Abstract: Through establishing the three-dimension model of a valve clack in a nuclear power station ventilation system, the stress changes of the valve clack under impact loads in the process of bumping the valve frame are simulated with the finite element method. The finite element analysis results from the comparison of four different working conditions show that, due to the unreasonable structure of the valve plate, the bending compression stress of the channel steel flange edge above the pin hole is higher than the material plastic extension strength when the valve plate is opened; when the valve plate is closed, the opposite direction stress and deformation will be produced in the same place. During the long operating process, the valve plate repeatedly hits the valve frame and high low-cycle fatigue stress happens in the channel steel flange edge above the pin hole, which leads to the fatigue damage of the channel steel flange until its rupture. Improvement needs to be made on the valve plate structure to prevent the fracture failure of the valve clack.

Key words: power generation, nuclear power plant, ventilation system, impact load, valve clack, fracture failure, finite element method