Architecture and management of a geological repository - Andra

A European Commission working group [90] has used the definition proposed by the IAEA. Inparticular, it has developed the place of monitoring in the staged operation of a repository.More recently, the IAEA has also introduced staged development of the repository in its approach toobservation [91].Finally, the NEA [16] also considers that monitoring of the various repository parameters and of thesite provides data related to safety assessment. It suggests that the safety reference base be periodicallyre-examined in the light of these data. The latter may concern confirmation of the properties of thesite, the site’s response to the presence of the repository and the beginning of changes to the repositorystructures.• Situation in CanadaIn 1997, AECL 142 examined monitoring methods in a spent fuel repository 143 [92]. The field covered isvast; it ranges from monitoring confinement structures and the environment to the monitoring of thesocio-economic fall-out.In order to minimise any interference between monitoring and operation of the repository, and to avoidany impact on the functions of the engineered barriers, AECL proposes that an experimental zone beestablished within the repository, in addition to the direct monitoring of the repository’s evolutionduring construction and operation and, if necessary, for an indeterminate period prior to closing therepository. This zone would enable experiments to be conducted in situ over an extended period, forinstance experiments associated with the long-term behaviour of materials (for example corrosion) andwith the performance of hydraulic barriers.AECL mainly uses existing technical means or those that appear to be able to be inferred from existingtechniques.• Situation in the USAThe development of a staged disposal approach (“adaptive staging”) proposed by the NationalResearch Council (NRC) [21] is similar to the reversibility approach presented by ANDRA, in whicha range of options is proposed for managing each stage of the process (see section 10.2). However, itdiffers from it in that its purpose is more technical, rather than meeting any social or politicaldemands.The approach proposed by the NRC is accompanied by a monitoring programme covering bothmanufactured and natural barriers. Various motivations are mentioned, similar to those presented inearlier paragraphs: characterisation of the initial state, analysis of the actual performance of the systemand structures, aid to decision-making, notably those concerning improvements to the system, checkon the meeting of requirements, personnel protection and nuclear safeguards. The NRC stresses thatthe approach proposed has to be seen in a context of responsible management in order to increasestakeholder confidence.The Yucca Mountain project (dedicated to civil and military spent fuels) is a good illustration of thisparadigm. The project involves monitoring adapted to the specific features of the concept. Indead, thisproject can be described as a ventilated underground storage facility that can be transformed into arepository. During an initial 70-year phase, it has to be managed like a storage facility. Theobservations made during this period constitute essential elements on which the decision-makers willbase their future choices [69].142 Atomic Energy of Canada Limited143 As a reminder, spent fuel to be managed in Canada comes from the CANDU reactor national subsidiary, which use natural uranium.They have a low combustion rate and, consequently, give off far less heat than French CU1 and CU2 type fuels. However, the volumesconsidered are large.DOSSIER 2005 ARGILE -ARCHITECTURE AND MANAGEMENT OF A GEOLOGICAL DISPOSAL SYSTEM388/495