ML17221A549

LER 86-011-01:on 860709,emergency Diesel Generator 2A Taken Out of Svc Due to Failure to Meet Required Start Time.Caused by Excessive Tightening of Friction Clutch Locknut.Cooling Fan Shroud Removed & Fan repositioned.W/871216 Ltr

ML17221A549
Person / Time
Site:	Saint Lucie
Issue date:	12/16/1987
From:	Powell J, Woody C FLORIDA POWER & LIGHT CO.
To:	NRC OFFICE OF ADMINISTRATION & RESOURCES MANAGEMENT (ARM)
References
L-87-513, LER-86-011, LER-86-11, NUDOCS 8712220118
Download: ML17221A549 (8)

Text

REGULATORY INFORMATION DISTRXBUTZON SYSTEM (RIDS)

ACCESSION NBR: 8712220118 DOC. DATE: 87/12/16 NOTARIZED: 'NO DOCKET NACIL:50-389 St. Lucie Plant, Unit 2, Florida Power & Light Co. 05000389 AUTH. NAME AUTHOR AFFILIATION POWELL,J.M. Florida Power & Light Co.

WOODY,C.O. Florida Power & Light Co.

RECIP.NAME RECIPIENT AFFILIATION

SUBJECT:

LER 86-011-01:on 860709,both diesel generators out of svc.

W/8 ltr.

DISTRIBUTION CODE: IE22D COPIES RECEIVED:LTR i ENCL j SIZE-TITLE: 50.73 Licensee Event Report (LER), Incident Rpt, etc.

NOTES S

RECIPXENT COPIES RECIPIENT XD CODE/NAME PD2-2 LA TOURIGNY,E LTTR ENCL

'1 1

1 1

ID CODE/NAME PD2-2 PD COPIES LTTR ENCL 1 1 j A

INTERNAL: ACRS MICHELSON 1 1 ACRS MOELLER 2 2 AEOD/DOA 1 1 AEOD/DSP/NAS 1 1 AEOD/DSP/ROAB 2 2 AEOD/DS P/TPAB 1 1 ARM/DCTS/DAB 1 1 DEDRO 1 1 NRR/DEST/ADS 1 0 NRR/DEST/CEB 1 1 NRR/DES T/ELB 1 1 NRR/DEST/XCSB 1 1 NRR/DEST/MEB 1 1 NRR/DES T/MTB 1 1 NRR/DEST/PSB 1 1 NRR/DEST/RSB 1 1 NRR/DEST/SGB 1 1 NRR/DLPQ/HFB 1 1 NRR/DLPQ/QAB 1 1 NRR/DOEA/EAB 1 1 NRR/DREP/RAB 1 1 NRR/DREP/RPB 2 2 I

NRR/~DRI.S/S B 1 1 NRR/PMAS/ZLRB 1 1

~REG~LE~ 02 1 1 RES DEPY GX 1 1 RES TELFORD,J 1 1 RES/DE/EIB 1 1 RGN2 FILE 01 1 1 EXTERNAL: EG&G GROH,M 5 5 FORD BLDG HOY,A 1 1 H ST LOBBY WARD 1 1 LPDR 1 1 NRC PDR 1 1 NSIC HARRIS,J 1 1 NSIC MAYS,G 1 1 j

A TOTAL NUMBER OF COPIES REQUIRED: LTTR 46 ENCL 45

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NRC Form $ 55 UA. NUCLEAR REOULATORY COMMISSION (94$ )

APPROVED OMS HO. $ 1500104 LICENSEE EVENT REPORT (LER) EXPIRES: S/$ 1ISS FACILITYNAME ll) DOCKET NVMSER l2) PA 5 TITLE lcl ST. LUCZE UNZT 2 050003891OF06 BOTH DIESEL GENERATORS SZMULTANEOUSLY OUT OP SERVZCE DUE TO ONE PERSONNEL ERROR AND ONE COMPONENT PAZLURE EVENT DATE (5) LEA NVMSEA (5) RCPORT DATE ITI OTHER SACILITICS INVOLVED (Sl MONTH OAY YEAR YEAR I)$ SCOVCNTIAL ~

NVMOCA ÃA NVMOSA II4 VrtlON MONTH OAY YEAR FACILITYNAMES DOCKET NUMSER(SI N A 0 5 0 0 0 0 7 0 9 8 6 0 1 1 0 1 1I2 1687 0 5 0 0 0 THIS RKPORT IS SVSMITTKD PV ASVANT T0 THE REQVIAEMENTS OF 'lo CSA : ICIrccp circ IN moro ot too Iollowprol (11 OPERATINO $

