Architecture and management of a geological repository - Andra

11 – Operational Safety11.7.1.3 Consequences of a cage falling in a shaftAfter an analysis of the fall’s energy balance, the primary package’s condition is examined to find outwhether the damages caused by the fall on the shock absorber are or aren’t liable to be evidenced inthe end by a loss of containment and a release of radionuclides.• Energy balanceThe energy balance illustrated by the fall of the C waste transfer cask (cf. Figure 11.7.2) shows thatthe largest part of the incident kinetic energy was transformed during the impact into internaldeformation energy in a very short time.800700600Global energy balance7%Breakdown of energy absorbedduring the fallEnergy (MJ)5004003002001000Kinetic energyAbsorbed energy0 20 40 60 80 100 120Time (ms)53%40%SHOCK ABSORBERCAGECASK + PACKAGEFigure 11.7.2Energy balance of a fall in a shaft of a cage transporting a transfer cask with CwastesMore than 99 % of the shock’s energy is absorbed by the shock absorber, the cage and the transfercask. The disposal package absorbs less than 1 % of the energy. This distribution remains valid for thefalls of B waste and spent fuel packages.• Mechanical consequences of the fall on the primary waste packagesThe estimation of the deformations observed on the primary packages allows understanding the risk ofa loss of containment of radioactive materials through the following two elements of estimation:- The maximum value of the deformation coefficient of the primary package, which is only anindication (because a high deformation value limited to a few mesh elements is not significant),- The surface of the primary package for which the deformation coefficient is greater than theacceptable characteristic value (ACV), which means a risk of breakage.The results of the simulations (cf. Table 11.7.2) show that for all the B, C and spent fuel packagesthere isn’t any risk of loss of containment of the radioactive materials since no deformation value isgreater than the ACV of the materials making up the primary package. However, it should be notedthat the B waste packages are the primary packages which undergo the greatest deformations and therepersists an uncertainty particularly for the type B2 waste packages on the behaviour of their crimpedlid to the shock.DOSSIER 2005 ARGILE -ARCHITECTURE AND MANAGEMENT OF A GEOLOGICAL DISPOSAL SYSTEM474/495