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In developing the severe accident management guideline (SAMG), it was highly considered to maintain the integrity of reactor pressure vessel (RPV) as a key strategy aimed to reduce the risk of containment failure and fission product releases into the environment effectively. For the operating nuclear power plants with no dedicated safety features for the severe accident management (SAM), the improvement of the current mitigative strategy in SAMG domain could be one of counter-measures to extend the survival time of RPV. In this study, the effectiveness of the RCS depressurization to delay the RPV survival time with different RCS depressurization rate was evaluated for station blackout (SBO) accident assuming only SIT is available for Uljin unit 1 plant by MELCOR 1.8.5 code. According to the analysis results, it was shown that the conditions for RCS depressurization such as depressurization capacity and the time interval are the key elements to extend the RPV integrity in such a way to earn time for restoring the heat sink in order to prevent the accident propagation to the RPV failure.