Architecture and management of a geological repository - Andra

11 – Operational Safety11.7.1 Assessment of the mechanical consequences of a cage falling in a shaftThis assessment was made for the following B, C waste and spent fuel disposal packages (cf. Table11.7.1).Table 11.7.1Main data related to the studied cases of a fall in a shaftPrimary packageB2.1 : bituminised sludge181CSD-V : vitrified wasteCU1 183 : spent fuelassemblies11.7.1.1 Fall scenarioDisposal packageConcrete package 182 (with4 primary packages in verticalposition)Metallic over-pack(with a CSD-V container inhorizontal position)Metallic container (with 4 spentfuel assemblies in horizontalposition)Transfer transfer cask(load weight)Parallelopiped transfer cask(approx. 40 t)Cylindrical transfer cask(approx. 50 t)Cylindrical transfer cask(approx. 100 t)The imagined scenario is that of the cage in free fall 184 over the entire height of the shaft, which wouldimpact on a fall shock absorber system placed at the shaft bottom 185 .This scenario, which is overestimating for the fall height, doesn’t take into account :- An action of the cage anti-fall system,- The possible braking effect due to a rubbing or a jamming of the cage’s suspension cables duringthe fall,- The effect of the end-of-travel braking stop at shaft bottom.11.7.1.2 Data related to the simulation studiesThe numerical simulation approach 186 is split into steps where the fall’s consequences on the cage, thetransfer cask, the disposal package and the primary package(s) transported are successively quantified.The condition of each element of these objects at the end of the fall is characterised by its plasticdeformation, which corresponds to the cumulative total of all the types of deformations undergone(expansion, deformation, …). The corresponding coefficient expressed in % can be compared to theacceptable characteristic value (VCA) of the material making up this element. The risk of breakage isanalysed versus the values of the deformation coefficient and the location, shape and extension of thedeformed zone.181 The B2.1 disposal package was retained to represent the family of B waste packages because it corresponds to the most fragile primarypackage (metallic container of small thickness).182 For the simulation, the characterictics of the fiber reinforced concrete package without rod reinforcement have been used, as this packageis more vulnerable to the effect of a drop than the package made of rod reinforced concrete.183 The CU1 packages (UOx), which contain several assemblies, appear mechanically more fragile with respect to the risk of a fall than theCU2 package (MOx), which contains only one assembly.184 In this scenario, the breaking of the cage suspension cables has also as a consequence the fall of the counterweight over about fiftymetres down to the shaft bottom.185 Several technical elements condition the sizing of the shock absorber : the highest weight transported, the limitation of the decelerationof the transfer cask to a value not causing major mechanical damage, the limitation of the crushing of the shock absorber to half itsheight. In order to minimise the effect of the impact on the moving body, it is also planned to use a fall shock absorber with an upperstage having a crushing threshold less than that of the lower stage so that it operates in the most progressive possible way.186 The fall simulation studies were carried out with the software Radioss, which allows studying by finite elements any strongly non linearbehaviour of a structure subjected to forces from almost static up to rapid dynamic forces. Radioss temporally integrates the non lineardynamic equations by an explicit approach.DOSSIER 2005 ARGILE -ARCHITECTURE AND MANAGEMENT OF A GEOLOGICAL DISPOSAL SYSTEM473/495