Architecture and management of a geological repository - Andra

the cell which conditions the evolution of the sleeve in terms of corrosion and stability and whichtherefore affects the conditions of possible retrieval of the packages.In the case of access structures (shafts and drifts), the observation enables the tracking of themechanical evolution of the linings and the identification of possible maintenance requirementsallowing an extension of their lifetime. It also makes it possible to monitor the mechanical evolutionof the near-field behind the lining at future seal emplacements and in particular the formation andevolution of a possible damaged zone.The industrial experience feedback in the monitoring of large civil engineering structures shows that itis possible to observe the repository process for a period greater than 50 years thanks to the use of ameasurement system made up of proven reliable sensors (vibrating wire sensors for example). Beyondthis time scale, the observation system can be re-arranged in particular when passing from one stage tothe next, by installing new sensors and a new data transmission technology. As an example, theinstallation of cell seals could give rise to the installation of wireless transmission technology (testedwith success in the Meuse-Haute Marne laboratory) so as not to affect the integrity of the swellingclay plugs by cable penetration. Thus the use of durable sensors and the gradual adaptation of themonitoring system enables us to envisage the observation of structures throughout the entire repositoryprocess, on the considered time scales for reversibility (one or more centuries)Finally, the principle of focusing the observation of the phenomenology of the repository process onjudicially selected structures (control structures), as they are representative of the whole of the zone inquestion, constitutes an operationally realistic basis.10.4 The capacity for package retrievalThe retrieval of the disposal packages is an operation that may be decided upon by future generations.The aim of this section is to highlight the design factors that would facilitate the retrieval of packagesand to assess the feasibility of this operation for the following three key stages:- after the packages are put in place (cell not sealed),- after cell closure (access drift accessible),- after closure of the module drifts (connecting drifts accessible).The analysis of the conditions and equipment required for retrieval is related to the phenomenologicalevolution described in section 10.2 and in particular to the evolution of the materials over time. Thisanalysis is illustrated by a few examples of technical solutions [106].The retrieval of C waste packages and spent fuel will be dealt with jointly as the two concepts havesimilarities in terms of cell geometry (moderately-sized drifts with metal sleeves), and of the package(cylindrical metal package), and in that there is no concrete in the structure or in the handling system(pushing robot or airborne carrier)The retrieval of the B packages will be addressed separately. The B concept, unlike the previousconcepts, is characterised by a large structure lined with concrete, concrete parallelepiped packagesand a lifting truck handling system.10.4.1 Retrieval of B packages10.4.1.1 Design factors favourable to package retrievalThe design of the packages and B disposal cells is characterized particularly by the stability of thelining which helps sustain the functional clearances within the cell and by the durability of the wastepackages. Both facilitate retrieval operations, where required.• Stability of the cell liner and durability of functional clearancesThe cell lining has two favourable characteristics for a retrieval operation.DOSSIER 2005 ARGILE -ARCHITECTURE AND MANAGEMENT OF A GEOLOGICAL DISPOSAL SYSTEM419/495