Architecture and management of a geological repository - Andra

5 – Repository ModulesIf the packages are further away from each other, there is a spacing distance (thermal decouplingvalue) as of which the thermal load per linear metre in the useful part is such that it is possible to placean infinite number of packages in a cell of length presumed to be infinite. It then becomes possible toadopt the longest possible cell length, given technological, construction and handling considerations.This length was set at a reasonable value of 40 metres (including 30 metres useful length) for all typeC packages.The role of the spacers is to achieve a situation in which there is "thermal decoupling" of the packages.As long as the packages are "thermally coupled" their number and the length of the cell are limited inorder to meet thermal criteria. "Thermal decoupling" corresponds to a package spacing configurationfor which it is thermally possible to adopt the maximum cell length (defined by technological criteria).Inter-axial distance between C waste cellsThe inter-axial distance between cells has a major influence on the scale of the repository installationsin that it enables the number of packages contained in the cell to be optimised. The number ofpackages that can be arranged in a cell in compliance with the thermal criteria rises as the spacebetween cells increases. The studies show that when this spacing increases from the minimum value(which for geotechnical reasons is about five times the diameter of the cell), the footprint of theinstallations drops, reaches a minimum and then increases again. The inter-axial distance betweencells is therefore a parameter to be optimised.• Results of thermal design and sensitivity to important parametersThe results of the thermal design can be expressed in terms of variations in the geometricalcharacteristics of the installations as a function of the preliminary storage period. The repositorymodule architectures presented here are calculated for a preliminary storage period of 60 years for C1and C2 packages and 70 years for C3 and C4 packages. This corresponds to "earliest possible"disposal: the packages are separated by thermal decoupling spacers.For C0 packages (which are stored for at least 20 years), the architecture corresponds to the "mostcompact" repository: the number of packages contained in the cell is maximum (18 or 22 juxtaposedpackages) and the inter-axial distance between two cells is close to the minimum determined by thegeotechnical considerations.For these preliminary storage periods, the thermal design enables the following geometricalparameters to be determined (see Figure 5.2.13):- inter-axial distance between two adjacent cells (or the pitch Px),- the number (N) and spacing of the packages they contain (linked to the useful length of the cell,Lua, and the number N of packages),- the distance between cell ends (the pitch Dy).- The footprint per emplaced package can then be easily deduced.DOSSIER 2005 ARGILE -ARCHITECTURE AND MANAGEMENT OF A GEOLOGICAL DISPOSAL SYSTEM208/495