ML19332E268

LER 89-016-02:on 890616,for Unknown Period Since 890614, Auxiliary Feedwater Pump FW-10 Operated Outside Design Basis for Certain Accident Conditions.Caused by Inoperable Speed Control Loop.Action Plan implemented.W/891201 Ltr

ML19332E268
Person / Time
Site:	Fort Calhoun
Issue date:	12/01/1989
From:	Morris K, Stecker W OMAHA PUBLIC POWER DISTRICT
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
LER-89-016, LER-89-16, LIC-89-1036, NUDOCS 8912070008
Download: ML19332E268 (10)

Text

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a Omaha PubHC Power District

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LDecember 1, 1989- 402/536 4000.

.LIC-89-1036-l.-

1 U. S. Nuclear Regulatory Commission Attn:: Document Control Desk .{ '

Mail Station P1-137 Washington, DC 20555 .

Reference:

. Docket No. 50-285

-Licerisee Event Report 89-016, July 17, 1989-l., Licensee Event Report 89-016, Rev.1, September 1,1989 L Gentlemen: -

Subject:

' Licensee Event Report 89-016, Rev. 2 for the Fort Calhoun Station Please. find attached Licensee Event Report 89-016, Revision 2 dated December 1, 1989. Revised or supplemental information is noted by

' vertical bars in the margins. This report is being submitted per '

requirementsof10CFR50.73(a)(2)(i)(B)and50.73(a)(2)(ii)(B).

If.you should have any questions,-please contact me.

y Sincerely,. ,

n J. Morris Division Manager Nuclear Operations e es

-KJM/tcm Attachment.

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c: R. D. Martin, NRC Regional Administrator A. Bournia, NRC Project Manager P. H. Harrell, NRC Senior Resident Inspector-INPO Records Center American Nuclear Insurers 8912070008 891201 PDR ADOCK 05000283 t

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E Bi A Pi C 10 i X i 91919 Y E' BI A Pl C101 XI 91919 I l l I 1 I I SUPPLEMENTAL REPORT EMPICTED tien MONTM DAY TEAR Tt$ III,ee comome EMPECTfD Sues,ISSION OA Til NO l l l A T R ACT m- ,e , e,. , e-....e., ,,,,e .,,, o ,, A. . ,,. , i,.I On June 16, 1989, Engineering evaluation of test results revealed that, for an unknown period prior to June 14, 1989,' Auxiliary Feedwater Pump FW-10 operability was outside the design basis for certain accident conditions due to inoperability of the pump pneumatic speed control loop. Problems with the control loop had been found on June 13, 1989 after FW-10 was taken out of service for special~ testing. These problems would have limited pump speed and

discharge pressure below that needed to inject water into the steam generators l under some accident conditions. Because the control loop could not be repaired L and tested expeditiously, the air supply to the control loop was valved out on June 14, 1989. This allowed pump speed and discharge pressure to be controlled by_the mechanical speed limiter on the main governor as designed to meet accident mitigation criteria. The pump was determined to be operable and

! returned to service. An investigation was initiated to determine the duration and cause of the control loop inoperability. The NRC Regional Office was l

briefed on June 13, 1989 and, following the determination of reportability, the NRC Operations Center was notified on June 16, 1989 at 1646 hours0.0191 days <br />0.457 hours <br />0.00272 weeks <br />6.26303e-4 months <br />, pursuant to 10CFR50.72(b)(1)(ii). Fort Calhoun Station Unit No. I was at approximately 100% power at the time of determination. Inoperability of the control loop was due to inadequate preventative maintenance, surveillance testing, and I. configuration control. A comprehensive action plan has been implemented and I

corrective actions have been initiated.

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0;2 0l2 or 0l9 TEXT M mese asses e sosimus, ses esmusant MC sonn 31547 (m Auxiliary Feedwater Pump FW-10 is one of two redundant auxiliary feedwater pumps at Fort Calhoun Station Unit No. 1.. FW-10 is a steam turbine driven pump designed to be independent of AC power requirements, while redundant pump FW-6 is an AC motor driven pump. Each pump is designed to deliver a minimum flow of .

