Tome Architecture and management of a geological repository - Andra

4 - General architecture of the repository in a granite mediumProtection measures such as installing an energy absorber on the carrier structure, limiting lengths ofstraight drifts and possibly escape bays for emergency braking areas, should enable this risk to bemanaged and avoid cask breakage.In the case of package transfer via a shaft, dangerous situations would be the uncontrolled drifting ofthe cage, or possibly free-falling in the very improbable event of its suspension cables snapping 19 off.The prevention measures for these situations (cf. Figure 4.4.1) are drawn from feedback acquired indeep underground mines. They cover first equipment design (independent braking devices on the drivepulley, independent cage suspension cable clusters, etc.) and as well maintenance, inspection andoperation procedures.An additional safety system independent of the cage’s control system could be a cage drop-preventionsystem that would be triggered in the event of excess speed.These systems could be supplemented by other protection measures:- an end-of-travel braking system, similar to the statutory type installed in mines, a few metresbelow the underground station, would limit the mechanical consequences of a drift;- an energy absorber located in the lower part of the shaft would appear to be a solution to deal witha free-falling cage. Simulations on a similar system, made as part of the repository study in a claymedium [27], show that the cage, the shock absorber and the transfer cask would absorbpractically all the kinetic energy of the travelling body. C waste and CU packages shouldwithstand the impact without breaking, although loss of confinement cannot be ruled out for themost fragile B waste packages (B2 bituminised sludge packages);- these preliminary results would lead to providing risk reduction devices, with primarily thepossibility of installing filtration on the shaft air extraction circuit (cf. Figure 4.4.1) ) to controlreleases into the atmosphere following a cage fall 20 .1920In Germany, a study carried out for the Gorleben radioactive waste repository project [32] estimates that the probability of a cage in ashaft dropping is 5.10 -7 /year (operating at 5000 hours per annum), for a similar installation to the planned Andra repository.This measure has already been adopted in the American WIPP transuranic waste repository, in New Mexico. It should be noted that thisfiltration unit, installed on the exhaust air shaft, only operates in the event of an incident.Dossier 2005 Granite - ARCHITECTURE AND MANAGEMENT OF A GEOLOGICAL REPOSITORY90/228