Architecture and management of a geological repository - Andra

6 – Overall underground architectureThe already filled operation units can continue to be traversed by a low-rate ventilation (approximately2 m 3 /s). This allows the already filled units to be slightly depressurised with respect to the worksites inactivity.The ventilation of spent fuel repository zones would be organised in a similar manner. Because of thesize constraints which make it impossible to install large section ducts, air would be returned throughan additional dedicated drift, with smoke being removed through small section ducts.6.5 Sizing the connecting infrastructuresThe size of the drifts is determined by the size of the vehicles circulating in these drifts and, inparticular, the package transfer vehicles equipped with their transfer cask and the cosntructionmachines.In addition, the total section of a group of parallel drifts is amply determined by ventilation needs: airspeed is limited to approximately 3 m/s maximum in the air entry drifts where the personnel move andwork and approximately 8 to 10 m/s in the air return drifts and ducts in order to limit ventilationcircuit load losses.6.5.1 Access drift diameter and number of driftsIn order to respond to the same flow requirement, a choice can be made between a smaller number oflarge sized drifts or a larger number of small sized drifts. At this stage, the second option was retained.A usable diameter of 5.7 m in a current drift is sufficient for all the flows to go through. Thiscorresponds to an excavated diameter of approximately 7 m (see chapter 7).With these drift diameters, and according to the number and type of zones to be served, the mainconnecting infrastructures will normally consist of 4 to 5 drifts. This number may be increased by oneor two units for the scenarios including the disposal of highly exothermal spent fuels. Similarly, thesecondary infrastructures within a sub-zone will include 4 or 5 drifts.6.5.2 Distance between connecting driftsThe minimum distances between drifts of the same group will be determined by geotechnical factors:the pillar separating two drifts must have a width at least equal to five times the excavated diameter ofthe drifts.6.5.3 Connections between connecting driftsIn the main infrastructures, 2 m dia. crosscuts 112 connecting the connecting drifts spacedapproximately every 100 metres apart allow the smoke removal ducts to pass; 4 m dia. crosscutsspaced approximately every 400 metres apart allow the personnel to be evacuated and emergencyvehicles to pass, if necessary.In the secondary infrastructures, the crosscuts are located opposite to the access drifts to the cells.112 Drifts interconnecting parallel drifts. They are normally perpendicular to the connected drifts.DOSSIER 2005 ARGILE -ARCHITECTURE AND MANAGEMENT OF A GEOLOGICAL DISPOSAL SYSTEM279/495