Abstract
AP1000 reactor is the typical ``third-generation'' nuclear power plant in the world at present. The primary system of AP1000 nuclear power plant was modeled using RELAP5/MOD 3.3 code, and the transient thermal hydraulic characteristics were analyzed under complete loss of flow accident (CLOFA). The calculation results by RELAP5 code were compared with those of the LOFTRAN codes. The research results show that the RELAP5 model can accurately simulate the transient thermal hydraulic characteristics of AP1000 under the accident of complete loss of forced reactor coolant flow. Meanwhile, comparison was made between the results of complete loss of reactor coolant flow initiated by loss of voltage and frequency reduction of offsite power, and the analysis indicates that the results of complete loss of flow initiated by complete loss of voltage bound the complete loss of flow initiated by reduction in the reactor coolant pump motor supply frequency with a frequency decay of up to 5 hertz per second.