Tome Architecture and management of a geological repository - Andra

3 – Design study of a repository in a granite formation3.3.5 Integrating reversibilityIn addition to operational safety and, in the long term, repository design must fulfil reversibilityrequirements. As mentioned previously, reversibility is related to a cautious and staged managementof a possible repository which, given the timeframes considered, leaves the options open for futuregenerations.Beyond the ability to withdraw the emplaced packages (retrievability), reversibility can be defined asthe possibility of gradual and flexible management of the repository which leaves future generationsfree to decide. With this aim in mind, the disposal process can be broken down into a succession ofstages to be undergone which provides from the construction of the initial modules up to the closure ofa module or of a repository zone, the possibility of waiting and observation time, before deciding to goon to the next stage or reverse the process. Completing a step is thus a thought-out choice, exercised infull knowledge of the scientific, technical and economic parameters.Reversibility requirement involves, over the course of time, human presence, monitoring andmaintenance which do not put at stake whatsoever long-term safety, the primary aim of the repository.On the contrary, reversibility through a cautious and gradual management of the disposal process is atthe core of the long-term safety foundations in managing uncertainties and safeguarding the rights offuture generations. In any event, allowing for reversibility must not endorse any compromise on safetyobjectives. Thus no provision, that could significantly disturb a safety function, is added for the sakeof reversibility.The design approach adopted by Andra aimed at putting forward generic design options that meet therequirement for reversibility.This covers three aspects:- architectural arrangements beneficial to a gradual repository management,- technical measures for going backward to the various disposal stages,- means of observing repository status and its evolution at any time in the process.• Repository architecture incorporating and fostering reversibilityThe repository architecture options put forward by Andra build in the reversibility requirement andmake its implementation easier.Simple, robust repository conceptsConcepts proposed by Andra at this stage of the study are, by principle, simple and robust. Simplicityis based on the concern for technical feasibility and performance control. Making the most ofmechanical resistance of granite rock especially allows to limiting support systems in structure design.Simplicity of options proposed by Andra facilitates the description of their evolution over time as wellas their modelling. Robustness is based on resistance of the concepts in terms of safety and necessaryscientific knowledge.Durable materials and systems to facilitate potential withdrawal of the packagesThe possibility of future generations retrieving the packages is helped by the choice of durablematerials for the packages and self-stable geometries for the underground excavations.These choices contribute to maintaining the handling spaces between the disposal packages and thedisposal cells, thus allowing the use of identical handling equipment to that used for emplacement, incase of retrieval.Dossier 2005 Granite - ARCHITECTURE AND MANAGEMENT OF A GEOLOGICAL REPOSITORY48/228