MODE (SI 20A02(b) 20.405(cl SO.T $ 4)(2) litI T$ .710r)

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NAME TKLEPHONE NUMSCR J. M. Powell, Shift Technical Advisor AREA CODE COMPLETE OHE LINE SOA EACH COMPONENT FAILUAC OCSCh(SCD IH THIS RCPORT l1$ l 3 5465 -35 50 4$ %y4W CAUSE SYSTEM COMPONENT MANUFAC EPORTASLE i r 'spy'; CAUSE SYSTEM COMPONENT MANUSAC. EPORTASL TURER TO NPROS

, 4~iI TURER TO NPRDS EK 65 W29 0 4 @,

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SUPPLEMENTAL REPORT EXPECTCD I(4) MONTH OAY YEAA EXPECTED SUSMISSION YKS IIIycr, COmolcrc EXI'ECTEO SVSICISSIOHOATEI DATE (15)

NO AssTRAGT ILimit to (coo Ipccrr, I.o., cpprocimcrcly IIItrcn rlnplc.rpocc Iypcwri rtrn IInccl (I ~ I On July 9, 1986, while Unit 2 was at full power, the 2A Emergency Diesel Generator ID/G) was taken out of service due to failure to meet the required start time during a normal surveillance test run. The redundant 2B D/G was subsequently started, came up to rated voltage and frequency within the required time, but was declared out of service as one of the cooling fans was rubbing its shroud.

Repairs were made to both diesels; both were returned to service within the applicable Technical Specification time The failure of the 2A D/G was caused by excessive tightening of a friction clutch locknut. Engineering evaluation of the 2B D/G fan event revealed the presence of resonant frequencies in the 12 cylinder engine, which resulted in the flapping of the fan drive belts. The vibration caused by the flapping belts resulted in the loosening of the fan hub set screws.

Corrective action included:

1. Znspection of torque values in all friction clutch locknuts.

2. Znstructing all plant D/G maintenance personnel to contact vendors 1

for information regarding component adjustment when necessary.

3. A torsionally soft coupling has been instalZed in the fan drive systems on the 12 and 16 cylinder engines.

8712220118 871.216 PDR ADOCK 05000389 8 DCD NRC Form $ 55 (94)$ 1

NRC Form 388A U.S. NUCLEAR REGULATORY COMMISSION (943(

LICENSEE E NT REPORT (LER) TEXT CONTINUA ON APPROVEO OMB NO. 3I50-0(04 EXPIRESI 8/31/88 FACILITY NAME (1I OOCXET NUMBER (3( LER NUMBER (BI PACE (3) r( SEQVENTIAL ~>& RSVrSION YEAR g$ NVMOOR +4 NVMOSR ST. LUCZE, UNIT 2 TEXT ///more F/>>ce /F n//r/lrerL Iree /I/Oi5onro/NRC Forrrr 388l3/ (In o so oo389 8 6 0 1 1 0 1 0 2 OF 0 6 EVENT DESCRIPTION At 0854 hours0.00988 days <br />0.237 hours <br />0.00141 weeks <br />3.24947e-4 months <br /> on July 9, 1986, St. Lucie Unit 2 was operating at 100%. The Unit rem'ained at 100% throughout the event.

At 0855 hours0.0099 days <br />0.238 hours <br />0.00141 weeks <br />3.253275e-4 months <br /> on July 9, 1986, the 2A Emergency Diesel Generator (D/G) (EZISEEK) was started for a once per*seven (7) days surveillance test (once per 7 days based on" three (3) valid failures within the last 100 valid starts). The 2A D/G failed to meet the required generator voltage and frequency of 4160+420 volts and 60t1.2Hz within 10 seconds after the start signal. An alarm was received which indicated that one of the engines in the 2A D/G set had failed-to start. The engine fail to start alarm is actuated by high differential temperature between the turbo charger exhausts of the engines in the D/G set.

The power unit consists of two (2) EMD diesel engines, a 12 cylinder-645E4 and a 16 cylinder-645E4, driving one (1) Electric Products generator coupled with EMD tandem couplings, forming a diesel-generator assembly. The 2A D/G was manually tripped by the operator at 0856 hours0.00991 days <br />0.238 hours <br />0.00142 weeks <br />3.25708e-4 months <br />.

