The purpose of the study was to investigate the application of deterministic safety analysis for a prevention strategy of the extended station blackout (SBO). A method for the assessment of portable pump flow rates for a steam generator (SG) makeup is proposed. The RELAP5/MOD3.3 computer code and input model of a two-loop pressurized water reactor (PWR) is used for analyses, assuming different injection start times, flow rates, and reactor coolant system (RCS) losses. The calculated results show the effectiveness of the proposed extended SBO prevention strategy. The results demonstrate the need for mitigation of the common cause failure (CCF) potential of the on-site and off-site power sources.