Architecture and management of a geological repository - Andra

2 – General DescriptionTo assess the very long term impact of an earthquake, the maximum physically possible earthquake isdetermined for the configuration of the nearest faults to the site, by assuming that they are active(length, rooting depth and segmentation). Current simulations give this earthquake a magnitude of 6.1at a distance of 6 kilometres from the laboratory site and at a depth of approximately 12 kilometres.Such an earthquake would cause maximum acceleration of approximately 0.3 g at the repository depth([6] - Volume 3, [36]).Although the safety margin computed earthquake and maximum physically possible earthquakecharacteristics are highly conservative, their amplitude remains moderate in comparison with those ofearthquakes currently occurring around the edge of the Mediterranean Sea.2.4 Principles of repository architecture designA repository installation would consist of disposal cells (underground caverns), excavated in theargillite formation, containing waste disposal packages. These waste packages consist of primarywaste packages, as conditioned by waste producers, supplemented by an over pack according torepository requirements.The architecture studied contains disposal cells for various categories of waste within specificrepository zones. The repository zones for B waste, C waste and, if applicable, spent fuel are thereforephysically distinct from each other. This arrangement is envisaged to offer independence in terms of(i) the management of the various types of waste and (ii) the behaviour of each zone, in view of thespecific characteristics of the waste contained [37]. The extent of the underground footprint for the Bwaste repository zone is 100 hectares for the inventory presented in chapter 3. For C waste (and spentfuel, if applicable), the footprint depends on the scenarios studied and the length of storage time priorto disposal in the repository. Indeed, preliminary storage reduces the thermal power of the waste whenit is emplaced in the repository and therefore helps to reduce the footprint of the correspondingunderground installations. Therefore, assuming 60 to 70 years’ preliminary storage for C waste(depending on package types), the corresponding repository zone has a footprint of 500 hectares in afuel (UOX and MOX) retreatment scenario (see chapter 6).For cell construction, waste emplacement and reversible management of the installations, access isgained via vertical shafts between the surface and the repository level, then via connecting driftsbetween these shafts and the repository zones. While attempting to restrict the number of suchstructures, four vertical shafts are required to fulfil all of the functions presented in section 2.1.4.These shafts can be used for all types of waste in the repository.During the operating phase, the waste is received and the disposal packages prepared in surfaceinstallations. These installations include workshops and offices supporting the underground work andoperation. Excavation crushed rock are stockpiled in a specific zone called a crushed rock disposal. Itsfootprint depends on the volume of crushed rock and the hypotheses adopted for its geometry; it couldbe around 100 hectares for a fuel (UOX and MOX) retreatment scenario.DOSSIER 2005 ARGILE -ARCHITECTURE AND MANAGEMENT OF A GEOLOGICAL DISPOSAL SYSTEM53/495