Factors influencing the long term stresses in an engineered barrier around deep radioactive waste

Some proposed schemes for deep geological disposal of radioactive waste include the installation of waste containing canisters in geological nonsaline formations such as clay, marl or granite. An engineered barrier, generally composed of an expansive material (either active clays or compacted mixture of clay powder and high density clay pellets) is then contemplated between the canister and the host formation. Once the sealing barrier is placed, a coupled hydro-thermo-mechanical process takes place. The initially dry material of the barrier will expand during its hydration by drainage of the surrounding formation. At the same time, deformations associated with the drying-wetting cycle caused by the transient flow towards the barrier will develop in the host formation. In addition, the heat produced by the waste will decrease with time generating a temperature cycle which influences both flows and deformation. The study of such complex processes requires the development in parallel of real scale tests and numerical tools. In the present work, an improved model handling both saturated and unsaturated flow conditions is used to analyse the long term response of the barrier. The factors influencing the final stress state are then discussed on the basis of stress paths computed with distinct input parameters