The excavation damaged zone (EDZ) of the Callovo-Oxfordian argillites can be regarded as a double-porosity media consisting of blocks of undisturbed argillites separated by cracks generated by shear or traction stresses. However, owing to hardware limitations, most of the hydraulic-gas simulations undertaken on large scales are based on an equivalent-porous-media model of the EDZ, where the fractures are not explicitly represented. The aim of this study is to improve the equivalent-porous-media model's consistency with the double-porosity flow behaviours shown by experimental data while keeping the same level of simplification. The new model has been developed through a performance assessment (PA)-like approach in two steps: a phenomenological model including explicit fractures has been designed in accordance with the actual geometrical and hydraulic understanding of the EDZ; then, the properties of the simplified model have been calibrated to comply with the hydraulic behaviour of the explicit-fracture model. This methodological approach has been used on an access gallery parallel to the main horizontal stress axis. The new equivalent-porous-media model differs from the previous one on the following three main points: the gallery EDZ has an anisotropic intrinsic permeability that is lower than previously; the same retention law is used as the undisturbed host rock; and there is a higher relative permeability for gas and water than previously.

The aim of the study is to describe the ambient conditions in an underground repository of nuclear waste over a 100-year-long operation period. The evolution over time of the moisture and the temperature in the ventilation network was assessed by means of numerical simulations. Condensation events are described in terms of location, frequency and flow rate. The physical conceptual model takes into account the heat and vapour advection and exchanges with walls, and heat conduction through the host rock. The results of simulations were analysed to highlight how the architectural design, the gradual extension of storage zones, the ventilation rate and the weather conditions are likely to influence the ambient conditions all along the shafts, the galleries and the storage modules. They illustrate the significant effects on ambient conditions of the wall thermal inertia, the variation in atmospheric pressure over the shaft height, and the ventilation partition in some galleries between incoming and outgoing air from storage modules.

In the 2009 Andra repository concept, Intermediate Level Long Lived Wastes are stored in several 100-m-long storage cells. Concrete over-packs are stacked in piles before being emplaced by row. The large sections opened in the slab floor to enable emplacement by the conveyor could have a major effect on the temperature distribution in the storage cell. The aim of the study is to assess the ability of the ventilation to regulate temperatures along the cell. We focus on the period before closure, when the ventilation rate is at a minimum. The issue has been addressed by undertaking numerical simulations. A specific modelling approach based on head-loss correlations has been used to calculate the distributions of temperature and air velocity at a decimetre scale along the storage cell. The heat transfer and the air flow problems have been solved on a 3D mesh representing 225 rows of waste packages, the concrete walls and the surrounding rock. Different scenarios have been considered about the air flow rate, the heat release and the closure of the conveyor sections at several locations. Results have been analysed in terms of flow patterns, temperature distributions and thermal gradients in air and in concrete.

In the Andra repository concept, a large amount of hydrogen gas will be generated through radiolysis of water and corrosion of metal parts from the infrastructure and the packages containing radioactive waste. The fate of the gas could have a significant impact on the rate of resaturation of the porous media, and needs to be accounted for in order to make accurate predictions of the long-term evolution of the repository. The central zone of the repository consists of a 4.5-kmlong network of galleries which connect the storage zones with the surface through three shafts. These shafts, which will be backfilled and sealed after closure, will have a key role in gas and water exchange between the repository and the overlying aquifer. The aim of this work was to describe the evolution in time of both the water and gas flows in the central zone up to the end of the hydraulic-gas transient. The issue was addressed by means of numerical simulations. The simulations produced local predictions of flow rates and pressures, water saturation and amounts of dissolved gas. The results were analysed to determine how water and gas flows combine in the central zone, when the saturation of the seal will be complete, when the free gas will reach the overlying aquifer, and when the saturation of the central zone will be complete.