- 162 - ASN considers it necessary to implement EDF's proposal to constitute a hard core of material and organisational measures, associated with tightened requirements, to prevent a degraded situation (type H1) from evolving into a severe accident. Complying with this requirement will lead EDF to: define the list of necessary structures, systems and components (SSC) to prevent core meltdown in lasting whole-site H1 or H3 situations; demonstrate the earthquake and flood robustness of its SCCs and implement any necessary additional measures to ensure this robustness; make an additional verification of the robustness and accessibility of these SSCs, considering the hazards and effects induced by an earthquake or flood beyond the current baseline safety standard. ASN considers it necessary for EDF's proposals relative to the equipment items included in this hard core to meet the requirements set forth above, and must notably be dimensioned to withstand hazards of a higher intensity that those considered in the existing baseline safety standards. Once EDF has defined the "hard core" elements targeted for greater robustness against risks exceeding the baseline safety standard, (see section 16), ASN will ask it to revise its baseline safety standard in the light of the Fukushima experience feedback and start examining the robustness - against the baseline safety standard risks - of those equipment items that are not included in the "hard core" but nevertheless used in whole-site H1 situations. These demands are applicable to the reactors of the fleet in operation and to the EPR. Medium- or long-term accident management: The complementary measures proposed by EDF with respect to H1/H3 situations aim essentially at allowing water make-ups to be made (to the secondary system, primary system and spent fuel pools) to extend the autonomy of the reactors and spent fuel pools. Making these make-ups, when it is not possible to restore a cooling system, enables core meltdown to be delayed but not necessarily prevented. In the case of the primary system, once a certain volume of water has been injected into the reactor building, the ability to restore lasting means of cooling may be compromised. ASN insists on the necessity to ultimately restore a cooling system in order to reach a safe condition, on the existing plant units and the Flamanville 3 EPR alike (the "EVU spraying of SEA water" modification brings only a limited additional time margin), and to integrate this necessity in the strategy of the FARN48. EDF must study the means for ultimately restoring lasting cooling of the reactors and spent fuel pools, using elements from the Fukushima accident experience feedback, including in cases where the heat sink has been seriously damaged. Lastly, the FARN activation criteria in the event of a hazard or accident, and the dimensioning of the associated means, will have to be adapted to enable the FARN to effectively take over management of all the postulated accident situations (all reactor states considered) and thus avoid core exposure. It would moreover be pertinent for the FARN's reflections to focus more generally on the means of ensuring or restoring the safety functions in the medium/long term, independently of specific accident scenarios. 5.3 Loss of the main cooling system combined with loss of the off-site electrical power supplies and the on-site backup supplies For each reactor, ASN has asked EDF to: indicate for how long the site can withstand loss of the "main" heat sink combined with loss of the offsite electrical power supplies and the backup energy sources, without external aid, before serious damage to the fuel becomes inevitable; 48 See § 6 of this chapter.
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