05000395/LER-2004-003
| Docket Number | |
| Event date: | |
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| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(iv), System Actuation |
| 3952004003R01 - NRC Website | |
PLANT IDENTIFICATION
Westinghouse - Pressurized Water Reactor
EQUIPMENT IDENTIFICATION
"A" Emergency Diesel Generator (EDG) "A" Residual Heat Removal Pump (RHR) "A" Emergency Feedwater Pump (EFW)
IDENTIFICATION OF EVENT
At 2152 on October 26, 2004, the normal incoming ESF feed (1DA) to the V. C. Summer Nuclear Station (VCSNS) opened on an undervoltage condition. The "A" Emergency Diesel Generator (EDG) started and loads sequenced on as designed. The "A" Residual Heat Removal (RHR) pump started but did not inject any water into the Reactor Coolant System (RCS). The "A" Emergency Feedwater (EFW) pump started and ran for approximately 19 minutes. Other plant equipment and systems also responded as expected.
At the time of the event restoration of "A" EDG from scheduled maintenance was in progress. While resetting the "A" Engineered Safety Features Loading Sequencer (ESFLS) the Operator inadvertently bumped the bus undervoltage (UV) toggle switch. This action caused the ESFLS to trip open the normal and emergency feeder breakers to IDA, resulting in an auto-start of the "A" EDG. Closure of the"A" EDG output breaker initiated the blackout sequence on "A" train ESF equipment. Loads sequenced on as designed and equipment operated as expected. Operations personnel monitored the plant and verified conditions were stable prior to realigning the ESF bus to its normal feed and securing the EDG at approximately 2231 on October 26, 2004.
EVENT DATE
October 26, 2004
REPORT DATE
March 14, 2005, LER 2004-003-01 December 21, 2004, LER 2004-003-00
CONDITIONS PRIOR TO EVENT
Mode 1, 100% Power
DESCRIPTION OF EVENT
At 2152 on October 26, 2004, the normal incoming ESF feed (1 DA) to the V. C. Summer Nuclear Station (VCSNS) opened on an undervoltage condition. The "A" Emergency Diesel Generator (EDG) started and loads sequenced on as designed. The "A" Residual Heat Removal (RHR) pump started but did not inject any water into the Reactor Coolant System (RCS). The "A" Emergency Feedwater (EFW) pump started and ran for approximately 19 minutes. Other plant equipment and systems also responded as expected.
At the time of the event restoration of "A" EDG from scheduled maintenance was in progress. While resetting the "A" Engineered Safety Features Loading Sequencer (ESFLS) the Operator inadvertently bumped the bus undervoltage (UV) toggle switch. This action caused the ESFLS to trip open the normal and emergency feeder breakers to 1DA, resulting in an auto-start of the "A" EDG. Closure of the "A" EDG output breaker initiated the blackout sequence on "A" train ESF equipment. Loads sequenced on as designed and equipment operated as expected. Operations personnel monitored the plant and verified conditions were stable prior to realigning the ESF bus to its normal feed and securing the EDG at approximately 2231 on October 26, 2004.
Condition Evaluation Report C-04-3386 was generated to document the event and lessons learned.
CAUSE OF EVENT
At the time of the event restoration of "A" EDG from scheduled maintenance was in progress. While resetting the "A" Engineered Safety Features Loading Sequencer (ESFLS) the Operator inadvertently bumped the bus undervoltage (UV) toggle switch. This action caused the ESFLS to trip open the normal and emergency feeder breakers to 1DA, resulting in an auto-start of the "A" EDG. Closure of the "A" EDG output breaker initiated the blackout sequence on "A" train ESF equipment. Loads sequenced on as designed and equipment operated as expected.
Subsequent to the event, the Operator informed the Control Room Supervisor that he had inadvertently bumped the "A" undervoltage toggle switch as he was resetting the sequencer. Operations personnel monitored the plant and verified conditions were stable prior to realigning the plant to the normal feed and securing the EDG at approximately 2231 on October 26, 2004.
A root cause evaluation determined the cause to be the operator being very casual while manipulating the reset switch and no equipment guard to prevent actuation of the undervoltage test switch.
ANALYSIS OF EVENT
The undervoltage and degraded voltage relays associated with 1DA functioned properly upon detecting the loss of voltage on the incoming 115kV line subsequent to the inadvertent undervoltage test switch signal. The "A" EDG started and loads sequenced on as designed. Operators acknowledged alarms and walked down the main control board to ensure equipment was functioning properly. Building operators were also dispatched to monitor proper operation of some of the more critical equipment such as the EDG, the RHR pump, and the EFW pump.
ANALYSIS OF EVENT (Continued) Once operations personnel were satisfied that conditions were stable, operating equipment that was not needed was secured. The "A" RHR pump was secured without injecting any water into the RCS. The "A" EFW pump was also secured after running for approximately 19 minutes. Additional plant equipment was also restored to normal alignment as necessary. Reactor power remained at approximately 100% throughout the event.
All normal offsite power sources were available at all times throughout the event. Operations personnel monitored the plant to ensure conditions were stable prior to realigning 1DA to its normal offsite power feed. This realignment occurred at approximately 2225 hours0.0258 days <br />0.618 hours <br />0.00368 weeks <br />8.466125e-4 months <br /> on October 26, 2004, and the "A" EDG was subsequently secured at approximately 2231 hours0.0258 days <br />0.62 hours <br />0.00369 weeks <br />8.488955e-4 months <br />. There was no equipment damage or abnormal operation noted and no unexpected transients occurred. Since "A" train equipment was the 'maintenance' train, no "B" train protected equipment supplying normal functions was affected.
CORRECTIVE ACTIONS
All equipment at VCSNS responded as expected.
VCSNS corrective actions include:
Condition Evaluation Report (CER) C-04-3386 was generated to document the event and lessons learned. An action was added to the CER to provide a discussion of the event as an operating experience item during operator requalification training. A root cause evaluation was performed to determine additional appropriate corrective actions.
OTHER CORRECTIVE ACTIONS
The following corrective actions to prevent recurrence were established during the root cause evaluation performed for this event, which will be tracked under the corrective action program (CER 04-3386).
1. Evaluate the feasibility of installing a hinged box cover over the INITIATE switches on both Sequencer cabinets.
2. The human performance concerns identified in the root cause analysis will be addressed to the Operations Department as operating experience.
PRIOR OCCURRENCES
There are no prior occurrences of the loss of the normal incoming ESF feed to the plant due to an inadvertent actuation of the undervoltage test switch on the ESFLS.