Architecture and management of a geological repository - Andra

During the operational phase, the disposal process is thus progressive. Once the waste packages havebeen placed in the disposal cells, the latter could be managed with a flexibility reminiscent of a storagefacility, characterised by total reversibility.Unlike a storage facility, a repository is also designed to be closed, in order to create a system that issafe over the long-term, without requiring any human intervention. This closing is carried out insuccessive stages. The level of reversibility gradually reduces as each stage is passed. Theconfiguration in which all the installations are closed constitutes the lowest level of reversibility.10.1.2 Progressive closing of the repositoryOn completion of a monitoring period, the duration of which is, in principle, undefined, in the event ofa formal decision which thus marks the desire to pass a milestone and initiate the closing process, thefilled disposal cells are closed.The closing process thus begins with the sealing of cells. On completion of sealing, the drift givingaccess to the cells remains accessible. A new monitoring phase can then begin.The next decision concerns the back-filling of the access drifts to the cells (drifts inside the module).This operation lasts from 2 to 4 years depending on the size of the repository module. On completionof this work, the connecting drifts giving access to the back-filled module remain accessible. A newmonitoring phase can again then begin.Depending on the decisions taken, the closing work on certain modules already full within therepository zone can be carried out at the same time as packages are being placed in other modules.The subsequent decisions concern the closing of the connecting drifts. This begins, in a first repositoryzone, by back-filling drift sections giving access to the most remote repository modules, and bysealing them. On completion of this work, the main connecting drifts giving access to the closedrepository zones will remain accessible.It should be noted that the modular design of the repository makes it possible to envisage closing somestructures whilst others are still in operation.After closing repository zones, the next stage of the process involves the back-filling and sealing ofthe main connecting drifts. Finally, the last stage concerns the sealing of the access shafts to thegeological formation.On completion of this final stage, which ends the closing process, the entire repository is in the socalled“post-closure” configuration. The repository then requires no further maintenance or additionalwork. It gradually becomes passive and safe in the very long term.Thus, the progressive nature of the repository closing process offers the possibility of implementing adecision-making process consisting of several successive stages, with the ability to introduce a periodof monitoring and to decide to maintain the installation in its present condition, move on to the nextstage, or reverse the process. The decision to move on to the next stage is facilitated by data providedby monitoring the behaviour of the structures. This logic forms a favourable element in thereversibility of the disposal process, given that allows, at any moment, to reverse to the previous stage.DOSSIER 2005 ARGILE -ARCHITECTURE AND MANAGEMENT OF A GEOLOGICAL DISPOSAL SYSTEM367/495