ML20091L093

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Special Rept 95-002:on 950727,valid Failure of EDG B Occurred.Util Believes Overspeed Plunger Partially Extended & Repositioned Overspeed Trip Lever.Adjusted Governor to Reduce Max Frequency Experienced by EDG B During Startup
ML20091L093
Person / Time
Site: Wolf Creek Wolf Creek Nuclear Operating Corporation icon.png
Issue date: 08/22/1995
From: Carns N
WOLF CREEK NUCLEAR OPERATING CORP.
To:
NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
95-002, 95-2, WM-95-0124, WM-95-124, NUDOCS 9508280295
Download: ML20091L093 (5)
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W$LF CREEK NUCLEAR OPERATING CORPORATION Neil S. " Bun" Carns Chairman, President and Chief Emecutwo Officer Augu5t 22, 1995 WM 95-0124 U. S. Nuclear Regulatory Commission ATTN: Document Control Desk Mail Station P1-1 37 Washington, D. C. 20555

Subject:

Docket No. 50-482: Special Report 95-002 Gentlemen The attached Special Report is being suomitted in accordance with Wolf Creek Generating Station Technical Specification 4.8.1.1.3 concerning a valid failure of Emergency Diesel Generator "B" and an invalid failure of Emergency Diesel Generator "B."

If you should have any questions regarding this response, please contact me at (316) 364-8831, extension 4000, or Mr. William M. Lindsay at extension 8760.

Very truly yours,

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. W Neil S. Carns NSC/jad Attachment cc: L. J. Callan (NRC), w/a D. F. Kirsch (NRC), w/a J. F. Ringwald (NRC), w/a J. C. Stone (NRC), w/a 9508280295 950822 PDR ADOCK 05000482 S PDR PO. Box 411/ Burlington, KS 66839 / Phone: (316) 364-8831 l j

An Equal opportunity Employer M T/HC/ VET l

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o 18 Attcchment to WM 95-0124

-page 1 of 4 I i

, Special Report 95-002 (Part 1) '

Valid Failure of "--raaney Diasal n===rator *B" This report describes a valid failure of Emergency Diesel Generator (EDG) "B" -

which occurred on July 27, 1995. This report is being submitted in accordance ,

with Wolf Creek Generating Station (WCGS) Technical Specification 4.8.1.1.3. ,

Background Tnformations On June .28, 1995, Wolf Creek Nuclear Operating Corporation (WCNOC) ~ issued '

Special Report 95-001, by letter Irr 95-0064. .This letter documented an Jinvalid failure of EDG "B." Corrective actions for this event included replacement of the EDG "B" Governor. ,

'At the time of this event the "A" EDG was administratively declared inoperable

to maximize personnel safety during the replacement of its lube oil. keepwarm pump. WCGS had conservatively entered Technical Specification Action Statement 3. 8.1.1 (a) . t Technical Specification Action Statement 3 . 8 .1.1 (a) defines the actions WCGS must implement when one EDG is inoperable, Technical Specification Action Statement 3. 8.1.1 (b) defines the actions WCGS i must implement when two EDGs are inoperable.

i Description of Events:

On July 27, 1995, at approximately 2121 hours0.0245 days <br />0.589 hours <br />0.00351 weeks <br />8.070405e-4 months <br /> CDT, WCGS performed Surveillance Test STS KJ-005B, Revision 22, " Manual / Auto Start, Synchronization & Loading Of Emergency D/G NE02." This test was performed to demonstrate operability of Emergency Diesel Generator "B," in accordance with the testing requirements specified in the Wolf Creek Generating Station Technical Specifications. This  !

test' implements a fast start and load of the EDG "B".  ;

During the performance of this test, the unit experienced an initial frequency peak of about 64 cycles before stabilizing at 60 cycles. Upon completion of the test, the EDG "B" was shutdown in accordance with the guidance contained in STS.KJ-005B. During the EDG "B" coast-down, the unit tripped on mechanical overspeed. WCGS declared the unit " Administratively" inoperable at 2132 hours0.0247 days <br />0.592 hours <br />0.00353 weeks <br />8.11226e-4 months <br /> CDT on July 27, 1995, entered WCGS Technical Specification Action Statement ,

3.8.1.1(b), and began an investigation to determine the cause of the EDG's trip. Both EDGs remained simultaneously inoperable for approximately 4.8 ,

. hours. WCGS declared an unusual event at 2211 hours0.0256 days <br />0.614 hours <br />0.00366 weeks <br />8.412855e-4 months <br /> CDT, on July 27, 1995, and notified the NRC at 2308 hours0.0267 days <br />0.641 hours <br />0.00382 weeks <br />8.78194e-4 months <br /> CDT, on July 27, 1995.

( ,At approximately 0200 hours0.00231 days <br />0.0556 hours <br />3.306878e-4 weeks <br />7.61e-5 months <br /> CDT, on July 28, 1995, WCGS started the "A" EDG to warm the unit and thus restore the lube oil to the required temperature band. ,

Subsequently WCGS declared the "A" EDG operable, on July 28, 1995, at 0218  !

hoursfCDT, and WCGS Technical Specification Action Statement 3.8.1.1(b) was l exited and Technical Specification Action Statement 3. 8.1.1 (a) , was entered j

due to the inoperability of the EDG "B".  ;

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Tbisevent occurred while the EDG "B" was in the standby mode. The EDG "B" f was administratively inoperable for approximately 70 hours8.101852e-4 days <br />0.0194 hours <br />1.157407e-4 weeks <br />2.6635e-5 months <br />, of which it was  ;

available for use and would have functioned correctly in an emergency for all but 20 of the 70 hours8.101852e-4 days <br />0.0194 hours <br />1.157407e-4 weeks <br />2.6635e-5 months <br />. During the 20 hour2.314815e-4 days <br />0.00556 hours <br />3.306878e-5 weeks <br />7.61e-6 months <br /> time period the unit. was tagged ,

out to facilitate replacement of the mechanical overspeed trip mechanism. t Root cause mad Corrective Actions  !

Root ("luse r WCGS believes that when the EDG *B" frequency peaked at approximately .64 ,

cycles, during startup of the EDG "B", the mechanical overspeed plunger l partially extended and repositioned the overspeed trip lever. The movement of j the overspeed trip level was not enough to result in an immediate trip of the

  • EDG "B". However it is believed that, during the coast down process, the overspeed trip lever vibrated into the full trip position resulting in a  ;

mechanical trip signal.

Immediate Corrective Actions i

The unit was tested in an effort to determine the exact cause of the trip.

This troubleshooting determined that the most likely cause of the mechanical overspeed trip was the overspeed trip lever, which had been repositioned during the EDG "B" startup, and vibrated into the " Tripped" position.

WCGS performed an evaluation and determined that this failure could have f adversely affected the function of the EDG "B" when in the isochronous (emergency) mode.

To prevent recurrence of this action, WCGS adjusted the governor to reduce the maximum frequency experienced by the EDG "B" during startup to 62 cycles.

WCGS has determined that this frequency is sufficiently low enough to prevent the overspeed trip switch from being repcsitioned during the initial startup of the EDG "B", and the subsequent vibration of the overspeed trip switch into the " Tripped" positioned.

Future Corrective Actioni The above discussed action has been determined to be appropriate to prevent recurrence of this problem.  ;

Failure Classification ,

In the event of an emergency, EDG "B" would have started and supplied power to [

its emergency bus as required. The repositioned overspeed trip switch could have prevented the EDG "B" from assuming the necessary emergency house loads.

Therefore, this failure is classified as an valid failure in accordance with Position C.2.e (2) , Regulatory Guide 1.108, Revision 1.  ;

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.- special Report 95-002 (Part 2)-

' Invalid Failure of *-roancy Dianal annarator *B"

-This report describes an invalid failure of Emergency Diesel Generator (EDG) ,

Descrintion of Eventar On August 3, 1995, at approximately 0905 hours0.0105 days <br />0.251 hours <br />0.0015 weeks <br />3.443525e-4 months <br /> CDT, the "B" emergency diesel {

generator was started in accordance with Surveillance Test Procedure STS KJ-005B, Revision 22, ' Manual /-Auto Start, Synchronization & Loading Of Emergency l D/G NE02." This . test was performed to meet monthly testing requirements specified in the WCGS Technical Specifications. The emergency diesel l generator was successfully started and loaded. The "B" emergency diesel  !

generator operated normally for approximately 27 minutes. At 0932 hours0.0108 days <br />0.259 hours <br />0.00154 weeks <br />3.54626e-4 months <br /> CDT,. ;

on August 3, 1995, a "Hi Lube Oil Sump Level" Alarm was received. The l validity of the alarm was evaluated by Operations and System Engineering personnel. At 1000 hours0.0116 days <br />0.278 hours <br />0.00165 weeks <br />3.805e-4 months <br /> CDT, the "B" emergency diesel generator was secured,  :

j the unit was declared 4noperable, and WCGS entered Technical Specification Action Statement 3.8.1.. s).

WCGS personnel immediately began an investigation into the cause of the high lube oil sump level. This investigation determined that lube oil, contained in the lube oil makeup tank, was leaking past the automatic lube oil makeup valve. This leakage resulted in the emergency diesel generator lube oil sump level increase and caused the lube oil sump high level alarm to actuate. WCGS ,

manually isolated the automatic makeup valve and returned the emergency diesel generator lube oil sump to the correct level. The emergency diesel generator I was retested and demonstrated operable at approximately 0439 hours0.00508 days <br />0.122 hours <br />7.258598e-4 weeks <br />1.670395e-4 months <br />, on August j 4, 1995.

l This event occurred during routine testing, as required by the WCGS Technical Specification 4 . 8 .1.1. 2 ( f ) . The EDG *B" was unavailable for approximately j 28.5' hours. During this time period, the cause of the problem was determined i and corrected. I Root canna and Corrective Actiona l

. Jtoot Caune:

l WCGS determined that oil, contained in the lube oil makeup tank, was leaking l past the automatic lube oil makeup valve. This leakage resulted in the level l in the emergency diesel ' generator lube oil sump increasing to the high level alarm setpoint. i l

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.-*- Attechment to WM 95-0124 Pega 4'of 4

-Immad'inte corrective Action WCGS secured the "B" emergency diesel generator and declared it inoperable until the lube oil sump level could be returned to the manufacturer's specified level.

WCGS manually isolated the automatic lube oil makeup va;ve and returned the emergency diesel' generator lube oil sump to the correct level. The automatic lube oil makeup valve will remain isolated until repairs can be effected.

This action was determined to be acceptable, based on the ability of the EDG "B" to operate continuously for a minimum of 10 days without the addition of-oil, as discussed below.

Future corrective Actions The above discussed corrective actions are adequate to prevent recurrence of ,

this problem. WCGS will repair the automatic lube oil makeup valve during a l future emergency diesel generator outage. The oil contained in the lube oil  ;

. storage tank is not necessary because the capacity of the engine lube oil sump l provides a sufficient volume of oil, so that the engine can operate at the nameplate continuous rating for at least seven days without replenishing the oil in the sump. When operating at nameplate continuous rating, engine oil ,

consumption is approximately 60 gallons per day. At full capacity, the engine l oil sump contains 1200 gallons of oil. The engine sump is considered empty at  !

300 gallons. This provides 900 gallons of oil that can be consumed which represents between 14 and 15 days ci continuous operation without replenishment. At the low sump level alarm point, there is approximately 963 1 gallons in the sump which provides 663 gallons of consumable oil or approximately 11 days continuous operation without replenishment. If  !

continuous operation starts when the oil level was at the add oil level (approximately 948 gallons), there is 648 gallons of consumable oil which represents a 10 day supply.

Failura Classificationt In the event of an emergency, EDG "B" would have started and supplied power to its emergency bus as required. The high level in the sump and the subsequent isolation of the automatic makeup valve would not have prevented the emergency diesel generator from ptrforming its designed function. Therefore, this failure is classified ca an invalid failure in accordance with Position C.2.e (2 ) , Regulatory Guide 1.108, Revision 1.

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