I 260 gallons per minute (gpm) to the steam generators against a steam generator '

L pressure of 1000 psia. During normal startup and shutdown operations, pump E FW-6 is routinely used to supply feedwater. Pump FW-10 is not normally used for plant operations and is usually only run during testing. Both auxiliary .,

feedwater pumps are designed to automatically start on low steam generator level. If a loss of all station AC power also occurs, FW-10 is the primary ,

source of feedwater. However, motor-driven pump FW-6 can be powered from an emergency diesel generator after normal AC power supply is lost.

! Thespeed(andresultantdischargepressure)ofFW-10isdesignedtobe governed by a pneumatic-hydraulic speed control loop which maintains the feed o pump discharge pressure at a fixed differential greater than the steam l

generator pressure. A Moore differential pressure transmitter (PT-1039) senses the differential pressure between the pump discharge and the steam generator and sends a signal to a pneumatic controller. The Nullmatic Two-Mode Model 55M controller (PC-1039)fecdsanairsignalthroughaNullmaticModel59 .

derivative controller unit which dampens the signal to reduce pump speed oscillation. This should permit smooth response to a pump speed needed to provide discharge pressure above steam generator pressure. The differential pressure setpoint is adjustable in the field, and would normally be set so that the pump discharge pressure is at least 40 psi above the steam generator pressure at rated flow. The pump control system is supplied from the Instrument Air System. The control system is also designed to allow maximum speed of the pump upon total loss of Instrument Air. In this condition, pump speed is limited by the setting of the mechanical speed limiter on the main governor. As originally installed, the speed control loop did not provide for manual control of pump speed.

At 1300 hours0.015 days <br />0.361 hours <br />0.00215 weeks <br />4.9465e-4 months <br /> on June 13, 1989, with the station operating at 100% power, pump FW-10 was taken out of service in preparation for testing following redundant component testing of pump FW-6. Technical Specification 2.5 allows one auxiliary feedwater pump to be inoperable for up to 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />. The testing (controlled by procedure SP-FW-12) was intended to provide baseline data on pump performance by developing a method for manual control of pump s)eed, in order to establish a reference speed for future testing and verify t1e governor-limited maximum speed. Tem)orary modification 89-M-031 was implemented, which installed a varia)le air supply test-tee inlet to the control loop in order to simulate signals from the differential pressure sensor and provide manual pump speed control to the test personnel. At 1645 hours0.019 days <br />0.457 hours <br />0.00272 weeks <br />6.259225e-4 months <br />, FW-10 was started and warmed up for the test. At 1727 hours0.02 days <br />0.48 hours <br />0.00286 weeks <br />6.571235e-4 months <br /> the test air supply was valved in and initial readings were taken. Between the hours of i 1750 and 1835 the test air pressure signal was varied numerous times with no change in pump speed observed. At 1835 hours0.0212 days <br />0.51 hours <br />0.00303 weeks <br />6.982175e-4 months <br /> the pump was stopped and the control system was returned to normal configuration. The Shift Supervisor, Duty Supervisor, System Engineering Supervisor, and Plant Manager were informed 1

l of the situation.

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0 l2 ' 0 [3 or 0l9 mm o . o -c ~,,,-,nm At 2000 hours0.0231 days <br />0.556 hours <br />0.00331 weeks <br />7.61e-4 months <br /> on June 13 an emergency maintenance order was initiated to  ;

. investigate and make minor repairs to the pneumatic controller and derivative

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unit. This activity included cleaning of restriction orifices and checking adjustments of the controller as described in the vendor manual. The pneumatic derivative unit was found to be leaking air and to have erratic response. No other repairs or adjustments were possible at the time. With the ,

control components in this condition, pump FW-10 maximum speed was found to be 6980 rpm with a resultant discharge pressure of 996 psig, a value below the minimum pressure required for operability during a Design Basis Accident.

