- 143 - In the CSA reports for the reactors in service, EDF also considered the loss of the auxiliary feedwater system (EFWS) turbine-driven pumps, even though they function independently of the electrical power sources. For the reactors in service, this is not a situation analysed for the baseline safety standard. For the EPR reactor, as this situation is included in the baseline safety standard, the "2-hour" and "12-hour" batteries are provided. In the situation of loss of the off-site electrical power supplies and all the backup supplies of a reactor: if the reactor is initially under power or in hot shutdown state, the rod cluster control assemblies (RCCAs) drop down into the core; the residual power is removed by natural circulation if the primary system is closed, and by evaporation if the primary system is open; the primary system is no longer provided with water make-up; the thermal barrier of the reactor coolant pumps (RCP) is no longer cooled; on the secondary system, the steam generators are no longer supplied; the spent fuel pool cooling systems are no longer supplied with electricity. EDF has carried out a conservative analysis of this situation for all the reactors in service, considering all the reactors of a given site together, not each reactor individually. In its CSA reports, EDF considered the EPR reactor to be isolated from the other reactors on the site. For the case of loss of the off-site electrical power supplies and all the on-site emergency power supplies, EDF specified in its CSA reports that the capacity and autonomy of the batteries were the same as in the preceding case of loss of the off-site electrical power supplies and the conventional backup supplies. Regarding the time without external intervention before serious damage to the fuel becomes inevitable in the event of loss of the off-site electrical power supplies and all the on-site emergency power supplies, EDF specified in the CSA reports that, for the reactors in service when the primary system is closed, considering deterioration of the RCP seals leading to a significant breach in the primary system, the core would become exposed after about one day; when the primary system is just open, the accident operating procedures currently demand maximum cooling of the primary system, resulting in complete emptying of the SG; if no water make-up is provided, the fuel would become exposed in about ten hours; when the primary system is sufficiently open, a gravity make-up of a limited fraction of the spent fuel pool water is applied to compensate for the vaporisation caused by the loss of the primary cooing system at shutdown; this is followed by a make-up from the PTR system: o on the 900 MWe series, the CVCS system charging pumps are no longer available; if no additional measures are taken, the fuel will become exposed a few hours after the start of the accident; o on the 1300 MWe and N4 series, the technical specifications (TS) limits this situation to one and only one reactor on site, always leaving the possibility of using the mobile motor-driven cooling pump; the fuel will become exposed several days after the start of the accident; for the spent fuel pools, as all the pumps of the fire-fighting water production or distribution system (JPP or JPD) are unavailable, the fuel will become exposed within a day and a half. For the EPR reactor, EDF has specified in the CSA reports that in the event of loss of all the external and onsite electrical power supplies: if the reactor is at full power, the fuel in the core will suffer damage after a few hours; if the core is unloaded, the fuel in the pit will become exposed more than one day after the initiating event (more than four days after the event if the core is in the vessel). In this situation of loss of the off-site electrical power supplies and the conventional backup supplies and of all other on-site emergency electrical power sources, ASN observes that the CSAs reveal short-term cliff-edge
RkJQdWJsaXNoZXIy NjQ0NzU=