Tome Architecture and management of a geological repository - Andra

6 – C waste repository zoneA thickness of 55 mm has been retained at this stage in order to ensure this service life, fixed byadding together the following two terms [48] :- thickness of 28 millimetres for the cylindrical shell and 50 millimetres for the base and lid, toprovide enough mechanical strength to withstand a load of 12 MPa (evenly applied); this loadcovers the interstitial water pressure and the clay engineered barrier swelling pressure;- over-thickness of 27 millimetres, that is a penalising modelling assessment of the loss of substancethrough generalised corrosion. This thickness could be adjusted according to water chemistry of aspecific granite.• Compatibility with the handling facilitiesOnce the disposal packages have been manufactured in the surface installations, they are storedupright. During these operations the handling height is about 1.60 metres. Once the packages havebeen transferred to the underground installations, they are placed upright in disposal boreholes that areabout 9 metres deep.Dimensioning for these operations entails calculating the thickness of the handling interface andchecking package resistance to dropping.The admissible stress on the material that acts as the over-pack handling interface is adopted from theEuropean Federation of Materials Handling (FEM) calculation rules for lifting apparatus, namely 2/3of the elastic limit. The dimensions of this interface provide robustness with regard to all the demandsthat will be made of it during and after the handling operations.As regards package resistance to dropping, a number of cases have been simulated, such as: (i)dropping on a corner from a height of 1.6 metres and (ii) a vertical drop from a height of 20 metresonto a support presumed to be infinitely rigid. The materials are modelled using a Johnson Cook typelaw that expresses the plastic behaviour of the materials. The resulting deformations are restricted tothe base of the disposal package envelope and will not affect the primary packaging of the waste.The case of a C disposal package drop (while in its cask) has also been considered during shafttransfer from surface to underground: the maximum deformation of the package envelope would notlead to loss of confinement in the event of the cage dropping 500 m onto a shock absorber at thebottom of the shaft.Generalised corrosion of the disposal package and cell sleeve has been considered as an impediment topackage retrieval. For the purpose of dimensioning the handling pocket in this situation, the hypothesisis made that generalised corrosion (2 mm) 38 would affect all the outer surfaces of the handlinginterface. To allow for this situation in the dimensioning it has to be checked that the package can begripped and significant traction effort exerted to overcome the friction and sticking forces caused bythe corrosion. The calculation gives a maximum applicable effort equivalent to the elastic limit ofabout 40 tonnes. Theoretically reaching breaking strength would enable a traction effort of about 85tonnes with however the concomitant risk of damaging the package handling head up its totaldeterioration.6.3.3 Manufacturing techniquesThis section covers the disposal package manufacturing techniques that may be envisaged on the basisof comparable existing industrial techniques.382 mm of corrosion would lead to product a 3 mm thickness being built up over the original dimensions (the total thickness of thecorrosion products being then 5 mm). The geometrical dimensioning of the groove makes allowance for this corrosion thickness so thatthe residual central space can accommodate the fingers of a specific package retrieving tool.Dossier 2005 granite - ARCHITECTURE AND MANAGEMENT OF A GEOLOGICAL REPOSITORY172/228