Test procedure SP-FW-12 was revised to allow determination of the mechanical 4 limiter setpoint on the main governor for FW-10 by injecting the test signal downstream of the derivative unit. The test revealea on June 14 at 1005 hours0.0116 days <br />0.279 hours <br />0.00166 weeks <br />3.824025e-4 months <br />  :

that, upon loss of instrument air supply, pum) speed would increase to 7725 rpm with a discharge )ressure of 1210 )sig. In t11s mode the pump was considered  !

operable, since tie speed and disc 1arge pressure were well above the design basis minimum values, yet pump speed was within the maximum allowable. It was determined that failure analysis and repairs.of the pneumatic controller components could not be accomplished within the remaining degraded mode period allowed by the Technical Specifications, so the instrument air supply to the control system for FW-10 was valved out. The pump was restarted to verify that o it would perform its intended safety function in this configuration; it was i subsequently declared operable and returned to service at 1130 hours0.0131 days <br />0.314 hours <br />0.00187 weeks <br />4.29965e-4 months <br /> on June 14 with the instrument air supply valve tagged closed.

It could not be immediately determined what caused the malfunction of the controller system or when the system became inoperable. An evaluation including review of previous test data was initiated in order to determine reportability. Because of the significance of the event, the situation was explained to the NRC Region IV office by plant management on June 14 The

,. engineering evaluation concluded on June 16, 1989 that FW-10 controller loop l performane.e was degraded for et least several years prior to discovery; the I plant thus operated outside the design basis of the auxilicry feedwater system for an indeterminate period. This was reported to the NRC Operations Center on June 16, 1989 at 1646 hours0.0191 days <br />0.457 hours <br />0.00272 weeks <br />6.26303e-4 months <br /> pursuant to 10 CFR 50.72(b)(1)(ii). As an additionalconsequence,theLimitingConditionforOperation(LCO)ofTechnical Specification 2.5 was violated for an indeterminate period.

This event is safety significant to the degree that, under certain conditions, Auxiliary Feadwater Pump FW-10 would not have been capable cf performing its l function. These conditions would be the coincident (1) loss of main feedwater, (2) unavailability of motor-driven Auxiliary Feedwater Pump FW-6, (3) steam generator pressure over approximately 1000 psia, and (4) availability of L

Instrument Air supply to FW-10. The pneumatic controller problems limited FW-10 discharge pressure to approximately 996 psig. Further analysis of the consequences of this event was performed, with results noted in Action i

safety Item (8)ofthisreport.

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0 ;2 0l4 or 0l9 Tur u- . e ,.m,-m An action plan was formulated to address cause, consequences, and corrective actions for this event, and to resolve concerns and questions from NRC Region IV inspectors. The action plan items and results are:

(1) Determine.thedirectcauseofthederivativecontrollerfailureintha FW-10 speed control loop. ,

A Special Procedure SP-FW-13 was performed to control the trouble-shooting and repair of the speed control loop on FW-10. The aneumatic controller '<

vendor participated in the effort. The failure of t1e derivative unit was caused by excessive clearances which developed between close tolerance parts within the unit during its installed life. These increased clearances between the diaphragms and nozzles caused erratic operation and eventual complete failure of the unit. The body bolts which hold the stacked body parts together were found to be loose. Similar problems of l-

. increased clearances and loose body bolts were found with the two-mode controller upstream of the derivative unit. In addition, the zero setpoint adjustment screw on the two-mode controller was found turned to the extreme clockwise position further prohibiting the normal functioning of the unit.

-When and why this adjustment was made could not be determined.

Both of the units were removed to the shop and disassembled for inspection. No evidence of moisture or foreign material intrusion was found. The diaphragms were found to be slightly stiff or embrittled but not cracked or flaking off. The looseness of the body bolts was attributed L to the permanent deformation of the edges of the diaphragms due to aging and compression. New controllers have been calibrated and installed in the loop on FW-10.

