- 278 - has ruled out the risk of the Cadarache facilities being flooded by the River Durance or overflowing of the Ravin de la Bête stream. The reference rainfall levels considered for the design are the 100-year storm events, as defined in the "REX Blayais" (Blayais site experience feedback). The dimensioning of the BNI's storm water drainage system for these rainfall events was examined during the last periodic safety review of the facility (2006). As regards extreme rises in the water table, the CEA considered a level corresponding to the 100-year flood, where the extreme level of the water table would reach the 317 m NGF elevation for Masurca. Measures to protect the facility against the flood risk The licensee concludes in its CSA report that no particular measures are required to ensure a safe condition after flooding. It specifies that in the event of immersion of fissile materials, the safety of the facility would not be jeopardised. To prevent the risk of water infiltrating into the facility, building watertightness is ensured at construction. The facility also has a drainage system external to the buildings. Drainage grids and channels and a network of pipes collect the storm water (water runoff from impermeable surfaces) and drainage water (infiltration through permeable surfaces) and channel it to the Centre's storm water drainage system. Maintenance of the systems evacuating the water from the drain channels is ensured either by Autumn/Winter servicing by the Centre's specialist services, or at the request of the licensee if found necessary during inspection rounds, for example. Gallery GA1 has 4 sumps which collect water resulting from a rise in the water table or infiltration of water into the facility. Each sump is equipped with a lift pump that is started automatically by a float mechanism if the water reaches a given level. The pumps evacuate the water from the sumps to the storm water drainage network. This system thus detects and mitigates the consequences of such a situation.. A flood detector in the highest sump is linked to the Centre's remote alarm network. If the alarm is triggered, the local security organisation (FLS) intervenes using mobile pumps to evacuate the rising water. Furthermore, the fissile materials store is equipped with five water detectors, one in each storage cell. The information from these devices is processed by the remote alarm network and transmitted to the Centre's safety control station. Conformity of the facility with the current frame of reference The conformity of the facility is determined by the periodic inspection and, where necessary, cleaning of the storm water drainage system, the drainage grids and inspection chambers, the run-off water collection channels and the associated grit chambers. Furthermore, in the follow-ups to the facility's periodic safety review, a reassessment of the external flood risk analysis based on in situ recording of the storm water drainage system and the drainage channels is in progress. Any works and developments necessary to guarantee collection and evacuation of the storm water corresponding to the design-basis rainfall event will be carried out to guarantee conformity of the facility with respect to the external flood risk. Evaluation of safety margins The CEA does not consider a more severe scenario than a flood caused by the river Durance (flood and/or dam failure). The CEA rules out the risk of the Masurca facility being flooded by an overflow of the Ravin de la Bête stream. The licensee puts forward risks of the storm water drainage system overflowing in the event of rainfall events exceeding the design basis rainfall. The CEA considers that the storm water not collected by the drainage system would not have an impact on the buildings due to the small surface area of the upstream watershed, and the steep slopes downstream favouring water runoff towards the Ravin de la Bête. This being said, the truck manoeuvring area to the north of the storage and handling building BSM building, slopes downwards towards the BSM in front of the delivery hall.
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