IR 05000461/1997018

AIT Insp Rept 50-461/97-18 on 970805-18.Violations Noted. Major Areas Inspected:Circumstances Surrounding 970805 & 970722 RHR Pump a Circuit Breaker Failures at CPS

ML20202D063
Person / Time
Site:	Clinton
Issue date:	11/24/1997
From:	Jeffrey Jacobson, Wright G NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION III)
To:
Shared Package
ML20202D037	List: IR 05000461/1997018 ML20202D032
References
50-461-97-18, NUDOCS 9712040134
Download: ML20202D063 (32)

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i U.S. NUCLEAR REGULATORY l ')MMISSION

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REGION 111 i

AUGMENTED INSPECTION TEAM

Docket No.: 50-461 '

Ucense No.: NPF 62 Repon No.: 50461/97018 Licensee: lilinois Power Company

. .. i Facility: Clinton Power Station ,

Dates: August 5-15,1997 Inspectors: G. Wright, Chief Reactor Projects Branch 4 S. Alexander, Specialinspection Branch, NRR S. Campbell, Senior Resident inspector Davis Besse, R Ill

- Z. Falevits, Senior Reactor Inspector, R Ill J. Knox, Electrical Engineering Branch, NRR T. Tella, Senior Reactor inspo " lll j" l ? m"

, emm LeaderAhief

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Rea ects Branctf 4

% ^ D YW

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J. Ja bo n, Acting Deputy Director l Divi nof escior foty i

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97120401'J4 971124 l PDR ADOCK 05000461 G PDR i

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i TABLE OF CONTENTS

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, introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . - . . . . . . . . . . . . . 4 Purpose and Scope of the inspection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

Inspection Methodoloav . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 Narrative Description of the Breaker Failure Events . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 Failure of the Reserve Auxiliary Trwnsformer (RAT) Makifeed Circuit Breaker to Division 1 Bus 1 A1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 Failure of RHR Pumo A Circuit Breaker . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 Explanation of Circuit Breaker Operation . . . . . . . . . . . . . . . . . . . . . . . . ... . . . . .,. . ,. . 7 , Closina Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 Openina operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 Eallurs_Mecharilsm . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 - RAT Main Feed and RHR Pump A Breaker Histories and Previous RHR A Breaker Failures and Root Cause Evaluations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

. History of the Failed DHP Breakers at CP3. . . . . . . . . . . . . . . . . . . . . . . . . . . 10 4. Bus 1 A1 RAT Main Feed Breaker . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 4.1.2 RHR Pumo A Breaker . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 Previous RHR Pumo A Failures and Root Cause Evaluatiori . . . . . . . . , . . . . 10 Review of CPS Maintenance on Westinghouse Breakers . . . . . . . . . . . . . . . . . . . . . . 12 Review of the PM and Testirio Procedures , , . . . . . . . . . . . . . . . . . . . . . . . . . 12 Adecuacy of Vendor Technical Geldance . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 Interviews of Maintenance and Operation Personnel . . . . . . . . . . . . . . . . . . . 14

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, Rool Cause investigation and Evaluation of the Failed Breakers . . . . . . . . . . . . . . . . 15 - j

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i Rool Cause investinadian of RAT Main food Breaker to Bus 1 A1 tw Cutler: ,

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Hammer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 5 i

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6. Inspection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

6.1.2 Vendor Finchnas . . . . . . . . . . . . . . 4 .........................16 6.1.3 AIT Findinos From Review of 't.'n'id,ase Prehminary Rang (1. . . . . 16 j

'  ; Root Cause investination and Evaluation of RHR Pumo A Breaker . . . . . . . . . 17

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6.2.1 Agget . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

6.2.2 Observation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . ..... .. . 18 s t

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6.2.3 BIT _ Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20 Summary of AIT Findinos and Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

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PJ Exit Meetina . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 3

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APPENDIX A: AIT Char 1er APPENDIX B: Persons Contacted

- APPENDIX C: Documents Reviewed  ;

APPENDIX D: Acronyms and intialisms  !

FIGURE 1: POLE UNIT ASSEMBLY  :

FIGURE 2: CONTACT ASSEMBLY ,

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Resort Details I

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, Introduse6en i Purpose and Socos of the inapection j

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The NRC has established a policy in NRC inspection Manual Chapter 0325 to provide for j the timely, thorough, and systematic inspection of sigrMcant operational events at i nuclear power plants. This includes the use of an Augmorded inspection Team (AIT) to l determine the causes, conditions and circumstances about an event, and to l

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communloale its findings, safety conooms, and recommendations to NRC managemen '

On July 22,1997, main feed citouN breaker to Bus 1 A1 failed to open. On August 5, '

1997, the circuN breaker for the RHR Pump *A* also failed to open. Two similar breaker

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failures within a short time was considered 1 sigrecard everd and therefore, the NRC (1) dispatched an AIT to Clinton Power Steilon (CP8) on August 5,1997, to review the j circumstances surrounding the circuN breaker failures and (2) issued Con #rmatory Action

, Letter (CAL) No. Rill 97-000 to the licensee. These breaker failures were of particular i conoom because they occurred within a short period and, because of the poor maintenance history at CPS, they represented a potential common mode failur ,

The AIT consisted of six NRC inspectors and included specialists from NRR and Ril I The AIT Charter (Appendix A) directed the team to conduct fact finding, to determine the ;

sequence of events associated with the breaker failures, to evaluate the performance of I

wrsonnel involved in the event, and to assess the licensee's response to the event, neluding their root cause for the failed RHR Pump A breake ;

The AIT was on she fmm August 515,1997. An entrance meeting was held with the l licensee on August 6,1997, at CPS. A public exN meeting was held at CPS on l August 20,1997. At the exN meeting, the AIT provided its conclusion that the August 5,

1997. RHR Pump A circuit breaker failure was caused by inadequate and inappropriate preventive maintenance and a failure of the corrective action program to identify, evaluate, and correct issues associated with circuit breakers (see Section 7 for details). j 1.2 - Inspection Methodolony

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Following an initial briefing by licensee personnel during the entrance meeting on

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August 6,1997, the AIT monitored the licensee's investigation into the breaker failure and independently inspected available information on the RHR Pump A breaker. The licensee contracted independent engineenng consultants and vendor representatives to help in the ,

root cause detormination. These specialists, with electrical maintenance and operations ;

personnel from CPS, comprised the licensee's Special investigation Team (SIT). The SlT was tasked to develop and implement a systematic approach to the investigation in the ,

root cause determination for the failed breake ;

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AIT members independently reviewed breaker maintenance procedures, condition reports, the Westinghouse breaker technical manual, control room logs,' and maintenance

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work requests (MWRs) associated with the breakers to determine their maintenance and operational history. The AIT interviewed members of the licensee's training, engineering, electrical maintenance, and operations departments responsible for training electrkians, i 4  ;

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performing maintenance on the breaker, and operating the breaker. A list of persons ,

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, contacted is contained in Appendix j i The AIT also reviewed records and documents conce ning the licensee's determination of !

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the event's safety signincones, root cause analyses, and intamal investigations of the j event. A list of documents reviewed is contained in Appendix !

