- 119 - In its CSA reports, in order to evaluate the robustness of the facility to cliff-edge effects, EDF: identified the cliff-edge effects caused by off-site flooding and calculated the corresponding water levels; conducted "beyond design-basis" vulnerability analyses, by increasing certain current design scenarios by a fixed amount; compared the water levels reached for each of the increased scenarios with the water levels leading to cliff-edge effects; proposed studies to confirm the existence of the cliff-edge effect or the steps to be taken to reinforce the robustness to such a cliff-edge effect. Scenarios adopted EDF considered the following scenarios, according to the geographical situation of the site: 1. For all the sites: Maximum high-intensity rainfall (PFI): PFI rainfall intensity used in the design, doubled ASN considers that a factor of 2 corresponds to a correct order of magnitude for reaching a hazard that is significantly more penalising than that of the current safety requirement baseline. However, ASN considers that the duration adopted is in principle not sufficiently penalising, given the saturation of the rainwater networks. ASN considers that EDF's commitment to a vulnerability study for rainfall times longer than the network concentration time is satisfactory. Combination of a PFI lasting 60 minutes with complete blockage of the site's SEO rainwater drainage network outlets ASN considers than in the CSAs, this combination can go significantly beyond the rainfall levels currently adopted for the sites. This combination is a means of identifying the flooding levels as of which cliff-edge effects appear and thus meets the requirements of the specifications. Flooding caused by an earthquake bigger than design-basis: identification of the structures present on or directly above the platform and liable to constitute potential sources of flooding following an earthquake of an intensity greater than the SSE, if the structure or equipment is not considered robust to an earthquake beyond design-basis. During the investigation, EDF made the following commitment: "In order to complete the analysis of the flood risk caused by an earthquake "beyond baseline safety standards ", presented in the RECS (complementary safety assessment report), EDF will by the end of 2012 evaluate the risk of damage to the walls surrounding the cooling towers on the four sites concerned, on the basis of: the effective distance between wall and cooling tower, the possibility of justifying the absence of significant damage to the cooling tower shell for earthquakes bigger than the SSE If damage of the wall following collapse of the cooling tower under the effect of an earthquake "beyond baseline safety standards" cannot be avoided, the effects in terms of induced flooding will be analysed. As applicable, additional measures will be proposed in order to guarantee protection of the equipment in the "CSA hard core". ASN considers that the study approach proposed by EDF would appear to be satisfactory. ASN considers that the approach adopted by EDF and the undertaking made, provide a satisfactory response to the specifications. 2. For coastal sites, EDF chose a CMS scenario (combination of the maximum level of the astronomical tide and the thousand year storm surge) plus a additional increase of 1 metre (which, according to EDF, corresponds to a storm surge with a return period between one hundred thousand and one million years).
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