Architecture and management of a geological repository - Andra

11 – Operational Safety11.1.1.4 Internal exposure risk through ingestion of radioactive materialsIn surface installations, this risk could be related to the dispersion of radioactive particles fromtransport transfer casks, waste packages (primary packages, disposal packages) or transfer transfercasks.In surface installations, the management of this risk would depend on the organisation of the receivingand preparing facilities into containment systems 148 in order to prevent the dispersion of radionuclidestowards areas in which personnel circulate or into the environment. These installations would also beequipped with filtering devices on their ventilation circuits, as is done in existing nuclear facilities ofthe same type 149 . Finally, it is important to mention that non contamination inspections 150 of transporttransfer casks, waste packages and transfer transfer casks would be carried out systematically.11.1.1.5 Criticality riskThe criticality risk corresponds to an uncontrolled nuclear chain reaction. This is initiated by anincrease in neutron activity in fissile materials (uranium-235, plutonium-239 and plutonium-241).The safety-criticality tests showed that B waste and C waste packages do not contain enough fissilematerials (critical mass) for this type of reaction. Spent fuel packages are the only type affected by thisrisk [55]In surface nuclear installations, in the case of spent fuel 151 , the absence of the inflow of water into theconditioning cells must be ensured to eliminate the risk of criticality as is practiced in similar existingstorage facilities on waste production sites.In underground installations, package transfer and emplacement in the repository is carried out dry.There is no criticality risk associated with this.11.1.2 Dosimetric evaluation on site and around the periphery of the siteThis preliminary evaluation, based on the radiological characteristics of the packages summarisedhereafter takes into account the measures envisaged (radiological protection shields,non-contamination inspections, monitoring, etc.).11.1.2.1 Data taken into account• External exposureThe equivalent dose rate (EDR) values relating to primary packages are given for different types ofpackage (cf. Table 11.1.1).148 The principle of a containment system is to create a difference in air pressure between adjacent areas.149 These filtering devices are, however, justified when taking accident situations into account, in particular for the reception andconditioning of bare spent fuel whose surface would be contaminated by corrosive products deposited and activated during transfer fromthe fuel assembly in the reactor (cf. 11.2.2.2).150 The acceptance thresholds could be those established by transport regulations, that is to say, labile (not fixed) surface contaminationrestricted to 4 Bq/cm 2 in β,γ emitters and 0.4 Bq/cm 2 in α emitters [110]151 The presence of water, which attenuates the energy of the neutrons and slows them down, makes them more reactive to fissile materialsand increases the reactivity of the system. In addition, the procedures used for conditioning the packages are dry procedures, no water isused.DOSSIER 2005 ARGILE -ARCHITECTURE AND MANAGEMENT OF A GEOLOGICAL DISPOSAL SYSTEM438/495