At 0915 hours0.0106 days <br />0.254 hours <br />0.00151 weeks <br />3.481575e-4 months <br /> on July 9, 1986, the redundant 2B D/G was started to satisfy Technical Specification ACTION (a) of Limiting Condition of Operation (LCO) 3.8.1.1, i.e. the performance of Surveillance Requirement 4.8.1.1.2a.4(redundant D/G operability check) within one (1) hour and at least once per eight (8) hours thereafter. This surveillance was performed since the 2A D/G had to be removed from service based on the 08355 failure. The 2B D/G came up to voltage and frequency within ten (10) seconds, therefore, meeting the Surveillance Requirement; 4.8.1.1.2a.4. At 0917 hours0.0106 days <br />0.255 hours <br />0.00152 weeks <br />3.489185e-4 months <br /> the 2B D/G was stopped due to an operator observation of one (1) of the 12-cylinder cooling fan blades rubbing the cooling fan shroud.

A decision was made to take the 2B D/G out of service to evaluate the seriousness of the rub. In accordance with ACTION (e) of LCO 3.8.1.1, operability of offsite power sources was verified and immediate actions were taken to repair both the 2A and 2B Diesel Generators.

The 2B D/G rub was determined to be minor and at 1048 hours0.0121 days <br />0.291 hours <br />0.00173 weeks <br />3.98764e-4 months <br /> repairs were completed on the 12-cylinder engine cooling fan. The 2B D/G was started for an operational check and met the required start time. The 2B D/G was declared back in service at 1059 hours0.0123 days <br />0.294 hours <br />0.00175 weeks <br />4.029495e-4 months <br />. With the 2B D/G back in service ACTION (a) of LCO 3.8.1.1 was maintained.

Trouble shooting of the 2A D/G revealed a problem in the mechanical portion of the Woodward governor. The problem was corrected and the 2A D/G was returned to service at 2010 hours0.0233 days <br />0.558 hours <br />0.00332 weeks <br />7.64805e-4 months <br /> on July 9, 1986.

NRC FORM SOOA (943 I

NRC Foim 3ddA U.S. NUCLEAR REOULATORY COMMISSION (943)

LICENSEE E NT REPORT (LER) TEXT CONTINUAT ON APPROVEO OMB NO. 3)EOM)04 EXPIRES: 8/31/88 FACILITY NAME ll) OOCKET NUMBER )1) PAOE l3)

LER NUMBER (8)

V EAII SEOVENTIAL REVISION NVMSER NUM EII ST. LUCZEP UNZT 2 p 6 p p p 3 8 9 8 6 011 0 1 0 3 OF 0 6 TEXT ///more dpece /e redo/ra/, Iree //r/ooe/H/IC %%drm 3BSEB/ )IT)

CAUSE OP EVENT 2B Diesel Generator Set The intermediate cause of the 2B D/G 12-cylinder engine cooling fan event was vibration withj.n the 12-cylinder engine Vertical Cooler Unit (ES-165), thereby, causing the set screws in the fan hub to loosen. With the loosening of the fan hub set screws, the fan shifted and began rubbing the shroud. The root cause of the vibration within the Cooler Unit is a design problem associated with fan drive belt flapping. Engineering evaluation of the problem of belt flapping on the 2B D/G has determined that the root cause of the problem was the presence of resonant frequencies in the 12 cylinder D/G fan drive system which were excited by large inherent 3rd and 6th order forced vibrations of the diesel generator set. The investigation revealed excessively high oscillating torque readings measured on the 12 cylinder power takeoff (PTO), North Pan and South Pan shafts. The peak torque levels were found to exceed the mean torque by factors of 3 1/2 - 5 1/2, and evidence of torque reversals were found.

2A Diesel Generator Set The intermediate cause of the 2A2 diesel failing to start was the failure of a roll pin (Ref. No. 82340-44) in the mechanical section of the Woodward EGB-13P engine governor. This governor consists of an electrical section which operates at or near rated engine speed, and a mechanical section which is mainly used during engine startup and shutdown. During startup, a small speed setting motor is used to run up the mechanical governor to allow the engine to reach rated speed where the electrical governor assumes control of engine speed.

This speed setting motor operates on the linkage of the mechanical governor by a fiiction clutch.

Znvestigations revealed a roll pin which holds the intermediate gear on the pinion shaft of the speed setting controls had broken. This gear arrangement drives the dial stop gear which actuates the upper and lqwer stops of the speed setting motor. With, the failure of the roll pin the speed setting motor runs continuously. Continuous running of the speed setting motor caused excessive wear on the friction clutch which, in turn, allowed excessive slippage of the friction drive shaft and prevented the mechanical governor from demanding sufficient fuel flow to pick up load on the 12-cylinder engine and allowing the electric portion of the goveinqr from taking control at the designated engine speed...