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i Narrative N:: 'f.:.. of the Breaker Failure kvents Failure of the Reserve Auxiliary Transformer (RAT) Main Feed Croult Breaker to l Division 1 Bus 1A1 i According to the record of the licensee's event entique, operator logs, MWR remarks and :

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interviews with CP8 staff, the E"ci.g events occurred on the aftemoon of July 22, l

igg 7, after a Division 2 Emergency Diesel Generetor surveillance ru i a

Just after 1:00 p.m., CPS control room operators were transferring the power supply *for j Division 14.16-kV Bus 1 A1 from the Reserve Auxiliary Transformer (RAT) to the  :

I Emergency Reserve Auxiliary Transformer (ERAT). The operator closed the ERAT food breaker switch, which automatically paralleled across and olorad the ERAT feed breaker l to Bus 1 A1, The operator allowed the ERAT breaker control switch to retum to " AUTO,"

which should have automatically tripped open the RAT breaker. As expected, the red j * breaker-closed" position indicating light for the RAT breaker went out, but the green

" breaker open" light for the RAT breaker did not come ort Also, an expected " auto :

breaker trip" annunciator signal wm not received. These indications signified that the j j RAT breaker had failed to trip open, which was further confirmed by the operators noting I

that ammeters indicated there was load on both the RAT and ERAT powering Bus 1 A1.

i At 1:11 p.m., the RAT breaker fai;ad to open on a second attempt. At this time, the RAT

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and ERAT were both supplying power to Bus 1 A ,

i At 1:12 p.m., the licensee sent an operator to the Division 1 switchgear. The operator 4 observed smoke coming from the upper portir of the RAT main food breaker cubicie and i immediately informed the control room. The control room notified the fire brigade at 1:14 p.m. who, upon arrival in the switchgear room, reported no fire in the cubicle. The L licensee later determined that when the breaker failed to open, the designated auxiliary

! "a" contact did not de+nergize the trip coil as it would normally. The trip coil, being

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designed only for momentary energitation, had overheated and opened, terminating the '

over temperature condition which had produced the smoke. The RAT breaker again failed to open on a third attempt at about 1

15 p.m.

l Operators assessed impact on electricalloads and plant conditions with a loss of l

Bus 1 A1 and decided to de-energite the bus in order to safely deal with the RAT breake :

The operators removed the major loads from Bus 1 A1, including residual heat ~moval (RHR) Pump A (1:11 p.m.) and the reactorwater cleanup pump (1:35 p.m.). RHR ,

Pump B was placed into operation (2:07 p.m.) to maintain core cooling. The ERAT '

. breaker was then opene CPS electricians and engineers then opened the RAT breaker cubicle door and observed the blackened condition of the trip coil, indicating it had severely overheated. The trip trigger below the trip coil was not fully down and reset, indecating that the trip mechanism ,

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was unla' . ,* and the tweaker mechanical poshion indication was intermediate, i.e., ony

. partialy ope. The licensee did nM continue investigation of the RAT breaker until Bus 1 A1 was fuly & ;aeM at 5:58 p.m. by opening the 345-kV line supply breaker to l the RAT in the switchyar :

Elodriolans documented the as-found conditions of the RAT breaker on MWR D7560 Following the completion of the visualinspection of the breaker, an electrician confirmed !

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that the trip mechanism was unnatched by manually 16fting the trip trigger, with no result He then Isfled the closing trigger which initiated 1 closing operation; however, with the trip ;

mechanism unlatched, the breaker started to we then tripped free, as should occur with I

the 5teaker in hs outrerd condition. The Bus 1 A1 RAT breaker was subsequenty removed from hs oubicle for further examinatio ,

I The licensee held a critique at 6:00 a.m., on July 23,1997, to gather facts regarding the failure of Bus 1 A1 RAT main food breaker to open on demand. The critique was documented in Critique Report EM 97-015 and the breaker failure was documented in [

Condition Report (CR) 1 g7 07 222. The licensee sont the failed breaker to

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Westinghouse & Cutler-Hammer Aftermarket Produd Center in Greenwood, South '

Caroline, to investigate the cause of the failure. Representatives from CPS traveled to i Greenwood to help in the investigatio ! Failure of RHR Pumo A Circuit Breaker Division 1 RHR Pump A had been placed in the shutdown cooling (SDC) mode on August 2,1997, to maintain core cooling. On August 5,1997, at 3:5g m.m., Division 2 RHR Pump B was started and placed in the SDC mode to secure Division 1 equipment for the purposes of conducting surveillance tests. After the operators placed RHR :

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Pump B in the SDC mode, an operator in training, under the direction of control room personnel, shut the discharge valve for RHR Pump A. The trainee then attempted to stop RHR Pump A by opening the circuit breaker to the pump. When the trainee tumed the control room hand switch to open the breaker, as expected, the red * breaker closed" position indicating light for the RHR Pump A breaker went out, but the green " breaker-open* light did not come on. In addition, cordrol room indicators for pump flow and motor currerd did not fall to zero as expected. These indications meant that the pump had not .

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stopped. When the trainee rolessed the hand switch, the red " breaker-closed * light liluminated. A licensed reactor operator then attempted to stop RHR Pump A and -

experienced the same results. RHR Pump A discharge valve was immediately reopened to prevent overheating the pump (which placed both Divisions 1 and 2 in SDC mode).

The licensee estimated that RHR Pump A operated for approximatey 10 seconds with its discharge valve closed.

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At 4:13 a.m., the licensee dispatched operators, electricians and engineers to the Division 1 Switchgear (Bus 1 A1) to determine the actual breaker position and conditio '

Unlike the Bus 1 A1 RAT main feed breaker event, the personnel dispatched to Division 1 switchgear did not observe smoke from the RHR Pump A breaker cubicle. The licenses later determined that with a different control circuit, the RHR Pump A breaker's trip coit

, was de-energized upon releasing the hand switch; hence it did not severely overheat and l smok ,

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l Personnel at the switchgear noted that the red "braaker-closed" local position, indicating  ;

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light on the cubicle door, was liluminated. After the door to the breaker cubicle was .

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opened, the licensee determined that the breelwr was not fully open, but in the l

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intermedio6e position. This determination was based on the trip trigger not being reset, the mechanical ponnion indlestor showing the breaker to be partiany open, and the  !

.M a.; esr=:tI oubicie (MOC) owitch cperating lever be3ng almost horizontal i

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instead of at a 45' @ angle (normal breaker-open positi.,n) or 45' down (breaker closed l

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i position). Realial,a that a potential safety hazani existed with Bus 1 A1 still energized, the

licensee discontinued the breaker inv6stigation until the bus could be de-energize j i The licensee then developed procedures to remove electrical loads and de-energize i

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Bus 1 A1, At 7

49 a.m., with Sus 1 A1 stripped and the Division 1 diesel and RAT main feed brooker locked out, the ooidrol room operators opened Bus 1 A1 ERAT feed breaker

- to de energize Bus 1 A1. However, the RHR Pump A breaker ugervey, relay dropped out upon d: ;wJ.;..s tlw bus and boomuse the fuses for control power to the breaker

- had not been removed, the breaker's trip coil energized again. This action did not open - ,

j the breake .

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The licensee conducted a critique at 9

00 a.m., on August 5, igg 7, to gather facts on the

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L failure of the breaker to open on demand. The licensee documented the critique in

Critique Report EM g7-016 and the breaker faliure was documented in CR 197-08-04 The breaker was quarantined to preserve its as found condition until the licensee formed its SlT and the NRC dispatched the AIT.

! The AIT observed the SIT's development, execution and documentation of its ,

troubleshooting plan, which included the in situ intomal examination of the breaker with a i video boroscope. The plan included provisions for using a training breaker similar to the  !

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failed breaker for testing examination techniques prior to performance on the failed j breaker, The examination also included manipulation of the trip trigger, tripping latch and <

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trip com to verify the trip mechanism was unlatched; checks of various elechical components (e.g., tr6p coil winding resistance and breaker pole / contact resistance); and 1

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careful removal of the breaker from its cubicle. Despite extensive efforts to remove the breaker without disturt>ing its as found condition, the RHR Pump A bronker fell open while being pulled from its cubicie on August 11,1997. The SIT continued its failure analysis, which culminated in the presentation by tne SlT of its root cause evaluation on August 14, 199 .0 Explanation of Circuit Breaker Operation (See Figures 1 and 2)

'l The circuit breakers that failed at CPS were Westinghouse Type DHP,4.7-kV-rateo,

air-magnetic circuit breakers. DHP breakers of various current ratings are used in both safety-related (Divisions 1 and 2) and non-safety-related portions of the 4.16-kV electrical

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distribution system at CP . Closinn Oooration

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Each breaker has three poles or phases, "A"(left), "B"(center) and "C"(right) when facing

- the frord of the breaker. Each phase has one pair of arcing contacts and two pairs of

main contacts.. The moving contacts are mounted on moving arms (one for each of the three pole. or phases in the breaker) connected to the load side of each pole by an

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1 elocidcolly conducting hinge, The breaker's orntad operating linkages and the

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. mechanism close the main and arcing contads by releasing the energy stored in a closing spnne by a charging motor and a rechet medianism. This is s+cf:W either

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elecinceny or mar,ually. An operator can sercedoelly dose the breaker by energining the closing (apring release) ooil locally (by a hand control switch on the breaker culdde door)

or remotely (oy a hand control switch in the control room). The breaker can also be

closed electrically by automatic sigtnis such as emergency core cooling system actuation

signals or load sequencer signals for the emergency diesel generator. An operator can

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manually close the breaker by lifting a device on the front of the breaker called a closing trigger.- This is the same comfionant lifted by the closing coil (also known as a magnet or solenoirf) during electrSal operation. The breaker's closing spring is recharged by the motor immediately after each closing operation. This retchet mechanism can be

-:5+t:1 by hand, using an accessory handle to charge the closing spring, for mairderance, if the charging motor is ;r-:isC;;, or if 125 Vdc control power is not -

svallable to the breake M Openirin Ookation .

