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.