Tome Architecture and management of a geological repository - Andra

4 - General architecture of the repository in a granite mediumSimulations of the risks from packages made during the studies for a repository in a clay medium [27]show that in both cases the risk is controlled in the operating phase by ventilating the variousrepository installations, and that if ventilation of the installations is interrupted there are no realdangers as there is plenty of time to intervene. These conclusions can be transposed to a repository in agranite medium.4.4.3.2 Radiological risksThe various radiological risks arising from dangerous situations during the repository operationactivity have been identified. The findings are presented by type emphasising those identified risksthat appear to be the potentially most harmful to mankind or the environment. As with the studycarried out in clay [19], this analysis has the benefit of feedback from nuclear installations that arecomparable to a repository.These risks and their main associated risk reduction measures are as follows:• Risks arising from radiological protection failuresAn exposure risk may be linked to a failure in the protection provided by the cell doors, covers andviewing ports, the transfer casks, C waste and CU disposal borehole plugs and B waste disposal tunnelgates. This event could be due to play between moving parts that does not comply with the initialdimensioning. The measures associated to this risk would be: installing radiation detectors on the cells,transfer casks and disposal cells and also workers wearing suitable dosimeters.Accidental exposure can also be envisaged during a maintenance operation in a room adjacent to aradiating cell. The maintenance operations will be preceded by a radiation check in the room. Themaintenance zone could be sited away from the potential radiation field of the radioactive sources inthe cell.Malfunctioning of equipment while handling or transporting a package could lead to it immobilisationand require the intervention of maintenance personnel. The preventive measures would be adequatemaintenance of the equipment used and redundancy of some of its components (motorisation, etc.).This intervention would expose the personnel operating close to the radiating source. The mosteffective measures to suppress or limit personnel exposure would be to provide means to remove theload and bring back the empty equipment to its maintenance shop, minimising the time that operatorswould be present by accurate intervention planning, and dimensioning radiological protectionthicknesses.• Risks relating to the consequences of a fireA fire in the nuclear installations of the repository could have radiological consequences if a packageof radioactive material is involved. The use of package carriers on the surface or underground, wouldcall for specific precautionary measures as fire could degrade the radiological protection in place orworse could lead to the loss of confinement of radioactive material and their dispersion into theatmosphere.At package reception, there should be no radiological consequences of a fire on the carrier withpackages placed in over-packs that would withstand a fire breaking out at 800°C during 30 minutes[28].Studies carried out for the repository in a clay medium on cask carriers [27] show that temperaturerises are likely to affect the metal envelope of the casks without undermining the structure of the caskitself.Dossier 2005 Granite - ARCHITECTURE AND MANAGEMENT OF A GEOLOGICAL REPOSITORY88/228