Architecture and management of a geological repository - Andra

5 – Repository Modules• Cell geometry: Medium to wide diameter tunnels or large cavitiesCell geometry is governed by the need for compactness, geo-technical conditions and packagecharacteristics.The above-mentioned need for compactness points design towards high-capacity disposal structuresconsequently of large size. B waste being either non-exothermic or virtually so, packages can bedisposed side-by-side in large numbers, a fact which encourages this orientation towards large-scalestructures. Maximum size for the various options considered is in the twenty metre range, withvirtually circular tunnel-type geometry (Figure 5.1.1) or large cavity or silo-type geometry (Figure5.1.2).It is also necessary to decide what constitutes reasonable size keeping in mind constraints related toconstruction, mechanical behaviour and conservation of undisturbed argillites above and below thestructures.The cell size of 10 to 12 m finally decided upon reconciles these two aspects.• Horizontal or vertical handlingThe choice between vertical and horizontal handling of packages greatly influences cell design.For vertical handling, an apical space must exist along the entire length of the cell to allow fordevelopments in handling tools (Figure 5.1.2 and Figure 5.1.4). This space, which cannot be used fordisposal, reduces cell compactness.For horizontal handling, it is possible to transport packages sideways (Figure 5.1.1 and Figure 5.1.3).This configuration, which allows the whole cell section to be used for disposal, fosters designcompactness.The quest for compactness together with the choice of structures excavated to the order of 10 to 12 min diameter have led to opting for horizontal handling of packages.• Arrangement of disposal packages in guide tubes or in pilesAs regards arrangement of packages within cells, two major methods were compared.The first consists of disposing packages in guide tubes. Installation of tubes in the cell and filling ofspaces between tubes is done during construction. Several ways of installing the tubes have beenconsidered: metallic tubes with poured concrete or prefabricated concrete components with hexagonal‘beehive’ cross-section (Figure 5.1.1). The second solution results in major reduction of spacingbetween disposal tubes, and therefore greater compactness. However, the components must be alignedone against the other lengthwise to create concrete tubes for package disposal. It is thus possible toobtain considerable compactness by so equipping 10 or 11 metre diameter cells. However, withhorizontal configuration, installation of packages in guide tubes requires rather complex handlingmethods in the access drift to get packages up to the tubes (up to around 9 m above the apron) andthen push them into place. Moreover, this method of package placement may require limiting celllength.The second method consists of piling and juxtaposing packages with nothing between them in order toobtain maximum compactness. To do this, a parallelepipedic disposal chamber is set up in theexcavated cell during application of concrete lining. Chamber dimensions are adapted to disposalpackage dimensions (themselves parallelepipedic) in order to minimise space between packages andbetween packages and walls. This arrangement requires high-precision handling tools for packageinstallation, but which poses no problem given existing means. With horizontal configuration, itresults in very good repository compactness. Furthermore, minimising spaces in the disposal chamberavoids having to fill them up when closing the cell, and thus facilitates any future retrieval ofpackages.DOSSIER 2005 ARGILE -ARCHITECTURE AND MANAGEMENT OF A GEOLOGICAL DISPOSAL SYSTEM164/495