Failure electric motor shaft

The second failure involves an error made during the weld repair of an electric motor drive shaft, which again resulted in a fatigue failure. 

Over a total period of power plant operation 2 failures of the pumps have occurred both leading to the power reduction of the plant with a loop disconnection, i.e. in 1980 the motor and tachometer generator shaft coupling failed and in 1985 the electric motor brush unit failed. 

Sodium pumps. Problems with the pumps resulting in unplanned energy losses occurred in 1981-1985, and were caused by unstable operation of the pump speed control stem. Impulses from the electric motors caused failures of the pump-motor couplings, and increased vibration and fatigue cracks in the pump shafts. The use of advanced shafts and couplings and changing to a steady mode of pump operation after attaining the preset reactor power level have eliminated any failures of the reactor coolant pumps since 1985. 

---