Manual and electric operation failure of electric actuator for containment spray system valve's remote actuating mechanism was found in regular check of a nuclear power station

seven fractures were found in inner planet carrier with rough surface and mild macroscopic plastic deformation.The physical and chemical inspection results show that large amounts of shrinkage casting defects exist on the fracture area

wear trace exist on the edge of fracture.Analysis shows the failure cause is that motor starting torque is greater than protection level torque of the electric actuator

making the electric actuator stop again and again

applying repeated impact load on the planet carrier of deceleration mechanism

resulting in the failure of the plant carrier.Therefore

many improvement measures were proposed

such as cascading a concatenated friction clutch in the transmission mechanism outlet

increasing starting torque of inverter control motor and protection level torque of the electric actuator.After these measurements were carried out

the containment spray system has been functioning continuously.