ML20058D602

Problem Investigation Rept 2-C90-0143:on 900422,turbine- Driven Auxiliary Feedwater Pump Inoperable

ML20058D602
Person / Time
Site:	Catawba
Issue date:	10/25/1990
From:	Hampton J DUKE POWER CO.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
2-C90-0143, 2-C90-143, NUDOCS 9011060178
Download: ML20058D602 (7)

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IMe hatt Compay '

(803)831 4 000 Catado NulearStation l a Bas 156 Clocer, SC19fl0 DUKEPOWEM

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1 October 25, 1990 Document Control Desk U. S. Nuclears Regulatory Commission Washington, D. C.

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Subject:

Catawba Nuclear. Station-Docket 50-413 and 50-414 IIR C90-062-2p PIR 2-C90-0143 Gentlemen:

Attached is a report.concerning INOPERABLE. TURBINE DRIVEN 1

AUXILIARY FEEDWATER PUMP.DUh, TO EQUIPMENT MALFUNCTION.- This-1 report is being. submitted as a "Special-Report" to ensure industry awareness:of this event.

1 The health and-safety of-the public were not affected by

.i this incident.

Very truly Yours, a

J. W. H pton I

Station Manager 1

i kon: REPORT.SP J

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Mr. S. D. Ebneter.

American' Nuclear' Insurers'

. Regional' Administrator, Region? II-

-c/o_Dott1e~.Sherman, ANI Library j

U. S.= Nuclear Regulator Commission The Exchange, Suite 245' 101 Marietta Street, NW,' Suite 2900 270 Farmington Avenue-1 Atlanta,7GA :30323 Farmington, CT "06032' 1

y LMr. i. Jabbour-M & M Nuclear Consultants K

1221 Avenues of'the' Americas U. SJ Nuclear Regulatory Commission-New York, NY 10020.

. Office of Nuclear Reactor Regulation 1

Washington', D. C2 20555:

'i INPO Records-Center?

Suite 1500 Mr. W.'T.. orders-1100 circle-75 Parkway.

.HRC Resident Inspector-Atlanta,_GAa30339

' Catawba' Nuclear Station'.

'9011060178 901025 -

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DUKE POWER COMPANY' CATAWBA NUCLEAR STATION-pHOBLEM INVESTIGATION REPORT No.1 2-C90-0143~

INOPERABLE TURBINE DRIVEN AUXILIARY FEEDWATER PUMP DUE TO EQUIPMEt'T MALFUNCTION I

ABSTRACT 2

On April 22, 1990, at approximately 1715 hours0.0198 days <br />0.476 hours <br />0.00284 weeks <br />6.525575e-4 months <br />; with Unit 2.Jn, Mode 1, Power Operation, the Auxilia~ y~ Feedwater. Pump Turbine -(CAPT) would not: achieve rated r

speed'during a post-mainten'anceitest. iThe-CAPTlsuccessfully started b't.would u

not increase above tihe' minimum speed sett.ing. After troubleshooting, it'was concluded that the problem was internal to the Woodward governor. A vendor'

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representative postulated that the shutdown bellows ball check valve, a'part of the pressure actuated shutdown" assembly, was notiscating on st' art-up'and was preventing the governor from building speed setting oil pressure. Adjustmento; were made to-the shutdown. bellows, providing greater margin 'for the governor toi e

start, seat the ball check valve,tand develop speed' setting oil-pre'ssure. ~This incident is attributed'to an' equipment malfunction-due to the shutdown bellows:

ball check valvo problem. Corrective actions included installation of a refurbished governor for Unit 2 CAPT, lowering'the Unit 1 and 2. shutdown bellows assembly setpoint from 160 psig to 100 psig/ and increased surveillance of the Unit 1 and Unit 2 CAPTs. The CAPT was restored to operable status within the time required by Technical Specifications. 'Both motor driven CA pumps were-operable throughout this incident. This report-is submitted as.a special report to advise the industry of lessons learned.

