ML17216A488

LER 86-006-00:on 860312,both Emergency Diesel Generators Out of Svc.Caused by Damaged Idler Pulley Wheel & Loose Locknut in Friction Clutch Assembly.Generators Repaired & Remaining Generators inspected.W/860410 Ltr

ML17216A488
Person / Time
Site:	Saint Lucie
Issue date:	04/10/1986
From:	David Williams, Woody C FLORIDA POWER & LIGHT CO.
To:	NRC OFFICE OF ADMINISTRATION (ADM)
References
L-86-157, LER-86-006-01, LER-86-6-1, NUDOCS 8604150428
Download: ML17216A488 (9)

Text

FLORIDA POWER III LIGHT COMPANY g>R 1 ON8S L-86-157 U,S. Nuclear Regulatory Commission Document Control Desk Washington, D.C. 20595 Gentlemen:

Re: Reportable Event 86-06 St. Lucie Unit 2 Date of Event: March 12 1986 Both Diesel Generators Out of Service Due to Mechanical Failures The attached Licensee Event Report is being submitted pursuant to the requirements to 10 CFR to provide notification of the subject event.

Very truly yours, C. O. Woo Group Y resident Nuclear Energy COW/PLP: de Attachment cc: Dr. 3. Nelson Grace, Region II, USNRC Harold F. Reis, Esquire PNS-LI-86-110 OoL ~ '

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governors wi.ll be inspected during the Unit 2 refueling outage which is scheduled for April 1986.

The failure of each diesel generator set was unrelated.

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Str Lucie, Unit 002 rCrrl~~vv r~ ~~~a 2 masllln 0 5 0 0 0 3 8 9 8 6 0 0 0 OF 0 4 EVEHT DESCRIPTION On March 10, 1986, an engineer inspecting the cooling water system (EIIS:LB) for the -2B Emergency Diesel Generator (D/G) (EIISSEK) noticed failed bolts oa a idler pulley wheel for one of the belt"driven engine cooling fans for the 12-cylinder engine. Of the four bolts holding the pulley onto a mounting bracket, one 'was sheared and the others were loosened. Unit 2 was operating at full power at the time of discovery. At 1410 hours0.0163 days <br />0.392 hours <br />0.00233 weeks <br />5.36505e-4 months <br />, the 2B D/G was removed from service for repair and the unit entered a 72 hour ACTION statement in accordance with Technical Specifications.

The redundant 2A D/G was demonstrated operable within one (1) hour and once per eight (8) hours thereafter. Difficulties in accessing the idler pulley delayed repair of the diesel until the morning of March 12.

At 0637 hours0.00737 days <br />0.177 hours <br />0.00105 weeks <br />2.423785e-4 months <br /> on March 12, the 2B D/G was started locally for post-maintenance testing. Following this testing, the diesel was stopped and allowed to cool to ambient conditions as required by the operability survei.llance. It was'lso necessary to add oil to the engine sump time. At 1214 hours0.0141 days <br />0.337 hours <br />0.00201 weeks <br />4.61927e-4 months <br />, the 2A D/G was started for an operability check. at'his An alarm was received which indicated that one of the engines in the 2A D/G set had failed to start. The D/G sets installed in Unit 2 are General Motors-EMD 645-E4 units. Each set consists of a 16-cylinder and 12-cylinder engine mounted in tandem driving a single generator. The engine fail"to"start alarm is actuated by high differential temperature between the turbocharger exhausts of the engines in the D/G set. Local observations indicated that the 12-cylinder engine (designated 2A2) was receiving insufficient fuel flow and the 16-cylinder engine was carrying the entire electrical load. At 1222 hours0.0141 days <br />0.339 hours <br />0.00202 weeks <br />4.64971e-4 months <br />, the 2A D/G was stopped. In accordance with ACTION (e) of .,Technical Specification 3.8.1.1, the operability of offsite power sources was veri, fied and immediate actions were undertaken to refill the 2B D/G engine oil sump and return this unit to service.