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The mair, sr4 syng contacts of the breaker are opened normally by the energy stored in

> (w r/g-(hg spr%gs (which act on the moving contact arm drive knkages) and the kickout

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spdng1 (!h et act directiv on the moving contact arms themselves). The opening energy is stored in ins spdngs by the action of the closing opwsion, i.e., some of the energy that is expended by the clow.g spring in closing the breaker goes into storing energy in the

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springs used to open the breake Similar to the closing function, the opening operation may be initiated (i.e., the breaker

' may be tripped) manually or electrically. Manual tripping is sooomplished by lifting the trip trigger on the front of the breaker by hand. This same trip trigger is lifted by the trip coil in

, electrical operation in response to local or remote hand conul switches or automatic j signals such as from protodive relays, intertocks, or load shedding functions. Ulting of <

l F the trip triggu unnatches the tripping mechanism which releases the mechenical look on

the contact operating mechanism. This allows the contacts to move with the force of the l I

opening springs (during the entire opening operation) and the kickout springs (used to disengage the main and arcing contads at the t,eginning of the opening stroke).

l failure hchanism

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! In orter to understand the August 5, igg 7, failure of RHR Pump A breaker to open it j must be realized that once the trip latch mechanism is unistched and the moving contact

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arm linkages collapse, the opening forces supplied by the springs must exceed the l

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system resistances to open the breaker, in-situ boroscopic inspedion of RHR Pump A ,

i circuit breaker identified three significant items: the moving contacts were in various '

stages of opening, the trip mechanism had unin ched with the moving arm linkages collapsort, and no foreign material was identified impeding the breaker's ability to opo ]

. Testing on the failed breaker revealed the available opening forces did not exooed the

system resistannes, causing the breaker to fail in a partially open condition, The largest i contribution to the forcea opposing opening came from the main and arcing contact Additional testing of the failed RHR Pump A bronker confirmed that the degraded l candition of the contact surfaces created excessive friction beb.een the moving and

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stationary contact surfaces. The increased friction signifloantly increased the force

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necessary to open the breaker. The contact -f+.--MF, was directly attributable to -

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inappropriate and inadequate maintenanos. Further inspection and testing of the RHR ,

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Pump A breaker revealed that the C-phase kickout spring was loose, slightly bent, and olighth short in length; signifloanty reducing the force it was able to prov6de to open the CS5ase contact t i

Otner sources of friction that resist opening in the moving contad arm operating linkages i or mechanism that had a relatively lower contribution induded the following

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• contact arm hinges,  !

- e the upper and lower contact arm operating rod pins, f

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e and the pole shaft bearings,

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with minor contnbutions by the: .

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• - main link pin, l

• the com follower roller, .

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• the main link retum spring, f

. the restraining link pins and the trip com (primarily its pivot pin).

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) in addition, during the opening sequence, the contact arm operating mechanism drives the puffer and auxiliary switch linkages which both normally retard the opening operation to a small degree. Tests and examination of the failed RHR Pump A breaker established ,

l that although some of these components may not have been property maintained (mainly

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lubrication), they did nct figure significantly as sources of the excessive friction that contributed to the failur As noted earlier, it was established through testing and examination that the RHR broeker's trip mechanism functioned property to release the breaker into the so-called

" trip free" condition. Had this not occurred, the moving contacts would not have disengaged at al ,

. ,Q909hthtG The principal mechanical (proximate) causes of the August 5, igg 7, failure of the RHR Pump A breaker to open when operated were excessive main and arcing contact friction coupled with insufficient opening force, primarty due to a degraded kickout spring on "C" phase. The possible root cause of these conditions was inadequate and inappropriate maintenance by the licensee and inadequate corrective action exacert>ated by weak _

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maintenance guidanos from the breaker manufacture i

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/ RAT Main Food and RHR Pump A Breaker Hieteries and Previous RHR A Breaker l

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. Failures and Reet Cause Evaluations

" lnacention Somos ,

j' The AIT reviewed the history of the RAT and RHR breake.s to identify conditions which j may have oordributed to the July 22 and August 5 failure j Observations and Findmos h History of the Failed DHP Breakers at CP8  ;

a l . 4.1.1 - Bus 1A1 RAT Main Feed Breaker  ;

The breaker used for the RAT main food was purchased from Westinghouse in 1977 and received at CP8 on July 10,1979. CPS commenced commercial operation on August 29,1986. The last full preventive maintenance (PM) was performed on the ,

breaker on July 20,1993 Recent major corrective maintenance on the breaker was to

clean and inspect it and rework the motor outoff switch and levering-in device (MWR D75429), begun on May 9,1997. On May 23,1997, the breaker was racked in j'

and on May 24, cycled three times as a post-maintenance functional check. Between

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June 3 and July 2,1997, the breaker was closed and opened about r,ine time i 4.1.2 RHR Pump A Breaker ,

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RHR Pump A breaker was also purchased in 1977 and roosived on site July 10,197 ;

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i The last full PM on the RHR Pump A breaker was initiated on June 21,1993, and '

completed March 27,1996. Recent major work on June 9,1997, included cleaning and

,. inspecting, and rework of the motor cutoff switch and levering-in devios (MWR D63306).

On July 26,1997, as part of the conective action for the fa';ure of the Bus 1 A1 RAT main food breaker, the licensee checked and a4usted (as required) the latch check switch

,

(MWR D75611) on this and other DHP breakers. The RHR Pump A breaker was racked i

'

out and back in for this job. Between June 12 and August 2,1997, when the RHR Pump A was started in SDC mode for the last time prior to its failure to open, the breaker was cycled open and closed about nine time .2 Previous RHR Pumo A Failures and Root Cause Evaluation

'

I The AIT reviewed MWRs for the RHR Pump A breaker from 1985 to the present. The AIT identified the following RHR Pump A breaker failures, causes, and correct:ye actions from the MWRs that were reviewed:

MWR B18432, perfonned in November 1985, attributed a failure of the breaker to close electrically during testing to binding of the linkage that operates the closing spring char 93 ng motor outoff switch due to dirt. The MWR indicated that the condition was

_

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corrected by cleaning the linkage. The AIT's review of the MWR could not conclude that r dirt alone _would cause the switch to malfunction; mechanical misalignment or faulty switch intemals (a problem with earlier vintage switches) could have been a contributing cause. It appeared (Tat either the diagnosis was not adequately described or was Incomplete. The MWW also stated that a CR was initiated to determine if this failure / root ;

l 10

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l _,_..___,_ _ ___,. _ _.._.._ _ .._ ._. _ __ _ _ _ __ _ _ _ _ __ _ _ _ _

.- _ . _ . _ - _ . _ . _ _ - . - - . - - - .

cause was a genedc problem; the licensee was unable to produce the CR. This MWR ,

, had no apparent beanng on the recent failure of RHR Pump A breaske MWR C24360 (Jub/1988) concemed a broken infomal ceramic piece on the Phase C arc dute. The MWR indicated that the probable criuse for the broken arc dute was a material defect. This material defect had no relation to the failure of ta RHR Pump A breake MWR D01719 (June 1989) concemed problems with a bent piece of sheet metal near the

