Architecture and management of a geological repository - Andra

Figure 10.4.16C Cell after reconstruction• C waste and spent fuel packages retrieval processOnce the cell has been reconditioned, the retrieval process is the same as the one described in theprevious stage.However, correct operation of the process and serviceability of the retrieval equipment describedabove are contingent upon the condition of the cell and packages. A number of phenomena mayinterfere with this operation. These phenomena are, for the most part, related to the risks induced bythe changes in the packages and in the work over a very long period of time. The main risks andcorresponding safety measures are described in the following section.10.4.2.4 Analyzing the situations likely to hinder package retrieval from the cellThe main risk likely to hinder package retrieval is related to an obstruction of the functional clearanceresulting from a corroded or mechanically deformed sleeve.If despite all the provisions made to prevent or mitigate corrosion the sleeve or package shouldbecome locally or extensively corroded, the presence of corrosion products would result in theswelling of the corroded surface, which could render package retrieval unfeasible or even lead tojamming if the functional clearances were to be completely obstructed. This unlikely last risk isprevented by the existence of a durable functional clearance between the package and the sleeve(approx. 3 cm for C waste packages and 8 cm for spent fuel packages). Even when considering ahighly penalizing corrosion speed of 1 mm per century, the clearances will not become obstructed forseveral centuries. Package “sinking” risks are also prevented by the presence of sliding runners for Cwaste and CU2 type spent fuels packages or rails for CU1 type spent fuels packages which maintainthe lower package generatrix above the sleeve.Lastly, mechanical jamming of the disposal packages can also be considered should the dimensions ofthe cell sleeve change. However, this is prevented by using a sleeve thickness calculated to limitlongitudinal and radial deformations over a 100-year to multi-century period of time. Thus, during thisperiod, the handling clearance is maintained between the sleeve and the package.10.4.2.5 Retrieval conditions at the “After closing of module drifts” stageDeconstruction of the seals on the connecting drifts may be carried out by using the same process asthat described for the deconstruction of the B cells seal.The backfills are also deconstructed by using traditional mining techniques: of the “roadheader” type.These processes can be used for backfills whose temperature reaches 55°C provided machinery withair-conditioned cabs is used and the air in the drift is cooled down as backfill removal progresses. Theuse of air-conditioning systems is common practice in deep, high-temperature mines, particularly inSouth Africa.DOSSIER 2005 ARGILE -ARCHITECTURE AND MANAGEMENT OF A GEOLOGICAL DISPOSAL SYSTEM432/495