Interactions between concrete and claystone in unsaturated conditions during ventilation phase in deep geological ILLW repository P. Thouvenot (1), O. Bildstein (1), I. Pointeau (1), B. Cochepin (3), I. Munier (3), X. Bourbon (3) and E. Treille (3) (1)CEA, DEN, DTN/SMTM/LMTE, Saint-Paul-lez-Durance – France (2) ANDRA Châtenay-Malabry Cedex - France Context : behavior of materials in ILLW cells during ventilation phase Concepts of deep geological repository of intermediate level long-lived radioactive waste (ILLW ) largely involve concrete materials. During the operating period (up to 100 years), part of the concrete components will be subject to ventilation with air drawn from the surface, in order to maintain operating safety and contribute to the evacuation of residual heat from waste. The interactions between concrete and claystone during this period lead to (1) the hydrolysis, sulfatic and carbonated attacks of the concrete components, processes which trigger a progressive lowering of pH inside the cement paste and (2) to the alteration of the claystone submitted to the migration of a high pH plume especially in the excavation damaged zone (EDZ). These processes may occur in unsaturated conditions involving intricated couplings between transport of water and CO2 in the gas and liquid phases, capillary processes during the desaturation of the concrete and clay stone, and chemical reactions between minerals and aqueous species. Conclusions Carbonation in satured and unsatured conditions Model description Modelling results show that the water saturation reaches a value close to complete saturation (98%) in the EDZ within the first year and then progressively drops to 35 % in a time span of 100 years. The system remains unsaturated from the shaft (concrete) to the EDZ and is therefore characterised by a high mobility of CO2 through the gas phase. pH increases in the claystone close to the interface with concrete by one pH unit during the same period. In the claystone, precipitation of calcite and dolomite, sepiolite, hydrotacite and zeolites (K-philipsite, laumontite) is predicted at the expense of siderite and celestite, while sulphate migrates into the concrete to form ettringite. The alteration front is limited to few centimeters over this period of 100 years. Simulations of carbonation processes are performed with Toughreact v1.2 – 1D radial geo- metry – 100 years of ventilation – a variety of secondary phases in order to evaluate the alteration extension of both media. During drying of the concrete, atmospheric carbonation in unsaturated conditions involves intricate couplings between capillary flow, transport of both vapour and liquid water as well as aqueous and gaseous CO 2. Chemical reactions lead, in the same time, to the alteration of the cement hydrates (reactions with dissolved CO 2 ). Primary mineral are destabilized and secondary minerals are formed according to kinetics laws. 2 different approaches are compared for the complete multiphase reactive model : an unsaturated case and a saturated case Waste disposal package Disposal cell Protection airlock (dual gate system) Access drift Note that the transport properties depend on the liquid saturation : D = D 0  a+1 S l b (Millington Quirk ) Profile of primary minerals in the micro-fractured and fractured EDZ at initial time Complete dissolution at the concrete/argilites interface of illite, microcline, dolomite, pyrite, kaolinite, siderite, and celestite Precipitation of calcite and magnetite Precipitation of secondary minerals : hydrotalcite, sepiolite, straetlingite CSH 1.2, dawsonite, phillipsite, and laumontite. After 50 years  precipitation of secondary ettringite Processes are exarcerbed in satured compared to undersaturated conditions (as shown here for laumontite precipitation (Andra, 2005) Profile of primary and secondary minerals in the micro- fractured and fractured EDZ at 50 years of simulation Claystone primary mineralsVolume fraction Quartz alpha0,185 Calcite0,263 Dolomite0,0116 Pyrite0,0067 Célestite0,0006 Sidérite Fe Ca ,0059 Montmorillonite-Na0,021 Montmorillonite-Ca0,041 Illite-Mg0,221 Kaolinite0,0086 Microcline0,0556 Total = 0,82 Porosity  0,18 Concrete primary mineralsVolume fraction Portlandite0,050 CSH 1.60,120 Ettringite0,031 Hydrotalcite0,003 C3FH60,018 Monocarboaluminate0,020 Calcite0,627