' secondary contact block lever" (more correctly called the secondary " disconnect" block lever). The MWR also discussed a problem with a primary disconnect finger cluste None of the problems had any apparent bearing on the RHR Pump A failur MWR D04500 (August 1990) stated that the breaker tripped after closure was attempted from the main control room during swveillance of RHR Pump A. The MWR noted a similar failure of the breaker to clot,e two days eariier which had been corrected by cycling the breaker in and out of the cubicle. The MWR determined the cause of the failure to be a misadjustment of the latch check switch centact in the closing circuit. The failu'reWas thought to have been corrected by adjusting the latch check switch, but the failure recurred. The MWR also noted trouble racking the breaker back into the cubicle. It was determined to be caused by a loose racking mechanism. The racking mechanism was tightened to correct the proble The AIT questioned the diagnosis of the failure to close, which attributed the breaker's tripping open upon closing to latch check switch adjustment. The MWR indicated that a closing operation was initieted and that the breaker tripped free. The latch check switch is a permissive for energizing the closing coil. It is supposed to be closed only when the trip trigger is almost fully reset, thus, ensuring that the closing coil cannot be energized if the tripping mechanism is not latched, otherwise the breaker would trip free on attempting to close. However, if the latch check switch was .nisadjusted such that it was open, a closing operation never would have been initiated. If the latch check switch was misadjusted such that it was closed, even with the trip trigger not reset, it might have allowed a closing operation to be initiated when it should not have, but it would be the trip ,

trigger not being reset that caused the trip, not the latch check switch. Therefore, the AIT noted (and the licensee agreed in later discussions) that the MWR diagnosis was incomplete and that there was another reason, e.g., sticking or misadjustment of the trip trigger or tripping latch, that actually caused the breaker to go trip free on closing. This MWR had no apparent bearing on the recent brmker failur MWR D03344, performed in June 1993, noted questionable operation of truck-operated cubicle (TOC) switch. There was also information indicat!ng unsatisfactory condition of a refurbished replacement breaker, but nothing with a direct bearing to the August 5 failur Conclusions The AIT was not able to definitively conclude that the problem described in the above MWRs did not bear on the RHR Pump A breaker's failure to open. While the documentation suggests no connection, after reviewing the MWRs and subsequent discussions with the licensee, the AIT concluded that the actual causes for specific equipment failures were not always correctly established and completely or accurately

. _ __ __ _ _ _ _ ,_. ~ _ _ . - - _ . _ _

- _ _ _. _. .._ _. _ _ _ . _ . _ _ _ _ _ __ _ __._ _._ _ _ _ _ ._ _ _ _ .... _ . _ . _ _ _ .- _ _

documented in MWRs. The AIT also noted a great deal of variabikty (and some

, inaccuracy) in the terminology used to desenbe breaker ei-,,A and components. This ,

!

information raises questiuns regarding the effectiveness of training for individuals who work on breakers. As discussed in NRC Inspection Report No. 50461/97003, a - '

formallred proceso for estabilshing root cause, generic imphomeon, and conhnued operabinty of equipment had not been effectively establishe ;

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Bn 1 A1 RAT main feed breaker MWRs were not reviewed boomuse the AIT was unable to compare root causes for past failures with the recent July 22,19g7, failure because the 4 licensee had not determined a root cause for the July 22,19g7, failur ,

t I Review of CPS Maintoaanos en Westinghouse Breakers Inao6ction Scope j

!

The AIT reviewed the piovenHve maintenance procedural guidance, vendor

,

recommendations, and preventive maintenance performance on the RAT and RHR * ' '

breakers to identify problems which could have caused the breaker failures.

! Observations and Findinas l Reyjgw of the PM and Testina Procedures The AIT reviewed recent PMs for the RAT Main Feed breaker to Bus 1 A1 and RHR Pump A breaker. These PMs were conducted under Tasks PEMRHA002 (the RAT main feed breaker), dated July 20,19g3, and PEMRHA501 (RHR Pump A breaker), dated March 22,1996, using Procedure 6410.01, " Westinghouse DHP 6900 V,4160 kV V Power Circuit Breaker," Revisions 15 (for the 1 A1 Main Feed breaker) and 16 (for RHR l

Pump A breaker). The following preventive maintenance was performed under these procedures:

• Breaker Cubicle inspecuon

. Circuit Breaker inspection

. Con'act inspection and Adjustment

• Tapping Latch clearance Adjustment

- Holding Pawl Adjustment

.

. Lubdcation

. Testing ,

,

• Breaker Restoration Less than a year after the PM on the RHR Pump A breaker was comp ete, the'NRC conducted an Engineering and Yechnical Support and Startup Readiness inspection from January 6 through March 7,19g7. The findings from this inspection were documented in

,

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. . . . . . . . . . . . , - . - _ - . - --

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- -- . . -- - . . -.-.. - .-. - - . - .. . - - - . _ . . . _ . - _ .- . - . - - - - . . - . -

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I inspection Report No. 50461/g7003 issued May 5,1997. The report oorduded that the ,l

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licensee had failed to identify, trend, address and correct reoumng problems related to l 480 V,4.16-kV, and 6.g-kV oircuit breakers. These problems resulted from 17 years of  ;

ir-- C breaker maintenance, which included use of unapproved lubricants and  ;

unappro ved solvents that caused grease hardening. The hardened grease resulted in . j

.

binding of various breaker components and =haaP=d breaker failures. The inspeedon ,

i report also noted inadequate procedures and/or failure to follow procedures conV! outed to  :

breaker material condition deflaiencie ,

t in response to inspection Report No. 60-461/g7003 findings, the licensee ded-g+j an l Inspection and testing plan on April 23, igg 7, to inspect, partially clean, and conduct j

-

reduced control voitage opening and closing timing testing on selected Westinghouse and General Electric breakats. Specine to Westinghouse breakws, the plan Goded for .

Industry rotated problems (e.g., cracked levering-in devices and motor outen' switch failures) and to assess the ut e of unapproved lubricants and degraded lubricants. The ,

licenses wrote MWRs D7542g (the RAT main feed breaker) and D63306 (RHR Pump A  !

' breaker) to perform the CPS inspection plan for inspecting, cleaning and re-lubriceting * **

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only the sooessible areas in the breakers. The AIT reviewed these MWRs and determined this work was not a full breaker PM. The MWRs used portions of Revision 17

to Procedure CPS 8410.01 to perform limited cleaning of Division 1 breakers only. The program was completed for the RHR and RAT breakers on May 5 and g, igg 7,

~

respectively. The inspection plan was limited in scope in that the licensee decided not to ,

'

clean and inspect Division 2 breakers. CPS thought that a reduced control voltage test of Division 2 breakers was adequate to prove functionality rather than performing additional breaker maintenance. The AIT noted the inspection program was not based on a i comprehensive review of recommended maintenance and industry experience against

, CPS' current PM program requiremord The AIT reviewed Tasks PEMRHA002 and PEMRHA501 whis conducted the last full PM i on RHR and RAT bronkers and MWRs D7542g and D63306 that cleaned the breaker The AIT then compared these tasks, MWRs and Revisions 15,16 and 17 of Procedure CPS 8410.01 with the Westinghouse technical mhnual, Instruction

,

Book (IB) 32 253-48, instmetions for Porcel-line Type DHP Magnetic Air Circuit i Breakers," to assess consistency with the vendor manual. Although, the licensee used an earlier version of the vendor manual, IB 32-253 4A, which had been outdated since ig8g, the different manual revisions (4A and 48) provided similar instructions regarding ,

lubrication. The AIT assessment of the vendor's manual is documented in Section below.- The AIT identified that these work documents generally included most of the vendor's rece.T.,Ter '%s. There were however exceptions, most notably CPS' PM procedure CPS 8410.01 did not include the vendor recommendation for lubricating the main and arcing contact surfaces (Point 4 of Figure 2).

The vendor's manual stated that lubrication of the contact surfaces (Po;nt 4 of Figure 2)

at normal maintenance intervals would be beneficial. However, the licensee Ov&;',ooked this recommendation while developing their breaker rnaintenance p;ocedures, e Compoundbg the omission was the fact that previous CPS rni.ntenance practices of using flies, plastic scouring pads, and unapproved solvents on the main contacts may

~ have removed lubricant applied at the factory. Lubrication of the upper and lower contact operating rod pins (Points 1 and 2 of Figure 2) was not mentioned in the vendor's manual or CPS' maintenance procedures, The vendor manual stated that lubrication of the l

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,w__,,~-wl__-,.....m.y,_,..,_._.-. . mm ,-.m- - , . . . . .v __,v.....,-.4_m..-_ -, _,_, . . . . ~ . , m- ._ _ _ _ _ _ __ _ _ _ _ _ _ __ _ _ _ _

_ __ _ _ . _ . _ _ _ _ _ _ _ _ _ _ . _ . _ _ _ . . _ _ _ _ _ _ _ _ _ _ . . . . _ _ _ .

