In situ and laboratory investigations of fluid flow through an argillaceous formation at different scales of space and time, Tournemire tunnel, southern France |
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Authors: | Jean-Yves Boisson Lucien Bertrand Jean-François Heitz Yann Golvan |
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Institution: | (1) Institute for Nuclear Protection and Safety, CEA/IPSN/SERGD – CEN FaR – BP6, 92265 Fontenay-aux-Roses, Cedex, France,;(2) ANTEA (BRGM Group), 45061 Orléans, France,;(3) Research Centre for Environment, Energy and Waste (CREED-VIVENDI Group), 780520 Limay, France, |
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Abstract: | In the context of a research and development program on waste disposal, an experimental site (Tournemire tunnel, Aveyron,
France) was selected by the French Institute for Nuclear Protection and Safety (IPSN) in order to undertake studies on potential
fluid flow at different scales of space and time within a 250-m-thick argillaceous formation. The argillite has a low natural
water content (~3–5%) and very low radii access porosity. Diffusion (tritiated water) coefficients (1×10–12 to 2×10–11 m2/s) and hydraulic conductivities derived from different types of laboratory tests (10–14 to 10–13 m/s) are characteristics of a very low-permeable rock. In situ hydraulic tests (including long-term hydraulic-head measurements)
were used to obtain values for hydraulic head and hydraulic conductivity at a scale of 1–10 m (10–13 to 10–11 m/s). Despite uncertainties on these data (due to a scale factor, presence of fissures, and possible artefacts due to hydro-chemo-mechanical
coupling), it is expected that fluid flow is essentially governed by diffusion processes. Identification of possible natural
flows at larger scales of time and space was investigated using natural isotopic tracers from interstitial fluids. Modelling,
based on the deuterium profile along the clay formation and assuming pure diffusion processes, provides estimations of possible
flow times. However, lack of knowledge concerning the past geological evolution of the site and the possible role of a fracture
network do not permit reduction of uncertainties on these estimations at this stage.
Electronic Publication |
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Keywords: | diffusion hydraulic properties hydraulic testing laboratory experiments/measurements confining units |
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