Architecture and management of a geological repository - Andra

5 – Repository ModulesFigure 5.3.17Thrust frame in the access drift (difficult case of an access drift without apositioning chamber)Fitting the thrust tubes (future lining)The thrust tubes are fitted in approximately 2 m long sections, or longer if the dimensions of theaccess drift allow. They are welded together after adjustment by a system of jacks connected to thedrift’s face.• Fitting the clay buffer and sleeveThe clay buffer described above is formed by complete rings in a single piece. The external diameterof the rings is approximately 2 meters and their thickness (along the cell axis) is 0.5 m. Thesedimensions are due to manufacturing constraints. Each ring pre-fabricated in this way will weighapproximately 5 tonnes.There are two compacting techniques for parts of this size : uniaxial pressing and isostatic pressing.The former is used, for example, in Sweden [72], [73]; the latter has been tested in Japan, on 1.3 mdiameter 1.7 m high cylinders [74]. The advantages of the isostatic process is its speed and thehomogeneous nature of the material; it can be used to compact large blocks. However, uniaxialpressing currently has more references.A high-capacity uniaxial press (for example : 30 000 tonnes) makes it possible to achieve the pressuresin excess of 50 MPa required to obtain dry densities of around 1.9.Inserting pre-assembled buffer ringsIn order simplify the positioning operations, the rings can be assembled in the workshop in groups offour. This assembly method is currently under study as part of the European ESDRED project.There are various possible techniques for fitting these rings into the cell. For reasons of size and theavailability of experience feedback, the air cushion technique appears to be particularly suitable. Thepre-assembled rings are placed on a cradle fitted with air cushions (see Figure 5.1.17). After the aircushions have been inflated, a trolley rolling on guide rails pushes the cradle to the required position inthe cell. The air cushions are then deflated. The rings then sit on the rails, thus freeing the cradle.DOSSIER 2005 ARGILE -ARCHITECTURE AND MANAGEMENT OF A GEOLOGICAL DISPOSAL SYSTEM247/495