Architecture and management of a geological repository - Andra

10.2 Mastery of the repository behaviour and ability take action [82]This section describes the changes to the condition of the structures and packages that gradually occuras the disposal process proceeds. For each key stage defined above, it underlines the principalphenomena and explains to what extent they are liable to affect the ability to take actions affecting theprocess and any operation that may be undertaken to retrieve the packages [83]. In each case, it detailsthe time constants particular to each stage, given that they correspond to changes that occur withoutany modifications to or major operations being carried out in the repository management process. Italso underlines the potential effect, in the longer term, of changes to the repository with respect tosafety functions.10.2.1 Behaviour of type B waste disposal cellsFor type B waste cells, only two stages have a significant impact on their behaviour during operationof the repository. They are the “Post package-placement” stage, during which the cell is ventilated,and the “Post cell-sealing” stage (which is the same as the “Post module-sealing” stage) during whichthe cell is no longer ventilated. The subsequent “Post repository zone-closing” and “Post-closing”stages have no notable impact on the physical or chemical evolution of type B waste cells.10.2.1.1 “Post package placement” stageDuring this stage, the tops of the cellsfilled with packages are accessibleunder the same conditions as at the timethe packages are placed in position (seeFigure 10.2.1). The disposal chamberventilation is maintained and the headsof the cells are still fitted with theirradiological protection airlocks andassociated mechanical devices used toplace the packages in position. Theaccess drifts are ventilated, maintainedand accessible. Part of the structures,notably the cells, are monitored usingvarious devices described in paragraph10.3.7.• Evolution of the cellFigure 10.2.1 Accessibility of B cell headsThe chemical alteration of the concrete liner is very slow, due notably to the low relative humidity ofthe ventilation air (estimated at 50%).The liner is gradually loaded by the thrust of the rock. However, the de-saturated state of the rock onthe wall tends to reduce the speed of these delayed deformations and slow the increase in thrust on thelining. The thickness of the liner used enables it to resist the thrust of the rock without any loss inrigidity for at least a century and it has been shown in Chapter 5.1 that it can provide the cell withgeotechnical stability for at least two or three hundred years and probably longer. Thus, the handlingclearances left free around the disposal packages do not change significantly during this timescale.As for the liner concrete, the low relative humidity of the air in the cell has little impact on theconcrete forming the disposal packages, which is initially highly de-saturated, and the physicochemicalevolution of the concrete of the packages (atmospheric carbonation, reinforcement corrosion)is extremely slow [48]. The slowness of the alteration of the disposal packages and their mechanicalstrength keeps them intact for at least a century without any intervention. The slow corrosion rate ofthe metals also concerns the waste primary containers placed inside the disposal packages.DOSSIER 2005 ARGILE -ARCHITECTURE AND MANAGEMENT OF A GEOLOGICAL DISPOSAL SYSTEM370/495