements in an Engineered Barrier System, F. Dupray and L. Laloui, Acta Geotecnica, pp. 1-15, 2014
- An experimental and constitutive investigation on the chemo-mechanical behaviour of a clay, P. Witteveen, A. Ferrari and L. Laloui, Bio- and Chemo- Mechanical Processes in Geotechnical Engineering, p. 32-43, 2014
- Thermo-hydro-mechanical characterisation and modelling of MX-80 granular bentonite, Seiphoori, A., PhD Thesis 2014, EPFL Ecole polytechnique fédéral de Lausanne.
- Shot-clay MX-80 bentonite: an assessment of the hydro-mechanical behaviour, Ferrari, A., Seiphoori, A., Rüedi, J., Laloui, L. Engineering Geology -Amsterdam-, vol. 173, p. 10-18, 2014.
- THM coupling sensitivity analysis in geological nuclear waste storage, Dupray, F., Li, C., Laloui, L., Engineering Geology -Amsterdam-, vol. 163, p. 113-121, 2013.
- Multiphysical Testing of Soils and Shales, L. Laloui, A. Ferrari, Springer, 2012.
- An advanced calibration process for a thermo-hydro-mechanical triaxial system, Seiphoori, A., Ferrari, A. and Laloui L. Deformation Characteristics of Geomaterials, 2011, vol. 1, p. 396-403.
- New experimental tools for the characterization of highly overconsolidated clayey materials in unsaturated conditions, Salager, S., Ferrari, A. and Laloui L. In: Mechanics of unsaturated geomaterials, Laloui, L. (ed.), John Wiley & Sons, 2010, p. 113-126.
- An oedometer for studying combined effects of temperature and suction on soils, François B. and Laloui L. Geotechnical testing journal, vol. 33, num. 2, 2010, p. 112-122.
- ACMEG-T: Soil Thermo-Plasticity Model, Laloui L. and François B. Journal of Engineering Mechanics, vol. 135, num. 9, 2009, p. 932-944.
- Explaining thermal failure in saturated clays, Hueckel T., Laloui L. and François B. Géotechnique, vol. 59, num. 3, 2009, p. 197-212.
- Thermo-hydro-mechanical simulation of ATLAS in-situ large scale test in Boom Clay, François B., Laloui L. and Clément L. Computers and Geotechnics, vol. 36, 2009, p. 626-640.
- On the use of the generalised effective stress in the constitutive modelling of unsaturated soils, Laloui L. and Nuth M. Computer and Geotechnics, vol. 36, num. 1-2, 2009, p. 20-23.
- Advances in modelling hysteretic water retention curve in deformable soils, Nuth M. and Laloui L. Computer and Geotechnics, vol. 35, num. 6, 2008, p. 835-844.
- Finite element modelling of thermo-elasto-plastic water saturated porous materials, Sanavia L., François, B., Bortolotto R., Luison L. and Laloui, L. Journal of Theoretical and Applied Mechanics, vol. 38, 2008, p. 7-24.
- Experimental investigations of temperature and suction effects on compressibility and pre-consolidation pressure of a sandy silt, Salager S., François B., El Youssoufi S., Laloui L. and Saix C. Soils and Foundations, vol. 48, num. 4, 2008, p. 453-466.
- ACMEG-TS: A constitutive model for unsaturated soils under non-isothermal conditions, François B. and Laloui L. International Journal of Numerical and Analytical Methods in Geomechanics, vol. 32, 2008, p. 1955–1988.
- Numerical simulation of the non-isothermal mechanical behaviour of soils, Laloui L. and Cekerevac C. Computers and Geotechnics, vol. 35, 2008, p. 729-745.
- Effective Stress Concept in Unsaturated Soils :Clarification and Validation of an Unified Framework, Nuth M. and Laloui L. Int. Journ. of Numerical and Analytical Methods in Geomechanics., vol. 32, 2008, p. 771-801.
- Prof. Laloui gave a conference about nuclear waste storage in Sion on 19 January 2012.
- Burying Nuclear Wastes into Swiss ground.
- Prof. Laloui was interviewed on January 19, 2012 on Radio Chablais about the Nuclear Waste Storage solutions investigated in Switzerland.
- Burying the nuclear wastes
Interview of Prof. Laloui about the nuclear waste storage solution chosen in Switzerland.