Architecture and management of a geological repository - Andra

11 – Operational SafetySuch a damage level doesn’t seem probable as it appears from the fall simulation results. However, asa precaution, design measures aimed at preventing any water from being in the shaft would have to beretained (cf. § 11.2.2.2) to completely exclude this risk.11.7.4 ConclusionIn the transfer phase of packages in the shaft, the risk of the cage falling represents a very lowprobability of occurrence because of the recommended preventive measures. Despite thesearrangements, should the moving body free fall in the shaft, the presence of a fall shock absorber inthe shaft bottom would allow limiting damage to the transfer transfer cask, which would preserve itsmechanical integrity according to the results obtained from the simulation studies.However, due to the uncertainties of the fall simulations (definition of the moving body, fallconditions), the possibility of a release of radionuclides into the environment at the reject point wasconsidered. In order to assess the radiological consequences of such an event, various illustrative caseswere defined under a parametric approach. Thus, technical solutions could be proposed to limit therelease of the radionuclides : one solution would consist of trapping the radionuclides by a filtration ofthe exhaust air at the ventilation shaft ; another would be to isolate the area comprising the wastetransfer shaft and the reject point to prevent any risk of spreading. In both cases, the installationswould have to be securised and control measures taken before proceeding, if necessary, withdecontamination operations.The risk of criticality associated with a fall of a spent fuel package is not imaginable because of all thearrangements proposed to limit package damaging and because of the absence of water in the shaft.11.8 Study of the consequences of a B waste disposal package falling duringits emplacement in disposal cellsB waste disposal packages are emplaced by a vehicle remotely controlled by an operator locatedoutside the cell. After the risk analysis, an accidental scenario was retained where a package would fallin a disposal cell while being stacked at the upper level of a package pile, that is, at a maximum heighton the order of 4 to 6 m (cf.Figure 11.8.1). This scenario is an envelope scenario with respect to thehandling operations in all the facilities.The simulations [107], supplemented with actual size fall test, first characterize the mechanicalconsequences of the fall on the waste packages and then estimate what could be the possibleradiological consequences.11.8.1 Assessment of the mechanical consequences of B waste packages falling in a disposal cellThe assessment of the mechanical consequences of a package falling was made for the two types ofcontainers considered: standard container and container with reinforced retention capability. They arerepresented by a type B2.1 package and a type B5.2 package respectively. Their main characteristicsare listed in Table 11.8.1.DOSSIER 2005 ARGILE -ARCHITECTURE AND MANAGEMENT OF A GEOLOGICAL DISPOSAL SYSTEM477/495