05000313/LER-1986-001, :on 860113,during Performance of Monthly Surveillance Test on Emergency Diesel Generator K4A,engine Tripped on High Crackcase Pressure.Caused by metal-on-metal Contact on Wristpin Bearings.Bearing Replaced

:on 860113,during Performance of Monthly Surveillance Test on Emergency Diesel Generator K4A,engine Tripped on High Crackcase Pressure.Caused by metal-on-metal Contact on Wristpin Bearings.Bearing Replaced

ML20206B581
Person / Time
Site:
Issue date:	10/31/1988
From:	James M. Levine, Taylor L ARKANSAS POWER & LIGHT CO.
To:	NRC OFFICE OF ADMINISTRATION & RESOURCES MANAGEMENT (ARM)
References
1CAN108808, LER-86-001, LER-86-1, NUDOCS 8811150494
Download: ML20206B581 (6)

LER-1986-001, on 860113,during Performance of Monthly Surveillance Test on Emergency Diesel Generator K4A,engine Tripped on High Crackcase Pressure.Caused by metal-on-metal Contact on Wristpin Bearings.Bearing Replaced

Event date:
Report date:
Reporting criterion:	10 CFR 50.73(a)(2) 10 CFR 50.73(a)(2)(v), Loss of Safety Function 10 CFR 50.73(a)(2)(1) 10 CFR 50.73(a)(2)(viii)(A) 10 CFR 50.73(a)(2)(iii)
3131986001R00 - NRC Website

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i Foro 1062.01A NRC Form 366 U.S. Nuclear Regulatory Commission (0-83)

Approved OM8 No. 3150-0104 Expires: 8/31/85 L 1 C E N S E.E EVEN1 REPORT (L E R)

FACILII) ' AME (1)

Arkansas Nuclear One, Unit One 100CnET NUMBER (2) IPAGE (3) 101510!0101 31 Il 31110F1015 llTLE (4M Emergency Olesel Generstor Failure Due to Fellure of Wrist Pin Bearings Results in Plant Shutdown Required By Technical Specifications

- EVENT ATE (5) l LER NUMBER (6)

I DEPORT DATE (7)

OTHER FACILITIES INVOLVED (8) 1 I

I i 15equentiall IRevisioni i

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MODE (9) i N! (Check one or more of the following) (11)

P0nERI i l '0.402(b) l I 20.405(c)

I[i50.73(a)(2)(tv)

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I 366A)

LICEN5EE CONTACT FOR THIS L;R (12) 4 Name i Telephone Number i

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Larry A. Taylor. Nuclear Safety and Licensing Specialist ICode i f

1510111916l41-13111010 COMPLETE ONE LINE FOR EACH CCNPCNENT FAILURE DESCRIBED IN THIS REPCRT (33) t i

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On 1/13/86 at 0628 hours0.00727 days <br />0.174 hours <br />0.00104 weeks <br />2.38954e-4 months <br />, during the perforeAnce of the emergency diesel generator (EDG) monthly surveillance test for EDG K4A, the engine -

<d on high crankcase pressure. The cause was determined to be the failure of pistra w*

bearings for four cylinders. An engineering evaluation concluded that the f ailu'es we-iuseo by long term metal on metal contact of the wristpin bearings due to inadequate lube oil file. The ultimate initiation and propagation of the failure occurrei as a result of 3 factors (or combinations thertof): 1) previous history of water in the lube L

oil; 2) excessive fast starts; 3) extended operation of the EDG at low or no load condition. On 1/15/86, when the entent of necessary repair indicated an overhaul of K4A should be initiated, the j

plant staf f determined that it would be prudent to shut the unit down to cold shutdo.n conditions. An I.

evaluation of the redundant EOG (K48) sher.ed the existvace of pcssible ce**?n f ailure precursors. On 1/24/86, maintenance activit'es commenced on overhauling EDG A4B after EDG K4A was restored to operabie i

status. Maintenanca activities and eperational checks of the diesel were completed on 1/31/86.

(,

Subsequent inspections of the EDGs daring the following refueling outage (1R7) did not identify any N:

t abnormal wear. Procedure cnanges ere made to minimize los load and unloaded operation of the EDGs.

N Additionally, monthly sube oil sampling and analysi; was initiated 1

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Form 1062.018U.S. Nuclear Regulatory Comnission (9-83)

Approved OM8 No. 3150 0104 Expires: 8/31/85 LICENSEE EVENT REPORT (LER) TEXT CONTINUATION FACILITf NAME (1) lDOCAET NUM8ER (2) i LER NUMBER (6) l PAGE (3) l i

l 15equentiall l Revision l Arkansas Nuclear One, Unit One l

l_Yeari Number Number l 10151010101 31 11 31 81 6 01 01 1 Of 1101210510151 TEXT (if more space is required, use aeditional hRC Form 366A's) (17)

I.