The root cause of the roll pin failure was the result of friction clutch adjustments made on the 2A 12-cylinder D/G mechanical governor as described in LER 389-86-006 (SEE PREVZOUS SZMZLAR EVENTS SECTZON). The root cause of LER 389-86-006 was determined to be a loose locknut in the friction clutch. This allowed excessive slippage and prevented the mechanical governor from demanding sufficient fuel flow to pick up load on the 2A 12-cylinder engine. The corrective action was to tighten the loose locknut on the clutch. 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.

NRC FORM SddA (943)

NRC Form SQIA UA. NUCLEAR REGULATORY COMMISSION (94LII LICENSEE EYENT REPORT (LER) TEXT CONTINUATION APPROVEO OMS NO. 3150MIOO EXPIRES: 8/31/88 FACILITY NAME Ill OOCICET NUMBER 13) LER NUMEER IS) PAOE 13)

YEAR SSOVENTIAL IISVISIIIN NVM SII NVMSSII ST. LUCIES UNIT 2 0 6 o 0 0 3 8 6 011 0 1 0 4 OF 0 6 TEXT ///more 4/Mde /3 /Pr/rer/ cd er/I/ir/aire/i/RC %%drrri CSEA'3/ (ITI Previous to tightening the loose locknut a review of the technical manual was completed to determine the torque value for the locknut. A torque value was not supplied in the technical manual. A self-determined adjustment was made and the engine was retested with positive results. Upon later conversations with the vendor it was learned that the locknut and the clutch of the 2A 12-cylinder D/G mechanical governor had been tightened beyond the vendor prescribed torque value. The overtightened locknut provided the stress necessary for the roll pin in the speed setting control to break. Thus, the root cause of this component failure was a cognitive personnel error by utility maintenance personnel.

EVENT ANALYSIS The event is reportable under 10 CFR 50.73(a)(2)(v) as neither diesel generator set was operable between the time the 2B D/G failed and'he 2B D/G was returned to service. This condition is allowed for a period not to exceed two (2) hours by LCO 3.8.1.1, provided both offsite power sources are available. Both offsite power sources were operable throughout this event and the time both D/G sets were out of service was less than two (2) hours (1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br /> 44 minutes). Also, as per Surveillance Requirement 4.3.1.1.3, ~Re orts: All diesel generator failures, valid or non-valid, shall be reported to the Commission pursuant to Specification 6.9.1.

The 2A D/G governor component failure was readily detected during routine surveillance testing. The event was determined to be a valid failure in accordance with Regulatory Guide 1.108.

The 2B D/G 12-cylinder cooling fan event was observed while satisfying ACTION (a) of LCO 3.8.1.1. The effect of the cooling fan rubbing the shroud did not inhibit the 2B D/G set from coming up to voltage and frequency within ten (10) seconds. During troubleshooting it was determined that had for the 2B D/G to perform its safety function the 12-cylinder cooling fan would it been necessary have worn the point of contact on the shroud to where no further rubbing would have occurred. The 2B D/G was taken out of service strictly as a precautionary measure and based on the above observation would not be considered a valid failure per Regulatory Guide 1.108.

it was determined that the event In the unlikely event of a complete loss of AC power (onsite and offsite) for St. Lucie 2 and, for the benefit of a conservative analy39isr the simultaneous loss of offsite power and one diesel generator at St. Lucie 1, the remaining diesel generator in St. Lucie 1 is able to operate the minimum safeguard loads such that both Units are maintained in a safe, hot stand-by condition. The present St. Lucie design does have the capability of electrically connecting the two units (

Reference:

St. Lucie 2 PUSAR, Updated Final Safety Analysis

'eport, Section 8.3.1.1.2,Pg.8.3-19d).

This was the fourth valid failure in the last 100 valid tests. Thus, the current surveillance interval is once per (3) days. This surveillance interval is in conformance with the schedule of regulatory position c.2.d of Regulatory Guide 1.108.

NRC FORM SSSA

'I

NRC FoIm 355A U.S. NUCLEAR REOULATORY COMMISSION (943(

LICENSEE EVENT REPORT (LER) TEXT CONTINUATION APPROVEO OMS NO. 3150-0(04 EXPIRES: 8/31/88 FACILITY NAME III OOCKET NUMSER (3( LER NUMSER (Sl PACE (31 YEAR N~ SEQVSNTIAI NVMOSII ~

.0+'IEVISION NVM SR ST. LUCZE/ UNIT 2 o s o o o 3 8 9 86 01 0 1 05 OF TEXT /// mac tpeoo II /o9o8a/, ooo sd/O'ono/ HRC /omI JSQS/ (ITI CORRECTIVE ACTONS 2B D G SET The 2B D/G cooling fan shroud was removed and the fan was repositioned in order to provide sufficient clearance between the fan blade tips and the fan shroud.