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DUKE POWER COMPANY /CAyAWBA NUCLEAR STATION i PIR 2-C90-0143/Special Report

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HACKGROUND

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The Auxiliary Foodwater [EIIS:BA] (CA) System assures sufficient-feedwater

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supply to the Steam Generators [EIIS:HX] in the event of loss lof the Condensate 1

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[EIIS:SD] (CM) System /Feedwater [EIIS:SJ) (CF). System, to remove primary coolant

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stored and residual core energy.- The CA System is designed to start l

automatically in the event of loss of.offsite electrical power, trip of both 1

main feedwater pumps, safety injection signal, or low-low Steam Generator water j

level.

Three Auxiliary Feedwater Pumps [EIIS:P]Lare provided'(two full capacity l

motor (EIIS:MJ]! driven pumps and'one full capacity turbine [EIIS:TRB] driven Pump).

1 The turbine driven pump consists of a BinghamLType MSD 3x6x9 Pump powered by a Terry Corporation GS-2N Turbine.

A Woodward governor [EIIS:ES] Type PG-PLi..

-l Model 99032 111 equipped'with'a pressure actuated shutdown assembly is used for l

speed control. The shutdown bellowsLis;an auxiliary component in'the PG-PL.

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governor wh:ch vents the speed s'ettingioil pressure during coastdown from a trip or controlled shutdown. This action will allow-the:- turbine to -be imediately restarted if required.

The Main Steam to Auxiliary Equipment (EIIS:SA]'(SA): System supplies steam;

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intermittently as required to the Auxiliary Feedwater Pump and-continuouclysto the three condenser steam jet air ejectors.

The Nuclear Service Water [EIIS:BI]'(RN)' System is tNe ultimate heat-sink for various QA Condition 1 heat loads during! normal operation and postulated-q accidents.

s Technical Specification 3.7.1.2.in applicable in-Mode 1,: Power: Operation,-Mode-2, Startup, and Mode 3, Hot Standby, 'and requires one operable: Steam ~ Turbine Driven Auxiliary Feedwater Pump. capable of'being powered from an operable steam l 1

supply system and two operable motorLdriven' auxiliary feedwater pumps capable of being poworod from separate emergency busses'-

~With one Auxiliary Feedwater Pump; inoperable, the required Auxiliary Feedwater Pumps must be restored to operable status within-72 hours or be=iniat leastLHot Standby within the next six hours'and in Hot" Shutdown within the following six hours.

EVENT DESCRIPTION

' j On April 19, 1990, with Unit 2 in Mode l~, Power Operation, the; monthly survoillance test of the Unit 2 Auxiliary Foodwater Pump Turbine (CAPT) wasl successfully performed per PT/2/A/4250/06, CA Pump Head and Valve Verification.!

q The CAPT operated properly at rated speed at this time.'

on April 21 at 0420 hours0.00486 days <br />0.117 hours <br />6.944444e-4 weeks <br />1.5981e-4 months <br />, the CAPT was declared: inoperable to perform preventive maintenance on the SA; drain orifice. 'In addition,-the-periodic RN

- i System clam flush was performed ~.

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3 DUKE POWER COMPANY / CATAWBA HUCLEAR' STATION pIR 2-C90-0143/Special R;pors c pcg 33 i

i On April 22, at approximately 1715 hours0.0198 days <br />0.476 hours <br />0.00284 weeks <br />6.525575e-4 months <br />, the CAPT did not achieve rated speed

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while performing PT/2/A/4250/06 as a post-maintenanco test prior to returning the CApT to operability. Work Roquest 46484 ops was written to investigate / repair the reason for the CAPT not achieving rated speed.

When the CApT failed to increase above the minimum speed cotting, Maintenance Engincoring Services (MES) personnel were called in for assistance.

Initial troubleshooting consisted of visual observation of two successive starts.

During these tests the turbino started with the proper initial sequence of controlling action, i.e. the governor and control valve [EIIS:V) operated-correctly to control the.turbino-speed and prevent overspeed.. The turbine then remained at low speed and did not accelerate to rated speed as required. When tho turbine was shutdown the governor responded normally to the decreasing speed 3rA opened the control valve to, the wide.open position; This ruled out'tho s

control valvo and. associated _ linkago acLthe root cause of failure.

