Shutdown of the plant due to high temperature of the RCP motor bearing.
Wednesday, April 3, 2002
On February 24 the operators noticed trend of increase of the temperature of the axial bearing of the motor of the Reactor Coolant Pump #2 as indicated by one of the two temperature sensors. On February 25 morning the trend increased so the decision was brought to start manual shutdown of the plant to prevent the temperature of the bearing to go above 90 degrees C which is a limit set by the pump motor producer. The starting shutdown rate of 10 MW/min was later increased to 20MW/min but at 28% of the reactor power at 2:09 hours the reactor was manually tripped to keep the temperature limit. The trip sequence went in accordance with the design. The pressure transient on the secondary side caused a 7.6-mm pipe of the extraction steam to open and the leak damaged a local fire protection installation. The investigation of the event concluded that the cause of the high temperature indication was a deteriorated temperature sensor and not actual increase of the temperature.