Architecture and management of a geological repository - Andra

5 – Repository ModulesThe result is a sleeve thickness (which takes account of the mechanical dimensioning and a corrosionallowance of a few millimetres) of 40 mm for type CU1 cells and 25 mm for type CU2. Thesedimensions are based on the same loading case as for type C cells (12 MPa).The excavation of cells with a clay buffer, followed by the fitting of buffer rings, requires the use of ametal securing support. As indicated above, the pre-dimensioning calculations lead to the use of a ringapproximately 30 mm thick for type CU1 packages and approximately 25 mm thick for type CU2packages [65].5.3.3.3 Constructing the cellThis section describes the procedures and resources required to excavate and coat the cell, thenprepare and position the components of the buffer and, finally fit the other cell equipment.• Excavating and lining the cellSeveral methods can be used for excavating the cell. The micro-tunnelling technique appears to be thebest-suited, the thrust tubes remaining in place and forming the metal lining. This technique isindustrially proven in the field of civil engineering for tunnels with small diameters compared with thecross section of the cells for spent fuel. The cutting tool is a solid-faced wheel type cutter, a techniquewhich, thanks to the homogeneous nature of the cutting face, minimises induced terrain damage 99 . Oncompletion of excavation, the micro-tunnelling head is extracted from the cell.This excavation/lining method enables the work to be carried out at all times sheltered by the metallining.Cutting tool and shieldThe cutting tool is a solid-faced wheel with retractable cutting wheels.his arrangement allows themicro-tunnelling head to be retracted inside the metal lining left in place (Figure 5.3.16).Figure 5.3.16Cutting wheel (cutters pivoted) being retracted inside the liningThe cutting tool can work ahead of a shield, i.e. a metal ring protecting the micro-tunneller rotationmotor-drive. The shield is then lost on completion of excavation: after dismantling its internalcomponents, it is abandoned in-situ and forms the end section of the metal lining.The thrust on the cutting wheel can be exerted by rams fitted to a thrust frame; it is transmitted viathrust tubes which, left in place, form the cell lining.99The solid faced wheel could be replaced by a point cutting type machine if in-situ trials demonstrated that it gives an identical quality ofcut to that obtained using the solid-faced wheel type cutter.DOSSIER 2005 ARGILE -ARCHITECTURE AND MANAGEMENT OF A GEOLOGICAL DISPOSAL SYSTEM246/495