Research on Atmospheric Steam Dump System Control Commands Oscillations and Valve Failure of CPR1000 Nuclear Units

For CPR1000 nuclear units atmospheric steam dump system（GCT-a）, one event happened was mainly caused by the sustained oscillation of the valve control command which led to the valve malfunction eventually. By optimizing the PID parameter of control loop and testing the valve parameters with Flow- scanner 6000, and also considering the operation data, it is demonstrated that the valve failure is caused by the design defect on the cage contributing to the control command oscillation and damage on sealing surface, and the resolution is proposed.