ML19269D395

Discusses Faulty Overcurrent Trip Delay Devices in Engineered Safety Feature Circuit Breakers.Forwards Draft Bulletin,Utils Notification,Westinghouse Press Release, Westinghouse Technical Bulletin & AEC Operations Bulletin

ML19269D395
Person / Time
Site:	Point Beach
Issue date:	05/04/1979
From:	Eisenhut D, Hanauer S Office of Nuclear Reactor Regulation, NRC OFFICE OF THE EXECUTIVE DIRECTOR FOR OPERATIONS (EDO)
To:	Jordan E NRC OFFICE OF INSPECTION & ENFORCEMENT (IE)
References
NUDOCS 7906020182
Download: ML19269D395 (14)

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4 UNITED STATES

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1 NUCLEAR REGULATORY COMM!sSION j i(

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WASHINGTON, D. C. 20555 MAY 4 1979

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g MEMORANDUM FOR:

E. L. Jordan, Assistant Director, Office of Inspection and Enforcement S. Hanauer, Assistant Director for Plant Systems

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i FROM:

D. G. Eisenhut, Deputy Director, Division of Operating Reactors

SUBJECT:

RECOMMENDED BULLETIN ON FAULTY OVERCURRENT TRIP DELAY DEVICES IN ENGINEERED SAFETY FEATURE CIRCUIT BREAKERS Westinghouse Electric Company informed IE, via telephone, on Friday, April 1.3,1979, that the licensee of the Point Beach Unit 2 facility had found defects in overcurrent time delay dashpot end caps in (1) one safeguards bus supply breaker and (2) two non-safety breakers of the same type. As we understand, these were found during required equipment surveillance.

Seven out of 17 spare

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end caps in stock were also found to have similar defects. This j

defect, a crack in the overcurrent time delay dashpot end cap can result in unacceptably short delay time in the overcurrent trip of the breaker. Thus, when attempting to start a motor the starting current (inrush) could cause the defective time delay trip device to trip the breaker prematurely, effectively preventing the motor from starting. The defect is symptomatically similar to the defect j

which was the subject of Bulletin 73-1 (see Attachment E) but, in this case the defect is believed to be a manufacturer's raw materials batch problem.

The telephone notification by W was supplemented by written notification from the licensee to Region III, which we received on April 16, 1979 (see Attachment B).

Shortly after the NRC was informed of this problem, Westinghouse issued a Press Announcement (see Attachment C).

W has also issued a Technical Bulletin to W PWR facilities on this matter (see Attachment D).

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We recommend that a Bulletin on this matter be issued promptly. A draft Bulletin (Attachment A) is enclosed for your consideration

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and use.

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F

. G. Eisenhut, Deputy Director Division of Operating Reactors

Contact:

J. T. Beard X28077 Attachments:

A.

Recommended Draft Bulletin dated April 30,1979 B.

Licensee's Notification dated April 12,1979

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C.

W Press Release dated

" April 13, 1979 D.

-W Technical Bulletin No.

NSD-TB-79-02 dated April 17, 1979

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E.

AEC OperationsBulletin 73-01 dated February 1973 2257

.;,42 cc: See next page

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cc w/ attachments:

H. Denton E. Case V. Stello D. Eisenhut R. Vollmer F. Rosa R. Satterfield M. Srinivasan G. Lainas D. Tondi J. T. Beard I. Ahmed E. Wenzinger 33s J. Fouchard

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2257 343 1.4-.'.

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i J. T. Beard / DRAFT #6 ATTACHMENT A 4/30/79

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DRAFT BULLETIN 79-FAULTY OVERCURRENT TRIP DEVICE IN CIRCUIT BREAKERS FOR ENGINEERED SAFETY SYSTEMS g

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DISCUSSION f

We have received information from Westinghouse and a licensee relating to the potential failure of a circuit breaker in an engineered safety system. This circuit breaker had a defect in one of its three time delay dashpots and is believed to result in a shorter time delay for overcurrent protection. The defect was a small hairline crack in

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7 the end cap of the dashpot.

Further investigation by this licensee disclosed that 7 out of 17 spare dashpot end caps and 2 non-engineered h

safety feature breakers also had similar defects. The circuit breaker

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is a Westinghouse type 08-75. Westinghouse type 08-50 breakers i-also use the same type of dashpot and end cap. DB-50 and -75 breakers are used extensively in PWR's,and some BWR's may also have the same

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breakers.