'

s

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moving hinge conted point (Poird 3 of Figure 2) was unnecessary unless the contads

, were replaced sna that lubrication of the pWe shaft roller bearings (Point 5 of F4 pure 2)

should not twrmally be required because these bearings were packed at the factory with ;

a " top grade slow oxidizing grosse that should last for many years." The manual further ,

stated these beenngs should remain undisturted unless the besskar exhibited .

, sluggishness or evidence of dirt existed. The vendor's manual also recommended that ,

the roller bearings should be cleaned and relubricated if the parts were dismantled fo ;

. some reason. Although the vendor manual described routine lubrice%n points, its use of I wording such as "beneficW" and "for many years" did not emphasize or ascribe l appropriate level of importance to these action Besides lutwication of these areas, the maintenance procedures did not include a measutomord of force and length of the opening, compression and kickout springs for

. degradetion and kickou', spring alignmord. As mentioned above (in Section 3.0), these springs provide the forces needed to open the breaker. 'ihe vendor manual excluded a check of the springs, therefore, CPS did not include it in their procedure ;

• Adeauncy of Vendor Technical Guidance

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The team concluded that the vendor technical guidance and recommendations were not sufficiently thorough or clear in a number of areas. The latest revision of the technical ;

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manual (Revision 48), effective in 198g, cordained most of the same deficiencies as Revision 4A. Westinghouse had not incorporated into revision 4B, technical guidata.

- from a Westinghouse letter to CPS in January 1987, which described a method that d6ffered from the technical manual on how the trip latch and trip cam adjusting screw were to be adjusted. In addition to various technical errors in diagrams and text, porticularly in the area of lubricction, the vendor's manual omiited several points that

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, should have been lubricated (some with light machine oil, some with Molykote BR2).

'

Further, the manuel was weak in Hs recommended lubrication of sliding electrical parts, i

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most notably the main and aruing contacts with graphite grease. While the manual did  ;

require complete inspection, lubrication, cleaning, and adjustment at a minimum of every three years, it did not exphcitly call for compMe breaker refurbishmen ,

!- Interviews of Maintenance and Operation Personnel i

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To determine if operating and/or maintenance activities contnbuted to the two breaker failures, the AIT interviewed individuals responsible for operating and maintaining the ;

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RAT main feed and RHR Pump A breakers. The SIT and the AIT interviewod the-individual who last operated the RHR Pump A breaker. During the interview, tlw. operator

"

described how he racked-in the breaker before placing RHR Pump A in service on Au0ust 2,19g7. From his description, the AIT and the SlT determined that the 1,reaker was rocked-in property and this activity did not contribute to the breaker failure.

Electricians interviewed by the AIT indicated they did not lubricate Points 1,2, 3,4, and 5 '

of Figure 2. The electricians stated that during routine breaker maintenance they had used plastic scouting pads and files to dress the contacts as necessary (i.e., when pits or -

burrs were found). The electricians also indicated that the main contacts were not

lubricated with conductive grease following maintenance. Further, the electricians stated .

'

that while they had not recently used unapproved solvents, such as Freon, on the breaker main contacts, unapproved solvents had been used on these areas in the past, i

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.. - . ._ - _- - - -. . Conclusion

' The AIT concluded the vendors manual was weak and did not, in all cases, provide apNopriate guidance for proper maintenance of the breakers and did not effectively assist the licensw in developing comprehensive effective preventive maintenance procedures. Even though the vendor manual was weak, the AIT considered it sufficient (if used in e mjunction with other indsstry material and maintenance practices) for the licensee b t sve established a good PM program. However, CPS had not critically evaluated tne vendor manual in developing its PM procedures and failed to include steps to inspect and lubricate Points 1,2,3, and 4 shown on Figure 2. These omissions were compounded by previous maintenance practices e.g., .)g unapproved solvents and abrasives, which had the effect of eliminating the original lubrication on the main contacts. Also, these PMs failed to verify opening at. A kickout springs for degradation plus a check of the Idckout springs for proper all;nment. Even after deficiencies were identified durire the conduct of Inspection Repor1 No. 50 461/97003, CPS was not proactive in assessing and revising the PM procedures or in developing a special inspection procerJure. This lack of action resulted in missing several opportunit es to c arect the material condition of the breakers. The AIT believes that the breaker'falfures wvuld have been prevented had more comprehensive procedures been developed to perform acceptable PMs. Root Cause investication and Evaluation of the Failed Breakers Insoection Scope The AIT reviewed the licensee's root cause evaluations for the RAT and RHR breakus to assess completeness and accuracy of the evaluation Observations and Findinas , Root Cause Investiaation of RAT Main Feed Breaker to Bus 1 A1 by Cutler-Hammer 6. Inspection The AIT reviewed the July 28,1997, letter to IP from Westinghouse Nuclear Services Division, Repair and Replacement Services. The letter reported the preliminary findings from the exsmination and testing of the CPS RAT breaker inspected at the Westinghouse Cutler-Hammar, Gree:Twood, Sou'h Carolina, manufacturing plant on July 25,19g7. The letter stated that the Greenwood facility performed the failure analysis on the DHP breaker, Shop Cicer No. 01YN005B4, Serial No. 2, according to the instructions in IP Purchase Orc'er No. 705276. The letter stated that the failure analysis steps to be performed, rer the purchase order, were approved b'y representatives of both IP and Cutler-Hamme ._ __

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6.1.2 Vendor Findinas

• Aeee A,ii to the letter, the Greenwood facety petformed the following investigations:

(1) The facility did a visual inspection upon receipt and noted only that the opening

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coil had apparently failed as evidonood by its blockened discoloration and that the coil was ope (2) The facety cycled the breaker without failure and reported that it operated freely and conceded this was ' evidence of good preventive maintenance.'

.

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(3) The foollity checked the main contacts for wear, alignment, synchronization and penetration and found these parameters were good although the main contads,  ;

had wider gaps than ' outlined" in Westinghouse vendor manual 1.B. 32 253-4 l The wider gap would reduce cordact frictio )

(4) The facility replaced the open-coil tripping solenoid and the discolored closirg coil.

, (5) The facility electrically operated the breaker at minimum, nominal, and maximum l

! control voltage and found the results satisfactor i (6) - Timing was checked using the interval method and the facility found the opening intervallonger than norma ;

j (7) The facility replaced the opening and kickout springs.

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(8) Timing tests were performed after spring replacement and after puffer and hinge  !

bolt were adjusted  ;

(g) The facility dismantled the breaker and inspected individual parts. They found pole shaft bearings in good condition, but some drying lubricant was found,

'

notably on parts not specified in the Westinghouse vendor's msnual to be lubricate The letter concluded that *Part replacement and mechanism tear down did not provide j evidence that would identify a particular cause for the in service failure." Cutler-Hammer found no evidence of a mechanical deficiency, a generic problem with the breaker or the existing preventive mair.tenance program. The report, stated that no cause of failure had i been determined, however, mechanism parts would be measured to determine if replacemei.t would be recommende f'. 3 AIT Findinas From Review of Westinnhouse Preliminary Report  ;

._

Based on a review of the preliminary letter and discussion with the SIT, the AIT identified the following:

(1)_ The breaker was received by the Cutler-Hammer (facility) in a condition where the as-found condition was altered or lost through removing the breaker from its

>

_ _ _ _ _ _ _ _ _ ;_ _ _ ,a

-. . - - -- .- . - - - - - . - - . . . , . . - - - . - . - . _ . - . . - . . . - - - . - . - -

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- cubicle and repetitive cyclitig of the breaker on site. Had the as-found condition .

"

, ,

been presers A, it might have facelstated an accurate or conclusive identification of ;

-

,

the cause(s) of the breaker's failur (2) The facility did nct appear to recognize the delicate force balance (opening spring i forces versus resistive forces) nature of the breaker dynamics and were looking

'

for a mora noticeable failure. They therefore drew no inference from subtle

anomalies (or twoopnized the potential for a cumulative effect or synergism) such

! as the contact condition, puffer a4ustment, dried lubricant, or slower than a ,

minimum required opening interval, etc.

i

.. (3) The facility measured opening and closing latervals, as opposed to the design

'

parameters, as stated in the vendor's manual, of moving contact erm speed on

closing and 17-rNilisecond contact separation on opening. The opening interval was found long, but the facility did not recognize this as an indicator of the

!

degraded condition, i.e., potential excessive opening resistance.

