EVOLUTION OF A GENERIC CLAY/CEMENT INTERFACE: FIRST REACTIVE TRANSPORT CALCULATIONS UTILIZING A GIBBS ENERGY MINIMIZATION BASED APPROACH FOR GEOCHEMICAL CALCULATIONS

The long-term evolution of deep geological repositories for nuclear waste is governed by geochemical processes in conjunction with mass and energy transport. A key role for the design of the multi-barrier system is the knowledge of long term changes at the interfaces between different materials. We investigate the porosity evolution at a generic interface between clay and cement containing materials. We use novel reactive transport codes that couple a Gibbs Energy Minimization (GEM) chemical equilibrium thermodynamic solver with mass transport solvers. Our simulations show that in the cementitious material, the porosity is increased due to the dissolution of portlandite. At the interface, the porosity is strongly reduced in the clay and cement compartment due to calcite precipitation and due to the precipitation of C-S-H solid solution. The time for clogging the interface is highly variable and depends on transport conditions and on the geochemical setup.

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