05000395/LER-2008-003

LER-2008-003, Inadvertent Actuation Of The Emergency Diesel Generator In The Emergency Start Mode Due To Bus Undervoltage

Docket Number
Event date:
Report date:
Reporting criterion:	10 CFR 50.73(a)(2)(iv)(A), System Actuation
3952008003R00 - NRC Website

PLANT IDENTIFICATION

Westinghouse - Pressurized Water Reactor

EQUIPMENT IDENTIFICATION

XEG0001A-E - "A" Emergency Diesel Generator

IDENTIFICATION OF EVENT

At 1704 on May 21, 2008 during Refuel 17, the "A" Emergency Diesel Generator (EDG) was placed in service to support post-maintenance testing. When the voltage regulator was taken from automatic control to manual control the electrical bus voltage decreased. The voltage decrease actuated the undervoltage relays on electrical bus 1DA and the EDG shifted from the test start mode to the emergency start mode. No other equipment changed state. Voltage was restored to normal and the EDG response was verified to be appropriate. The EDG was then unloaded and secured. The EDG change in state is considered to be a valid actuation and a reportable event under 10CFR50.72(b)(3)(iv)(A) and 10CFR50.73(a)(2)(iv)(A).

EVENT DATE

May 21, 2008

REPORT DATE

July 14, 2008

CONDITIONS PRIOR TO EVENT

Mode 5, 0% Power

DESCRIPTION OF EVENT

Post-maintenance testing was being performed on the "A" EDG to verify proper operation of a new speed governing system.

During this testing when the EDG was loaded and paralleled to the grid, a voltage regulator adjustment was made, but the response was not as expected. Electrical bus 1DA was then isolated from the grid with the EDG carrying the bus load to further investigate the voltage regulator response. In an attempt to establish better voltage control, the voltage regulator was switched from automatic to manual control. When the voltage regulator was placed in manual, electrical bust DA voltage decreased and the undervoltage relays were actuated. Actuation of the undervoltage relays resulted in the EDG being shifted from the test start mode to the emergency start mode. In the emergency start mode the voltage regulator control was restored to automatic and electrical bus 1DA voltage returned to its nominal value of 7200 Volts. The EDG responded normally to the actuation prior to being unloaded and secured. The voltage to electrical bus 1DA was never lost during this event. Subsequent inspection and testing of the voltage regulator could not recreate the initial voltage control issue. Numerous additional runs were performed prior to declaring the EDG operable without further issues.

CAUSE OF EVENT

A root cause analysis of the event that caused the EDG to shift from the test start to emergency start mode has been completed.

The results of this analysis indicate that the root causes of this event are: 1) inadequate procedural guidance and 2) a lack of training on operation of the voltage regulator with the voltage regulator in manual control.

�NRC FORM 366A (9-2007) PRINTED ON RECYCLED PAPER

ANALYSIS OF EVENT

At the time of this event, the "A" train EDG was out of service for testing. All systems and components necessary to maintain the reactor in safe shutdown and remove residual heat were being provided by the "13" Engineered Safety Features (ESF) train. None of the "B" ESF train components were affected by this event. Since the "A" EDG was operating at the time and only switched to the emergency start mode, it was still functional and would have been available in an emergency. Therefore, there were no potential safety consequences or implications as a result of this event.

CORRECTIVE ACTIONS

The corrective actions include: 1) Revise operations training lesson plans to provide training on the design of the EDG voltage control circuit to provide the knowledge required for use of the manual voltage regulator control, and 2) Revise operating procedures to provide precautions and guidance on when to use the voltage regulator manual control and what the expectations should be when the voltage regulator is switched to manual control.

Condition Report CR-08-02247 was generated to address the investigation, cause and corrective actions associated with this event.

PRIOR OCCURRENCES

There is no historical evidence of a prior occurrence.

�NRC FORM 366A (9-2007) PRINTED ON RECYCLED PAPER