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(4) The facility replaced the openl1; and kickout springs, but did not measure the as-found free isngth and spring constard and the as-found adjustment of kickout

, springs that a3ects compression, j (5) The facility performed timing tests after spring replacement and after puffer and

hinge bolt a4ustments but did not make direct force measurement ;

i (6) No special significance was attributed to the rough condition of the main contact ,

i Through interviews with the individual who accompanied the breaker to ths '

Cutler-Hammer facility the AIT leamed that the main contacts were in a similar  ;

condition to those of the bioaker for RHR Pump i

. l

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, Root Cause investination and Evaluation of RHR Pumo A Breaker

!

6. Scope l i '

To evaluate the licensee's plans, plan implementation, the root cause evaluation, and

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proposed corrective action, the AIT reviewed the following documents: j

* licensee's written troubleshooting plan and failure analysis documents, ]

. the chart of possible causes, j

. the associated mair.tenance work requests and test procedures, breaker maintenance Procedere, CPS 8410.01, Revisions 14,17, and 18, and the

'

a i

associated Checklist, CPS 8410.01C001, Revision 14, j

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. - a summary of the maintenance history of the failed RHR Pump A breaker and l selected MWRs in detail, j

• the CPS-approved and in use editions of the Westinghouse DHP technical l 7 manual, l.B. 32-253-4A, dated Septemtar 1978,

17

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_ _ . _ . . _ -__ . . ~ .- . ._, _ _ _ . - _ _ _ , _ _____ _ _

i ._ _ .. - -.. .- - - - -.

l

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• Westinghouse's January 21,1987 letter to CPS modifying the procedure for ,

,

checking the trip latch rolier-to-trip trigger cisaranco, e and the current edition of the breaksr vendor technical manual, l.B. 32 253-4B, dated January 1989 (which had not incorporate j the new trip istch roller

,

adjustment guidance in the 1987 Westinghouse letter).

The AIT attended several meetings conducted by the SIT, operations briefings, and licensee management briefings. The SIT simulated their proposed inspechon activities using a DHP breaker of a model similar to, but older design then, the failed RHR Pump A breaker. These simulations wers observed by the AIT. The training breaker and a similar (non-safety-related) breaker in the plant with a slightly larger current rat 2ng were examined by AIT members for comparison with the failed RHR Pump A breaker. The AIT observed the examination end testing of the failed RHR Pump A breaker in the plant, and hterviewed SIT members and personnelinvolved with troubleshooting activities of tne RHR Pump A breaker. The failed RHR Pump A breaker was examined by AIT members after the completion of the licensee's initial troubleshooting, including manual slow closing (without latching) and manipulation of the moving contact arms. Finally, the AIT rev!;wed the licensee's root cause evaluation prepared by its principal contractor in this effor Subsequent to the onsite ponion of the inspection, tne AIT reviewed several revisions of the licensee's proposed procedure for full examination and testing of the failed RHR Pump A breaker and released the quarantine on the breaker at appropriate points. The AIT also reviewed the proposed procedure for interim condition assessment and restoration of the remaining safety related DHP breaker . Observation

' Troubleshootina Plan and Analyses The licensee intended the troubleshooting plan to be comprehensive. The plan was developed to rule out non-contributing factors and to try to preserve the as-found

,

condition of the failed breaker. Possible non-contributing factors included mechanical binding of the breaker intomals (interference in the tripping mechanisms, debris / interference obstructing the main moving contact blades) and electrical component l

anomalies (electrical shorts, high resistances, tripping cnit failures) on the breaker circuitry. However, as these possibilities were eliminated, the plan appeared to concentrate on assessing friction factors including:

a main and arcing contacts, a moving contact arm hinge pins,

• and upper and lower main contact operating rod pins and did not initially consider others. The decision to not evaluate these items was based on the conditions of the corresponding components in the RAT main feed breaker for Bus 1 A1 that had failed in July 1997, including:

i T ~ -w --

.ye., ,

-- .. - .-. . -- .. . _ _ - - - - . . - . . _ - . - _ ~ - - - - - .

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)

i ' pole shaft bearings,'

,

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• main link pin and com follower roller, _ 'k

. and restraining link pin The plan also initially failed to account for the possibility that the components supplying j the noening fortas could have contributed to the failure. Specifically, the plan did not ,

investyste whether the kickout and opening springs physical proportees e.g., spring >

!

constant and free length, were consistent with design values. Existing conditions could be different from those specified by the manufacturer, thus providing less than the design value of opening force.

.

- 2.- Implementation / Execution of the Plan Before removing the breaker from the switchgear cubicle, the SIT developed a plan to perform a boroscopic examination of the breaker intemals to check for mechanical

• ' '

interference. After reviewing the plan, the AIT released the quarantine for the

' examination. The boroscopic inspection did rnt ihntify any mechanical interference

inside the breaker. The examination revealed that Phase A moving main contacts were disengaged from the stationary main contacts, but Phase A moving arcing contact was j just touching its stationary on one side Phase B main and arcing contacts were slightly

.

engaged with minimal penetration. The main and arcing contacts for Phase C had the most engagement and penetration of the three phases, it appeared that the P'h ase C l contacts were holding the breaker in the intermediate position. Fole resistanos readings confirmed the observed contact positions. Phase A had the highest resistance of about

- 1100 micro-ohms, Phase B had a reading between 900 and 1000 micro-ohms and Phase C had the lowest reading of approximately 800 mic,wohms. The presence of a resistance reading on Phase A confirmed that Phase A arcing contact canied the Phase A load current of RHR Pump A motor after the breaker failed to fully open. Chart recorder printouts and interviews with operators on shift on August 5,1997, confirmed no observed change, in pump motor current or pump flow. Loss of one phase would have

noticeably affected pump flow and pump motor current reading . AIT Observations of Plan imo'ementation

Wdh few exceptions, the SlT carefully canied out the plan. In one instance, the technician performing a detailed procedural step, first per*ormed the step out of

. sequence. The technician tried to depress the tripping latch before first raising the trip

,

trigger per procedure, he was unable to do so (as expected) and initially misinterpreted this result as a stuck tripping latch. An AIT member closely observing this phase of troubleshooting questioned the sequence of events. When the proper test sequence, i.e.,

holding the trip trigger in the trip position (necessary, but not specified in the procedure)

was directed by the supervisor (system engineer), the technician was able to depress the

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trip latch roller. He acsnT5 4shed this without the breaker opening, thus confirming that

,

the opening operation of the contacts was not being hindered by any binding of the tripping latch on the top of the trip ca ~

The AIT also observed that the SIT had not adequately prepared for some planned

- evolutions. For example, the digital low-resistance ohmmeter, used for the individual pole 19-

.

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. , ,y -,m, , , , ,- .-

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,

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resistance tests, apparently had not boon functionally checked beforehand. As a result,

after several unsuccessful attempts to measure pole resistance on Phases A and B, .

which initially indicated open, the digital low-resistance ohmmeter fuses were found blown. Also, it was not initially realized that the grourdng jumpers, installed for an added measure of personnel safety, would have to be removed during the pole resistance test )

' Removal of these straps would separate the phases :!:M:"; and avoid erroneously 1 measuring parallel resistances.- In addition, the SIT experienced difficulty setting up the l video equipment to record and display the boroscope video examinatio j

<

6.2.3 SLT_ conclusion j On August 14,1997, the SIT presented the root cause for RHR Pump A breaker failure to j

open on demand to IP management and the AIT members. The SIT concluded that the breaker failed to trip open because the available spria,g force (F for opening was not l r

sufficient to overcome the sum o (E) the resistive forces ( i The spnng forces necessary to open the breaker included the kickout, opening, and .

i perhaps a small contribution from the buffer springs (although this was not initialif + '

considered at all by the SIT). The frictional forces considered by the SlT were the upper and lower pole operating rod pins, the moving contact arm hinge, and the moveable and stationary main and arcing contacts (Points 1,2,3, and 4 of Figure 2) respectivel The as-found lubrication at Points 1 and 2 was gummy, indicating an unacceptabic lubricant, and containing bright natal chips from metallic wear. Acceptable lubricant was found on Point 3. The SIT found mechanical wear on the main contacts, Point 4. The SIT concluded that larger open'ng forces (FW to open the breaker were necessary to

o_vercome increased frictional forces created by the mechanical wear on the contacts.

