Architecture and management of a geological repository - Andra

11 – Operational SafetyThe internal exposure associated with the radioactive gases emitted by some B waste packages andreleased into the environment has been estimated on the basis of the assumption that the repository hascompleted operations, that is to say, with the entire inventory of B waste taken into account (cf.Chapter 3). This preliminary estimate was made at the periphery of the repository site, taken as 500 mfrom the exhaust air chimney. The calculation, which takes into account the radiological activityreleased by the waste packages and a transfer factor in man that combines all three means of exposureshows that the annual dose for a member of the public of the order of 1μSv, would be negligible.Internal exposure associated with radon gas diffused by broken rock stored above ground or related toemissions from the underground installation ventilation system will depend on a number of factors: theradon exhalation rate from the argillites, ventilation flow in the underground installations and theheight of the exhaust air chimney, length and type of open drifts (drifts under construction or inoperation) and local atmospheric conditions. As in the preceding case, it can be considered negligiblewhen the nature of the geological environment and experience in comparable facilities is taken intoaccount.Although the emission of radioactive gas from the underground installations appears to be negligible,it would, nonetheless, be monitored by measuring the radioactivity of the air as is conventionally donein the context of the operational surveillance of a nuclear facility.11.1.3 ConclusionGiven the measures employed to counter the radiological risk in the design of the installations andtheir mode of operation, the doses received by the personnel on site or by a member of the public atthe periphery of the site should be below the annual limits fixed by Andra for radiolologicalprotection, and well below statutory limits. It should also be remembered that these are preliminaryestimates and do not take into account any subsequent optimisation approach.11.2 Risk analysisThis section assesses the risks identified in the installations for all disposal activities (construction,operation and closure) and proposes associated reduction measures. It distinguishes between "internal"risks related to work carried out in the facilities and "external" risks, related to the environment (whichare dealt with in a more generic fashion).The risks examined in the context of the study are those that are liable to have an impact on people orthe environment. However, the operational consequences (deterioration of work tools, drop inproduction) are not dealt with at this stage.This assessment [107] can be used to highlight certain particular risks which have been the subject ofadditional studies (cf. Sections 11.3 to 11.8) on account of their specificity or their impact on thedesign of the repository and its equipment.11.2.1 MethodologyThe analysis begins by identifying sources of danger associated with disposal activities. It has beencarried out with the support of experts in the different technical fields concerned (nuclear installations,shaft transfert equipment, underground tunnels, etc.) that have used standard danger lists 153 and havebrought their experience with comparable installations to bear.This analysis, which has been structured around physical components (surface installations, accessshafts, underground installations) and activities (construction, operation, closure), systematically takesaccount of compliance with operational safety functions. It offers the most exhaustive view possible atthis stage in the studies of the risks likely to be encountered by personnel and the environment.153 Among the standard danger lists, the MADS (Methodology for the Analysis of the Malfunction of Systems) and the MOSAR (MethodOrganised for a Systematic Analysis of Risks) approaches are the most frequently used in the risk analysis of an industrial installation.DOSSIER 2005 ARGILE -ARCHITECTURE AND MANAGEMENT OF A GEOLOGICAL DISPOSAL SYSTEM442/495