Architecture and management of a geological repository - Andra

5 – Repository ModulesStorage periodThe evolution over time of the residual heat rating of the packages has a determining influence on thechoice of preliminary storage of the primary packages. There is a duration below which it isimpossible to comply with the temperature criteria, even for an isolated package (the temperature onthe cell wall exceeds 90°C). Above this period, the footprint and excavated volume needed forpackage disposal (comprising the volumes linked to the cell and to the access drift) diminish in linewith the age of the package. Figure 5.2.12 for example shows the influence of the cooling period onthe excavated volume for disposal of a C1 package, identifying 3 domains. Domain (A) corresponds tostorage periods incompatible with the thermal criteria, even for an isolated package. Domain A coversthe 0 - 45 year range approximately. In domain (B), at between about 45 and 60 years, the excavatedvolume is highly sensitive to a slight variation in the age of the package. In domain (C) which beginsas of about 60 years, the architecture is less sensitive to a variation in the age of the package at thetime it is placed in the repository. At the end of domain (C), after about a hundred years, it becomesvirtually impossible to reduce the excavated volume (and footprint) of the repository by increasing thepreliminary storage period.Domain C was therefore chosen as the design domain for the repository architectures. The beginningof the domain is called "earliest possible" disposal and constitutes the reference for the proposedconcepts.Volume excavated per package (ratio)3ABC210Figure 5.2.120 20 40 60 80 100 120 140 160Package age (years)Influence of the preliminary storage period on the excavated volume per C1package (standardised volume in relation to the volume for a preliminarystorage period of 60 years)Spacing between C waste packages inside a cellThe spacing between packages is an important parameter in limiting the excavated volume needed fordisposal of a package. It is linked to the notion of thermal decoupling. To understand the reasons thisparameter is important, we must differentiate between the useful volume (corresponding to the part inwhich the packages are emplaced) and the non-useful volume (corresponding to all the otherunderground infrastructures in the repository zone, such as cell heads and access drifts).The intuitive configuration which would be to have abutting packages leads to a considerable increasein the non-useful part because when the packages are juxtaposed, the heat given off by the packages inthe event of earliest possible disposal is such that only a few packages can be emplaced in each cell (1to 2 depending on the type of package). This entails a considerable imbalance between the useful andnon-useful parts of the same cell. The total number of cells thus increases as the number of packagesper cell decreases, which leads to extremely long access drifts.DOSSIER 2005 ARGILE -ARCHITECTURE AND MANAGEMENT OF A GEOLOGICAL DISPOSAL SYSTEM207/495