,

Finally, the SlT found the stationary contacts misaligned, indicating that the moving ,

contacts riid not squarely strike and enter the stationary contacts. The SIT concluded that misalignment of stationary contacts was a contributing factor in the mechanical l - binding of the contacts in the failed breaker opening. The SIT stated its position that the required spring force to account for misalignment may not have been considered in the breaker desig l The AIT noted that failing to property adjust the contacts would cause the misalignmen The AIT found, after reviewing maintenance procedures, that appropriate instructions were included to perform this adjustment and concluded that the licensee had not property adjusted these contacts during previous PM The SIT attributed the failure also to the following contributing causes:

. The vendor either did not specify or vaguely specified in its manual the lubrication requirements of Points 1,2,3 and *

The vendor did not include sufficient spring force to overcome EFm in the I breaker desig ,

.- CPS staff contributed to the breaker failure because of a history of unacceptable i breaker maintenance practices. These practices included the use of unapproved 1 i 1 20 {

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P solvents on the main contacts, which removed the lubncani appised at the factory

^

_ (and not replacing it) and not adequately controlling lubricants used on the ,

breaker ,

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. CPS failed to track, trend and investigate breaker failures to address the problem

,

adequate $ Conclusion

-

The licensee's failure analysis of the RAT main food to Bus 1 A1 breaker was inadequat As-found conditions immediately after the failure were not preserved and, as far as .

reported in the proleminary report, insufficient measurements and measurements of limited effectiveness had, up.to that time, been employed at Cutler-Hammer. This

-- -ix ed to be due to a failure to recognize the subtleties of the cumulative effects of minor degradations that may not be individually significan '

The licensee's failure analysis of the RHR Pump A breaker fa.iure was significantly improved over the analysis for the RAT breaker. The RHR breaker failure analysit w'as based on a systematic approach and _was designed to maintain as-found conditions and to identify as much information as possible before moving the breaker. This approach provided valuable information on determining the root cause of the failure. While AIT involvement was necessary to ensure a thorough evaluation, the licensee's SIT development and implementation of the investigation program was successful in identifying the root cause of the failur ! Summary of AIT Findines and Conclusions Adeauacy of the Proposed Failed Breaker Examination and Testina ProcUgg The procedure for initial breaker examination and testing was adequate. However, later phases were not as comprehensive and required prompting by the AIT to cover all the sources of potential problems in the breaker including some sources of friction and the opening force potential weaknesse Conclusions The AIT reviewed the history of the RHR Pump A breaker, the history of breaker-maintenance in general, the licensee's response to NRC Inspection Report No. 50461/97003, the licensee's response to the July 22,1997, breaker failure, and the

'

licensee response to the August 5,1997, failure. Based on these reviews the AIT concluded the August 5,1997, breaker failure was caused by: . Inadequate and inappropriate maintenance activities; i failure to adequately assess the findings in NRC Inspection Report No. 50-461/97003; inadequate comPctive action for the findings in inspection Report No. 50-461/97003; J

.

p g- 9cemt-+vvv 9 m- ge-y 9r9 9 rw----yy-,et**rg-ge--- r T-ev 1r imy- y py%+ -

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- - - .- -. ,-- . - . _ . - - . . - - . - . - . _ . - . - - . . - . _- - .

- failure to perform an adequate root cause evaluaGon and implement effective '

,

corrective action for the July 22,19g7, breaker failur in addition, the AIT concluded that the failure to propedy mairdain the safety related l olectrical circuit breakers introduced a common mode failure into at least all 4.16-kV Westinghouse electrical circuit breakers at CP .

Mamtenance on breakers over their life has not been consistent with vendor recommendations (see NRC Inspection Report No. 50-461/97003) for frequency or scope '

of preventive maintenance. In this case, the most significant item was failure to M+C; maintain and lubricate the main and arcing contacts (both movmg and stauonary). Further, there has been a history at CPS of using unapproved cleaning agents which could have led to the removal or contamination of existing lubricat!on, inspection Report No. 50-461/g7003 identified a number of items associated with breaker maintenance and corrective actions for past breaker failures. CPS' assessment of that inspection report did not effectively address the scope of the potential problems and therefore did not identify and implement offective corrective actions. Specifically, CPS faiPA to iderdify that the main and arcing contacts were not being lubricated and, Gerefore, did not include a specific check for contact condition in their short term corrective action CPS' response to the July 22,19g7, breaker failure did not appropriately integrate the failure and historical problems with bmakers into a comprehensive investigation plan.

The breaker's as-found condition was not preserved and the breaker was cycled several times prior to sending it to the vendor for additional inspection. Even though the breaker

, was sent to the vendor, the scope of work authorized by CPS did not provide a comprehensive assessment of the breaker. CPS' and the vendor's lack of understanding l

of the breakers operation also contributed to the poor evaluation of the failure. For example, the condition of the main and arcing contacts was observed; however, no i significance was placed on their condition.

The AIT also evaluated CPS' investigation into the August 5,1997, breaker failure and concluded that overall the methodology was a significant improvement over that used for L the July 22,1997, breaker failure. The licensee took prudent action in quarantining RHR j Pump A breaker to preserve the as found condition of the breaker following its failure.

t Contracted engineering consultants and industry experts comprising the SIT provided guidance to the licensee to inspect the breaker methodically and determine a possible root caus The SIT determined that the primary cause for the breaker failure was that available opening forces were insufficient to overcome the system's resistances. At this point however, the SIT appeared to focus on the system resistances associated with the main

contact blades and did not initially consider all potential sources of system resistance, e.g., the potential contribution from pole shaft bearing. Further, the SIT did not consider

, the opening forces during their initial' investigation. Specifically, the SIT did not initially

.

consider the kick-out and opening springs as being potential contributors to the failure.

'

AIT discussions with the SlT regarding these issues resulted in a more complete evaluation being conducte . .-. - . _- _ - - _ . . - . - _ - .

_ . ._ _ __ _ _ _ _ _ _ _ _ _ . _ . _ _ _ _ _ ____ .____ __ _

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The SIT's final determination, that lack of appropnate maintenance of the main and arcing

, contacts combined with a short and bent kid 9 t spring were the causes of the August 5, 1997, RHR Pump A breaker failure was consluient with the AIT's independent evaluation, , Exit Meetina The AIT met with licensee representatives (denoted below) during a public exit meeting on August 20,1997. During this meeting, the AIT discussed the purpose of the inspection, the inspection methodology, and presented the team's findings and conclusions. The team also discussed the likely informational content of the inspection

'

report regarding documents or processes reviewed by the team during their inspection activities. No prioprietary information was identife ,

Personnel Participatina in the ExR Meetina

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IP Company

J. Cook, Senior Vice President .

W. Romberg, Assistant Vice President

P. Yocum, Plant Manager, CPS R. Phares, Manager, Nuclear and Performance improvement '

,

D. Thompson, Manager, Nuclear Station Engineering Department

,- M. Stickney, Supervisor, Regulatory interface 4 U.S. Nuclear Reaulatory Commission A. Beach, Regional Administrator, Rill

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J. Caldwell, Deputy Regional Administrator, Rill

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G. Grant, Director, Director, Division of Reactor Projects, Region lli G. Wright, AIT Leader and Acting Chief, Reactor Projects Branch 4, Region 111

'

T. Pruett, Senior Resident inspector, CPS

. K Stoodter, Resident inspector, CPS S. Campbell, AIT Member and Senior Resident inspector, Davis-Besse Plant i Z. Falevits, AIT Member and Senior Reactor Engineer, Region lli

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l 23 i

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I%f NUCLEAR REGULATORY COMMISSION APPENDIX A'

f  ?> . . REGION ih .

