- 157 - 5.2.3 Conclusion on the planned measures to protect the installations against the risk of losing the ultimate cooling system or the heat sink In all the configurations studied by EDF, for both the reactors and the spent fuel pools, the estimated time before the feared situation (nuclear fuel exposure) occurs is greater than the required time estimated by EDF to restore correct operation of the heat sink. The identified cliff-edge effects depend on the quantity of feedwater available. Moreover, EDF adds that the time lapse before the core becomes exposed will be much longer in the states where the primary system is open than that calculated for situations of electrical power supply loss (evaluated at several days). ASN agrees that the time lapses before exposure occurs could be longer in states where the primary system is not pressurisable than in H347 situations, due to additional primary cooling system make-up possibilities. Nevertheless, ASN observes that the EDF's calculations and reasoning imply hazard robustness of the equipment used to manage a whole-site H1 situation. Yet the cliff-edge effects associated with the temperature resistance of the equipment required in H1 situations have not been investigated. Consequently, ASN considers the demonstration of EDF's capacity to manage a lasting whole-site H1 situation insufficient, since the complementary measures implemented rely partly on existing equipment items used in H1 situation management (CVCS pumps, electrical panels, I&C, etc.) which could have been damaged or lost, notably because in this configuration they are no longer cooled and can ultimately become unavailable. Likewise, in the current baseline safety standard EDF has not defined systematic requirements relative to earthquake resistance and flood protection of the equipment used in H1 situations. Yet ASN observes certain weaknesses in the capacity of the facilities to withstand a whole-site H1 situation induced by an earthquake, including at the level of the current baseline safety standards earthquake, or by flooding beyond the baseline safety standard. In the event of such hazards, ASN considers that the core could become exposed in just a few hours in an H1 situation (for all plant unit states). Likewise, for the EPR reactor, ASN notes that the operability of the SRU system (which is the EPR's alternate heat sink) is not guaranteed in the event of a design-basis earthquake. In its studies EDF envisages examining the possibility of giving the means for guaranteeing water make up a higher hazard robustness margin than the current baseline safety standard. ASN considers that the proposed improvements - which meet the CSA specifications - must be implemented. ASN will issue a requirement this subject. In case of confirmed insufficiency, ASN will ask EDF to reinforce the robustness of the equipment contributing to the management of a whole-site H1 situation. Likewise, the the temperature resistance of the equipment situated in areas that are no longer cooled has not been exhaustively verified. ASN considers that certain key equipment items could ultimately be lost through the heating up of such areas. These include: the RCV pumps, whose rooms are cooled by a ventilation system that is no longer cooled in an H1 situation; electrical or I&C equipment supporting other equipment used in H1 situations; the low pressure safety injection (LPSI) pumps used in an H1 situation, while their motors (1300 MWe, 1450 MWe) and the pumps themselves (1300 MWe) are cooled by the CCWS system, which will ultimately be lost in an H1 situation. 47 Short-term cliff-edge effects characterised by a shorter time before core exposure than that planned by EDF for the implementation of the FARN have been identified in the H3 situation. This time is a few hours for the 900 MWe series in states with the primary system open - reactor cavity not full (due to the current absence of independent means of injection to the primary system), and about 10 hours with the primary system just open (all plant units). In the primary system open state on the 900 MWe series with the current operating procedure, the time to core exposure in a whole-site H3 situation is about 8 hours (because the pump injecting at the primary pump seals is common to two plant units). Moreover, in the case of an H3 situation combined with loss of the LLS, TPS ASG and TAC/GUS, the time is just a few hours with the primary system closed. In the primary system open states on the 1300 MWe and 1450 MWe series, and in the primary system open and reactor cavity full (all series), the time in an H3 situation (excluding summed effects) is longer (several days).
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