Information Notice 2007-27, Recurring Events and Trends Involving Emergency Diesel Generator Operability
| ML071760544 | |
| Person / Time | |
|---|---|
| Issue date: | 08/06/2007 |
| From: | Michael Case NRC/NRR/ADRO/DPR |
| To: | |
| Stephen Pannier, NRR/DIRS/IOEB | |
| References | |
| IN-07-027 | |
| Download: ML071760544 (5) | |
UNITED STATES
NUCLEAR REGULATORY COMMISSION
OFFICE OF NUCLEAR REACTOR REGULATION
WASHINGTON, DC 20555-0001 August 6, 2007 NRC INFORMATION NOTICE 2007-27: RECURRING EVENTS INVOLVING EMERGENCY
DIESEL GENERATOR OPERABILITY
ADDRESSEES
All holders of operating licenses for nuclear power reactors, except those who have
permanently ceased operations and have certified that fuel has been permanently removed
from the reactor vessel.
PURPOSE
The U.S. Nuclear Regulatory Commission (NRC) is issuing this information notice (IN) to inform
addressees of the results of a staff evaluation of recent operating experience to identify
recurring events involving the operability of emergency diesel generators (EDGs). The NRC
expects that recipients will review the information for applicability to their facilities and consider
actions, as appropriate, to avoid similar problems. Suggestions contained in this IN are not
NRC requirements; therefore, no specific action or written response is required.
DESCRIPTION OF CIRCUMSTANCES
The Office of Nuclear Reactor Regulation (NRR) recently conducted a review of operating
experience related to EDG failures that have occurred since the beginning of 2004 and
identified the following recurring events and overall tendencies:
- Vibration-induced failures of EDG piping and tubing (recurring)
- Failure to take prompt corrective action, especially to repair EDG fluid leaks
- Inadequate EDG post-maintenance testing
- Failure to follow procedures.
The following are representative examples of the EDG-related events:
Kewaunee Power Station
During an EDG test run, a minor fuel oil leak was identified at a brass fitting located on a copper
diesel fuel oil line. Plant personnel failed to follow the procedural requirements to enter the
identified degraded condition into their corrective action program, and no written operability
determination or repair was performed. Fifty one days later the EDG had to be secured during a
surveillance run when a plant operator noticed that the leak rate had rapidly increased to a point
where a pencil-sized stream of fuel oil was observed to be issuing from the original leak
location. Approximately three EDG run hours had elapsed between the initial identification
of the leak and the time when the leak became more significant. The licensees analysis could
not prove that the EDG was operable for this 51 day period. The resulting NRC inspection
finding involving corrective action was determined to be of substantial safety significance
(Yellow). (NRC Inspection Report 05000305/2007007; Preliminary Yellow Finding for
Kewaunee Power Station, dated March 2, 2007, Agencywide Documents Access and
Management System (ADAMS) Accession No. ML070640045 and Final Significance
Determination for a Yellow Finding and Notice of Violation (NRC Inspection Report 05000305/2007009) Kewaunee Power Station, dated April 3, 2007, ADAMS Accession No.
River Bend Station Unit 1
During EDG testing, a minor leak was identified at a compression fitting in the jacket water
cooling system. A mechanic performed a tightness check on the fitting, but the leakage rate did
not change. During a subsequent EDG run, the jacket water tubing separated at the same
fitting, causing a significant leak. The results of an event analysis determined that the EDG was
inoperable for approximately 23 days. The most probable cause of the failure was a
combination of normal engine vibration and damage caused by over-tightening during past
maintenance. The resulting NRC inspection finding involving corrective action was determined
to be of very low safety significance (Green). (Licensee Event Report 05000458/2005-003-00,
November 4, 2005, ADAMS Accession No. ML053180172 and River Bend Station - NRC
Integrated Inspection Report 05000458/2005004, dated November 14, 2005, ADAMS
Accession No. ML053190140)
Crystal River Unit 3
An EDG output breaker failed to close during a surveillance test. The breaker closing spring
was found not charged with the charging motor control power switch in the OFF position. The
licensees root cause investigation determined that following breaker maintenance, the charging
motor control power switch was not verified to be in the ON position. The EDG was
determined to be inoperable for approximately 28 days. The resulting NRC inspection finding
for exceeding the EDG technical specification allowed outage time was determined to be of very
low safety significance (Green). (Crystal River Unit 3 - NRC Integrated Inspection Report 05000302/2006005, dated January 25, 2007, ADAMS Accession No. ML070260154)
Indian Point Nuclear Generating Unit 2
During an extent of condition review for post-maintenance test concerns, the licensee
determined that one EDG had not been run at its full load rating following a governor
replacement that took place about six months earlier. During a subsequent full load test, the
EDG could not achieve its rated load of 2300 kW. The licensee determined that the fuel rack
linkage was improperly set after the EDG governor replacement. The resulting NRC inspection
finding for inadequate post-maintenance testing was determined to be of very low safety
significance (Green). (Indian Point Nuclear Generating Unit 2 - NRC Integrated
Inspection Report No. 05000247/2006003, dated August 11, 2006, ADAMS Accession No.
