- 281 - JHR The CEA assessed the risk of localised blockage of the water drainage system induced by debris carried by a very strong wind or hail, associated with a rainfall event. The measures implemented for such an event are described in part 4. The CEA concludes that these events cannot lead to a cliff-edge effect. The CEA also considered the possibility of lightning strike, and decided that its consequences would have no impact on the management of the external flood insofar as the implementation of active means is not necessary in the short term. It adds that the JHR lightning protection takes into account the applicable standard NF EN 62305-2. In its study of extreme natural phenomena, the CEA assessed the risk of flooding resulting from failures of the Sainte-Croix and Esparron/Gréoux dams on the river Verdon, less than 30 km from the Cadarache site. It calculated the maximum levels at the site for independent failures of the dams, and found them to be lower than the level reached with failure of the Serre-Poncon dam. Consequently it ruled out the risk of flooding induced by failure of a dam on the river Verdon. The CEA also studied the risk of flooding resulting from a breach of the Provence Canal situated near the site. The most penalising breach would be failure of the underground water intake called the "puits du médecin" (the doctor's well). The CEA calculated the induced water levels along the length of the valley de la Bête up to the site, and concluded that there was no risk of flooding for the JHR. Measures to improve the safety of the facility - Opinion of ASN The CEA envisages adapting the roads and utility networks (VRD) so as to improve water drainage. It also envisages moving the standby diesel generator set (DS) outside the water run-off zone. ASN considers that the licensee's proposals will improve the robustness of the facility, especially moving the standby diesel generator set outside the zone of possible water run-off in the event of flooding in the coolants building. ASN will formally request this of the CEA. ASN also notes that the adaptation of the roads and utility networks will be examined in the complementary safety analysis of the Cadarache site, for which the submittal date is 15 September 2012. Phénix The CEA has assessed the risk of localised blockage of the water drainage system induced by debris carried by a very strong wind or hail, associated with a rainfall event. The CEA estimates that the risk of blockage induced by the wind is very limited due to the site configuration, but identifies risks of flooding caused by hail combined with exceptional rainfall events, through breaks in the storm water downpipes inside the buildings and infiltrations further to the formation of a pool of water on the ground. The licensee considers that the risks of flooding of the buildings would be similar to those induced by a river flood, but with much lower water flow rates. Combination of an earthquake exceeding the DBE and induced flooding The CEA estimates that failures of the Donzère and Bollène dams on the river Rhône, although much closer to the site than the Vouglans dam, would lead to water levels much lower than the flood safety margin level (CMS) in view of the significantly lower capacities and the scenario chosen for the CMS. The licensee therefore rules out the risk of Phénix being flooded by failure of these dams. The CEA analysed the risk of a leak in the water tower (semi-buried tank of 1300 m3) situated about 200 m to the west of the facility on the slopes of the Dent de Marcoule. Assuming that 50% of the volume of the water tower spills out entirely at level+0.00 m of the Steam Generator building, then runs into its basements before being discharged to the exterior, the CEA estimates that water depths of 75 cm and 45 cm maximum could form on the ground floor and basement. In this case, after operating the two raw water pumps supplying the water tower for one hour, the water level in the auxiliary buildings would reach the level of the penetrations with the reactor building, the handling building and the steam generators (SG) building. The CEA estimates that this is sufficient time to detect the leak and stop the pumps. It nevertheless envisages establishing an instruction for shutting down the raw water pumps further to an earthquake. If the rupture takes place in the gallery outside the buildings, the pressure could raise a manhole cover plate situated in the SG building hall entrance. The CEA therefore envisages modifying this cover plate to guarantee it remains closed.
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