Tome Architecture and management of a geological repository - Andra

4 - General architecture of the repository in a granite mediumThe external exposure dose is the main component of the radiological risk. The maximum dosereceived by the operators per annum would be of the order of 4 mSv. These doses could be optimisedas part of an ALARA ("as low as reasonably achievable") approach in the later development stages ofthe repository project4.4.2.2 Risk of internal exposure by ingestion or inhalation of radioactive materials in theform of aerosolsThis risk is most likely to occur in the surface installations. It could be linked to the dispersion ofradioactive particles from the transport packaging, the packages (primary packages, disposalpackages) or transfer casks.Management of this risk depends on how the primary package reception and disposal packageconditioning installations are organised into confinement systems 14 to avoid radionuclide dispersal intothe operator circulation zones or the environment. Furthermore the ventilation systems of theseinstallations need to be equipped with filtering devices, as they are in other existing nuclearinstallations of the same type 15 . Lastly, it must be stressed that routine contamination checks 16 wouldbe made on transport packaging, packages and casks.4.4.2.3 Risk of internal exposure by inhalation of radioactive gases emitted by disposalpackagesCertain B waste disposal packages B (B2 and B5) emit small quantities of radioactive gases (tritium,carbon-14, etc.).In the surface installations, the limited number of waste packages present would make the totalquantity of gases released in to the atmosphere negligible. In the repository tunnels where a highnumber of packages are stored, ventilation with air extraction via ducts to the repository exhaust shaftwould remove these gases without affecting the operators working in the underground installations.Atmospheric releases could be assessed along with their potential impact as part of the studies carriedout on a real site. In the light of the ventilation flows and the negligible quantity of radioactive gasesreleased, the calculated doses would be very low.4.4.2.4 Risk of internal exposure in the underground installations of the repository byinhaling radon gas emitted by the groundThis risk, present from the start of construction activity, is linked to the natural exhalation rate of thegranite on the site of the underground installations.Data relating to mining operations in this type of environment [29] shows that management of this riskrequires the underground drifts to be permanent ventilated to dilute and remove the radon emitted intothe outer atmosphere.4.4.2.5 SummaryPreliminary dosimetry estimates indicate that the doses received, taking all possible invasive pathwaystogether, would be below Andra’s annual limits set for workers and the general public.141516The principle of a confinement system is to create a difference in air pressure between adjacent premises.These filtering devices are as well justified by planning for accidental situations, in particular for receiving and conditioning bare spentfuel contaminated by corrosion products deposited and activated as the fuel assemblies is present into the reactor.The acceptance thresholds could be those laid down by French Transport Regulations, namely labile surface contamination (not set)limited to 4 Bq/cm 2 for β, γ emitters and 0.4 Bq/cm 2 for α emittersDossier 2005 Granite - ARCHITECTURE AND MANAGEMENT OF A GEOLOGICAL REPOSITORY86/228