Multidimensional modelling of clay cement interactions using the alliances coupling geochemistry transport tool

In the context of geological disposal of nuclear waste, safety studies have to consider time scales accounting for the long period of the high level and long lived radionuclides. Moreover, safety assessments involve various phenomena, which are often interdependent. However, time scales of laboratory experiments are necessarily short compared to repository ones and the experiments are often focussed on only one specific phenomenon. Numerical modelling offers a reliable way to deal with the extrapolation of experimental results to longer time scales as well as to account for coupled phenomena. Staring the lack of numerical tools in this field, 4 years ago, Andra and CEA decided to launch the Alliances project, which aim is to create a user friendly numerical tool enabling the simulation of multi-phenomenology through numerical couplings. Among those ones, the transport chemistry coupling in a multidimensional space was demonstrated to be of particular interest in the context of a geological disposal. Therefore, it was decided to put the effort on transport-reaction coupling for the early development of the Alliances tool. The goal of this presentation is to show an application case of the Alliances tool. Coupled transport reaction phenomena occurring at the interface between cement and argillaceous materials involved in a geological disposal of high level and long lived radioactive wastes will be described. The necessity to perform multidimensional modelling in order to correctly describe the system evolution in time and space will be demonstrated. (author)