05000293/LER-2007-002
| Docket Number | |
| Event date: | |
|---|---|
| Report date: | |
| 2932007002R00 - NRC Website | |
_ FACILITY NAME (1) DOCKET NUMBER (2) LER NUMBER (6) PAGE (3) J05000-293PILGRIM NUCLEAR POWER STATION 2007 J
BACKGROUND
The safety objective of the emergency diesel generators (EDGs) is to provide a source of on-site AC power adequate for the safe shutdown of the reactor following abnormal operational transients and postulated accidents assuming a complete loss of off-site power, as described in Pilgrim Updated Final Safety Analysis Report (FSAR), Section 8.5. Two EDGs and their associated fuel supply systems provide a single failure proof source of standby AC power. Pilgrim EDGs are 2600 KW ALCO 251-F type diesel generators.
These generators are designed to automatically start upon receiving remote signals, and come to generator operating speed ready to assume load. Each generator is sufficient to power all loads on its emergency bus upon failure of all off-site power. Each generator has the ability to pick up loads in sequence within a specified time period. The shutdown transformer (SDT) powered by a 23KV line provides backup to the EDGs.
In addition to the EDGs and SDT, Pilgrim has installed a Station Blackout Diesel Generator (SBODG) to provide power to cope with station blackout events. The SBODG can power one emergency bus to bring the reactor into a hot shutdown condition pursuant to the requirements of 10 CFR 50.63.
The unit auxiliary transformer (UAT) provides power for on-line operations and the start-up transformer (SUT) provides power for shutdown operations.
If the normal UAT power source is lost, the start-up transformer (SUT) is automatically connected to the bus by fast transfer breaker logic. If both the UAT and the SUT power sources to an emergency bus are lost, the diesel generator associated with that bus automatically starts, and its output supply breaker will close onto the bus in approximately 10 seconds. The diesel generator will then supply power to the affected emergency bus. Both the SDT and SBODG provide back-up power in that order if both EDGs fail.
Technical Specification 3.5.F.1 provides for a 72 hour8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> LCO when one EDG is inoperable and the 72 hour8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> LCO can be extended to 14 days provided the SBODG is verified operable in accordance with 4.5.F.2.
"B" EDG WOODWARD GOVERNOR MAINTENANCE HISTORY In April 2002, Woodward Governor s/n 961104 was rebuilt by Engine Services Inc (ESI), a distributor and authorized repair facility for Woodward Governors. In June 2002, the rebuilt governor was installed on the "B" EDG during a scheduled diesel overhaul. On June 23, 2002, a failure to shutdown occurred during post work testing, specifically; the "B" EDG failed to stop when the local push button was depressed following the post work test. On June 24, 2002, the shutdown solenoid from a different governor (s/n 1953289) was removed and installed in the recently rebuilt governor (s/n 961104).
In August 2002, governor s/n 1953289 and the defective shutdown solenoid assembly from governor s/n 961104 were sent to Fairbanks-Morse for inspection and repair. They noted a cracked coil retaining nut which allowed the shutdown solenoid assembly to fall from its proper position. Since this solenoid is "energize to shutdown", it could not reposition to port oil to shutdown the engine.
Fairbanks-Morse repaired the governor and it was returned to the Pilgrim warehouse.
� FACILITY NAME (1) DOCKET NUMBER (2) LER NUMBER (6) PAGE (3) In January 2007, in accordance with the established preventative maintenance frequency (every 4 years) Pilgrim changed the oil in the governor during a scheduled engine overhaul. On January 25, 2007 during an operability test following the overhaul of "B" EDG, unexpected KW oscillations up to 150 KW total span were observed. These oscillations did not approach the abort criteria. Investigation of the condition was ongoing between January 25 and February 23 and troubleshooting plans were developed that were implemented during the next scheduled run of "B" EDG on February 23. Although the condition observed during the January 25 run warranted investigation and increased surveillance was planned for the next run of "B" EDG, information at the time indicated the "B" EDG was operable following the test on January 25, 2007. Investigation between January 25 and February 23 revealed no information to confirm the "B" EDG was inoperable.
EVENT DISCRIPTION
During the February 23, 2007 EDG 'B' operability run, the control room operator reported KW oscillations increasing in magnitude at full load of 2600 KW. The engine had been running for approximately 50 minutes. KW oscillations were observed to span 100 KW (+/- 50 KW) and increased over time to 200 KW (+/-100 KW) at 2600 KW. The total range of the oscillations was 2500 to 2700 KW. The operator began to unload the engine in steps. The engine load was reduced to 1800 KW and the KW oscillations were observed to remain at 200 KW. At this time the control room supervisor ordered that the EDG be secured due to procedural abort criteria being reached.
During the investigation following the February 23 operability test of "B" EDG, the oil in the Woodward governor was examined. The oil was observed to be discolored, gray and cloudy and had a noticeable burnt odor unlike the new oil that was installed in January. Additionally, the oil was found to be contaminated with aluminum particles of varying size. Pilgrim replaced the governor. Post work test showed no abnormal load oscillations.
CAUSE
The "B" EDG governor s/n 961104 was shipped to Fairbanks-Morse in Seattle, Washington, for testing and failure analysis. Upon opening the governor, the vendor noticed shreds of aluminum in the governor oil. The source of the aluminum was an aluminum label, originally attached to the shutdown solenoid valve by the coil retaining nut that separated and was free to move about in the oil inside the governor.
A small fragment of the label approximately half the size of a dime was found inside the governor. An intact label is approximately 1 1/4 inches in diameter with a 9/16 inch hole in the center. Fairbanks- Morse stopped re-installing these labels in the early 1980s due to similar problems. Removing the labels prior to installation is considered a standard work practice at Fairbanks-Morse; however, their repair process does not utilize written guidance to ensure that the labels are removed. In addition, Woodward Governor's repair department had information that the labels should be removed as part of a routine overhaul, but a written service bulletin from Woodward formally recommending the removal of the labels had not been issued.
_ FACILITY NAME (1) DOCKET NUMBER (2) LER NUMBER (6) PAGE (3) _NUMBER NUMBER
CORRECTIVE ACTION
The corrective action taken included the following:
- The governor was replaced. Post work test showed no abnormal load oscillations.
- An Operating Experience (OE) report was issued to the industry and Entergy fleet concerning the potential of a valve label becoming FME material during governor overhaul.
- Pilgrim maintenance personnel were trained on the lessons learned from the governor problems and KW oscillations.
EXTENT REVIEW
Verified similar condition did not exist in "A" EDG and Station Blackout Diesel generator.
SAFETY CONSEQUENCES
There was no safety consequence during the potential inoperable status of "B" EDG because during the time frame "B" EDG was potentially inoperable (January 25 to February 23), all other AC sources were available and /or operable except for brief periods for surveillance testing (i.e., startup transformer, shutdown transformer, unit auxiliary transformer, "A" EDG, and SBODG). The "B" EDG problem did not affect any other normal or emergency power sources.
REPORTABLITY
This report is submitted voluntarily although there is no firm evidence that the EDG was inoperable between January 25 and February 23, 2007. The cause was considered to have sufficient potential applicability to other Units to warrant reporting.
SIMILIARITY TO PREVIOUS EVENTS
A review was conducted at Pilgrim Station LERS submitted since 1984. The review identified no similar events.
ENERGY INDUSTRY IDENTIFICATION SYSTEM (EIIS) CODES The EIIS codes for this report are as follows:
COMPONENTS CODES
SYSTEMS CODES