Architecture and management of a geological repository - Andra

11 – Operational SafetyThis risk could be dealt with in accordance with the principles set out in Basic Safety Rules (RèglesFondamentales de Sûreté) RFS I.1.a [113] which recommends an evaluation of the probability of animpingement on "targets" within the facilities for which the loss of safety functions could have seriousconsequences. This evaluation is specific to the location of the site and takes different types of airactivity into account: general aviation, commercial aviation and military aviation. The objective is toensure that the probability of aircraft impingement leading to an unacceptable release of radioactivityis less than 10 -7 per year. Above this value, the risk of impingement must be incorporated into thedimensioning of the installations in question.In such a case, the measures employed to protect the installations, in particular those containingsources of radiation, would consist of dimensioning the concrete engineered structures to ensure thatthey are capable of withstanding aircraft impingement and marking out the highest obstacles (shaftsuperstructures) with beacons.11.2.3.4 Risks associated with the loss of power and utilitiesEven if this event is improbable (it could occur, for example, as a result of extreme weatherconditions) and may not put personnel present in immediate danger, it could cause difficulties becauseof the large number of systems that would be stopped: ventilation, lighting, pumping and transfer cage.Preventive measures consist of redundant sources of power and emergency supplies (generators,batteries, etc.) for essential systems.11.2.4 SummaryThe operational safety analysis is based on the systematic analysis of risks supported by input fromexperts in the various technical domains concerned.The construction of the various facilities is no different from the construction of other surfaceindustrial installations or underground engineered structures (mines, tunnels, etc.). Because of this, therisks associated with this activity are the conventional risks (crushing, falls, etc.) listed in allconstruction work for this type of installation. No further studies are required at this stage but would,however, be taken into account during the detail design of structures and equipment.Nuclear activity in the surface installations of the repository, which includes the reception, preparationand storage of waste packages, is comparable to activities carried out in the French nuclear facilitieswhere the packages originate. Because of this, the analysis did not require specific studies of therepository installations themselves.Nuclear activity in the underground installations, including the transfer of transfer casks (containingwaste disposal packages) in the shafts and drifts and the emplacement of waste disposal packages intheir cells, is carried out at the same time as drift and cell construction work. This is a specific issue,even though underground repositories exist all over the world 162 and it is proposed that the designshould ensure that these activities remain independent of each other by separating the respective trafficcircuits and ventilation systems.The closure activity does not entail any additional elements over and above those included in otheractivities. There is no particular difference between the closure of surface installations and that of aconventional dismantling site. The closure of underground installations, which takes the form ofbackfilling and sealing drifts and shafts, would be comparable to construction work in terms of siteorganisation and the type of equipment used.The analysis has highlighted the risks that require particular attention on account of their specificcharacteristics or their impact on the design of the repository and its equipment.162 These disposal facilities include the Waste Isolation Pilot Plant (WIPP) in New Mexico, USA, where transuranium waste packages(comparable to some B waste packages) are disposed of in underground installations access to which is via 650 m-deep shafts [114] andthe SFR in Sweden where low- and intermediate-level waste packages are disposed of at a depth of between 60 and 100 m.DOSSIER 2005 ARGILE -ARCHITECTURE AND MANAGEMENT OF A GEOLOGICAL DISPOSAL SYSTEM453/495