On April 22, 1990, numerous other parameters wero_ checked and verified to be correct such as:. manual speed knob: position,' governor oil level, air supply pressure, and valve line-up.. It wasethon concluded that the problem was internal to the Woodward governor. At this. time a vendor (Woodward) representative was requested to assist in tho identification of:the root cause of the governor failuro.' It,was also determined that previous maintenance work and a steam burst with subsequent local firo protection system activation on April 21 (LER 414/90-08) wero.not a factor because local temperatures were not high enough to alter governor oil proporties. Upon completion of the CApT. test runs the gavernor oil was changed in an effort to see if there was any " trash" present in the oil which could be causing the problem; no problem was found. A L

subsequent turbine start showed no chango in governor responso.

l On April 23, 1990, when the vendor representative arrived on-site) another turbine' start was performed.- This time tho turbine started and accelorated to rated speed (3650 RPM). At this timo, the MES Engineer and.the vendar representativo discussed governor operation and the functions of the various l'

governor devices. The vendor representative' described a-similar problem ho_had' observed ataan earlier time which was attributed to improper ~ operation of=the shutdown bellows assembly and rs ommended a small adjustment be made to the shutdown-bellows setting. The vs 'or representative made a slight' adjustment (1/16th turn)Lto the shutdown bellow adjusting' screw.. It:was postulated that the shutdown bellows ball check valve w, not properly seating on start-up and-thus preventing the governor building speud setting oil. pressure'. The inability.

to build speed setting oil pressuro would provent continued' opening of'the' governor valve and thus no increase in speed ~from tho' minimum-speed-sotting.

Adjustment of the shutdown bellows would provide greater-margin for-the governor to start, seat the~ ball check-valve, and develop speed l setting oil pressure'.

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.-DUKE. POWER COMPANY / CATAWBA NUCLEAR STATION _

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- - IIR 2-C90-0143/Specici R: port ~

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i Following this initial adjustment of the shutdown bellows, four subsequent tests were performed without failure. The tarbine_was turned over to Operations =to a

perform an operability test. On the second start,.the turbine failed to achieve I

full speed. To verify the internal condition ofLthe shutdown bellows and ball' check valvo, the' assembly was disassembled and. inspected with.no problems found.

Another adjustment was mado_by the vendor representative to the shutdown bellows assembly setpoint, reducing the pressure required to seat the ball check valve 1

t to where the vendor representative felt comfortable that it-would seat ~quickly during start-up and mnt within the required time.during: shutdown or: trip.

It was postulated that oil pump pressure was-not building quickly enough-during-the Initial operating. sequence to overcome internal leakage ^and seat the ball: check; 4

valve overy time before the speed returned to the minimum speed setting. 1This'

'i prevented the speed setting oil-pressure.from building and ramping _the turbine

- to full speed. Following the second. adjustment, additional full speed' starts were performed to observe the shutdown ~ bellows action while: starting and stopping. With the shutdown bellows ball check' valve seating. identified as the probable root cause, the turbine was turned over-for post-maintenance 1and:

performance operability testing. cace the operability tests were successfully completed, the turbine was decla.ed operable-on April 24 at: 0240 hours0.00278 days <br />0.0667 hours <br />3.968254e-4 weeks <br />9.132e-5 months <br />..

Measures were taken to test the CApT every 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br />'until additional investigations were completed. A used governor was sent to the Woodward facility for refurbishment. Woodward Ec.gir.eering and Station MES, personnel determined that impreved re11a3111ty could be achieved by lowering the shutdown bellows assembly setpoint from 160 psig to 100 psig'.The governor was returned and installed on the Unit 2_CAIT.

A successful operability retest'was completed. On April 126,'1990 tie Unit 1 CApT governor. shutdown bellows' assembly setpoint was adjusted to the Un.t 2 specif/ cations.

