- 161 - ASN considers that these planned improvements will enhance the robustness of the facilities, even though it may express some reserves or require additional information regarding their appropriateness or application in certain cases. One ASN reserve concerns EDF's proposal to use existing equipment (CVCS or SIS pumps, electrical panels, EFWS equipment, PTR tank, etc.) as part of the complementary measures, knowing that some of these equipment items may have been damaged or lost. In effect, robustness to hazards beyond the baseline safety standard is not guaranteed. As an example, the ultimate make-up means (pumping from the water table or reservoirs) powered by the new ultimate backup diesel generator will be used to supply the secondary system via the ASG tank, the lines and an existing motor-driven ASG pump, and to supply the primary system via the PTR tanks and the existing lines. It is important for EDF to guarantee their robustness, taking into account: the reliability, hazard robustness and ease of use of the additional equipment; the risks of common mode failure (associated for example with an induced internal hazard) or common cause failure (associated with the design, production or maintenance ) between the key existing equipment items and those added as part of the additional measures; the risks of failure - whether intrinsic or associated with a hazard - of the existing equipment that EDF proposes to reuse as part of these ultimate defence measures (electrical panels, RCV pumps, ASG equipment, etc.). ASN considers that the complementary measures proposed by EDF for the whole-site H3 situation provide robustness with respect to the H1 situation (less degraded) and cover failure of the means used specifically in this situation. However, with a defence-in-depth approach, it is important to prevent an H1 situation from evolving irreversibly towards more a severely degraded situation (whole-site H3) in which the consequences can no longer be mitigated by a small set of equipment. With this aim in view, ASN considers that EDF must start reflecting on the development of its baseline safety standards, in the light of the Fukushima experience feedback, to integrate the lasting whole-site H1 situation. ASN considers it necessary for EDF to examine the temperature resistance of the "key" equipment situated in premises where the ventilation system is no longer cooled in the event of lasting loss of the heat sink for the entire site. To enable the complementary measures to provide a robust ultimate line of defence against the cliff-edge effects identified in the CSA reports for whole-site H1 situations, and notably those induced by an earthquake or flooding beyond baseline safety standards, EDF must, when it defines the hard core equipment items, look for new measures that are independent and diversified with respect to the existing means, including in their supporting systems in order to minimise the risks of common mode failure between the existing means and the complementary means. In particular, EDF must look for easy-to-use and robust injection means situated as close as possible to the steam generators and the primary cooling system (rather than have the ultimate make-up means depend on the reliability of the RCV pumps, whose temperature resistance displays uncertainties). ASN considers it necessary for EDF to install hazard-resistant backup systems that can continuously remove the residual power in the event of total loss of the heat sink. ASN also considers it necessary for EDF to propose reliable and hazard-resistant means of injecting borated water into the reactor core. For the EPR, ASN will ask EDF for complementary studies of SRU system reinforcement in "diversification" mode (that is to say with intake from the sea outfall structure rather than the main pumping station, as is the case in normal mode), given the high probability of having to switch to this mode in an accident situation.
RkJQdWJsaXNoZXIy NjQ0NzU=