Tome Architecture and management of a geological repository - Andra

4 - General architecture of the repository in a granite medium4.4.3 Risk analysis in accidental situationsThis paragraph presents the main risks likely to occur carrying out repository activities and theassociated risk reduction measures.The risk analysis is related to the inherent risks of the repository ("internal" risks) at this stage of thestudy. It covers the "conventional" risks found in any industrial installation and the risks stemming fromthe presence of waste packages, that are essentially radiological (risk of external exposure, risk ofinternal exposure and even criticality risk).However, since there is no determined site, the "external" risks relating to the repository environment(seismic risk, climate risks, risk of aircraft crashing, etc.) are not developed. They would mainly affectthe surface installations that could be damaged by this type of event and could also lead to degradationor loss of safety functions ("radiological protection" function, "radioactivity confinement" function,etc.). Consequently, the allowance made for these risks will be based on the general rules applied tobasic nuclear installations (BNI) [30] [31].4.4.3.1 Conventional risksThe behaviour of the terrain may have an impact on disposal process risks: the risk of operators beingcrushed by block falls in the drifts (notably while excavating), risk of water ingress in the shafts ordrifts. They are also associated with equipment (loads dropping during handling operations, objectsdropping in a shaft, operators falling from elevated work platforms, crushing by moving equipment,etc.) or the use of heavy machinery (knocking over an operator, colliding vehicles).Maintenance personnel may get electric shocks while working on the equipment and vehicles or thelatter may cause a fire with consequences for many workers, especially when underground.It should be noted that there are minor risks associated with the package characteristics, that would becaused by temporary loss of ventilation in the installations: this relates to the risk due to the presenceof exothermic packages (C and CU packages) and the risk of explosion arising from the release ofsmall quantities of explosive gases 17 by certain B waste packages (B2, B5).Prevention is the key to risk reduction. It involves choosing materials that do not propagate fire,limiting the calorific load present, the use of suitable equipment and vehicles that are reliable andfitted with all the safety devices necessary, properly serviced and furthermore personnel training,awareness of the various types of risks incurred, observation of driving procedures and rules, andwearing individual protection gear 18 .As-you-go exploration at the working face of the excavations can help prevent risks relating to poorstate of the ground or ingress of water in the underground installations. The risks run by the staff canalso be reduced by installing physical protection devices (particularly for work in the shafts), the useof heavy machinery that can be controlled away from the working face, installing thermal shields(firebreak doors, fireproof materials), equipping with site safety systems (fire smoke extractionsystems, fire protection water circuits, communications networks, etc.) as the work progresses..1718These gases (mainly hydrogen) are caused by a radiolysis phenomenon that is due to the effect of ionising rays (β, γ) emitted by theradioactive materials on hydrogenated products present in the disposal packages (organic matter and conditioning matrix water).This protection gear includes safety shoes, ear protectors, dust masks, self-contained breathing apparatus (self-rescuers) to be used in thepresence of fumes…Dossier 2005 Granite - ARCHITECTURE AND MANAGEMENT OF A GEOLOGICAL REPOSITORY87/228