SENSITIVITY OF CEMENT/CLAY INTERACTION MODELLING TO MINERALOGICAL AND TRANSPORT HYPOTHESES
L. De Windt (ENSMP) , D. Pellegrini (IRSN), International Workshop - Mechanisms and modelling of waste/cement interactions, Meiringen (Suisse) 8-12 mai 2005.
Depending on the design options, a large amount of cement and concrete may be introduced in radioactive waste disposal - specially for intermediate level waste (ILW). Cementitious materials may present interesting properties for radionuclide containment and mechanical support. However, it is also recognized that these materials may lead to the modification of near-field clayey materials like bentonite or argillaceous host-rock. These are questions of concern for safety. Recent experimental works and natural analogue studies have greatly improved the understanding of cement/clay interactions, but uncertainties still remain on the occurrence and quantification of processes when considering representative disposal scales over thousands of years. Modelling that provides evolution trends as a support for performance assessment needs to account for these uncertainties.For this purpose, sensitivity analyses of cement/clay interaction to both mineralogical processes and transport properties have been performed with the coupled chemistry-transport code HYTEC. Two configurations are considered in the calculations: an ILW disposal tunnel in claystone, entirely filled with cement, surrounded by an excavation damaged zone (EDZ) and a MX80 bentonite plug held by a thick cement wall.