Architecture and management of a geological repository - Andra

4 – Waste disposal Packages• Safety-criticality [55]Criticality calculations [55] have shown the packages to be sub-critical whatever the moderationconditions in the package and surrounding neutronic reflection, taking into account fuel assemblyburn-up rate (burn-up credit 53 ).The solution of four assemblies per container covers about 99% of the UOX spent fuel quantitativeinventory considered in the studies (this involves the estimated part of fuel with a burn-up rate higherthan or equal to the rate considered for criticality assessment). Fuel assemblies with too low a burn-uprate to allow for a satisfactory demonstration of sub-criticality in packages with four assemblies can beconditioned safely in small diameter packages with one assembly.Assessment of the sub-critical property of all these packages takes into account conditions resultingfrom long-term changes to the fuel assemblies, container (geometric modification to the emplacementsdue to gradual corrosion of the insert) and its environment.4.3.3.3 Compatibility with handling equipmentIn a similar way to C waste disposal packages, three container handling cycle configurations wereconsidered in design and dimensioning. The first one corresponds to vertical handling of disposalpackages during container operations and temporary storage prior to transfer to undergroundinstallations.The second one corresponds to placing in disposal cells. The third one is related topossible removal of packages, while taking into account same corrosion of the latter, to be cautions.• Taking into account vertical handling operations in surface installationsHandling groove dimensions defined for handling in waste disposal cells (see below) are large enoughto withstand stress related to vertical handling operations in surface installations.Concerning resistance to falling, calculations with finite elements have been made for vertical fallsonto an infinitely rigid surface, so as to determine permissible fall height, characterised by plasticdeformation of less than 22 %. These calculations show that below a height of 5.90 m for the “withoutcladding” option and 6.40 m for the “with cladding” option there is no containment rupture. The lid isnot damaged and preserves its gripping function. Deformations to fuel assembly emplacements arelocalised and do not result in plastic deformations likely to damage fuel assemblies and prevent themfrom being removed from the container. These heights are much greater than elevation envisaged inthe installations (about 3 metres).• Taking into account operations for placement in waste disposal cellsWeight and diameter of large diameter packages (CU1) result in favouring the principle of transferusing air cushions as illustrated in Figure 4.3.9 (c.f. chapter 9).53The burn-up rate considered is 40 GWj/t for an assembly initially enriched at 4,5%DOSSIER 2005 ARGILE -ARCHITECTURE AND MANAGEMENT OF A GEOLOGICAL DISPOSAL SYSTEM152/495