05000334/LER-2003-003
| Beaver Valley Power Station Unit No. 1 | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(iv)(B), System Actuation 10 CFR 50.73(a)(2)(iv)(A), System Actuation |
| 3342003003R00 - NRC Website | |
U.S. NUCLEAR REGULATORY COMMISSION FACILITY NAME (1) LER NUMBER (6) DOCKET (2) PAGE (3)
PLANT AND SYSTEM IDENTIFICATION
Westinghouse-Pressurized Water Reactor (PWR) Medium Voltage Power System (4160 v) (EA) Medium Voltage Power System — Class 1 E (4160 v) (EB) Emergency Onsite Power Supply (EK) Main Feedwater System (SJ)
CONDITIONS PRIOR TO OCCURRENCE
Unit 1: Mode 1 at 58 % power There were no systems, structures, or components that were inoperable at the start of the event that contributed to the event other than as described below.
DESCRIPTION OF EVENT
At 1301 hours0.0151 days <br />0.361 hours <br />0.00215 weeks <br />4.950305e-4 months <br /> on 2/27/2003, Beaver Valley Power Station (BVPS) Unit 1 was operating at 58% power and returning to full power operation following a startup from a recent forced outage.
Following the start of the 'B' main feedwater pump, an ground instantaneous overcurrent trip occurred on the offsite power to 4KV feeder breaker 1D6 (EA). The opening of the feeder breaker de-energized the non-safety related 'D' 4KV bus which had been supplying power to the 'B' main feedwater pump. The 'B' train safety related `DF' 4KV emergency bus (EB) which is normally powered by the 'D' bus, then also became de-energized with the loss of power on the 'D' bus. The `B' train emergency diesel generator (EK) automatically started on the loss of voltage and re- energized the `DF' bus, with emergency loads automatically sequenced back onto the bus as designed.
The control room crew entered Abnormal Operating Procedure 1AOP-36.2, Loss of 4KV Emergency Bus and 1AOP-51.1, Emergency Shutdown. Power was manually reduced and the plant was stabilized at 43% power with the 'D' bus de-energized and the 'B' emergency diesel generator supplying all power to the `DF' bus.
With the normal offsite power supply to the `DF' bus inoperable, Technical Specification 3.8.1.1 was entered which requires that the operability of the remaining A.C. sources be demonstrated within 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br /> and at least once per 8 hours9.259259e-5 days <br />0.00222 hours <br />1.322751e-5 weeks <br />3.044e-6 months <br /> thereafter, and to restore the offsite circuit to operable status within 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br />. At 0133 hours0.00154 days <br />0.0369 hours <br />2.199074e-4 weeks <br />5.06065e-5 months <br /> on 2/28/2003, the `DF' bus was re-energized from the offsite power source and Technical Specification 3.8.1.1 was exited.
FACILITY NAME (1) DOCKET (2) LER NUMBER (6) PAGE (3)
REPORTABILITY
This event is reportable pursuant to 10 CFR 50.73(a)(2)(iv)(A) as an event that resulted in an automatic actuation of the onsite emergency diesel generator on 02/27/2003, a system listed in paragraph 10 CFR 50.73(a)(2)(iv)(B)(8). The NRC was notified of this event pursuant to 10 CFR 50.72(b)(3)(iv)(A) at 1715 hours0.0198 days <br />0.476 hours <br />0.00284 weeks <br />6.525575e-4 months <br /> on 2/27/2003 (ENS No. 39623).
CAUSE OF EVENT
The direct cause of this event was the unexpected opening of the 4KV feeder breaker 1D6 from offsite power when the 'B' main feedwater pump was started. The root cause of this event was that the ground sensor cable geometry induced a false ground fault current that actuated the ground fault detection relays. These relays were reset by a plant modification performed in February 2003 to operate at a lower setting to ensure coordination with station service neutral overcurrent protection.
The improper geometry combined with the lowered ground relay setting caused the ground relay to operate on a false ground current and trip the feeder breaker. This was the first time that this main feedwater pump had been started since this new ground fault relay had been installed.
A contributing cause was the a lack of knowledge regarding the importance of the effect of the cable geometry in the sensor during the development of the design change. Another contributing cause was that the post modification testing was less than adequate.
SAFETY IMPLICATIONS
This event was a loss of one non-safety related and one safety related bus, which are normally powered from offsite power. This is less severe than the design basis event for a complete loss of offsite power. The Loss of External Electrical Load and/or Turbine Trip is analyzed in BVPS Unit No. 1 Updated Final Safety Analysis Report (UFSAR) Section 14.1.7. The actual plant response on 02/27/2003 was bounded by the UFSAR analysis for a Loss of External Electrical Load. All safety related systems functioned as expected following the opening of the offsite feeder breaker.
The plant risk associated with the BVPS Unit 1 loss of safety related DF bus and the start of the No.
2 emergency diesel generator on 02/27/2003, is considered to be low. This is based on the - incremental core damage probability for the event when considering the actual component unavailabilities that were present at the time of the trip and the relatively short duration. Therefore, the safety significance of this event was low.
CORRECTIVE ACTIONS
1. Measurements, inspections and tests were conducted on numerous plant components. No equipment failures or miscalibrations of relays were found.
2. A potential transformer style fault sensor is now being used in place of the previous magnetic sensor on the 1D6 bus breakers and other similar breakers. Revised relay settings were also implemented.
3. The 'B' main feedwater pump motor will be monitored during its initial startup from the current refueling outage to verify that this motor is operating correctly.
4. Additional training will be provided to design engineering personnel on determining bounding technical requirements as determined through a training needs analysis.
5. The Engineering Standard on protective relaying philosophy will be revised as a result of this event.
6. The design change process will be reviewed with regard to the post maintenance testing criteria.
Completion of the above and other corrective actions are being tracked through the corrective action program.
PREVIOUS SIMILAR EVENTS
A review of past Beaver Valley Power Station Licensee Event Reports for the last five years found three similar events involving a loss of bus or ground overcurrent event at BVPS Unit 1 or Unit 2.
BVPS Unit 1 LER 00-004, "Inadvertent ESF Actuation Due to Loss of Power to 4KV Emergency Bus.
BVPS Unit 2 LER 99-005, "4KVS-2A Bus Trip on Ground Overcurrent Relay 51-VA207X.
BVPS Unit 2 LER 99-006, "Loss of Beaver Valley Power Station Unit No. 2 4KV Train 'B' Emergency Bus.
ATTACHMENT
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Beaver Valley Power Station, Unit No. 1 License Event Report 2003-003-00 Commitment List The following list identifies those actions committed to by FirstEnergy Nuclear Operating Company (FENOC) for Beaver Valley Power Station (BVPS) Unit Nos. 1 and 2 in this document.
Any other actions discussed in the submittal represent intended or planned actions by Beaver Valley. These other actions are described only as information and are not regulatory commitments. Please notify Mr. Larry R. Freeland, Manager, Regulatory Affairs/Corrective Actions, at Beaver Valley on (724) 682-5284 of any questions regarding this document or associated regulatory commitments.
Commitment � Due Date The 'B' main feedwater pump motor will be monitored during � As tracked through the its initial startup from the current refueling outage to verify � Corrective Action Program.
that this motor is operating correctly.
Additional training will be provided to design engineering � As tracked through the personnel on determining bounding technical requirements � Corrective Action Program.
as determined through a training needs analysis.
The Engineering Standard on protective relaying philosophy � As tracked through the will be revised as a result of this event. � Corrective Action Program.
The design change process will be reviewed with regard to � As tracked through the the post maintenance testing criteria. � Corrective Action Program.