Architecture and management of a geological repository - Andra

2 – General Description2.2.2.2 Safety and reversibilityAlthough its implementation will involve future generations, the design of a repository must be robustenough to protect man and the environment over the long term, and this is its primary purpose. Nocompromises with regard to safety are allowed while taking into account reversibility.Safety and reversibility are both founded on an attitude of modesty, recognising the existence ofuncertainties and managing them with due regard for the rights of future generations. Safety requiresthat robust technical options be taken at the repository design stage, and reversibility implies prudentmanagement of the repository.The uncertainties of our present state of knowledge have been systematically taken into account in thechoice of technical options described further on in this report.Measures that might be at least partly justified by reversibility considerations must not impair safetyfunctions. No technical measure that might significantly disturb safety relevant feature has been addedsolely for the purposes of reversibility. Such a measure would bring reversibility and safety intoconflict, and in that case safety would take precedence. For example, introducing materials wich mightcause a new type of disturbance, or a significantly greater disturbance than those already existing forother reasons, can not be justified soley for reasons of reversibility.2.2.2.3 Organisation of the stage-by-stage disposal processIf it is decided to build a disposal facility, the first stage of its operational life will be the building ofground-level service installations and the engineered structures for access to the host geologicalformation, and preparation of the underground disposal installations.This will be followed by an operating and monitoring stage when the waste packages are placed in therepository. For the sake of flexibility, the duration of the operating and monitoring stage should not beset in advance: it could last a century or several centuries.Allowing for reversibility means, first and foremost, flexible management of the disposed wastepackages, comparable to temporary storage.But a repository is also designed to allow closure and thus a passive evolution 5 . Closure mainlyconsists of filling in and sealing the undergound installations.Flexibility therefore implies gradual closure. This opens the way to progressively reducing the level ofreversibility as decisions are taken.The construction, operating and closure of a repository are therefore organised in stages, which can beimplemented independently for each class of waste.The first stage is the construction of a repository module, in which the packages are then placed.Closure is designed as a gradual process in several stages: closure of modules, closure of access tomodules, to the disposal installations for the class of waste concerned, and finally of the undergroundinstallations as a whole. Deconstruction of the surface installations 6 may begin, in part, before closureof the underground installations is finished, and be terminated afterwards.The first stages of the operating phase are similar to temporary storage, which would be implementedundergound. However, unlike a purpose-built temporary storage facility, many of the elementsrequired for long-term safety functions are already present and can be monitored in situ.Because of the modular design of the installations, they can be built in successive phases. This givesgreater freedom of choice in managing the development of the repository.56After closure, the safety functions decribed above are fulfilled without the need for human intervention.This operation includes deconstructing surface installations and definitive cleanup of surface spill.DOSSIER 2005 ARGILE -ARCHITECTURE AND MANAGEMENT OF A GEOLOGICAL DISPOSAL SYSTEM38/495