This report summarize the results of the IAEA's Cooperative Research Project, which began in 2005... more This report summarize the results of the IAEA's Cooperative Research Project, which began in 2005 and was completed in 2010. The CRP has the overall purpose to transfer modelling expertise and numerical simulation technology to countries needing them for their national nuclear waste management programmes. Basic activities as part of this CRP consisted of (1) demonstrating the use of modelling strategies to address relevant issues using site-specific data (if available), (2), gain insights in the reliability and uncertainty of numerical model predictions, and (3) improving the modelling capabilities at institutions in the participating Member States.
The large-scale in situ PRACLAY heater test: First observations on the in situ thermo-hydro-mechanical behaviour of Boom Clay
International Journal of Rock Mechanics and Mining Sciences
Abstract In the frame of RD&D on the geological disposal of radioactive waste in Belgium, the... more Abstract In the frame of RD&D on the geological disposal of radioactive waste in Belgium, the large-scale PRACLAY heater test is being carried out in the HADES underground research facility (URF) in Mol (Belgium). The thermo-hydro-mechanical (THM) behaviour of Boom Clay has been studied over several decades through small-scale laboratory tests and intermediate scale in situ experiments. The intermediate-scale in situ experiment ATLAS allowed to observe the impact of heat on the Boom Clay beyond the zone affected by the drilling of the borehole hosting the heater. On November 3, 2014, the in situ large-scale PRACLAY heater test was started, aiming at studying the THM behaviour of the clay in the near field, i.e. within the excavation damaged zone, and in the far-field of a heated gallery. An extensive monitoring network installed around the PRACLAY gallery allows to observe the evolution of temperature and pore water pressure in the Boom Clay. In this paper, the first observations that have been made since the start of the PRACLAY heater test are reported. These observations generally confirm the knowledge gained previously from experiments performed at smaller scales. The PRACLAY heater test provides a realistic estimate of what the thermal pressurisation of the Boom Clay would be around a geological disposal facility.
Gas migration through a potential host clay formation for the geological disposal of radioactive ... more Gas migration through a potential host clay formation for the geological disposal of radioactive waste in Belgium is experimentally investigated in the laboratory, and numerical modelling is performed to help in the interpretation of the results. Selected air injection tests under oedometer conditions on initially saturated Boom Clay samples with oriented bedding planes are presented in the paper. Priority in the experimental programme was given to the study of the deformation response along the injection and dissipation stages, as well as to the analysis of the pore network changes, which detect the opening of fissures that can act as preferential air pathways. The experimental results were simulated using a fully coupled hydro-mechanical finite element code, which incorporates an embedded fracture permeability model to account for the simulation of the gas flow along preferential pathways. Clay intrinsic permeability and its retention curve were assumed to be dependent on strains through fracture aperture changes. The numerical results could reproduce upstream / downstream pressures, outflow volume and soil volume change accurately. The experimental results, combined with the numerical simulation, provide good insight into the role of the volumetric response and of the bedding planes on the air transport properties of Boom Clay samples, confirming that fracture aperture occurs during gas injection, which eventually dominates further injection and pressure release stages.
IAEA-TECDOC-1717 The use of numerical models in support of site characterization and performance assessment studies of geological repositories
This report summarize the results of the IAEA's Cooperative Research Project, which began in ... more This report summarize the results of the IAEA's Cooperative Research Project, which began in 2005 and was completed in 2010. The CRP has the overall purpose to transfer modelling expertise and numerical simulation technology to countries needing them for their national nuclear waste management programmes. Basic activities as part of this CRP consisted of (1) demonstrating the use of modelling strategies to address relevant issues using site-specific data (if available), (2), gain insights in the reliability and uncertainty of numerical model predictions, and (3) improving the modelling capabilities at institutions in the participating Member States. Author's contributions comprise source term calculations using GRAPOS1 (a module of the EMOS code) and DUST-MS codes, contaminant transport calculations with PORFLOW, leading the comparison study on the impact on the impact of the disposal concept (Section 4.2.1), contributing to the comparison study on the impact of the conceptu...
Comparative study of three in-situ heating test of anisotropic media: the HE-D, TER and ATLAS experiments
The paper presents an interpretation ofthe Thermo-Hydro-Mechanical (THM) behaviour of three clays... more The paper presents an interpretation ofthe Thermo-Hydro-Mechanical (THM) behaviour of three clays in three in-situ heating tests. First, the in-situ measurements are explored and common rock features are identified. Then a 3D THM model is set up for each ofthe tests and the HM response induced by the drilling of the heating boreholes as well as the THM response during the heating phase are discussed.
