Architecture and management of a geological repository - Andra

10.1.3 Key stages of the disposal processThis section describes the key stages that enable the disposal process to be managed in an adaptable,flexible manner [83]. These stages form the basis of the description of the reversible disposalmanagement process given in the following sections (cf. Figure 10.1.1).• “Post package-emplacement” stageThe “Post package emplacement” stage corresponds to the period in which one or more cells are filledwith packages but not sealed. During this stage, the cell is made safe from a radiological point of viewby a totally reversible shielded physical barrier, which protects the operators present in the accessdrifts. The network of connecting and access drifts and shafts remains fully accessible. At this stage,the only difference between a type B waste cell and a type C waste or spent fuel cell is that the formeris ventilated whereas, in the latter, aire removal is strongly limited by a sealing closure device.Certain structures are monitored. The drifts are ventilated, thus allowing easy access to the entirenetwork. At all times, the physical disposal cell closing device can be opened so that the packages canbe retrieveed without further delay. This stage is comparable with a storage configuration.• “Post cell-sealing” stageThe “Post cell-sealing” stage starts once the cells have been sealed by a swelling clay plug. This pluglimits the physico-chemical exchanges between the cell and the access drift. At this stage, the cellaccess drifts are ventilated and the sealed cell heads are thus accessible. The monitoring of certainstructures continues. During this stage, it is technically possible to retrieve the packages. It requirespreparatory work consisting of removing the clay plug and restoring the head of the cell.• “Post module-closing” stageThe “Post module-closing” stage starts once all the components of a module have been sealed andback-filled. In the case of type B cells, this stage is no different from the previous stage since a moduleconsists of only one cell. However, in the case of type C waste or spent fuel modules, the closing ofthe module includes back-filling of its connecting access drifts. The module’s connecting drifts remainventilated and accessible.At this stage, it is also technically possible to retrieve the packages. The preparatory work for thisoperation is longer than that in the previous case. It consists of removing the back-filling from thedrifts using excavation techniques similar to those used during construction the, as during the previousstage, renewing the tops of the cells.The following stages concern the entire repository and no longer just individual modules.• “Post repository zone-closing” stageThe “Post repository zone-closing” stage starts when the repository zone’s internal connecting driftsare back-filled and sealed. At this stage, the main connecting drifts giving access to the repositoryzone in question remain ventilated and accessible. The transition to this stage has littlephenomenological impact on the evolution of the repository modules and only increases the lengths ofthe drifts to be re-excavated in order to gain access to the packages in the event of their retrieval.• “Post-closure” stageThe "post-closure" stage starts after sealing and back-filling the shafts. It corresponds to the end of thedisposal process. The repository is then in the “Post-closing” configuration. However, it is possible toenvisage an monitoring period for the repository and its environment. Although more complex, itremains technically possible to retrieve the packages in this configuration [20], [16].DOSSIER 2005 ARGILE -ARCHITECTURE AND MANAGEMENT OF A GEOLOGICAL DISPOSAL SYSTEM368/495