Architecture and management of a geological repository - Andra

5 – Repository ModulesFigure 5.2.22Microtunneller head (photographs courtesy of CREATIV ALLIANCE andROBBINS Equipment)The total execution time for the disposal cell using the microtunneling method is estimated at nine 8-hour shifts (total of 72 hours) broken down as follows:- Thrust bench installation and removal: 5 shifts- Disposal cell excavation, not including tube connection: 3 shifts (40 m at 2 m/h)- Miscellaneous (tube connection, cleaning, etc.): 1 shift5.2.6 Disposal cell closureThe disposal cell is closed by a plug that ensures a hydraulic barrier function. A system is alsoimplemented to ensure the radiological protection of personnel in the access drift.This section first discusses the various components intended to perform these functions and thendescribes each of them in particular, indicating their respective design and implementation.5.2.6.1 Principles of C waste disposal cell closure designIn order to minimise the transport of dissolved components, a low-permeability continuum must bereconstituted around the packages. This continuum is materialised by the geological argillite formationand the swelling clay-based plug.To achieve optimal hydraulic closure of the disposal cell, the plug must have the lowest possiblepermeability value. Three components are involved: the argillite contact aureole (potentially damaged)facing the plug, the swelling clay-based plug, and the interface between the plug and the argillite. Thedesign is intended to obtain the optimal hydraulic properties of each of these three components.In order to preserve the low permeability of the argillite around the disposal cells, damage must beminimised and fracturing avoided. Several design measures have been defined for this purpose, asindicated above (orientation, excavation and support methods, plug location outside the damaged zoneof the access drift). The damage expected under these conditions has been indicated in section 5.2.3.5.The permeability of the microfissured argillite aureole around the structures is estimated atapproximately 5 10 -11 m/s [13]. If the argillite rests on a body that limits its displacement, the creepphenomenon can further contribute to microfissuring, thereby reducing permeability.DOSSIER 2005 ARGILE -ARCHITECTURE AND MANAGEMENT OF A GEOLOGICAL DISPOSAL SYSTEM222/495