Architecture and management of a geological repository - Andra

The swelling clay plug and concrete retaining plug, which close the cell, cause a slight, transient desaturationof the wall rock and are then very slowly resatured, over several decades, from theperiphery to the core of the clay plug [8]. For spent fuel disposal cells the clay plug, which is placedinside the partially saturated swelling clay rings, re-saturates even more slowly than in type C wastecells, where it is placed in direct contact with the saturated rock. As the clay gradually re-saturates, itswells and fills the residual spaces, then exerts mechanical pressure on the surrounding materials(rock, metal plug and concrete retaining plug) with which it comes into mechanical equilibrium.As long as the access drift is ventilated, the concrete retaining plug at the entrance to the cell (type Cwaste or spent fuel) remains de-saturated throughout the thickness of rock already de-saturated on thedrift wall, without having any significant impact on the clay plug re-saturation kinetics or thetemperature in the cells.As during the previous stage, inside the cell the evolution of the sleeve and packages is very slow. Thesleeve remains intact and the functional clearances remain in place.Figure 10.2.9Schematic representation of the principal phenomena within type C wastedisposal cells after sealing• Possibilities available for taking action and possible duration of the stageAt this stage, the packages can still be extracted relatively easily as long as the sleeve has remainedgeometrically intact (with no significant deformation); i.e. at least 200 to 300 years after it has beenput in place. Continued monitoring of the thrust exerted by the terrain on the sleeve and, as far aspossible, of the deformation of the sleeves of a few reference cells, makes it possible to reassess thesleeve’s lifetime, whether or not these cells have been closed.However, the level of reversibility has reduced at this stage because the sealing of the cells makes theretrieval operations more complex. Retrieving the packages requires the head of the cell to be reequipped.The technical feasibility of this process is described in section 10.4. The volume to becleared in order to remove the clay plug and its concrete retaining plug is only a few cubic metres ofmaterial per cell.DOSSIER 2005 ARGILE -ARCHITECTURE AND MANAGEMENT OF A GEOLOGICAL DISPOSAL SYSTEM380/495