Architecture and management of a geological repository - Andra

These instrumented sections (cf. § 10.3.6.1) ) are distributed along the length of the drifts. Also, theycan be complemented by an overall visual inspection of the structures (or by optical means) and bymeasurements distributed by fiber optic cables integrated into the lining.It must be pointed out that the connecting drifts also offer possibilities for the observation of the nearfield,either of a cell, or of a module, without being restricted by their closure stages. Depending on thechoice of sensors installed in the bore-holes made from these drifts, this allows monitoring oftemperatures, interstitial pressures or deformations in the vicinity of the structure.The monitoring of the drifts and specifically of their near-field, provides indications regarding theinteraction between cells, which takes effect from the first years of repository for highly exothermicpackages, and, after several decades, between modules. For example, the gradual homogenization ofthe thermal field and of the interstitial pressure could thus be monitored.10.3.11.2 Evolution of the drift monitoring system after the packages are put in place thenafter the closure of the cellsPlacing the packages in the cells and closing the cells causes the drifts to heat up over time. The extentof the heating is limited, even negligible when the drifts are ventilated, and this heating has nosignificant consequences on the reliability or the lifetime of the sensors. Their lifetime is comparablewith that demonstrated by the experience feedback in other structures and varies in each case betweenseveral decades and approximately a hundred years.Moreover, while the drifts are still accessible, their monitoring system can undergo maintenance. Thefact that it is possible to install new sensors to replace faulty ones guarantees monitoring continuity forthese structures with no time limit before their closure.10.3.11.3 Evolution of the drift monitoring system after closureThe monitoring of drifts after they have been closed makes it possible amongst other things toascertain the state of the lining and thus the condition if it should be necessary to reverse the process.It would also be possible to monitor any settling of the backfill and the seal, as illustrated for thesealing of a B cell (cf. 10.3.7.3).The closure of a drift section causes very slow resaturation and, depending on its position, moderateand heating which takes place more or less slowly. In all cases, the evolutions expected during theoperating-observation phase are not likely to affect the lifetime or the reliability of the monitoringequipment.The installation of a drift seal restricts the transmission of signals from the upstream part (furthestaway from the shaft) of a repository. As long as the seal remains accessible downstream, the differenttransmission options described for the sealed B cell remain available. When the seal is madeinaccessible by backfilling of a further length of drift, wired transmission via the seal is no longerfeasible. Monitoring of the part upstream from the seal, and of a section of the seal itself, can only bemaintained by means of wireless transmission through the seal (see section 10.3.7).10.3.12 Observation of shaftsThe monitoring of shafts is directed to the main phenomena which characterise these structures,similar to those encountered with drifts, whilst taking account where necessary of the specificities ofthe geological layers passed through. All shafts are instrumented.DOSSIER 2005 ARGILE -ARCHITECTURE AND MANAGEMENT OF A GEOLOGICAL DISPOSAL SYSTEM415/495