During the. trouble-shooting process the differential pressure transmitter was also found to have failed. The bellows leaked internally resulting in failure to respond'to differential pressures applied at the inputs. A replacement transmitter has been ordered. For this reason, the speed control icop of FW-10 remains out of service with its air supply valve tagged shut. Disassembly and inspection of the transmitter to determine its failure mechanism will be conducted after replacement parts are l received.

The Moore Products field representative has recommended that the body bolts on the Moore controllers be torqued to 55 inch-pounds and checked periodically. This information has been transmitted to the Project 1991 preventive maintenance (PM) program upgrade group for evaluation and inclusion in the appropriate PM procedures. As noted above, the FW-10 controller loop remains out of service due to the failed bellows in the differential pressure transmitter. The replacement of this transmitter is expected to occur by January 31, 1990, subject to recei)t of ordered parts. Appropriate calibration and PM procedures will )e in place prior to returning the control loop to service.

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0j 2 0l5 or 0] 9 m, a - . u. a m,c r., anaw m, (2)DeterminetherootcauseofthefailureofFW-10torespondtomanually injected air signals during the conduct of SP-FW-12.

u A root cause investigation was conducted by members of the Nuclear Safety.

p Review Group. The root cause was determined to be failure to include the-speed. control loop for FW-10 in the preventative maintenance / calibration program at initial plant startup. Subsequent investigation by the Nuclear Safety Review Group determined the following contributing factors: the i r control loop components were never classified as CQE, and an inadequate ..

l surveillance test did not verify the proper operation of the speed. control  !

[ loop. '

L L (3)Reviewandevaluateavailableinformationtoascertain,ifpossible,when

. failure /misadjustments of the speed control components occurred.

L Immediately following the discovery of the failure of FW-10 to respond to

.p(neumatic ST-FW-1) was test initiated.1 control signals, Several a review of test different pastresult surveillance parameter test data combinations were graphed to find a trend or pattern that would indicate when the failure might have occurred. A graph depicting the trends of turbine steam inlet pressure, and the pressure differential between the pump discharge and steam inlet was constructed.

The data indicate that, since July, 1985,.the differential pressure between pump discharge and steam inlet pressures varied inversely with-the steam inlet pressure changes. If the pump speed control loop had been operating properly,.this differential 3ressure trend would be a relatively straight -

line. The inverse relations 11p was caused by the pump operating at a constant speed, and therefore constant discharge pressure, due to the control loop being unresponsive. That is, no matter what the air input signal from PT-1039, the turbine throttle linkcge positioner output air signal remained at approximately 12 psig output, causing the pump to. ,

operate at a relatively constant s)eed. This speed was not sufficient for developing the head required for t1e pump'to fulfill its safety related function during a DBA. Therefore, it is concluded that since July 1985, '

the pum) speed control loop was inoperable causing FW-10 itself to also be

.inopera )le.

Prior to July 1985, the test data points for the pum) discharge pressure

/ steam inlet pressure differential were widely varia)1e, indicating that the control loop was not properly functioning. However, the pump did operate at sufficient speeds to develop the discharge pressure necessary for injection of water into the steam generators under DBA conditions.

Therefore, although the controller may not have been fully operable prior to July 1985, it did not restrict the speed of the pump enough to cause FW-10 to be inoperable.

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(4)Reviewpreytuus'testingofFW-10todetermineif-thefailureofthespeed control loop should have been evident from the data available. Evaluate.

'the effectiveness of the existing surveillance tests on FW-10 used to demonstrate' operability. .

A review of previous testing of FW-10 per ST-FW-1 was performed by 0 PPD Special Services Engineering to determine if the failure of th'e speed-control loop should have been evident from the data available. As-evidenced by'the resolution of Action Item #3, the surveillance test did contain sufficient information to determine that a problem existed with the speed control loop. However, the pattern that indicated a failure was- t discovered only after much manipulation of the available data. In addition,until1988,therewasnoAFWsystemexpert'(systemengineer)with the detailed knowledge of the operation of FW-10 which-is necessary to properly review the surveillance test for deficient trends or patterns such as this. These facts, coupled with the fact that the failure occurred-prior to the implementation of a formal surveillance trending program, make it highly improbable that the failure of the speed control loop would have been recognized by the test reviewers. 4 l

A review of ST-FW-1 was also performed by Special Services to evaluate the p test's effectiveness in demonstrating the operability of FW-10. This D evaluation revealed the following deficiencies:

L

, A) Turbine steam bowl pressures were not recorded or trended. The L pump vendor has stated that trending of this parameter is one of ,

L the best ' indicators of pump and/or turbine performance '

l degradation. This parameter is now incorporated into ST-FW-1.