ML062260074) Brunswick Steam Electric Plant Unit 1 During a loss of offsite power event Unit 2, a Brunswick Unit 1 EDG experienced a high
lubricating oil strainer differential pressure alarm. The EDG later tripped due to a momentary
drop in lube oil header pressure that occurred while plant personnel refilled the cleaned lube oil
duplex strainer. The alarm condition was caused by the presence of fibrous lint material in the
strainer, the remnants of a cleaning towel that was inadvertently left in the EDG lube oil sump
during a previous maintenance activity. It was subsequently learned that the licensee had failed
to take effective corrective action after similar high differential pressure alarms were received
during two prior post maintenance testing runs. During the event follow-up it was discovered
that the EDG #9 crankshaft bearing was wiped. While the licensees bearing failure analysis
concluded that the exact cause of the failure could not be determined with certainty, the
analysis did conclude that the bearing lost effective lubrication and the surface of the bearing
was wiped. The resulting NRC inspection finding for exceeding the EDG technical specification
completion time was determined to be of low to moderate safety significance (White).
(Brunswick Steam Electric Plant - NRC Inspection Report Nos. 05000324/2007008 and
05000325/2007008; Preliminary White Finding, dated February 28, 2007, ADAMS Accession
No. ML070590404 and Final Significance Determination for a White Finding and Notice of
Violation (Brunswick Steam Electric Plant - NRC Inspection Report Nos. 05000324/2007009 and 05000325/2007009), dated April 20, 2007, ADAMS Accession No. ML071130028)
BACKGROUND
The examples of vibration-induced failures of EDG small bore piping and tubing are similar to
the concerns discussed in NRC IN 89-07, Failures of Small-Diameter Tubing in Control Air, Fuel Oil, and Lube Oil Systems Which Render Emergency Diesel Generators Inoperable, dated
January 25, 1989, ADAMS Accession No. ML031180501.
DISCUSSION
Licensees rely on EDGs to provide emergency alternating current power in response to loss of
offsite power events. EDGs are required to be operable as specified in plant technical
specifications. As described above, the NRR staff reviewed recent operating experience related
to EDG failures and identified several recurring events and general tendencies. The staff noted
that since the beginning of 2004, eight of the 27 greater than Green inspection findings within
the mitigating systems cornerstone have been EDG-related (one Yellow and seven White).
These findings involved either the failure to take prompt corrective action, the failure to perform
adequate post-maintenance testing, or the failure to follow procedures.
One recurrent event that continues to stand out involves the vibration-induced failure of EDG
piping and tubing. In many cases, major piping failures occurred after minor leaks were
identified and not immediately or properly repaired by the licensee. One licensee recently noted
that (1) the training for their employees did not cover common industry-known tubing failure
mechanisms, and (2) their managers and supervisors lacked knowledge of industry operating
experience relating to this type of failure. To prevent this type of failure, it is important that EDG
piping and tubing be properly routed, supported and maintained. This topic was previously
addressed by NRC IN 89-07.
CONTACT
This information notice requires no specific action or written response. Please direct any
questions about this matter to the technical contact listed below or the appropriate NRR project
manager.
/RA by TQuay for/
Michael J. Case, Director
Division of Policy and Rulemaking
Office of Nuclear Reactor Regulation
Technical Contact:
Stephen J. Pannier, NRR
301-415-4083 e-mail: sjp@nrc.gov
Note: NRC generic communications may be found on the NRC public Web site, http://www.nrc.gov, under Electronic Reading Room/Document Collections.
CONTACT
This information notice requires no specific action or written response. Please direct any
questions about this matter to the technical contact listed below or the appropriate NRR project
manager.
/RA by TQuay for/
Michael J. Case, Director
Division of Policy and Rulemaking
Office of Nuclear Reactor Regulation
Technical Contact:
Stephen J. Pannier, NRR
301-415-4083 e-mail: sjp@nrc.gov
Note: NRC generic communications may be found on the NRC public Web site, http://www.nrc.gov, under Electronic Reading Room/Document Collections.
Distribution: IN Reading File
ADAMS Accession Number: ML071760544 OFFICE IOEB:DIRS TECH EDITOR TL:IOEB:DIRS BC:IOEB:DIRS
NAME SPannier L-ACulp JThorp IDozier for MRoss-Lee
DATE 06/28/2007 07/02/2007 06/29/2007 06/29/2007 OFFICE D:DIRS PGCB:DPR PGCB:DPR BC:PGCB:DPR D:DPR
NAME ECollins CHawes DBeaulieu MMurphy TQuay for MCase
DATE 07/18/2007 07/30/2007 07/07/2007 08/02/2007 08/06/2007 OFFICIAL RECORD COPY