Architecture and management of a geological repository - Andra

10.5 ConclusionThe possibility to manage the disposal process in a reversible manner results firstly from the stabilityof the repository structures designed to last maintenance-free over very long periods of time.The choice of durable wall liners provides the operator, over a period of several centuries and as longas the closing process has not started, with the opportunity to readily retrieve the packages usingresources identical or similar to those used for installation. Under these circonstances, management ofthe packages is carried out under storage-like conditions. The stability of connecting structures –shafts or drifts – does not imply time limits at this phase because these structures, unlike the disposalcells, can be maintained on a regular basis. Thus, the repository may be kept in a totally reversiblestate, as long as the disposal cells are intact, i.e. for a period of two or three centuries and maybe more.Additionally, the modular design of underground architecture allows a progressive implementation ofthe disposal process, as pertains to the emplacement of waste disposal packages in their disposal cells,as well as to the closure of repository structure. The first stage of emplacing waste disposal packagesinto disposal cells initially only concerns a fraction of the waste inventory. As far as closure isconcerned, the progressive approach to a disposal process translates into a succession of stages. Eachstage is preceded by a decision-making milestone which only concerns the contents of the upcomingstage. Thus, the first stage of the closing process only concerned the sealing of the cells of certainmodules, with the other architecture components remaining accessible and maintained.In addition to this gradual development, observation methods implemented as early as the constructionof the structures allow to keep track of their evolution and more accurately assess how long they willremain stable after one century of existence. Repository observation and surveillance are toolssupporting disposal management. The decisions to be made when moving from one stage to the nextare based on the scientific understanding of the structures and their environments.Progressive closure of underground facilities leads to a progressive reduction of the reversibility level.At the same time, this progressively precludes the need for human intervention, given the passivesafety objective. However, a package retrieval operation remains technically possible after sealing thecells and backfilling the tunnels. The removal of the backfilling materials is not technicallychallenging and the maintained integrity of the cells for several centuries would facilitate the retrievaloperation proper.Lastly, it is also important to point out that a progressive disposal process provides the opportunity tobenefit from the feedback of the initial process phases and improve, accordingly, the design of therepository structures as well as construction, operating and closing equipment and processes.Particularly, the possible coexistence of cells, drifts or modules in different reversibility statesprovides for different management scenarios and allows to test a variety of configurations, wherebythe overall flexibility can be reinforced.DOSSIER 2005 ARGILE -ARCHITECTURE AND MANAGEMENT OF A GEOLOGICAL DISPOSAL SYSTEM434/495