Architecture and management of a geological repository - Andra

11 – Operational SafetyTransport transfer casks containing the primary waste packages delivered to the disposal site have aradiological protection function and their structure is designed specifically for the radiologicalcharacteristics of the waste transported. Once the primary packages have been removed from transporttransfer casks, they are handled and placed in disposal packages inside cells which are not accessibleto operators who work by remote control from behind radiological protection shields (walls, shieldedwindows).During transfer operations and up until emplacement in the disposal cells, control of the risk ofexternal exposure takes the form of the interposition of radiological protection shields 147 betweensources of radioactivity and personnel to reduce radiation flux. Disposal package transfer transfercasks, C and spent fuel cell access ports and B cell doors fulfill this role. The effectiveness of theseprotections would be controlled by means of apparatus that measures the level of irradiation, eitherinstalled permanently or used by the radiation protection teams.Radiological protection or distance from the control station of the vehicles used to transfert or handlethe packages in the cell would also contribute to the reduction of doses received by personnel.During closure operations, definitive radiological protection shields are installed such as blocks ofconcrete to replace the doors of the B waste disposal cells and metal plugs of C and spent fuel cells(cf. Chapter 5). These devices would facilitate any reverse operations (package retrieval) as decided.11.1.1.2 Internal exposure risk due to the inhalation of radioactive gas emitted from disposalpackagesSome B waste disposal packages (B2 and B5) emit small amounts of radioactive gas (tritium, carbon14, etc.).In surface installations, the limited number of waste packages present is such that the amount of gasemitted is negligible. In addition, most of the operations are carried out in cells that are not accessibleto personnel.During the course of disposal package transfers to the disposal cells in the underground installations,traces of radioactive gases are emitted from these packages in the transfer drifts and released via theventilation circuit.In the disposal cells where a large number of packages are disposed of ventilation with exhaust of theair by means of ducts to the ventilation shaft (cf. Section 6.4) removes these gases preventing themfrom affecting personnel present in the underground installations.11.1.1.3 Risk of internal exposure due to the inhalation of radon gas emitted from the rock inthe underground repository installationsThis risk, present from the beginning of construction activities, is associated with the level of radonnaturally exhaled from the rock in which the underground installations would be situated. Given theargillite nature of the Callovo-Oxfordian formation, this risk is limited. It can be controlled bypermanent ventilation of the underground drifts which would expel the radon and its descendants.147 The nature of the material from which these screens are made depends on the type of radiation emitted by the radioactive source:- In the case of γ radiation, heavy materials such as steel, concrete and lead glass are used.- In the case of neutron radiation, specific materials (with boron or cadmium, etc.) or hydrogenated materials.- α and β radiation do not need any particular type of screen as they are stopped by the package envelope.DOSSIER 2005 ARGILE -ARCHITECTURE AND MANAGEMENT OF A GEOLOGICAL DISPOSAL SYSTEM437/495