Tome Architecture and management of a geological repository - Andra

6 – C waste repository zoneThis principle, which results in dividing up the C waste repository zone architecture in line with thefracturing, is along the same lines as those considered abroad (Figure 6.2.3).Figure 6.2.3Switzerland – Architectural plan of a repository in the granite adapted to thefracturing (Nagra data [45])6.2.2 Designing engineered components that are complementary and redundant to thegranite mediumThe architectural options described above aim to make the most of the favourable properties of thegranite medium. Dividing up the repository zone may lead to the connecting drifts between modulescrossing water-conducting faults. At a smaller scale, the options studied do not rule out the presence ofminor fracturing inside the module.With respect to the main long-term safety functions, it means that engineered barriers must beprovided to be complementary and redundant with the granite medium.Thus low-permeability backfill is planned for the handling and connecting drifts, and sealemplacement at the module edges will complement the cell and module installation principles.Furthermore, a steel over-pack, that will remain watertight for a long enough period, surrounded by aclay engineered barrier, will contribute towards the primary waste package borosilicate glassperformance.6.2.2.1 Redundant backfill and drift sealsTwo complementary and redundant devices can be envisaged to protect the repository modules fromcirculations of water emanating from the faults bisected by the drifts: backfilling the drifts with a lowpermeabilitymaterial and the emplacement of very low permeability seals.The hydro-geological context of the granite site and the permeability of the rock govern therequirement for backfill permeability.Dossier 2005 granite - ARCHITECTURE AND MANAGEMENT OF A GEOLOGICAL REPOSITORY167/228