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Similar make and model circuit breakers, when used for scram purposes, do not require the overcurrent trip feature and thus are not of concern.

The end cap crack defect, if severe enough, could result in premature tripping of the circuit breaker because of insufficient time delay in overcurrent protection, i.e., the motor starting (inrush) current could i

cause the breaker to trip inadvertently and thus prevent the motor s ta ri..

2257 j44

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l The defects reported by the licensee in April 1979, occurred in the

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replacement end caps which were provided to solve the problem described

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in Bulletin 73-1.

The subject of Bulletin 73-01 was end caps made I

of black phenolic. As a result of that Bulletin, the black end caps sm.+

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l were replaced with a new type made of fibre-filled polyester material called " navy gray".

Prior to the April 1979 tests, there have been no reports of suspect " navy gray" end caps either from scheduled testing or unusual behavior in service. The manufacturer of the

" navy gray" end caps believes the cracks may be raw material batch

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i problem when molding ingredient materials used have neared the end e

of their shelf life.

It is not believed the end caps, after fabrica-

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tion, have a significant shelf life limit, due to the low residual

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t stress and low crack propagation probabilities.

Description of Event p=

The following informaticc was obtained from the Licensee Event Report dated April 12, 1979 and a subsequent meeting with the licensee,

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Westinghouse,and NRC staff.

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._.7-During the 1979 surveillance tests, a review of the previous refueling surveillance test results on a Westinghouse type DB-75 breaker (used

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as a 480v ESF bus supply breaker) indicated a drift in the overcurrent trip time from the manufacturer's design minimum value of 6 seconds to 5.50 and 5.12 seconds. The 1979 test results showed a deviation 2257 345 P

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and inconsistency in the delayed trip timings among three consecutive tests.

The overcurrent devices were removed from each of the three phases and a visual inspection indicated a hairline crack in t'he end cap of one of the devices. That cap was replaced (without checking for a possible crack in the replacement cap), and the breaker was again tested.

This test also showed deviations and inconsistency in the

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delayed trip timings. The subsequent inspection of the devices revealed a<. hairline crack in the end cap which had just been w

ins talled. This prompted an inspection of the in-stock spare caps.

Seven out of 17 caps were found to have similar cracks.

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Actions Required of _All Holders of Operatino Licerses

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1.

Determine whether circuit breakers of the above described manufacturer and types with overcurrent trip devices are in safety related Class IE service or in spares at your facilities.

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2.

If the subject breakers are in service in safety related systems:

within 30 days, review the existing test data for all overcurrent trip device calibrations since plant startup or since replacement caps were installed and tested in response to Bulletin 73-1, which-ever is most recent.

Determine if any delay times are: (1)outside of the acceptance band; (2) marginally acceptable - on the low side of the acceptance band; or (3) if any significant change in 2257 346 W

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i delay time performance has been observed. These devices should

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be retested and replaced as necessary to assure no loss of safety W

function.

3.

Inspect all end caps in spares for cracks using at least a 3x magnifying glass. Caps having visible flaws should be discarded and no such caps shall be used in Class IE applications.

4.

Review test procedures and test schedules for all safety related circuit breakers to assure that all such breakers are tested at least each refueling outage to confirm overcurrent time delay

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protection.

For facilities with an operating license, a written report of the above actions, including the date(s) when they will be completed shall be

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submitted within 45 days of receipt of this Bulletin.

For facilities with a construction permit, a written report of the

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above actions, including the date(s) when they will be completed shall be submitted within 60 days of receipt of this Bulletin.

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2257 347 i:

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ATTACHMENT B 42 i @sr d.,'i M y g :r _ v p' D i3 t w.:.y R(t:.n G f- %'

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Drent Danct-ipticaa During a. rovicu of Unit 2 R2fc:21 Lng 5 no:r-L'.chnical Opecificaticet-2 quirod equiscont curve 111ance, it use r.nter,1 that caso of thron (c'.uk por titocc.) overot2r: cat protoC:ti.'O.

tite delay eicchpots for tia: 2M; enfcguards =upply bun brec}c:r-T 1

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rgen vm;y caref'tr viccar c.m.inatic.=, tc. obenv-.

