[en] This report contains the analysis results to utilize the inventory of safety injection tanks effectively for the purpose of core cooling strategy in high pressure scenarios of severe accidents. If high pressure safety injection pumps are not working for a total loss of feed water sequence of nuclear power plants, then this results in a severe accident inevitably. Nevertheless, a rapid depressurization using the Piriot Operated Safety Relief Valves (POSRV) could still mitigate the severe accident by providing a cooling water into a damaged core from safety injection tanks(SIT) which are passive systems. The purpose of this paper is to estimate how long the reactor vessel failure can be delayed by using the passive safety injection tanks for typical high pressure sequences at the APR-1400. MAAP computer code has been used as a thermal-hydraulic analysis tool. The results can be referred to develop the core cooling strategy which is a part of severe accident management program