At 1238 hours0.0143 days <br />0.344 hours <br />0.00205 weeks <br />4.71059e-4 months <br />, the 2B D/G was started for its operability surveillance which was successfully completed at 1343 hours0.0155 days <br />0.373 hours <br />0.00222 weeks <br />5.110115e-4 months <br />. Troubleshooting of the 2A D/G revealed a problem in the mechanical section of the Woodward engine governor which is used for startup. The problem was corrected and the 2A D/G was returned to service at 0438 hours0.00507 days <br />0.122 hours <br />7.242063e-4 weeks <br />1.66659e-4 months <br /> on March 13. Unit 2 remained at full po~er throughout the event.

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The root cause of the loose idler pulley bolts on the 2B D/G is believed to be rel'ated to excessive flapping of the fan belts which has been observed previously on the 12-cylinder engines. The idler pulleys on the remaining engines were inspected and no similar failures were found. The Maintenance Department is planning to test a modification to the 12-cylinder engines during the next refueling outage which will enhance the ability of the fan belt system to absorb the energy of these belts. If the test is successful, the modification will be made permanent.

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2 ffXXAAAIIIAC ~ ~'IlIltl The root cause of the 2A2 diesel failing to start was a loose component in the mechani.cal section of the Woodward EGP-B13P engine goveznoz.

governor consists of an electrical section which operates at or near zated engine. speed, and a mechanical section which is mainly used during engine startup and shutdown. During startup, a small motor is used to run up the mechanical governor to allow. the engine to reach rated speed where the electric governor assumes control o'f engine speed. This motor 'operates on the li.nkage 'of the mechanical governor by means of a friction clutch.

A loose locknut in the friction clutch allowed excessive slippage and prevented the mechanical governor'rom demanding sufficient fuel flow to pick up load on the engine.

EVEHT hKLLTSIS The event is reportable . under '10 CFR 50.73 (a)(2)(v) as neither diesel generator set was operable between the time the 2A D/G failed and the, 2B D/G was returned to service. Thi's condition is aLlowed for a period not to exceed two (2) hours by Technical Speci.fication 3.8.1.1, provided both offsite power sources are available. Both offsi.te power sources were operable throughout this event and the time both diesels were out of service was less than two (2) hours.

Although the fai.led ,idler pulley was noticed by inci.dental observation, the failure would have been detected in later surveillances. Failure of the pulley to maintain tension on the cooling fan drive belt would have reduced the ability of the cooling water system to remove engine heat and a diesel trip on high cooling water temperature would have occurred during testing. This automatic diesel trip is bypassed on emergency starts and would not have prevented operati.on under emergency conditions. It should be 'noted that there are a total of four cooling fans on 'each'/G set, 'wo for each engine. The failed idler pulley affected only one of the fans for the 12-cylinder engine, the other fans remained operable.

Engine cooling requirements for prolonged operation under emergency conditions would be dependent on'he actual electrical load on the D/G set and 'the ability to manually shi.ft load to the other engine in the

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Failure of the locknut in the governor friction clutch on the 2A2 diesel was detected during surveillance testing. As was noted previously, this failure only affects the ability of the diesel to reach rated speed, and has no effect once the electric governor assumes'ontrol. Conversations with the governor vendor have 'indicated that this is the first known failure of this type. The friction clutches are supplied as assembled units and are not required to be disassembled and inspected as part of the vendor's recommended preventative maintenance program.

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3 6 p p g,OF 0 4 CORRECTIVE hCTIOSS The failed idler pulley bolts vere replaced on the 2B D/Gl Similar pulleys on the, remaining engines vere checked and found to be satisfactory, loose locknut on the friction clutch for the 2h2 diesel governor vas tightened and the engine retested. Similar component's on the 'emaining engine governors vill be inspected during the Unit 2 refuelling outage scheduled to begin in hpril..

hDDITIOML IHPORMhTION The failure of each diesel generator set vas unrelated. The 2h D/G Governor is a Voodvard 'Model EGP-BI3P. The 2B D/G fan idler pulley is part of an ES-165 Vertical Cooler assembly designed by the 06M Manufacturing Company.

See LER 389-83-1 for a previous event vhere both diesel generator's vere out of servicd.

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