- 139 - For the EPR reactor, ASN therefore considers that EDF must propose measures to give the "2-hour" batteries the diversification that meets the same requirements as for the generator sets. This point is currently being examined as part of the detailed design analysis of the Flamanville 3 EPR reactor generator sets. Given the cliff-edge effects that battery discharge creates for all the reactors, ASN will instruct EDF to significantly increase the autonomy of the batteries used in the event of loss of the off-site and on-site electrical power supplies. Regarding the time lapse before serious fuel damage becomes inevitable, in the event of loss of the off-site electrical power supplies and conventional backup supplies for a reactor without external intervention, EDF has specified in the CSA reports that for the reactors in service: when the primary system is closed, the autonomy depends on the volume of water reserves of the secondary system supplying the steam generators; failure to resupply the SGs followed by loss of their function leads to heating of the primary system and a rise in pressure until the pressuriser discharge valve opens, gradually emptying the primary system; if no complementary measures are taken, the fuel will become exposed a few days after the start of the accident; when the primary system is just open, as the residual power is lower, it takes longer for the fuel to become exposed than when the primary system is closed; 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 cooling system at shutdown; this is followed by a make-up from the PTR (reactor cavity and spent fuel pool cooling) system tank: o on the 900 MWe series, by the charging pumps of the CVCS system of the neighbouring reactor; if no additional measures are taken, the fuel will become exposed more than a day after the start of the accident; o on the 1300 MWe and N4 series, by the mobile motor-driven cooling pump; if no additional measures are taken, the fuel will become exposed several days after the start of the accident; for the spent fuel pool, permanent make-up by the fire-fighting water distribution or production system (JPD or JPP) pumps of the neighbouring reactor prevents the fuel from becoming exposed. For the EPR reactor, EDF has specified in the CSA reports that: the reactor presents no risk of core meltdown or radioactive release for at least the twenty-four hours of operation of the SBO generator sets; when cooling is ensured by the SGs, the auxiliary feedwater system (EFWS) tanks run dry after about two days, but they can be replenished from the tanks of the classified fire-fighting water production system (JAC) by the EFWS system resupply pumps (which can be backed up electrically by the SBO generator sets), giving a total water autonomy of seven days, perhaps a bit more: the fuel would start suffering damage about nine days after the initiating event; if the reactor is not in cold shutdown state with the reactor cavity full, the spent fuel pool cannot be cooled because the SBO generator set is dedicated to reactor management; one of the JAC system pumps can make -up water to compensate for the evaporation and avoid exposing the fuel during the twenty-four hours of autonomy of the SBO generator set; the fuel will become exposed about 5 days after the initiating event; if the reactor is in cold shutdown state with the reactor cavity full, cooling of the spent fuel pool is ensured for twenty-four hours; the fuel will become exposed more than 2 days after the initiating event. Regarding loss of the off-site electrical power supplies and the conventional backup supplies for the entire site, which is a situation that is not analysed for the baseline safety standard, EDF specifies in its CSA reports that, for the reactors in service: as the GUS and the TAC are common to the site, they will only be able to supply one reactor on the site;
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