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lirrn, sppr:;mioctely c; g-oightis ixtet: Iongs. en tho outor etMect ci t2.0 c q.

The cr.?c. m,o cf c. *m.vy ".a.rcy* pt.nctietyp: =nt=rt:A n;.d r m c threedce.1 t: stet int ort c:c' +rd. into M n rith c9ero=ict.tely c-as.~

I cishth inch of Plc.0 tic edAMary the inccet on. tho. cop 3C inner feco.

F.to cract uno totally withir.: the pinceic tr.atorie.l.

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t-f.3 itc cve.Tcurrect (cicy chnrect.rrintic= cn6 time, usa over ~

k hanicC cc a pecccc:t ecoct:ro.

ICo orccku t: crc observed in the p

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P.'.1 oth:;r cafoc.ht.nr6ct-rc1Ctod overcurr ect tir.O delay dachpoto-

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An both u. iter at Poitst Lucch.nro of n 1573. m'.ntage, eAcn c11 t.tre chen1;2d out bccccco of a cin.ilar crechting. Problor: in tho-e.::- thce. 60:or6 bod "~olcok caps"- (ccc. 2.bnorrerl. Occurrenco acpert Ra. 72-20).

Tho 1573 capc cra. of 12avy (ATay cateric1.

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{y stu.cgccroc bronber,, 1D61 nni 2B41, clect hrd c:cckmc ctwor, j

, thncc ccpa cS.co be.ving been incts.11od. Ox2:'irG PEhrlim; 4-c.

I A. vicuci err. :inctf.ca:. ed hho osG2 in atcy2, e.11 purc3.:rmnt cisec I

itr/ch, 1977, indiocted thct.of 17 in ctcc.t, circ hcd m. vo: y fina hnirlina orr_h., carcyincdaly ca.a.-alghttt irc27. Icag, cartcting.

.tinc.: tho c::'inc hc-le. on. Ehn 1-e curfeco of tbs ecp Of'the p

capc. uced o'? tJw three bc.tch, ordote on record, on.ly two havs i

bcon ucca in cafcWo: beer 6 tern bottc cz:. che 3B03; eupply

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'"nt Cui-f.ng. the p2rcen.t Elsfraling 5 en,ttu.;c. of thic camer cr@.

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vt:m..1 cr~m4 catica cnd tecfr;ing boic: fry botnT Fanc:5-1 for cervico-I 5

In. vicu'. of I;carrible gencef c prohin-.< ci.th tir.m dair,y dua!vot I

cad. ccpc dF14 uerc6 on. or cEttr C.rch, 1977, thic matter hec

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al reciduci hOct rcroval pepr, con.tciecent cprsy puma, ete j;

YAict. coul6 b::> cxpected to pia.* st ruu go etc=cr t c:t. tha. '.mol q

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Friday, April 13, 1979 P

6 pm

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ATTACHMENT C

a STATEMENT BY WESTINGHOUSE ELECTRIC CORPORATION Westinghouse Electric Corporation today infomed the Nuclear Regulatory b

Commission and eight electric utilities that a review of circuit breaker systems at their nuclear power plants should be carried out. The; company i

l said a component of the circuit breaker system, called an end cap, was found to have hairline cracks during a scheduled inspection at one nuclear plant.

The situation could conceivably effect the startup of some safeguard motors.

However, periodic testing of the system has not shown any such L

probl ems. As a matter of precaution, Westinghouse has advised the eight

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utilities with this type of circuit breaker system to review their test data and inspect and replace the end caps, if necessary, to avoid possible g

motor startup problems.

Westinghouse said replacement of the end caps could take place without interrupting plant operation.

1 (Dictated by Jim Daley to Pittsburg bureaus of United Press International hhl_

and Associated Press around 6 pm Friday, April 13, 1978)

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In answer to identical questions from both wire services, I explained L.

that the safeguard motors are used in activate pumps involved in backup

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l coolant systems.

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Both wires imeediately asked for the location of the plants involved, which I supplied without mentioning the names of the utilities:

Point Beach I & II, Two Creeks, Wisc.

Conn Yankee, Haddam, Conn.

San Onofre I, San Clemente, Ca.

