Architecture and management of a geological repository - Andra

5 – Repository Modules5.2.4 Arrangement of disposal cells and access drifts in the repository module5.2.4.1 Module structureAn operating unit is made up of 3 access drifts, perpendicular branch tunnels (called interconnectingdrifts) and from 150 to 200 disposal cells (Figure 5.2.17).Figure 5.2.17General layout of a C waste repository module operating unitThe disposal cells are arranged perpendicularly to the access drifts. The length of the access drifts hasbeen limited to approximately 600 m due to operating requirements.The operating units are distributed on both sides of a network of 4 parallel secondary access drifts (seechapter 7). Upon closure, each module comprising two operating units facing one another is separatedfrom the others by seals so as to divide up the repository zone.This arrangement allows a favourable orientation of the disposal cells and seals with respect to naturalstresses.The length of the disposal cells is constant. The distance between dead ends is also constant. Thecentre-to-centre distance between disposal cells and the spacing of packages within a disposal cellvary according to the packages (heat rating). As indicated earlier, the centre-to-centre distance variesfrom 8.5 to 13.5 m, the spacing between packages varies from 0 to 4 m, and the distance betweendisposal cell ends is 20 m.5.2.4.2 Ventilation constraints taken into account.In the operating phase, in order to eliminate the need for ventilation ducts (and thereby minimise thediameter of the drifts), two access drifts ensure the supply of fresh air in full cross-section whereas thethird access drift ensures air return, also in full section (see Figure 5.2.18)Activity zones are strictly restricted to the two air supply drifts and the interconnecting drifts betweenthem. This arrangement therefore ensures the constant availability of two fresh air inlets. In case offire, at least one of these two drifts is accessible as an emergency exit and entrance.DOSSIER 2005 ARGILE -ARCHITECTURE AND MANAGEMENT OF A GEOLOGICAL DISPOSAL SYSTEM216/495