[en] There have been many evaluations and recommendations for the extended Station Black Out (SBO) condition of the nuclear power plant. For example, the 'SECY-11-0093/0137', is a recommendation of NRC and the 'WCAP-17601-P' is an evaluation of the PWROG. The extended loss of AC power (ELAP) can be defined as same with the extended (or prolonged) SBO which has a Loss of Offsite Power (LOOP) condition and loss of all Emergency Diesel Generators (EDG), Alternative Alternating Current (AAC), but Direct Current (DC) source is available. This evaluation provides NSSS responses to an ELAP for the OPR1000 unit. And the results presented provide certain phenomena which occur during the ELAP, the maximum coping time until a core uncovery condition. It is assumed for this case that sufficient SG secondary makeup inventory exists or can be attained, so that the duration of the ELAP prior to core damage is dependent solely upon the loss of inventory from the RCS. Even with a limited RCS cooldown and depressurization, and conservatively high assumed RCP seal leakage, the plant can be sustained for over 65 hours prior to core uncovery