Robert E. Ginna, Ontario, N.Y.

j H. B. Robinson II, Hartsville, S.C.

Indian Point II, Buchanan, N.Y.

Cooper Plant, Brownville, Neb.

p Three Mile Island I, Middletown, Pa.

2257 350 t

Westinghouse h

ATTACsMENT D Nuclear E

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P.W@D) Service Technic'al Bulletin k

i Division s

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An advisory notice of a recent technical development pertaining to the installation or operation of Westinghouse-supplied Nuclea".: m Plant equipment. Recipients should evaluate the information and recommendation, and initiate action where appropriate 3 "

P.O. Box 2728, Pittsburgh, PA 15230 e

Suoject Nurnber

= T-Westinghouse DB Breakers - Overcurrent Devices uso.TB-79-02 E

Systern(s)

Date a

Electrical Power - La Voltage Switchgear April 17,1979

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Attected Plants All w1tn 05-50 or 08-h cireaKers (Probably excludes S.O.(s)

, all current in-construction W Plants except Diablo Canyon, Salem, 380-385 t1eferences.

and Sequoyah)

Sheet Of Various 1

2 e

o om BACKGROUND INFORMATION An operating plant recently advised that per. iodic overcurrent tests of DB Breakers Om revealed three breakers with abnormal overcurrent' trip characteristics. One of the breakers was in a. safeguards application,'while the other two were not safety L

related.

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Inspections of the overcurrent trip units revealed hairline cracks in the end caps E

of the overcurrent dashpot airchamber which provides the time delay function of the f =E overcurrent trip.

Inspection of 17 in-stock spare end caps at the same plant d

revealed seven with similar hairline cracks. All of the end caps involved here, t==

both from the operating breakers and from spares, had been procurred in 1977-1978 D=

period, and all were of fibre-filled polyester material commonly called " navy gray."

This matter relates back to a late 1972 event when similar experiences occurred at F

two plants (as documented in the AEC (NRC) Operation Bulletin 73-01). Up to that time the end caps were of a black phenolic material and a Westinghouse reconinendation

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was issued for replacement of the black end caps with the " navy gray." It was, and p

remains, our opinion that the " navy gray" provides improved reliability over the black 6.;;

phenolic material due to lower residual stresses, lower crack propagation probability, k and increased overall strength.

Rn The manufacturer of the end caps believes the end cap cracking may be related to a E

batch problem, when ingredient materials usec have neared the end of their shelf life.

It is not believed the end caps, after fabrication, have a significant shelf life

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limit, due to the low residual stress and low crack propagation probabilities stated f

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earlier.

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51 AdditionalInformation.if Recuired. may be Obtained frem the Oriainater. Tele

hone 412 - 256-5493 ornvm 236 5M93 lA.) N Q

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x W. H. Furfari S. G. Caslake, Mgr.

Electric Service Electric Service

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f Neitme weitingmouse Elec. i. corporation nor era emoloves make any warranty or representaticri with rece-t to the accuracy.comot

Westinghouse Nuclear.

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[jD}BF Service Technical Bulistin l

Division

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An advisory notice of a recent technical devel:;; ment pertaining to the installation or operation of Westinghouse-supplied Nuclese!

Plant equipment. Recipients should evaluate the information and recommendation, and initiate action where appropriate P.O. Box 2728, Pittsburgh, PA 1523C NSD-TB-79-02 Sheet 2 of 2 There have been no other reports of premature tripping of breakers which have the replacement caps.

The periodic functional testing performed in accordance with Technical Specifications should' reveal significant changes in breaker timing characteristics, and periodic current injection type overcurrent testing (Multi-amp or equivalent), will reveal marginal trends in time delay reductions.

l The only Westinghouse breakers potentially affected are types DB-50 and D8-75 4

having series overcurrent trip devices. Reactor trip breakers do not have overcurrent trip devices, and thus, are not affected.

Furthermore, the Westinghouse type DS breakers, as used on many of the more recent plants, are not involved as they utilized a totally different overcurrent device.

RECOMMENDATION:

Although we are not aware of any premature tripping of motors in the field, we recommended that affected plants take the following actions with respect to safety m.

related DB breakers.

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Review the most recent overcurrent trip device calibration test data for the.

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safeguards breakers.

