Architecture and management of a geological repository - Andra

The project’s monitoring programme is considered to be an important element of the repository’sperformance confirmation programme. Its objective is to check that the data used to demonstratesafety were adequate and to demonstrate that the structures are behaving in accordance with thepredictions [89]. It could also assist in increasing confidence or optimising the disposal process.• Situation in SwedenThe Swedish body responsible for radioactive waste management (SKB) is studying the integration ofobservation and surveillance activities in the phasing of the development of a spent fuel repository[93].SKB has identified the following phases: a site characterisation phase from the surface, a constructionphase of the central structures and of the first structures for waste package disposal, a wasteemplacement phase of an initial fraction (about 5 to 10%) of the inventory, followed by a so-calledindustrial phase (dedicated to the overall inventory), and then a closing phase.SKB states that at the end of each phase, the data acquired by monitoring could contribute to theupdating of the long-term safety assessment. The detection of changes other than those predictedwould first trigger an analysis of the differences, then an update of the models and finally, if required,a change in the design.It should be noted that the study is based, amongst other things, on experience feedback from themonitoring of the Swedish low and medium level waste underground repository (SFR), theunderground spent fuel disposal facility (CLAB) and experiments conducted in the Äspö undergroundresearch laboratory.• Situation in SwitzerlandThe expert group on radioactive waste management models (EKRA), created by the Federal Council,has proposed a concept of a “monitored durable geological repository” [94]. This model “associatesthree repositories forming a system: a test repository, a main repository and a pilot repository”, andincludes a “monitoring, control and possible retrieval” period. The test repository serves as anunderground laboratory specific to the site, the operation of which can continue after the mainrepository is commissioned. The main repository is designed to hold most of the waste. Itsinfrastructures (shafts and drifts) remain accessible throughout the monitoring phase.The pilot repository is designed to hold a small fraction of the waste and enables the behaviour of thetechnical barriers to be monitored, and the theoretical models to be confirmed, for a period which canextend beyond the closing of the main repository. “Based on the observations made in the pilotrepository” it may be decided to intervene in the main repository, including retrieving the waste.This concept of a monitored repository has been adopted by NAGRA, the Swiss waste managementbody [44]. This approach aims to involve a high level of interaction with the stakeholders based,notably, on the presentation of a safety demonstration at each milestone of the process. This approachalso offers flexibility in taking into consideration knowledge acquired during the process. Forexample, it enables the design to be adapted or earlier decisions to be revoked and, if necessary,packages to be retrieved.10.3.4 Constraints specific to monitoring a repositoryThe constraints specific to observation and surveillance of a geological repository for radioactivewaste, compared with those applicable to major civil engineering structures, are essentially associatedwith the long lifetime required of monitoring equipment and its “discretion”, i.e. this equipments noninterferencewith the monitored phenomena and with safety functions.In particular, it should be noted that at this stage of the studies, due to the constraints described below,it is not intended to instrument the disposal packages, so as to avoid impeding handling due to thepossible presence of cables or protruding sensors.DOSSIER 2005 ARGILE -ARCHITECTURE AND MANAGEMENT OF A GEOLOGICAL DISPOSAL SYSTEM389/495