The general characteristics of the loss of coolant accident (LOCA) for pressurized water reactor systems(PWR) is reviewed and the emergency core cooling system(ECCS) of the ``$\mbox{\underline{Ko Ri}}$ nuclear power plant unit 1`` and its time response characteristics against LOCA are investigated.
For the simulation analysis, a modified version of ``RELAP-4``, a computer program for the transient analysis of PWR following LOCA is run using the parameters of ECCS of the ``$\mbox{\underline{Ko Ri}}$ nuclear power plant unit 1``. In this computation, a cold- leg double-ended severance rupture is postulated. The result of the simulation computation is compared with those of similar studies for other PWR systems.