Tome Architecture and management of a geological repository - Andra

4 - General architecture of the repository in a granite mediumFigure 4.2.1View of two-level repository architecture4.2.2.2 The access shafts and ramp: description and constructionTwo types of structure are considered for access to the underground installations of the repository:shafts and ramps.- shafts are vertical structures, generally equipped with machinery to lower and raise loads in cagessuspended by steel cables;- ramps are inclined drifts, with a 10-15% gradient, that are used by vehicles with tyres 8 .These two types of structure are commonly used in mining and underground engineering (sediment ormetals mines, underground subways, deep tunnels, underground hydrocarbon storage facilities, etc.).Shafts have been in use since the 19 th century and ramps since the second half of the 20th century.Studies carried out in Sweden and Finland for underground repositories in a granite medium conludewith hybrid solutions combining several shafts and one ramp. In Sweden, the ramp is designed formaterials (broken muck, backfill, etc.) and also for disposal package transfers. However the elementsthat led to this choice cannot be directly transposed to the French context for the following reasons:- firstly, a higher daily disposal package throughput is considered in this study than in the Swedishand Finnish projects. This throughput makes a strong case for using shafts for package transfer;- furthermore, it is considered that physical separation of nuclear operation and constructionthroughputs means their easier co-activity.In contrast, the "all shafts" solution has been adopted in the existing WIPP facility (United States) andthe Gorleben repository project (Germany) where water-bearing overlying formations would havehindered ramp construction.To sum up, it appears that technically both the "all shafts" and hybrid "shafts-ramp" solutions aresuitable for an outcropping granite context.8 There are also so called “inclined” (sub-vertical) shafts dipping up to 20%. This type of structure is only used in specific conditions(dipping deposits, mountainous topography, etc.).Dossier 2005 Granite - ARCHITECTURE AND MANAGEMENT OF A GEOLOGICAL REPOSITORY61/228