Research on transient characteristics of AP1000 typical accidents based on RELAP5 code

The best-estimate code RELAP5/MOD3.3 was used to simulate the transient characteristics of reactor coolant pump shaft seizure accident, steam generator tube rupture accident and double-ended direct vessel injection line accident for the AP1000 sys- tem. The key parameters of those transients and response of the passive system in those transients were shown in this paper. The results indicate that the pressure of primary system could reach 16.82 MPa and the peak temperature of the fuel cladding could be 1299 K in the reactor coolant pump shaft seizure accident, which meets the requirements of acceptance criteria of this accident. In steam generator tube rupture accident, water volume of the ruptured SG is 231.54 m³, which is less than the total steam generator volume of 255.563 m³. For the double-ended direct vessel injection line accident, the passive core cooling system is able to cool down and depressurize the primary sys- tem, and prevent the core uncovery and fuel cladding heatup. (authors)