Global comparisons between experimental and numerical stress paths ______________ 6 Relevance of ... more Global comparisons between experimental and numerical stress paths ______________ 6 Relevance of the modelling work and results to the performance assessment (PA) and repository design _____________________________________________________________ 6.1 Background ______________________________________________________________ 6.2 Contribution of modelling works in WP5 to PA _________________________________ 6.3 Remaining open questions ___________________________________________________ 7 Conclusions ___________________________________________________________
Determination of the anisotropic thermal conductivity of the Boom Clay based on a combined numerical interpretation of two in situ heater tests at different scales
Interaction entre la zone endommagée autour d'un tunnel et son soutènement – Simulation numérique
Cet article porte sur la modélisation numérique de la localisation des déformations en bande de c... more Cet article porte sur la modélisation numérique de la localisation des déformations en bande de cisaillement autour d'une galerie creusée à Mol, dans le laboratoire souterrain d'EURIDICE. La simulation numérique a permis la mise en évidence d'un réseau de bandes de cisaillement en bon accord avec les observations sur site. La déformabilité de l'argile de Boom impose le placement d'un soutènement, qui limite la convergence et le développement de la zone plastique. L'anisotropie de contrainte initiale et de comportement ainsi que la localisation des déformations en bandes de cisaillement influencent fortement la répartition des pressions sur le soutènement. Il apparaît que celles-ci sont fortement couplées à la structure en bande de cisaillement et donc fort hétérogènes. Ceci devrait avoir des conséquences sur le dimensionnement du soutènement, qui doit être capable de reprendre une telle distribution d'efforts.
An experimental study on Ypresian clays – one of the potential deep and sedimentary clay formatio... more An experimental study on Ypresian clays – one of the potential deep and sedimentary clay formations in Belgium for the geological disposal of heat-emitting radioactive waste – has been undertaken to systematically study anisotropic features on the thermal conductivity using a setup with thermal flux measurement. A careful pre-conditioning protocol before the thermal tests has been followed to ensure a very high degree of saturation and the closure of fissures/gaps along bedding planes. Thermal conductivity data with this improved pre-conditioning protocol allowed obtaining results consistent with the values reported when using back-analysis in a constant volume cell with fully saturated material.
Thermal impact on damaged argillaceous rocks: Permeameter test and Isostatic test on Boom Clay and Opalinus Clay from the TIMODAZ project
Within the framework of the EC-funded TIMODAZ project, SCK·CEN performed two different types of l... more Within the framework of the EC-funded TIMODAZ project, SCK·CEN performed two different types of laboratory tests in Work Package 3.1: The first type is a permeability test on Boom Clay sample and Opalinus Clay sample in a cell of constant volume, and the test is named Permeameter test. The clay samples were initially introduced with artificial planar fractures; the different pore water compositions were injected into the samples for permeability tests; the permeability tests were performed at different temperatures; and the design of these Permeameter cells allowed the use of μCT scanning in order to follow the fracture aperture and density changes within the object before and after the permeability tests. The second type is a permeability test on Boom Clay sample and Opalinus Clay sample under confining cell pressure, the sample is subjected to consolidation without constant volume, and the test is named Isostatic Test. The clay samples were initially damaged by drilling internal c...
bituminized radioactive waste in Boom Clay behaviour of in situ Hydro-chemical modelling of service
The hydro-chemical (CH) interaction between swelling Eurobitum bituminized radioactive waste (BW)... more The hydro-chemical (CH) interaction between swelling Eurobitum bituminized radioactive waste (BW) and Boom Clay was investigated to assess the feasibility of geological disposal for the long-term management of this waste. First, the long-term behaviour of BW in contact with water was studied. A CH formulation of chemically and hydraulically coupled flow processes in porous materials containing salt crystals is discussed. The formulation incorporates the strong dependence of the osmotic efficiency of the bitumen membrane on porosity and assumes the existence of high salt concentration gradients that are maintained for a long time and that influence the density and motion of the fluid. The impacts of temporal and spatial variations of key transport parameters (i.e. osmotic efficiency (s), intrinsic permeability (k), diffusion, etc.) were investigated. Porosity was considered the basic variable. For BW porosity varies in time because of the water uptake and subsequent processes (i.e. d...