B) Prior to April, 1989, ST-FW-1 did not provide for a means of directly measuring pump suction pressure, which is used to determine pump developed head. Suction pressure was calculated from a. static elevation head measurement at-the emergency '

feedwater storage tank. This methodology has been changed by directly reading suction pressure from a test gauge installed at

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the pump's suction flow element. This results in a much more accurate indication of pump developed head and provides assurance that no operability concerns exist with the pump's suction supply.

C) ST-FW-1 did not require a variation from the steady state speed obtained when the pump was started and run in the recirculation flow configuration. If ST-FW-1 would have required such a speed .

variation to be 3erformed, the inoperability of the speed control l loop would have )een evident at the time an individual test was performed.

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e ' Fort Calhoun Station Unit No. 1 o js io jo g o ;2 ; 8;5 8; 9 _._ 0; 1; 6 0;2 0;7 op 0; 9 myw- ., a acu,,,asuim D) The surveillance program did not require that the full flow capability of the AFW pumps be measured periodically. In-fact, the full flow capabilities of FW-6 and FW-10 were never-adequately determined until April 1989. -Both INPO and the-NRC i

have-stated that periodic full flow testing is desirable for- <>

7 , determining pump operability. The installation of modification a MR-FC-68-017 will-provide a full flow test line for'FW-6 and FW-10. The installation and testing activities for this

^ modification are scheduled for completion by July 30, 1990, contingent on equipment delivery. A periodic full flow test procedure will be developed and performed for both FW-6 and FW-10 within two months following the modification installation and testing completion date. Special full flow testing of FW-6 and '

FW-10 will be conducted immediately before and after the 1990-Refueling Outage, respectively.

Considering-the above deficiencies, the surveillance test ST-FW-1 was not adequate-indemonstratingtheoperabilityofFW-10priorjoApril,1989.

1 (5)Investigatewhythespeedcontrolloopcomponentshavehad.noequipment  :

identification numbers, calibration procedures, or periodic maintenance.  ?

Evaluate whether speed control loop components are correctly classified withrespecttoEEQ,safetyclass,andprocurementclass(CQE,etc.).  ;

Investigation revealed that two speed control loop components did have assigned equipment numbers: The Differential Pressure Transmitter is PT-1039, and the Two-Mode Nullmatic Controller is PC-1039. The Derivative Nullmatic Unit and the Fisher Positioner and Linkage Actuator were not uniquely _ identified. 1 L 'Several factors appear to have contributed to the fact that these instruments were not included in the preventative maintenance / calibration l

L programs during and after initial p'lant startup: the instruments were supplied skid mounted with FW-10; the instruments were never identified as CQE (or safety related);.the instruments were not identified on the startup instrument punch lists; and the instruments were alwa partoftheMainSteamsystem(steamsupplytoFW-10)ysconsideredtobe instead of the Auxiliary Feedwater system.

y An investigation by OPPD Design Engineering was conducted into the proper

> classification-of the components in the speed control loop on FW-10. Their conclusions are summarized below:

A) The speed loop components should be classified as seismic Class 1 and CQE and maintained as such.

B) The speed loop components are not EEQ.

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, TEXT W mese ausse a seeinst ano esammener MC #smo mW (IM An Engineering Change Notice has been )rocessed to accurately depict the configuration of the control loop in tie field. Unique identification numbers have been assigned-to the individual loop components which were not previously tagged. The CQE list, the CHAMPS data base, and the AFW design basis document have been updated.

