|Vogtle Electric Generating Plant|
|Reporting criterion:||10 CFR 50.73(a)(2)(iv)(B), System Actuation|
10 CFR 50.73(a)(2)(iv)(A), System Actuation
|LER closed by|
|IR 05000424/2017002 (21 July 2017)|
|4242017002R01 - NRC Website|
|Person / Time|
|From:||Myers D J|
Southern Nuclear Operating Co
Document Control Desk, Office of Nuclear Reactor Regulation
|Download: ML17180A197 (4)|
Infocollects Resource@nrc gov, and to the Desk Officer, Office of Information and Regulatory Affairs NEOB-10202 (3150-0104). Office of Management and Budget, Washington. DC 20503 If a means used to impose an information collection does not display a currently valid OMB control number, the NRC may not conduct or sponsor and a person is riot required to respond to the information collection.
A. Event Description
On March 17, 2017, at approximately 1517 EDT, Unit 1 was in refueling outage 1R20 with the unit in Mode 6 being prepared for fuel offload. After work had been performed on the 1-B Reserve Auxiliary Transformer (RAT) and during power restoration, a valid undervoltage actuation signal was sent to the 1-B Emergency Diesel Generator (EDG). The EDG started and automatically tied to the electrical safety bus. Once the issue was identified and understood by the operators, the EDG was secured and the electrical safety bus was transferred to the appropriate offsite power source.
The reactor was Mode 6 at the time of the event and remained so throughout the event. Decay heat was removed via the Residual Heat Removal (RHR) system, to the Component Cooling Water System, to the Nuclear Service Cooling Water system,. and finally to the atmosphere.
B. Cause of Event
The cause of the event was a wiring error of the Open Phase system alarm and trip circuitry to the RAT. This resulted in a valid undervoltage actuation signal to be sent to the 1 B EDG as power was being restored to the Open Phase system. The EDG properly detected the undervoltage condition and responded per design.
C. Safety Assessment The EDG properly started and loaded the safety bus as required. At no time was decay heat removal lost to the RCS or the Spent Fuel Pool. Because all safety systems performed their safety function, the safety significance of the event is considered very low.
D. Corrective Actions
The wiring error was discovered using a continuity check during the post-event troubleshooting. The wires from the Open Phase system to the 1-B RAT were found mislabeled and landed on the wrong terminals. The wiring error was subsequently corrected and an extent of condition review was performed to verify proper labels and continuity and no other errors were found.
E. Previous Similar Events: