- 136 - In the scheduled and systematic actions to identify any deviations on its facilities (periodic tests, maintenance, regulatory inspections, installation conformity reviews carried out as part of the periodic safety review), EDF identified a number of nonconformities directly or indirectly affecting the generator sets of the reactors in service. ASN considers that although these nonconformities do not represent an immediate safety hazard, they do affect the robustness of the backup generator sets. EDF notified ASN of these nonconformities and they are being monitored specifically. Regarding the autonomy of the on-site electrical power supplies, EDF pointed out in the CSA reports that the reference case studied to determine the robustness of the facility considers a situation where the off-site electrical power supplies for the entire site are lost for two weeks. The following procurement measures have been planned on the basis of this situation: fuel autonomy is guaranteed for 3.5 days; procurement is covered by a national contract, that requires delivery within 24 hours in emergencies and 3 days in normal situations; EDF also points out that strategic fuel reserves are reserved for its needs; oil autonomy is 3 days for the reactors in service and 10 days for the EPR reactor; beyond this, procurement is possible in accordance with provisions specific to each site. Whatever the case, EDF considers that the availability of resources is ensured for two weeks; the initial cooling water reserves for the generator sets of the reactors in service provide two weeks of autonomy. For the EPR reactor, the initial cooling water reserves ensure at least 10 days of autonomy for the "high temperature" water and 22 days for the "low temperature" water; the compressed air reserves required to start each generator set allows five start-ups and can be replenished by compressors; the diesel engines have a stand-alone air-water cooling system. EDF indicates in its CSA reports that the ultimate backup generator sets (SBO) of the EPR reactor provide an additional electrical power supply of at least twenty-four hours. ASN considers that the supply management methods are capable of guaranteeing 3 days autonomy for the generator sets of the reactors in service and 4 days for the EPR reactors. ASN notes that EDF has not demonstrated that the site can be autonomous for two weeks under all circumstances, and notably after an earthquake or a flood leading to isolation of the site. ASN will ask EDF to ensure the reliability of the on-site fuel and oil stocks and their replenishment under all circumstances so that at least two weeks' autonomy is ensured. Regarding the measures taken to extend the utilisation time of the on-site electrical power supplies, EDF has specified in the CSA reports that: on the reactors in service, the use of independent thermostatic valves (i.e. controlled only by the fluid passing through them) instead of electropneumatic valves to regulate backup generator set cooling guarantees the operation of these generator sets if the compressed air distribution system (SAR) goes down; on the EPR reactor, ensuring the long-term operating reliability of the backup generator sets depends on the activation of additional protection mechanisms if problems arise that risk causing rapid destruction of the generator set if they are not solved quickly, and they can be repaired in a relatively short time. The aim is to limit the consequences of a possible failure that could damage the generator set by preventively shutting it down: long-duration failures can thus be avoided by making short-duration shutdowns for repair work; as a single generator set suffices for the safety systems, the others could be shut down, to save fuel for example. ASN considers that EDF's proposal to draft an operational procedure for "economising" a generator set when necessary should be put into application.
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