Description of Event

A.

U11t Status 1

The unit was charating at 43% power while maintenance was being performed on the "A" sain feedwater pump control system. A power reduction had been performed on 1/12/86 to allow the "A" naln feedwater pump to be isolated for the corrective maintenance.

B.

Component Identification The engines for the Emergency Diesel Generators [EK) used to supply onsite emergency AC i

power at Arkansas Nuclear One, Unit One (ANO-1), are General Motors Corporation Electromotive Division (EMD) Model EMO 645E4, 20 cylinder, 2 cycle, turbocharged diesels rated at 3600 brakehorsepower (at 900 rpm). The engine is used to drive a 2750 kw electric generator.

These packaged units (2) were supplied by Stewart and Stevenson to Arkansas Power & Light in 4

1972 The anits were subsequently modified to include a prelube/preware oil system per the manufseturer's recommendations.

C.

Sequence of Events j

At 0530 bours on 1/13/86, a licensed control room ope ator started the #1 Emergency Diesel Generator (K4A) to perform the monthly surveillance test. As part of this surveillance, the service water supply valve to the diesel engine cooling water systes must be verified to have opened autoeatically. Upon checking the Control room indicJtor of the valve position, it was noted by the licensed control reon operator to be in an intermediate position.

Another operator was inmediately dispatched to the valve to verify actual position. The valve was found to be approximately half open. The operator at the valve manually opened the valve to the full open pos'ition. At this point, the licensed control room operato" decided to unload the diesel and initiate the surveillance again. During the unloading l

sequerce, the diesel was inadvertently tripped on generator anti-motoring. At 0544 hours0.0063 days <br />0.151 hours <br />8.994709e-4 weeks <br />2.06992e-4 months <br /> I

the diesel generator was restarted from the control room and the service water supply valve opened frily.

The diesel was loaded to 2750 kilowatts (rated load) at 0548 hours0.00634 days <br />0.152 hours <br />9.060847e-4 weeks <br />2.08514e-4 months <br />. At 0628 hours0.00727 days <br />0.174 hours <br />0.00104 weeks <br />2.38954e-4 months <br />, the diesel generator tripped after running for 40 minutes under full load. An investigation by operations personnel found oil leaking from gaskets above the oil cocks; and, the oil dip stick (engine oil sump level indication) was noted as being almost blown from the crankcase. The "Low 011 Pressure

• and "Low 011 Pressure Shutdemn" annunciators were in alare at the local panel and the crankcase high pressure trip button was in the tripped condition. (Note: The high crankcase pressure trip device functions by dumping oil l

pressure sensed by the "Low 011 Pressure Trip" pressure switches.) Disassembly of K4A was initiated on 1/14/86 to inspect and repair the cause of the trip. At this tice, it was l

discovered that cylinders 1, 5, ll, and 14 had excessive piston-to-cylinder head clearances.

Upon examination of these cylinders and pistons assemblies (power packs), it was discovered that these four cylinders had heavily scored and burned wristpin bearings. On January 15, it was decided bj ANO maintenance persornel to overhaul K4A and install new power packs on all 20 ryltnders and to replace the main oil pump. When the dects.on was made to overhaul K4A, the plant staff determined that the required duration of maintenance would exceed the applicable Technical Specification limiting condition for operation time all wance (7 days);

therefore, on 1/15/86, the unit was shu'Jown. An inspection of the redundant diesel generator K48, indicated that the saee failure mesnanism precursors may have existed and maintenance activities were initiated to overhaul LAB on 1/24/86. Maintenance activities and operability 2

checks were completed 1/31/86 and the unit was returned to po.er operations.

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Fora 1062.018U.S. Nuclear Regulatory Commission (9-83)

Approved OMB No. 3150 0104 i

Expires: 8/31/85 LICENSEE EVENT REPORT (LER) TEXT CONTINUATION FACILITY NAME (1)

IDOCAET W MBER (2) I tER NUMBER (6) i PAGE (3)

I l

1 {5equentiall jRevision!

Arkansas Nuclear One, Unit One j

l Year Number l Number i r

10151010101 31 11 31 81 6 01 01 1

- l _ 01 Il01110F1015 TEAT (If more space is required, use additional NRC Form 366A's) (17)

II. Event Cause

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A.

Event Analysis

An analysis of this event was conducted by a team of Arkansas Power & Light Co. (AP&L) employees and a consultant from MPR Associates. Included in this team =as a mechanical i

engineer, a metallurgical engineer, and two diesel saintenance specialists. This team ensluattan consisted of: 1) a visual inspection of the power packs during the engine overhaul; 2) a nondestructive examination of the failed components (=ristpin bearings); 3) a review of the operational history for both A4A and K4B; 4) a review of industry experience with this make and model of diesel engine; 5) e review of the manufacturer's recommendations for operation of this diesel engine; and 6) a review of the lube oil analysis performed after the K4A failure. The following conclusions were drawn from the evaluations performed by this team:

1.

Based on the inspection of the diesel components, the failure of K4A cylinders 1, 5, 11 and 14 mristpin bearings mere noted as being the only major failures. The other 16 cylinders of the diesel showed noreal mear patterns; homever, the wristpin bearings on i

several of the other pistons did show some significant signs of wear as did several of i

the wristpin bearings in K48. There was no sign of crankshaf t, riston, or cylinder wall scoring which would indicate a lube oil system f ailure or lute oil breakdown.

Additionally, the lube oil pt *p mas inspected on 1/17/86 and pound to meet estat,11shed operational criteria.

2.

The mondestructive examination of the =ristpin bearings indicated that the failure of l

this component was due to progressive long tera degradation as opposed to a sudden i

failure etchanism. This conclusion is borne out by the fact that the =ristpin bearing failure ir.,olved a localtted near mechanism that propagated through successive stages t

(as evidenced by esamining several bearings).

3.

A review of the operational history of both diesela showed three significant itees of interest:

r a.

Water 6 the lube oil (1979).

i b.

Excessive fast starts (as high as 90/ year / diesel) and excessive operation at rated speed under low or no load conditions C,

Cylinder 813 power pack for 54A mas removed and replaced in October 1984 due i

to escessive head to piston clearance and abnormal wear (this probles did not cause the diesel to malfunction, but later inspection of the >enoved piston l

assembly indicated the =ristpin bearing had failed).

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4.

Industry emperience with this make of diesel has generally been good. A sampling of

[

ten other nuclear utilities that have EMD Model 645E4 diesels indicated that none had l

witnessed failures of the type seen at ANO. A review of N# lear Power Experience reports Electric Power Research Institute reports, thPC database, and hPR05 showed no l

failuret involving connecting rod or wristpin bearing failures. The operation data from other nuclear utility owners of EMD diesels provided a basis for comparison of operational emperience and practices at Arkansas Nuclear One.

5.

A review of the current manufacturer's recommendations for diesel operation and, also, discussions with the manufacturer concerning the failed =ristpins mere performed. The recent manuf acturers recossendatiois concerning cperation of these diesel engines shows that operation at Ic= or no load condition will increase near. Conversations with the i

manuf acturer concerning the f ailed =ristpin tearings provided concurrence =ith the l

Arkansas Power and Light's metallurgical engineer findings and supported these; but i

also included as a potential precursor event the cooling mater in the lute oil event recorded in 1979 (reference tER 50-313/79 016,79-017).

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Form 1062.018U.S. Nuclear Regulatory Convainston (9 83)

Approved CM8 No. 3150 0104 LICENSEE EVENT REPORT (LER) TEXT CONTINUATION FACILITY NAME (1)

(DOCAET NUMBER (2) i LER Nup6Eit (6) i PAGE (3) l l

1 15eQuentiall (Revision)

Arkansas Nuclear One, Unit One l

l Year Number Number l 10151010101 3l II 31 81 6 01 OI 1; 01 Il014!0Fl0j}

TEXT (If more space is required, use additional NRC Fors 366A's) (17) 6.

The lube ofI analysis showed no abnormalttles except for elevated levels of lead, iron, and silver in the K4A lube oil (post failure). These findings would be espected since the components found are the balance of materials used in the wristpin bearings.

The wristpin bearing failure appears from analysis to occur in a succession of steps:

first, the lead babbit metal wears down to the silver substrate; second, the silver substrate begins to flake (due to mechanical actions); and finally, catastrophic failure of the bearing occurs. Each of these stages was witnessed in the wristpin bearings of K4A and the initial failure precursors were cbserved in K4B.

B.

Root Cause The cause of the K4A malfunction is a wear failure of 4 wristpin bearings due to metal to metal contact as a result of insufficient lube oil film. The installed prelvbe system a

provides initial lubrication of diesel componer.t metal surfaces by maintaining the lube oli supply header full of oil prior to the engine start phase. This system also surmlies direct lubrication of the crankshaft surfaces and turbocharger bearings. There is no direct application of Ivbe oil to th+ wristp1. bearing by the prelvbe system; however, the ranufacturer has indicated that this is not a critical concern since the time to initiation of wristpin lubrication has been sintuited by filling the lube oil header via the prelube systes. There is no evidence to suggest that there was a loss of lube oli or insuff.clent lubrication of these bearings unce the diesel was operating at full speed and under loaded conditions. The root cause appears to be long ters wear initiated and propagated by each of the following or a coebination thereof:

1.

hater in the lube oil event.

2.

Fast starts.

3.

Unloaded or low load operhtion at rated speed.

