In-containment Refueling Water Storage Tank (IRWST): In-containment passive long-term recirculation means Passive Residual Heat Removal (PRHR) utilizing Passive Residual Heat Removal Heat Exchanger (PRHR HX): Automatic Depressurization System (ADS): Internal IEs: Three major types of IEs

Safety of a nuclear power plant and its related systems are the first key issue to assure experts and the public of the safe operation of the plant. The AP1000 reactor is provided with passive safety systems which require no operator actions due to utilizing only natural forces such as gravity, natural circulation and compressed gas to achieve the safety function. In this paper the core damage frequency due to Small Break LOCA Initiating Event has been presented and besides that, the reliability analysis of the passive core cooling system has been evaluated by the aid of RAT (Risk Assessment Tool) which was developed in the Nuclear Safety Center of Shiraz University. Multiple Greek letter Logic (MGL) method is used for the evaluation of CCF of high redundancy safety systems. The results show that the contribution of the SB LOCA in the final core damage frequency of AP1000 is decreased due to passive safety systems usage and human independent functions. The results are useful in core melt down frequency evaluation and final safety analysis report of an advanced nuclear power plant.