(6)Evaluatethedesignbasisofandtheneedforthedifferentia1' pressure controller on FW-10. The results of this evaluation are summarized below.

The FW-10 speed control loop is designed to limit pump discharge pressure  :

to a setpoint,sufficiently above steam generator pressure to permit injection at the required flow rate under various o)erational and design basis event conditions. The-primary advantage of t1e existing speed 1 e control loop design is that it allows the pump to run at optimum speeds, l- sufficient to meet system head requirements while minimizing pump and valve l wear. This efficiency feature is particularly advantageous for injection l~ into a steam heatremoval)generatorwithdecayingpressureconditions(i.e.,

. The disadvantage of this control configuration islongterm tlie ';

increased complexity over the alternative considered, ,

I l The best alternative to the current design was determined to be a constant pressure control scheme, which would control pump speed to maintain a 1 L

constant discharge pressure output regardless of system total head .

requirements. The controller setpoint would have to be high enough to ensure system operation at worst case design basis event conditions. The disadvantage of this ap) roach is the resultant hi h differential ressures

, across the downstream tirottle valves under norma operating cond tions, i

? causing higher wear rates for the pump and the throttle. valves. The ,

primary dvantage of this design is its simplicity. .

l It was concluded that the present variable speed control design.is most

! appror,ciate for this application. Repairs to restore the FW-10 speed control loop to operability are expected to be complete by January 31, 1990, subject to receipt of ordered parts.

(7) Evaluate'alossofinstrumentaireventtodetermine,ifpossible,the length of time between the loss of air and the instrument air pressure dropping low enough to cause FW-10 to operate on the speed limiter.

Include an evaluation of the impact of this time delay on events involving a-demand for FW-10. The results of this evaluation are summarized below. '

In its present configuration with the instrument air supply valve shut, FW-10 is considered operable; the evaluation for this action item covered

.the period prior to June, 1989 when the speed control loop was inoserable.

A loss of instrument air pressure to below ap3roximately 20 psi, tie

, setpoint of the in-line air regulator, would lave initiated an increase in FW-10 speed to the mechanically limited maximum. However, the length of peRC pmn asea (649)

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t time for air pressure to drop below 20 psi would depend on several i

-variables, including the type of initiating event and the instrument air E

system usage rate. For events involving no breach of the instrument air .

I system and a loss of offsite power, the rate of instrument air -!

depressurization would likely be low. It is impractical to accurately determine.the interval between loss of instrument air and FW-10 reaching maximum speed for all events involving a loss of instrument a'ir. ~ Also,. the.

anticipated operator response to most events would include restarting of an air compressor, using emergency power, long before air pressure degraded to i

20 psi. For.these reasons, it can be conservatively concluded that FW-10 L would-have been unable to mitigate certain accident conditions,'since credit cannot be taken for immediate and continuing loss of instrument air pressure.

L (8)Evaluatetheas-foundconditionofFW-10foralossofmainfeedwater design basis event concurrent with failure or unavailability of FW-6. The results of this evaluation are summarized below.

A review of USAR Chapter 14 indicated that for design basis events demanding ' auxiliary feedwater flow for mitigation, the most limiting event is the small break LOCA-concurrent with a loss of offsite power and single '

failure.or unavailability of FW-6. The loss of offsite power would cause loss of main feedwater and loss of instrument air and thus bounds a loss of main feedwater event.

In this scenario, steam generator pressure-is assumed to be 1000 psia. As discussedin. Item (7)above,nocreditwastakenforfulloperabilityof

'FW-10,.since-it is assumed Operations would power an instrument air compressor to the as-found from value an of emergency approximately power 996bus, psiglimiting 1010.7(FW-10 psia). dischargeIf piping pressure frictional losses and head differential are taken into account, FW-10 would not have been able to provide auxiliary feedwater to the steam generators.

In this situation, procedure E0P-20, RCS and Core Heat iemoval Success Path HR-4 directs the operators to initiate once-through-cooling utilizing

. safety injection pumps, which ensures adequate core cooling until secondary side pressure is sufficiently redusad.

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