Architecture and management of a geological repository - Andra

When the packages are put in place this may reduce the cell monitoring capacity as the evolution ofthe condition of the thermal and radiological environment may gradually reduce the reliability of thesensors on the sleeve. These conditions are less restrictive outside the buffer, which attenuates thedose rate and imposes a radial thermal gradient. Thus, the lifetime of the monitoring equipment can beextended to several decades outside the buffer.Cell sealing leads to gradual resaturation of the swelling clay in the cell plug and imposes the sametransmission constraints as those set out above for B and C cells. In addition to the bore-holetransmission options or the use of a wireless system, the concept of a spent fuel cell offers thepossibility of routing the cables through the metal lining.As the drifts are gradually closed, the evolution of the monitoring system, which relates essentially tothe measurement transmission equipment, is identical to that described for the C cells (§ 10.3.8.4).10.3.10 The monitoring system of standard cellsThe distribution of the monitoring equipment proposed in the above sections are appropriate for themonitoring of a selection of control cells. The monitoring of the standard cells relies upon a smalleramount of equipment. It is suggested that a standard B cell contains fiber optic cables and aninstrumented section in the useful part of the cell. A standard (C or CU) cell contain the fiber optic andan instrumented section at the metal plug.10.3.11 Observation of driftsThe monitoring of drifts focuses on the main phenomena which characterises these structures, inparticular the initial deconfinement of the host rock, the formation of a damaged zone, a gradualdesaturation of the near-field, the creep of the rock and the re-pressurising of the lining.10.3.11.1 Drift observation systemThe options for the use ofmonitoring equipment arecomparable to those describedfor the B cells (cf. section10.3.7.1). They are based oninstrumented drift sections. Onesuch section is illustrated inFigure 10.3.19. Only the depth ofthe bore-holes, which makes itpossible to install a greaternumber of extensometers,differentiates it from anequivalent section of a B cell(cf. Figure 10.3.1).The sensors distributed in eightmonitoring units make it possibleto monitor the mechanicalstrength and the dimensionalstability of the structure, thehygrometric conditions in theFigure 10.3.19 Illustration of the monitoring equipmentdistribution options in a drift sectiondrift, the mechanical and hydraulic evolutions in the near-field, the evolution in the thermal field, andpossibly the chemical modification undergone during the operation period.DOSSIER 2005 ARGILE -ARCHITECTURE AND MANAGEMENT OF A GEOLOGICAL DISPOSAL SYSTEM414/495