Architecture and management of a geological repository - Andra

4 – Waste disposal PackagesThe cylindrical shape of the over-pack minimises the spaces inside the disposal package, because itmatches the shape of the primary package. The inserts filling the spaces formed by the profile of thehead and base of the primary package also help to minimise functional clearances between the primarypackaging and the over-pack.It is envisaged to fit disposal packages with ceramic sliding runners, avoiding direct steel/steel contactbetween the over-pack and the sleeve of the disposal cells. This facilitates installation operations aswell as any eventual removal, by improving the possibility of sliding the package during horizontalhandling within the cell. Along with the handling resources presented in section 9.3.3, it also helpslimit clearance around the packages. It also maintains a space between the package envelope and thecell sleeve in the long-term, thereby avoiding the danger of the confined zone promoting thedevelopment of localised over-pack corrosion.The gripping system built into the lid can also be designed to limit residual clearances outside thepackage. This design is illustrated in Figure 4.2.1.Figure 4.2.1Principle of the C waste over-pack4.2.2.4 Comparison with options studied in other countriesMost of the studies performed in other countries consider completing the primary packages of vitrifiedwaste with an over-pack.In Japan [51] and Switzerland [44], it is planned to use thick non-alloy or low-alloy steel. Thedurability objectives are similar to those selected by Andra. The thicknesses envisaged, however, aregreater; this is because the choice was made to prevent radiolytic corrosion by significantly reducingthe radiation level at contact with the packages. The dimensioning conceived by Andra (see below)does not exclude this kind of corrosion, which is explicitally taken into consideration in the durabilityestimation of the object. The concept developed in Japan also has a further radiological protectionfunction allocated to the container.DOSSIER 2005 ARGILE -ARCHITECTURE AND MANAGEMENT OF A GEOLOGICAL DISPOSAL SYSTEM133/495