- 107 - that these design provisions cannot be simply compared to margins in the absence of a detailed justification concerning the uncertainties mentioned above. Furthermore, the margin values proposed by the licensee were established according to expert opinions in the light of the deadline for the complementary safety assessments. While duly noting the conservative nature of the approach beyond the initial or reassessed regulation designbasis earthquake, ASN thus considers that the overall margin evaluation needs to be taken further and in greater detail. ASN also considers that the identification of the equipment liable to experience behaviour discontinuities, given the time available for the exercise, cannot be exhaustive, particularly for those points that are hard to check or modify (for example: the fuel transfer tube between the reactor building and the fuel building). ASN will be asking EDF to complete its review of the items liable to experience behaviour discontinuities and initiate the necessary corrective measures as applicable. 2.2.1 Seismic level leading to significant damage of the fuel assemblies The robustness study performed by EDF for a hazard equivalent to 1.5 SSE identifies no failure of the systems performing fundamental safety functions. On this point, ASN has no remarks in addition to those made concerning the application of the robustness analysis approach by EDF beyond the design-basis earthquake. 2.2.2 Seismic level leading to a loss of containment The robustness study performed by EDF for a hazard equivalent to 1.5 SSE identifies no failure of the containment. On this point, ASN has no additional remarks to those made concerning the application of the robustness analysis approach by EDF beyond the design-basis earthquake. 2.2.3 Seismic level leading to non-design-basis flooding Combination of a seismic risk and an off-site flooding risk: In the initial design and following the partial flooding of the Le Blayais plant, EDF's calculations took account of the flood safety margin level which, if exceeded, entails the highest water level on the site. In its CSAs reports, EDF took account of the topography of each of the sites and identified the water reserves above the site (and thus liable to create flooding in the event of a break) which are not considered robust to a SSE. EDF evaluated the volumes of water that could flood the platform. The examination performed in principle identifies no risk not already covered by the existing or planned protection measures. Nonetheless, in order to consolidate this assessment, EDF propose complementary studies for certain sites: on an earthquake initiating a dam failure, to confirm that the protections for the sites concerned against the flooding created by this dam failure cannot be damaged by the earthquake; on an earthquake liable to lead to several dam failures, to confirm that the flood protections for the sites concerned are sufficient. In the light of the geographical situation of the structures concerned, the feared effect is the arrival of water on the nuclear island platform, exceeding the building access thresholds. The potential consequences of this scenario are presented in the flooding part (§ 3) of this chapter.
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