Testing of safety and performance indicators (SPIN)
Europace, 2003
To assess the overall safety of a geological repository by means of numerical radionuclide releas... more To assess the overall safety of a geological repository by means of numerical radionuclide release calculations, specific magnitudes are needed which follow from the calculation and can be compared with reference values. Such magnitudes are often called safety indicators. The most common safety indicator used so far is the effective dose rate. The uncertainty of dose rate calculations, however, increases with the time under consideration, and therefore it seems desirable to have additional indicators to improve the reliability of performance assessments. As long as not the overall safety but the performance of individual barriers is assessed, or the functioning of the system is to be showed, another type of indicators can be used, these are sometimes called performance indicators. The SPIN project identified and tested seven safety and fourteen performance indicators. Safety indicators have been mainly identified by evaluating the open literature, performance indicators through syst...
International Journal for Numerical and Analytical Methods in Geomechanics, 2017
Deep excavation in some geological media needs lining of the gallery. This could limit the extent... more 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.
Advances in Laboratory Testing and Modelling of Soils and Shales (ATMSS), 2017
Gas transport properties in argillaceous rocks are becoming an important issue within different c... more Gas transport properties in argillaceous rocks are becoming an important issue within different contexts of energy-related geomechanics (disposal of radioactive waste, production of shale gas, CO2 sequestration). The present investigation aims at describing the pathways generated on a deep Cenozoic clay during gas injection using different microstructural techniques. Mercury intrusion porosimetry results have allowed detecting fissures after gas injection tests that have not been observed on intact samples. The opening of these pressure-dependent fissures plays a major role on gas permeability. A complementary insight into the connectivity of these fissures has been quantified by microcomputed tomography.
Around galleries excavated at depth in geological media, the creation of a damaged zone with sign... more Around galleries excavated at depth in geological media, the creation of a damaged zone with significant irreversible deformation is generally unavoidable. In the case of a geological disposal system for high-level radioactive waste, the resulting change in the host rock properties in this damaged zone may potentially be important with respect to the long-term evolution and the performance of that system. In this context, predicting the extent of the so-called Excavation Damaged Zone (EDZ) and, possibly, the fractures' network topology remains a challenge. This study is aimed to simulate numerically the extension of this zone at the large scale's excavation, around the Connecting gallery (HADES URL, Mol, Belgium), in Boom clay host rock through analyzing the evolution of strain localization in shear bands mode. To realistically model the involved phenomena, the concrete lining is considered on the gallery wall highlighting its impacts on the evolution of convergence and EDZ around the gallery. The focus of the current paper is made on analyzing the coupled hydro-mechanical behavior of Boom clay host rock during and after the gallery excavation with respect to the evolution of localized shear bands around the gallery. This study is accompanied by the analysis of the contact mechanism on the interface between the clay massive and the lining. The obtained results reveal some interesting features regarding the contact phenomenon relatively to the evolution pattern of shear bands within the clay around the gallery. To assess the reliability of the proposed approach, a discussion on some in-situ observations during the gallery's construction is also performed based on which a good agreement is found between the in-situ evidence and simulated results.
Journal of Rock Mechanics and Geotechnical Engineering, 2010
In Belgium, the Boom clay was selected as a potential host formation for the disposal of high-lev... more In Belgium, the Boom clay was selected as a potential host formation for the disposal of high-level radioactive waste (HLW). To demonstrate the suitability of Boom clay for bearing thermal load induced by the HLW, a large-scale in-situ heater test, called PRACLAY heater test, will be conducted in the underground research laboratory (URL) in Mol. Owing to the limitations of the test (a short period of time compared with that considered in a real repository, different boundary conditions, etc.), the test is designed to simulate, in a conservative way, the most critical state and phenomena that could occur in the host rock. The PRACLAY gallery was excavated at the end of 2007; the heating phase will begin in 2010 and will last for at least 10 years. The PRACLAY gallery itself leaves an opportunity to study the possibilities of sealing a disposal drift in Boom clay and testing the feasibility of hydraulic cutoff of any preferential pathway to the main access gallery through the excavation damage zone (EDZ) and the lining with a seal in a horizontal drift (horizontal seal). Indeed, this is a generic problem for all deep geological disposal facilities for HLW. An annular seal made of compacted swelling bentonite will be installed in the front of the heated part of the PRACLAY gallery for these purposes. This paper provides detailed considerations on the thermo-hydro-mechanical (THM) boundary conditions for the design of the PRACLAY heater test and the seal test with the support of numerical calculations. It is believed that these important items considered in the PRACLAY heater test design also constitute key issues for the repository design. The outcome of the PRACLAY heater test will be an important milestone for the Belgian repository design.
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