If any individual readings are marginally acceptable on L

the low side of the acceptance band, or'ihdicate any significant reduction in delay, time from previous results, retests should be performed within 30 days.

If any individual reading from the retest is below the acceptable band or i

marginal, the end cap on the trip device should be removed and replaced if inspection under a minimum 3X magnification reveals any cracks. The trip device j

after assembly should then be recalibrated.

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2.

All end caps in storage should be inspected for cracks using a mir.imum 3X

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j magnifying glass. Do not use any end caps having evidence of cracking in g

safeguards applications.

3.

The safeguards breakers not retested under item 1 above should be tested in the same manner during the current or next planned outage.

Any personnel involved in service or replacement of the overcurrent device should be cautioned to be certain that the instantaneous overcurrent spring is properly attached after reassembly of the unit. Refer to our Technical Bulletin NSD-73-73-18.

2257 352 b

I ATTACHMENT E

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Bulletin 73-1

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FAULTY OVERCURRE.NT TRIP DELAY DEVICE IN CIRCUIT BREA*GRS FOR ENGINEERED 1

1, i

SA7.:2Y SYSTEis x

We have received infor=ation from two licensees relating to the failure

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of circuit breakers in engineered safety syste=s.

These circuit breakers, F

Westinghouse Models DB-25, DB-50 and DB-75, are used extensively at both IT PWR and BWR facilities.

These failures, which could negate operation of f

engineered safety syste= components, were attributed to faulty overcurrent C

trip delay, devices. Westinghouse has for=ulated an on-site testing progra=

to deter =ine if the ti=e delay devices are faulty and is developing a new i

end cap for the dashpot used in the ti=e delay devices.

Sicilar nahe and model circuit breakers, when used for scra= purposes, do not require the t

overcurrent trip feature and, therefore, are not included in'this pro-F f

ble=.

Pertinent details relating to this proble= are contained in 5

l Section A below.

Action requested by this Bulletin is contained in

r.:Il Section B.

il s

I A.

Descrintion of Circumstances 6

l

.i Plant A L.

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During the perfor=ance of the routine monthly surveillance test EF of the Safety Injection Syste=, the pu=p =otor tripped as it approached operating speed.

A second atte=pt to start the pu=p produced the sa=e result.

The cause of the pu=p t, rip was at-tributed to calfunction of an overcurrent trip device.

This device, which has an adjustable ti=e delay, tripped out the m.

pu=p motor on starting current because of leakage in the ti=e delay dashpot.

Subsequent examination of the dashpot disclosed a crack in the end cap of the air chamber.

The crack per-II-"

b mitted air to leak into the ch'a=ber at an excessive rate, n

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reducing the ti=e delay from approxi=ately 45 seconds to 5 seconds.

Testing of similar =odel breakers equipped with the

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overcurrent trip delay feature revealed four additional units with low trip delay times caused by cracks in the end caps.

f Approxi=ately 25 circuit breakers of the type described are utilized to energize components of engineered safety feature syste=s at this facility.

I Plant B A 480 vol: AC bus circuit breaker tripped open when the auxiliary building supply and exhaust fans sere started si=ultaneously. The cause of the failure was attributed to a crack in the end cap of f

the time. delay dashpot in the overcurrent trip device.

The trip delay unit and the circuit breaker in question are similar to the I

units which failed at Plant A.

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The cracks found La the end caps of the time delay dashpots are con-F _...

I sidered a coc=on mode of f ailure.

B.

Action Recuested of the Licensee I

It is requested that you determine whether safety 'related (Class IE) circuit breakers of the described cak'e and =odels utilizing I

overcurrent trip ti=e delay features are installed at your facil-

31. '

inies and provide this office with your findings.

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If the subject breakers are installed, please include in your re-i+ =r i

j sponse a description and the results of your program to determine j

if you have any faulty ove current trip time delay devices installed and the scheduled completion date of your corrective actions.

For m,.

facilities currently under constructicn, please inform us of your plans to assure that the appropriate =odification has been incor-porated in all safety related circuit breakers of the type described that have been or will be installed at your f acility.

This infor-i cation should be provided to this of fice, in writing, within forty-five days of your receipt of this letter.

Sincerely,

}

Ja=es P. O'Reilly Director O

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