Architecture and management of a geological repository - Andra

• Package retrieval processOnce the chamber is operational, the concrete blocks are removed through the same process used toinstall them and the packages are withdrawn following the same precautions as indicated in theprevious stage. However, correct operation of the process and serviceability of the retrieval equipmentdescribed above are contingent upon the condition of the cell and packages. A number of phenomenamay interfere with this operation. These phenomena are, for the most part, related to the risks inducedby the changes in the packages and in the structures over a very long period of time. The major risksand risk-controlling measures are described in the following section.10.4.1.4 Analyzing the situations likely to hinder the retrieval of the packages from the cell• Risks related to the changes in the cell linerThe structure of the cell remains mechanically stable and undergoes minor changes for severalcenturies. The liner is still adequately rigid to prevent the cell walls from warping. However, somedegree of scaling may occur on the surface of the filler concrete; this may require the use of a deviceequipped with a manipulator arm to remove the debris.• Risks related to the changes in primary packagesFor a major part of the inventory, primary packages give off hydrogen. The disposal packages aredesigned in such a way as to discharge the hydrogen produced even when moisture is present, whichprevents the risks related to the pressurization of the disposal package.The residual clearance between the primary packages and the internal waste recesses of the disposalpackage is sufficient (albeit small) to prevent all risk of bursting should corrosion affect the primarypackage and swelling of the formed products occur.• Risks related to the changes in the disposal packageThere are two types of risks to be analyzed: damage to the disposal package and mechanical adhesionof a package to another package or to the floor.The selection of the concrete for the construction of the disposal packages provides for a multi-centurymechanical durability, and for the absence of concrete-to-concrete binding phenomenons.• Risks related to the corrosion of the retrieval device tracksVentilating the cell with dry and fresh air prior to cell sealing and the absence of oxygen supply in thefollowing phase should largely mitigate corrosion of the tracks and associated attachment points. Thetrack system may sustain a minor degree of corrosion. In any case, it is possible to provide a trackcleaningdevice in the cleared area as the packages are withdrawn, thus obviating all risk of jammingat a long distance from the cell head section. The tracks are secured to the floor via a large number ofattachment points; a minor degree of corrosion would not affect the mechanical operation thereof.• Risks related to the presence of contaminated gases or hydrogen in the cellThe cell is ventilated during the retrieval operations. The risk of explosive atmosphere is managed byan atmospheric inspection and a ventilation process provided under conditions identical to thoseprevailing at the time of initial installation.DOSSIER 2005 ARGILE -ARCHITECTURE AND MANAGEMENT OF A GEOLOGICAL DISPOSAL SYSTEM425/495