This study focused on the best-estimated thermal-hydraulic calculations performed regarding the AP-1000 nuclear power plant (NPP) under primary coolant loop pump and fuel failures. Primary coolant pump and fuel failure transients are important design-basis accidents in NPP safety assessments. This work examined the primary reactor’s safety margins of fuel and cladding peak temperature, primary and secondary loop pressure, hydrogen formation, and primary and secondary flow rates. The Adaptive System Thermal-Hydraulics program was used in the simulation and event progression
analysis. The results showed that the peak fuel surface temperature was kept below the licensing design limit. No observation of corium was seen during the transient calculation. The structural integrity of the reactor was not jeopardized by changes in the
flow rates and pressure of both primary and secondary coolant loops. This result validates the defense-in-depth concepts and safety principles incorporated into the design of the AP-1000 NPP. Finally, based on observations of the beneficial effects in controlling accidents aided by the scram of control rods and reactor thermal-hydraulic feedbacks, the AP-1000 NPP can be concluded certainly to be safe against the combination of primary coolant loop pump and fuel failures. These findings provide useful information for assessing reactor safety capacities to withstand the effects of coolant flow loss and fuel failure at power