Tome Architecture and management of a geological repository - Andra

5 – B waste repository zonePillar thickness equivalent to three times the width of the widest tunnel, in the absence of parametersfor a particular granite, would seem sufficient to guarantee that there is no mechanical interactionbetween two neighbouring cells.The calculations for the buffer to be provided in mechanical terms between a cell and a fault on theedge of a module, indicate that a distance of about 10 m makes the risks of interaction between a celland a fault negligible [39].• Dimensioning and description of the connecting driftsThe connecting drifts are long "inverted-U" structures 6-7 m wide and about 6 m high. They aredimensioned for cell construction machinery traffic, allowing for vehicles crossing, package transferand the installation of all the utilities and systems (water, air, energy and instrumentation) duringmodule construction and operation phases.At least two parallel drifts are required for the construction followed by the operation of a disposalmodule. They are linked by an interconnecting drift at the level of each disposal cell and no less thanevery 400 m. The pillar between two connecting drifts is about twenty metres wide (about three timesthe width of a drift). The width of a cluster of two parallel drifts is about thirty metres.At the time of closure, the connecting drifts at the edge of the module are sealed with a swelling claycore placed between two concrete abutments of a similar design to the cell seals.5.5.2 Assessing the number of granite blocks to be identified in the disposal zoneThe B waste repository zone includes all the repository modules arranged on one or more levels, andthe drifts that link them to the underground-to-surface connecting structures.The repository modules are distributed on two levels in the reference architecture. Structural elements(as faults) that define the block geometry of most of the French granite massifs surveyed at one levelcan be transposed to the other level at the scale of one hundred metres.It can be envisaged that the construction of two to four 100 meter-long cells per module is feasibleaccording to the site configurations. The exploratory work thus required should identify some twelveblocks.In the case of a site configuration with geological constraints by fracturing, the number of blocks to becharacterised is close to the number of cells to be built.Dossier 2005 Granite - ARCHITECTURE AND MANAGEMENT OF A GEOLOGICAL REPOSITORY138/228