Schematic representation of the Andra repository concept and the main phenomena structuring the hydraulic-gas transient [17]: 1 – resaturation of the shafts and ramps seals; 2 – gas production; 3 – diffusion of dissolved gas in clay host rock; 4 – transfer of gas by the components of the repository; 5 & 6 – low permeability of the bentonite of sealing cores favouring the transfer of gas by concrete annular rings, the EDZ and interfaces between the different materials.