Architecture and management of a geological repository - Andra

5 – Repository ModulesThe cells are 2.7 m diameter, 600-800 m long circular horizontal tunnels. They have a 25cm thickconcrete lining and are fitted with 4 longitudinal pipes separated by swelling clay, in the case of UOXpackages, or a single central tube, in the case of MOX packages. The dimensioning thermal criteria area container wall temperature of under 100°C, and temperature increase in the overlying water-bearinggeological formation of under 6°C. The longer duration of the thermal phase for spent fuels requiresthe inter-axial spacing of the cells to be increased to 110 m (instead of 40 m for the Belgian vitrifiedwaste concept).Figure 5.3.5ONDRAF concept for the disposal of spent fuels, transverse section inaccordance with SAFIR 2• SwitzerlandFor spent fuels, NAGRA envisages a similar concept to that for vitrified waste, a brief description ofwhich is given at § 5.2.2.3. The detailed description of the NAGRA concept is available in itsTechnical Report [44]. The disposal package is a steel or copper container, described at § 4.3.2.4.The cells are orientated according to the major stress. The mechanical characteristics of the formationconsidered (Opalinus clay) take for granted under these conditions that the excavations will be selfsupporting:they are not lined; only a ground support by mesh and bolts is planned for safety reasons.The cells are “through” cells. They are 2.5 m in diameter and several hundred metres long. Thedisposal packages are placed on compacted swelling clay bases. The annular space between thepackage and the cell walls is filled by spraying-in a mixture of loosely compacted pellets and powder(target dry density 1.5). The cell is filled in cycles alternating the emplacement of a package and thefilling in of the swelling clay buffer.Longitudinal sectionTransverse sectionFigure 5.3.6Swiss NAGRA concept for the disposal of spent fuel packagesDOSSIER 2005 ARGILE -ARCHITECTURE AND MANAGEMENT OF A GEOLOGICAL DISPOSAL SYSTEM235/495