Aiming at the safety response problem of integrated fast reactor under unprotected flow loss accident, this paper established a core-main-loop and accident residual heat discharge system coupling calculation model based on SAS4A/SASSYS-1 program, and analyzed the transient thermo-hydraulic behavior and natural circulation ability under ULOF condition. The calculation results show that the core flow decays rapidly after the main pump is idle, and the power to flow ratio reaches 2.52 in 30.4 s. The peak temperatures of fuel, cladding and coolant are 858.0 ℃, 837.6 ℃ and 837.2 ℃, respectively. Subsequently, under the effect of negative reactive feedback, the reactor power continued to decline, and the system did not appear shell failure and sodium boiling. The further parameter analysis shows that the increase of the resistance of the primary circuit will weaken the natural circulation ability, and the appropriate increase of the elevation of the independent heat exchanger will enhance the waste heat export ability in the later stage of the accident. At 1800 s, the natural circulation flow of the core reaches 532.1 kg/s. The results show that the integrated fast reactor has good inherent safety and passive heat removal potential, which can provide a calculation basis for the optimization design and safety evaluation of related systems.
