- 142 - more small emergency generator sets that guarantee an electrical supply for the minimum necessary I&C and control room emergency lighting would solve this problem. ASN considers that EDF's proposal to provide an additional robust electrical power supply means called "ultimate backup diesel generator set (DUS) for use in the event of loss of the other off-site and on-site electrical power supplies, and which complies with the CSA specifications, must be implemented. Pending deployment of this additional electrical power supply means, ASN also considers that EDF's proposal to provide one or more small emergency generator sets must be implemented. ASN will issue a requirement on this subject. For the EPR reactor, the SBO generator sets already have robustness features. To have a level of robustness at least equal to that of the reactors in service with the deployment of an additional hazard-resistant means of supplying electrical power, ASN will ask EDF to study the integration of the SBO generator sets in the "hard core" of the material and organisational measures, which are subject to more stringent requirements, particularly with respect to the earthquake and flooding risks (refer to § 8 of this chapter). For the 900 MWe series, EDF proposes - for primary system just-open situations - to modify pressure build-up management so as to remove the residual power via the steam generators. ASN considers that EDF must prove that the proposed change in management of the primary system just-open situation will effectively result in a sufficient delay before the fuel becomes exposed to implement external means for the medium- and long-term management of a situation of loss of the off-site and on-site electrical power supplies on a site. 5.1.3 Loss of the off-site electrical power supplies and of the conventional backup supplies and any other on-site backup electrical power source For the situation of loss of the off-site electrical power supplies and the conventional backup supplies and any other on-site backup electrical power source, ASN has asked EDF, for each reactor, 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 backup energy sources without external intervention before serious damage to the fuel becomes inevitable; indicate what external action is planned to prevent fuel damage to the fuel: 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 all the backup supplies of a reactor results from the loss of the off-site electrical power supplies combined with failure to resupply the electrical panels that are backed up by: the emergency generator sets of the reactors in service or the main generator sets of the EPR reactor ; the ultimate backup diesel-generator set (GUS) for the 900 MWe series; the combustion turbine (TAC) for the 1300 MWe and N4 series; the ultimate backup generator sets (SBO) for the EPR reactor; the backup turbine generator (LLS) for the reactors in service.
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