Simulation of Coupled THM Processes in Opalinus Clay with an EPCA^3D Available to Purchase

This paper is a numerical study on the HE-D experiment within the Opalinus clay formation at the Mont-Terri underground rock laboratory (Switzerland) using a self-developed code, i.e. a 3D Elasto-Plastic Cellular Automaton (EPCA^3D),in which the unsaturated fluid flow, transient heat conduction and anisotropic model have been implemented. The temperature-dependent water viscosity was considered during the simulation. The simulated temperature evolution and the consequences on pore water pressure and rock deformation for Opalinus clay were well consistent with experimental data. It indicated that, the temperature distribution, pore pressure and mechanical behavior are greatly influenced by the anisotropic characteristic of Opalinus clay in HE-D.

Deep geological repository of high-level radioactive wastes is one of the most promising options to isolate wastes from the human environment. High-Level radioactive Waste (HLW) produces heat due to the continuous decay of radionuclide. Thus the geological disposal of HLW will impose a temperature increase upon the surrounding rock. Argillaceous rocks have a lower heat conductivity compared to granite or salt resulting in higher temperatures around the waste canister for a given heat loading. Moreover, the rock reacts sensitive to high temperatures. The increasing temperature will also influence the pore water pressure and might induce deformation of the rock, which again changes the pore water pressure.

Various in-situ heating tests (Gen et al. 2007) have been performed involving the observation of the response of natural sedimentary clay. For instance, in the Hades laboratory the following experiments have been performed: the CACTUS test (Picard et al. 1994), the ATLAS test and the CERBERUS test (Bernier & Neerdael 1996, Bruyn & Labat 2002).

A comprehensive understanding of coupled thermal, hydraulic and geo-mechanical processes (THM) will be a key element for the design of deep geologic repositories. Therefore, based on a self-developed numerical code, i.e. a 3D Elasto-Plastic Cellular Automaton (EPCN^3D) (Pan et al. 2009a, 2009b), this paper presents a numerical study on the coupled THM processes in Opalinus clay in HE-D test.