Architecture and management of a geological repository - Andra

5 – Repository ModulesThe local scale model is illustrated in Figure 5.2.11 giving the temperature isotherms during thethermal peak for a C1 type cell.Figure 5.2.11Temperature isotherms around a C1 cell at the time of the thermal peak• The significant parameters in thermal designFor the thermal design, it is essential to identify important parameters, any variation of which is likelyto have a significant impact on the scale of the underground repository installations (in terms offootprint and excavated volume). In this respect, the impact of the various operational and constructionprovisions was examined.In terms of operation, the first important parameter is the residual heating power of the waste at thetime of disposal, which depends on the duration of its preliminary storage.In design terms, several aspects were explored. For example, adaptation of the loading phasing wasenvisaged. However, this strategy offers no gains in terms of compactness. Construction measuresconsisting in increasing the exchange surface area between the packages and the geological medium(for example using finned sleeves) were also explored. These measures, which help reduce the fluxdensity are of limited interest because the gains achieved in terms of compactness are offset to varyingdegrees by the increased cost of cell construction. Cell ventilation was also envisaged, although at thisstage of the studies it was ruled out because a passive evacuation solution requiring no humanmaintenance was preferred. Finally, various geometrical configurations were studied with regard tocell spacing and spacing of C type waste inside a given cell. A parametric study highlighted theimportance of these parameters, in particular the spacing between packages, which plays a primordialrole as it enables the length of the horizontal cell to be increased up to a value that is reasonable interms of feasibility (40 metres).To conclude, the important thermal design parameters so far defined are:- the preliminary storage time for highly exothermic packages,- the spacing between packages inside the same cell and the inter-axial distance between cells.DOSSIER 2005 ARGILE -ARCHITECTURE AND MANAGEMENT OF A GEOLOGICAL DISPOSAL SYSTEM206/495