Architecture and management of a geological repository - Andra

• The instrumented sections and the fiber optic cablesThe instrumented sections are positioned in the main part of the cell (three sections), at the location ofthe future metal plug (one section) and at the head of the cell at the location of the future clay plug(one section). Each section groups the sensors allowing the monitoring of the sleeve and of the rockaround the cell.The sensors and the transmissioncables are attached to the externalsurface of the sleeve. Three sets ofsensors are distributed in aninstrumented section, as shown indiagrammatic form in Figure10.3.15. Each set is made up of twoextensometers and a vibrating wiretemperature sensor to monitor thetemperature and the axial andtangential deformation in the sleevelocally.Moreover, these sensors arecomplemented by a fiber opticproviding a continuous temperatureprofile over the whole length of thecell. These measurements also makeit possible to assess thethermomechanical stresses to whichthe sleeve is subjected and also thetemperature inside the cell.As the sleeve is gradually pushedinto place during the excavation ofthe cell, the sensors and the wiredequipment are attached to each section of sleeve, before being inserted into the cell.To protect the equipment when the tube is being pushed, it is covered with a protection cap welded tothe sleeve, as is common practice for the instrumentation of the foundations of structures fitted withmetal piles. This cap also enables the rock sensors to be isolated as long as the ground pressureremains at a low level, so that they only measure deformation of the sleeve, and not a combination ofdeformations of the sleeve and of the rock which would necessitate more complex interpretation.• Monitoring the atmosphere in the cellFigure 10.3.15 Example illustrating the surface auscultationof the cell C sleeveThe atmosphere in the cell is monitored by a vibrating wire temperature sensor and a hygrometerattached to the internal surface of the metal plug. As the resistance of the sensors to irradiation is notknown at this stage of the studies, it may be necessary to move these measurements to the externalsurface of the metal plug. These measurements are complemented by a laboratory analysis of samplesof the atmosphere taken from the useful part of the cell, either by means of a branchpipe passingthrough the metal plug, or by leaving a capillary tube in the residual clearance between the plug andthe sleeve available for use when required. This analysis is designed to ascertain the relative humidityrate and the oxygen rate in the cell, in order to calculate the corrosion rate, if applicable. A similarapproach can be used in the sleeve at the head of the cell, from the access drift.DOSSIER 2005 ARGILE -ARCHITECTURE AND MANAGEMENT OF A GEOLOGICAL DISPOSAL SYSTEM409/495