CONCI USION l

This incident is attributed'to equipment malfucction due to the' shutdown bellows.

l-ball check valve, a pcrt of the. pressure actuatei shutdown assembly, not properly seating. - The ruct cause-for the ball check valve not seatingJwas that -

the operating oil-pressure of the governor, expected to be'225 to 250 psig was found to be 190 poig. At this time it-is not known if the governor had been receivod with a 190 psig setting from Woodward Governor Company or:if internal' wear had reduced the operating oil. pressure to 190 psig. Testing is;being.

performed quarterly to monitor and trend the operating oil pressure for

- identification of potential internal wear problems. The check valve was set to

- close under approximately 160.psig. Because of.the narrow margin between the?

two points, the operating oil pressure was' unable to close the check valvo.

- This_ prevented the governor from building speed setting oil pressure, thus. the turbine would start but could not achieve rated speed.

Corrective actions included-MES troubleshooting, vendor adjustments, governor replacement, and. increased.CAPT surveillance. Ji Woodward representative was

- called in and-made adjustments allowing the: shutdown' bellows check' valve to' seat at a lower / pressure.> Woodward' Engineering andiStation MES personnel determined

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. DUKE POWER COMPANY / CATAWBA NUCLEAR STATION "PIR 2-C90-0143/ Spec 121 R; port-Prg)5 i

L that improved reliability could be achieved by lowering the shutdown ~ bellow assembly setpoint fromL160 psig toL100 psig...This was determined by running the governor on a test stand. The design criteria is.to,tu tbls to restart-the Turbine within 2 seconds of it coming to a stop.

The set point.of.100 psig allows a restart within 1.5 seconds and an increased =nargin between it and the operating oil pressure.

These changes were made to_ Unit 1 and Unit 2 governor with testing scheduled to substantiate operability. Appropriate design documents havo been changed.

These changes have increased the_ reliability'of1 the CAPT.

i Review of NPRDS data indicates numerous-failures associated with the PG-PL Woodward governors.

No previous failures' root causes can be attributed to the failure of the pressure actuated shutdown assembly. Catawba had one' event in 1

which the CAPT failed to pass 1180 RPM during a test, but-this was attributed to ambient temperature affecting the governor.

A' local steam = leak was directly hitting the governor.

This type of failure would not be classified as a recurring problem.

CORRECTIVE ACTION SUBSEQUENT 1)

Maintenance Engineering Services perform $d t'roubleshooting and concluded that problem was internal to_the Woo,dward governor.

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Vendor representative made'adjustmentsial1$ wing ball check valve to seat at lower pressure.

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Increased surveillance was performed every 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> for data on pump performance until additional investigation was' complete.

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A used governor.was se'nt to the Woodward facility,for, refurbishment.-

-While at the Woodward facility, Woodward Engineering'and Station MES personnel determined that improved reliabilityicould be achieved by

- i lowering the shutdown bellows assemblyfsetpoint from 160 psig to 100 psig.

The governor was. returned:and-installed on Unit 2 CAPT.-

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Vendor representative adjusted Unit 1 CAPT to' vent at 100'psig,-

-consistent with Unit 2 governor.

The Unit 1 CAPT.was then successfully tested, a

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Additional monitoring of turbine. governor performance 'w'as conducted. -

Monthly: testing of both Units',CAPT governors is being~ performed.to-check _the governor operating' oil pressure and-the pressure;at'which' the shutdown assembly. dumps the internal' oil pressure of the governor.

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- - -,PIR 2-C90-0143/Specitl R: port

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SAFETY ANALYSIS Each unit is equipped'with three Auxiliary Feedwater' pumps, Teach of which is able to supply the minimum total feedwater requirements to at-least two intact-Steam Generators. -The1use of redundancy, diversity,fand separation;has'boen' incorporated into thel design of the CALaystem and Auxiliary Feedwaterl pumps to :

ensure the capability to perform the design function.'f Duringuthip incident, both motor driven' Auxiliary Feedwater pumps were capable of; supplying.sufficientK feodwater to any two Steam Generators. ~ The CAPT,was repaired and returned to' operable status within the response time; requiked; byl T/Ss. > Thd health 'and.

safety.of thatpublic-were' unaffected by this incident.

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