,, ~ti fj~

801 WARRENVILLE ROAD '

1. USLE, ILUNOls 60532-4351

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• • • • • -

August 8. 199 . MEMORANDUM FOR: ' Geoffrey C. V 'right, Team Leader, Augmented Inspection l Team (AIT), Clinton Power Station ,

'FROMi ' A. Bill Beach, Regional Administrator, Rlli .

. SUBJECT: CLINTON AIT CHARTER - REVISION 1

. This revision is being issued to clarify aspects of the Charte On August 5,1S97, a 4.16kV Westinghouse circuit breaker failed to open on demand while the licensee was shifting from the 'A' RHR pump to the 'B' RHR pump. This breaker failure, when viewed with previous repetitive Westinghouse circuit breaker failures and the licensee's failure to clearly identify breaker malfunction root cause(s), raises concerns ,

regarding the operability of vital safety-related components. Current analyses of past failures indicates that one potential causal factor involves generic implications for proper

- breaker operation.~ Based on discussions with the Offices of Nuclear Reactor Regulation

. (NRR) and Analysis and Evaluation of Operationa. Data (AEOD) regarding repetitive breaker i ( .e

'

f ailures, Region 111 has decided, with NRR concurrence, to conduct an AIT in accordance with Msnagement Directive (MD) 8.3. Part i of MD 8.3 states that on AIT may result from events involving repetitive failures affecting safety related equipment and involving potential adverse generic implications, i-

'

Attached for your implementation is an AIT Char'er for the inspection of the circumstances associated wii'i the breaker failure. The objectives of the team are to identify and communicate the facts surrounding the breaker failure as well as any generic issues, and to document the findings and conclusions of the onsite inspection. The inspection should begin on August 6,1997, and be completed within approximately one week. The report

- should be ready for regional management's signature within approximately two weeks

from'the end of the inspectio Please contact me if you have any questions regarding these objectives or the enclosed

,

Charter.

W Attachment: AIT Charter

See Attached Distributioni

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q l A-1

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G. C.- Wright - 2 ' August 8.-1997 L,y . .

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Distribution:

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cc w/attachtnent: l G. M. Tracy, EDO

-

-J. E. Rosenthals AEO +

D. F. Ross,~ AEOD -

i G. E. Grant, Rill J. A. Grobe,' Rill '

s K. E. Perkins, RIV

- S. J. Collins, NRR -

A. E. Chaffee, NRR G. H. Marcus, NRR -

'J. B. Hopkins, NRR '

S. A. Richards, NRR

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' 4

- J.' A. Calvo, NRR -

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AUGMENTED INSPECTION TEAM (AIT) CHARTER j

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AIT formation, per MD 8.3, was based on the staff's need to fully understand the cause consequences and generic implications of repetitive _ Westinghouse 4.16kV breaker failures

- involving various safety-related system The Augmented inspection Team (AIT) is to perform an inspection to accomplish the following:

1.- Establish a chronology of events associated with the breaker failure incidding initiating activities, identification of the problem, and subsequent equipment -

troubleshooting and testin . . . Review previous Westinghouse 4.16kV breaker failures analyre factual information-and evidence related to the failures, and evaluate the licensee's actions in identifying root cause *

. . . Evaluate the adequacy of the licensee's Westinghouse 4.16kV breaker Preventive Maintenance (PM) Program including past PM's performed on such breakers and identify any aspects of breaker PM that could contribute to the breaker failures, include in the review, breaker maintenance and testing procedures and vendor manuals to determine whether maintenance activities correspond to recommended vendor practices.

- ' t; . interview plant personnel and evaluate maintenance worker training in performing 4.16kV breaker maintenance activities and operator training in placing 4.16kV a

breakers in operation, including their ability to properly perform breaker racking operations, to identify any contributing factors to the breaker failur Si Review the adequacy of the licensee's program for determining the root cause of the breaker failures. Observe and evaluate troubleshooting, testing, and analysis of quarantined equipment.

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A-3

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l 4 I i

Anoendix B - Persons Contacted

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Licensee Mananoment

'

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' J. Cook, Senior Voce President W. Romberg, Assistant Vice President P, Yocum, Plant Manager, CPS ,

R. Phares, Manager, Nuc6 ear and Performance improvement .

- D. Thompson, Manager, Nuclear Station Engineering Department l

M. Stickney, Supervisor, Regulatory interface Special mvestination Team (Root Cause Analysis)

S. Eisenhart Performance improvement Inc. (team leader)

-

J. Canning CR E8ectrical Distribution Service:: .

• **

i- J._ Roy . CR Electrical Distribution Services A. Storms Storms Advisory Services >

L Domick Domick Associates, Inc.

4 V. Torres Westinghouse S. Richitelli Cutler-Hammer D. Wheatley lilinois Power-Independent Ane'ysis Group D.Lukach Illinois Power- Nuclear Station Engineering

F. Taylor lilinois Power - Electrical Maintenance

G. Smith lilinois Fower- Electrical Maintenance

-

L Lehman lilinois Power- Audio / Visual Special investiaation Team (Corrective Action)

M. Stickney lilinois Power- Team Leader D. Lukach lilinois Power- Nuclear Station Engineering D. Wheatley lilinois Power-Independent Analysis Group l G. Reed lilinois Power- Operations F, Taylor - lilinois Power- Quality Assurance L Lehman - Illinois Power- Audio / Visual J, Canning CR Electrical Distribution J. Roy CR Electrical Distribution L De Ack Domick and Associates

.

H. Estrada - Independent

Electrical Maintenance. .

J. Bopp North American - Electrician

<

M. Calandrillo Illinois Power- Electrician -

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J. Celey_ lilinois Power- Electrician G.Englehart 1.'linois Power- Electrician

't B-1

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!

i l

Apoondix B - Persons Contacted (continued)

Electrical Maintenance (continued)

K. Trone : lilinois Power- Supervisor, Electrical Maintenance

'

Operationg ,

D. Uvingstone lilinois Power- Non-Uoensed Operator Electrical Maintenance Training Harley Fishel Training Administrator

. .

B-2

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Appendix C - Documents Reviewed ,

.

MWR D75611 Check and Adjust Breaker Latch Check Switches MWR B18632 RHR Breaker Failure to Close - Cican Unkage MWR C28360 Repair RHR Pump Breaker Phase C Intemal Ceramic Piece MWR D01719 Repair RHR Pump A Breaker Bent Sheet Metal MWR D04509 Repair RHR Pump Breaker Misadjusted Latch Check Switch MWR D03344 Replace RHR Pump Breaker TOC Switches PERMRHA002 Preventive Maintenance Task on RAT Main Feed Breaker PERMRHA501 Preventive Maintenance Task on RHR Pump Breaker Procedure 8410.01 Westinghouse DHP6900V,4.16-kV Power Circuit Breaker Mainter,ance, Revisions 14,15,16 and 17 MWR D75427 Clean and Inspect RAT Main Feed Breaker, May 9,1997 MWR D63306 Clean and Inspect RHR Pump A Breaker, May 5,1997 Westin9 house Technical Manual IB-32053-4A,1978 and 48,1980, " Instructions for Porcel-1.ine Type DHP Magnetic Air Circuit Breakers" Westinghouse Preliminary Report DHP Breaker Failure Analysis lilinois Power Company Clinton Power Plant Shop Order 014N005B4, Serial #2" Critique Report EM97-015 Critique of RAT Main Feed Breaker Failure Critique Report EM97-016 Critique of RHR Pump A Breaker Failure Condition Report 1-97-07-222 Failure of RAT Main Feed Breaker Condition Report 1-97-08-045 Failure of RHR Pump A Breaker

C-1

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6syndix D- Acronyms and Intialisms

.

AEOD Analysis of Events and Operational Data AIT Augmented inspection Tearn CPS Clinton Power Station CR Condition Repott EDO Executive Director for Operation ERAT Emergency Reserve Auxiliary Transformer i,.struction Booklet

P lilinois Power kV kilo-Volts MD Management Directive MOC Mechanism Operated Cubicle MWR Maintenance Work Rwquest NRC Nuclear Regulatory Commission .

• '

NRR Nuclear Reactor I;egulation PM Preventive Maintenance RAT Reserve Auxiliary Transformer RHR Residual Heat Removal GC South Carolina SDC Shutdown Cooling SIT SpecialInvestigation Team TOC Truck Operated Cubicle V Volts Vac Volts altemating current Vdc Volts direct current

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