Numerical simulation of the effect of key structural parameters on the operating characteristics of open natural circulation systems

Abstract

The passive containment cooling system of nuclear power plants is a crucial component for preventing the leakage of radioactive materials under accident conditions. The open natural circulation system is selected as the primary structure of the passive containment cooling system due to its simple loop design, fewer heat transfer stages, and strong heat dissipation capacity. To enhance the heat dissipation capacity, reliability during startup, and stability during operation of the passive containment cooling system, this paper employs a self-developed one-dimensional system analysis program to study the impact of key parameters in the open natural circulation system loop. The results indicate that the piping layout of the system affects the instability of loop startup and steady-state flow, as well as its heat dissipation capability. The inclined arrangement of the piping at the heat exchanger outlet can effectively improve stability and heat dissipation performance. A reduction in water level enhances flow and heat transfer in the loop; the system's heat dissipation capacity reaches its optimal level when the outlet position of the ascending section is level with the water tank liquid level. Increasing the pipe diameter can effectively enhance circulation and heat dissipation capabilities, where the acceleration pressure drop has a significant effect on the two-phase segment in homogeneous flow model calculations. Additionally, setting the dimensions of the flashing section separately can further improve heat transfer effectiveness.