Upon completion of the re-positioning, the fan hub set screws were securely tightened. Corrective actions resulting from this event are:

A. A list of instructions has been developed describing steps to be taken for preventative maintenance inspections of .the D/G vertical cooling fan units. The purpose of these instructions is to check for loose bolts and to insure fan drive integrity.

B. A torsionally soft coupling has been installed in the fan drive systems on both the 12 and 16 cylinder engines of the Unit 2 D/G sets. The coupling will behave as a dynamic filter to cut off transmission of high order excitation past the PTO sheave. Test runs with a model coupling have shown this to be an effective solution.

2A D G SET The 2A2 D/G governor roll pin was replaced by replacing the dial panel assembly in total; this included both the roll pin and the friction clutch. Adjustments to the stop cams had to be made and a test run was performed with satisfactory results. Corrective actions resulting from this event ares A. An immediate inspection of torque values of the like component, i.e.,

friction clutch locknuts, in the remaining St. Lucie Plant D/G's was made.

B. D/G maintenance personnel have been instructed to make every attempt to contact the appropriate vendor should component adjustments be necessary, particulary in the area where information may nest be provided or discussed in the technical manual.

ADDITIONAL ZNFORMATZON FAILED COMPONENT INFORMATION failure of each D/G set was unrelated. The 2A D/G governor is a Woodward V'he Model EGB-13P. The roll pin (broken component in governor) Reference No. is 82340-44. The 2B D/G cooling fan is part of an ES-165 Vertical Cooler Assembly designed by the OaM Manufacturing Company.

NRC FORM SOOA

o %0 NRC Form 3SSA U.S. NUCLEAR REGULATORY COMMISSION (983)

LICENSEE EVENT REPORT (LER) TEXT CONTINUATION APPROVED OMS NO. 3IEOM(04 EXPIRES: 8/31/88 FACILITY NAME (1) DOCKET NUMSER (3) LER NUMBER (S) PACE (3)

YEAR :gI SEOUENTIAL REVISION NUMSSR ~A

>SINAI NUM ER ST. LUCIE UNIT 2 p 5 p p p 3'89 8 011 0 1 06OF06 TEXT ///more Spree /e oer/ 're/ rree e /capone/HRC %%drIII ESCA'o/ ((7)

PREVIOUS SIMILAR EVENTS LER 389-86-6 reported a previous event where both diesel generators were simultaneously out of service for the following related causes:

On March 10, 1986, the 2B Emergency Diesel Generator (D/G) was taken out of service to repair an idler pulley wheel on the belt-driven engine cooling fan.

On March 12, while performing a required operability surveillance on the redundant 2A D/G, one of the two engines in the diesel generator set failed to start.

Repairs on the 2B D/G were completed and the unit was returned to operable status within the time limit allowed by the applicable Technical Specification.

The damage to the idler pulley is believed to be related to the belt flapping problem which has been observed on the 12 Cylinder engines in the D/G set.

The failure of the 2A D/G was caused by a loose locknut in the friction clutch assembly which operates the mechanical governor used for engine start-up.

Corrective actions were to repair both diesels and inspect the remaining idler pulley wheels on the diesels for similar failures. The friction clutches on the remaining engine governors were inspected during the Unit 2 refueling outage, April 1986.

P. O. BOX 14000, JUNO BEACH, FL 33408 0420 OEGEiViBER 1 6 1987 L-87-513 10 CFR 50.73 U. ST Nuclear Regulatory Commission Attn: Document Control Desk Washington, DE CD 20555 Gentlemen:

Re: St. Lucie Unit 2 Docket No. 50-389 Reportable Event: 86-11 Rev. 1 Date of Event: July 9, 1986 Both Diesel Generators Simultaneously Out of Service Due to One Personnel Error and One Com onent, Failure The attached Licensee Event. Report (LER) is being submitted to update the original LER as indicated.

Very truly yours, c

CD

~ 0 Wo y Execut'ice

~

President COW/GRM/gp Attachment cc: Dr. J Nelson Grace, Regional Administrator, II,

~

Region USNRC Senior Resident Inspector, USNRC, St. Lucie Plant GRM/ 0 04 ~ LER 2A FPL Group corrpany