- 137 - Regarding the measures that can be envisaged to enhance the robustness of the facility, EDF proposed in the CSA reports that the protection logic of the 1300 MWe series generator sets be modified by manually restoring the "non-priority" protection mechanisms that are disabled automatically in the "short-term" operating phases (this has already been done on the 900 MWe and N4 series generator sets). 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. ASN considers that the proposed improvements, which meet the CSA specifications, should be implemented. Regarding the extension of the off-site electrical power supply loss to the entire site, which is not analysed for the baseline safety standard, EDF specifies in its CSA reports that this does not change its analysis; this is because in this situation reactor management does not require any particular equipment or equipment common to several reactors. ASN considers that EDF must take into account this off-site electrical power loss scenario when ensuring the reliability of on-site fuel and oil stocks and their resupply. 5.1.2 Loss of off-site electrical power supplies and conventional backup supplies For each reactor, ASN has asked EDF to: provide information on the capacity and autonomy of the batteries; indicate for how long the site can cope with loss of the off-site electrical power supplies and the backup energy sources without external intervention before serious damage to the fuel becomes inevitable; indicate what external action external is planned to prevent fuel damage: o equipment already on the site, for example equipment from another reactor; o equipment available off the site, assuming that all the reactors on a given site have suffered damage; o generators that are geographically very close (e.g. hydroelectric generators, gas turbines, etc.) which can be used to power the facility via dedicated connections; o the time necessary for each of these systems to be operational; o the availability of competent human resources, in particular to make these exceptional connections and render them operational; identify the moments when the main cliff-edge effects occur; indicate whether measures can be taken to prevent these cliff-edge effects or to reinforce the robustness of the facility (design change, change in procedures, organizational arrangements, etc.). Loss of the off-site electrical power supplies and the conventional backup supplies of a reactor is a situation analysed for the baseline safety standard; it results from loss of the off-site electrical power supplies combined with failure to resupply the electrical panels that are backed up by the reactor's backup generator sets. In this situation of loss of the off-site electrical power supplies and the conventional backup supplies of a reactor in service: the residual power of the core is removed by natural circulation if the primary system is closed, or by evaporation if the primary system is open; if the reactor is initially under power or in hot shutdown condition, the rod cluster control assemblies (RCCAs) drop down into the core and cooling of the thermal barrier of the reactor coolant pumps (RCP) is ensured by the charging pump of the chemical and volume control system (CVCS) common to a pair of reactors and supplied with electricity by the backup turbine generator (LLS); if the primary system is open or sufficiently open, the ultimate backup diesel-generator set (GUS) for the 900 MWe series or the combustion turbine (TAC) for the 1300 MWe and N4 series can supply the charging pumps of the CVCS, thereby providing make-up water to the primary system;
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