This conclusion was based on the facta presented by the AP&L team of investigators and the manufa:turers representative. Also, these conclusions seem to be borne out by the current industry and NRC concerns about.f ast starts and other t;..

'ngine related operating conditions (i.e., Generic Letters 84 15 and 83 41. G EG/CR066?, etc.).

l C.

Basis for Reportability Arkansas Nuclear One, Unit One, Technical $pecification 3.7.2.C. allows one diesel generator to be inoperable for up to 7 days. When tne entent of the failure of KaA was determined and a course of maintenance action decided upon, the plant staf f realized that the planned maintenance activities and, therefore, diesel generator inoperability would exceed the time i

allowed in the Technical Specification. Based on this, an orderly shutdown of the unit to Ccid Shutdown conditions was initiated on 1/15/66. This report is be'ag submitted in accordance with 10CFR50.73(a)(2)(1) based on the guidance given in NUREG 1022 Supplement

1. Page 3. Question 1.t.

Since the unit was shutco n due to potential for exceeding the I

limiting condition for cperation time limits, the plant staff acted prudently in placing the i

plant in cold shutdown. There was no violation of the Technical Specifications, and the health and safety of the general public was not cegraded.

!!!. Corrective Actions A.

lamediate Inmediate corrective actions included an operational check of offsite AC power sources to the unit. As directed by the Technical Specification, the redundant diesel generator was immediately proven cperable and subsecuently surveilled on a daily basis, Maintenarce activities to determine and repair the cause of the diesel engine f ailure were also initiated. An engineering evaluation team was assembled to review this event, determine j

root cause, and make engineering recceendations to the plant staff.

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Fore 1062.018 hRC Form 366A U.S. Nuclear Regulatory Commission (9-83)

Approved OMB No. 3150 0104 l

LICENSEE' EVENT REPORT (LER) TEXT CCNTINUAT;CN FACILITY NAME (1) lDOCAET NUM8ER (2) l LER NUMBER (6) l PAGE (3) l l

l l5equential a (Revision!

Arkansas Nuclear One Unit one l

l Year Number Number l 10151010101 31 Il 31 81 6 01 110!510Flol$

01 01 1 TEXT (If more space is required, use additional NRC For1a 366A's) (17)

~

B.

Subsequent l

Based on the maletenance evaluation of the failure, K4A was disassembled and completely overhauled (20 new power packs, new bearings, rebuilt oil pump, etc.). Sines the failure l

mechanism observed in K4A was progressive, an evaluation of KaB was undertaken. When this investigation showed the same precursors to failure as witnessed in K4A, K48 was overhauled (1/24/86) as a precaution against common mode failure. Both diesels were subsequently i

proven operable and the unit was returned to power oper6 tion.

As a result of this event, several corrective actions have been taken to prevent recurrence:

1)

The operating procedure for the diesel generators has been revised to minimize the time that they will be operated at ualcaded or low load conditions, f

2)

The procedure for natural emergencies (i.e., severe weather, etc.) has been revised to C

delete a previous 'equirement to start a diesel generator and operate it in an unloaded i

condition upon receipt of a tornado warning for the plant area. The procedure now i

requires that an operable diesel generator is verified to be available.

j 3) in order to provide indication of wristpin bearing wear, monthly lube oil sampling and analysis has been instituted.

i 4)

Inspections of both diesel gererators were conducted during the refueling outage following the failure (1R7). These inspections included lead wire seasurements as an indication of wristpin bearing wear. Also during this out.ge, one power pack from A4A was disassembled to visually inspect the wristpin bearings. No abnormal wearing was observed during the inspbctions.

No further wristpin bearing failures have been identified since this event. The routine system performance monitoring will continue as required to ensure the operability of the f

diesel generators.

C.

Future i

None l

IV.

Additional Information

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A.

Siniter [ vents i

No previous similar events have bee 6 identified.

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Supplemental Information l

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ARKANSAS POWER & LIGHT COMPANY October 31, 1988 1CAN108808 U. S. Nuclear Regulatory Comission Document Control Desk Washington, D.C.

20555

SUBJECT:

Arkansas Nuclear One - Unit 1 Dockets No. 50-313 License No. DPR-51 Licensee Event Report No. 50-313/86-001-01 Centlemen:

Attached is the subject supplemental report concerning an emergency diesel generator failure due to failure of wrist pin bearings which resulted in a pl6.it shutdown required by Technical Specifications.

Very truly yours, NL

'J. M. Levine

. Executive Directur, Nuclear Operations JML:0AH: den attachment i

cc w/att: Regional Administrator Region IV U. S. Nuclear Regulatory Comission 611 Ryan Plaza Drive, Suite 1000 Arlington, TX 76011 INPO Records Center Suite 1500 1100 Circle, 75 Parkway Atlanta, GA 30039 g)T

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