ML20211P511

Part 21 Rept Re Failures of Shunt Trip Coils on Westinghouse Circuit Breakers in Reactor Protection Sys.Initially Reported on 860609.Breakers Replaced,Operation Aids (Labels) Added & Equipment Modified.Related Correspondence

ML20211P511
Person / Time
Site:	Peach Bottom, Limerick, 05000000
Issue date:	06/16/1986
From:	Daltroff S PECO ENERGY CO., (FORMERLY PHILADELPHIA ELECTRIC
To:	Murley T NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION I)
References
CON-#386-653, REF-PT21-86 OL, NUDOCS 8607230277
Download: ML20211P511 (8)

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WMD CORRESitNDENC4 h

h . PHILADELPHIA ELECTRIC COM ANY sy

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2301 MARKET STREET b ~ - :9 ,2O d .

P.O. BOX 8699 M :p ,

i PHILADELPHIA. PA.191o1 f f

SHIELDS L. DALTROFF i '; vI g auM.U"otE June 16, 1986' , '

Re: Docket Nos. 50-277 gb 50-278 50-35 [ D o C Dr. Thomas E. Murley, Administrator Region I U. S. Nuclear Regulatory Commission 631 Park Avenue "

King of Prussia, PA 19406

Subject:

Peach Bottom Atomic Power Station Units 2 and 3 Limerick Generating Station Unit 1 Reactor Protection System Power Supply Circuit Breakers 10 CFR Part 21 Report

Dear Dr. Murley:

In accordance with 10 CFR Section 21.21(b)(3), the following information is being provided regarding recent failures of the shunt trip coils on the Westinghouse circuit breakers in the reactor protection system (RPS) under operating reactor licenses for Peach Bottom Atomic Power Station (Peach Bottom) and Limerick Generating Station (Limerick)

1. Name of individuals informing the Commission: Oral notification was made to R. M. Gallo, U.S. NRC, on '

June 9,1986, by tihe following individuals: '

G. M. Leitch R. H. Logue

2. Identification of basic component which contains a defect:

Westinghouse Type LBB Circuit Breakers

Catalog Number LBB 22250 2-pole,.400 Amp, magnetic trip only, with 125 VDC shunt trip and .

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i 8607230277 DR 860616 ADOCK 05000277 PDR YJ_. , _ . ._. .-_ _n_____.__.. _ -

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Dr. Thomas E. Murley Page 2 D k

to 2250 Amps.  :

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3. Identification of firm supplying the basic component: 9 Westinghouse Electric Corporation (

4. Nature of defect and the safety hazard which could h be created j On one occasion at Limerick and several ;I v

instances at Peach Bottom, the shunt trip coils of the reactor protection system (RPS) power supply breakers were found to be damaged after apparent normal operation of the (,

breakers. An investigation into this matter <

has, determined that the failures were in all likelihood caused by the combination of misoperation of the breaker in the presence of a minor manufacturing defect.

After a successful trip of the breaker, the i shunt trip coil can be damaged if attempts are -

made to reclose the breaker with a trip signal present. This damage will occur provided that g the breaker also has a manufacturing defect

• known as " insufficient spin-over." The spin- (

over process is performed to remove excess metal from the bott'om of a rivet on the breaker handle post. The presence of the extra metal can cause binding between the breaker handle post and breaker operating mechanism. Attempts to close an unaffected breaker with a trip signal still present  :

apparently does not cause damage to the shunt  :

trip coils. c The power supply circuits served by the RPS j' circuit breakers are provid4d with relay protection against undervoltage, overvoltage and underfrequency. Any one of these abnormal conditions in the power supply will cause the shunt trip coil to actuate causing the breaker to open. For each of the two normal RPS busses for Peach Bottom Units 2 & 3 there are two of these circuit breakers in series.  !

Additionally, Peach Bottom utilizes an l alternate RPS power supply on each unit which j contains two of these breakers in series.  ;

Limerick utilizes two of these breakers in s  :

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e Dr. Thomas E. Murley Page 3 series in each of the two RPS power supplies. ,

These breakers and their associated protective  !

1 relays are designed to prevent abnormal j conditions in the power supply from damaging 1 or making the RPS equipment inoperable. j 1

Upon loss of power or upon opening of these circuit breakers, the RPS will deenergize and initiate a scram signal. If one of the two series breakers in one of the two RPS power supplies opens, a half-scram signal is generated. If one breaker in both of the RPS power supplies opens, a full reactor scram will be initiated.

The following sequence of events and ,

conditions provides a mechanism for common ,

i mode failure of these shunt trip coils. l i I o Following operation of the circuit )

i breaker (either after testing or j l required actuation from abnormal  ;

power supply conditions), plant personnel attempt to reset the ,

4 breaker with the trip signal from I the relays still present. This is contrary to normal practice. ,

l o The handle is pushed to reset and j then to the closed position.

o Excess metal on the bottom of a i rivet on the breaker handle post

! causes binding between the handle i and the breaker operating mechanism.

4 This binding does not prevent the  ;

l main contacts from opening.  :

o The binding prevents the 'a' contact l of ghe auxiliary cutoff switch in

',', l ser1es with the shunt trip coil from i opening and current passes through l I , the shunt trip coil (which is l

! designed to be a momentarily l

energized coil) until it fails. ,

o The failed shunt trip coil is not detected and the breaker is l subsequently successfully reset.

'o The breaker is now back in service l without the capability to trip for l undervoltage, overvoltage or under i i ~ frequency protection of the RPS , I

) power supply. .

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Dr. Thomas E. Murley Page 4 Operation with a degraded power supply on the RPS system has the potential to prevent a successful scram. However, this could only occur if all of the following conditions occurred.

o Both shunt coils on the breakers of one RPS supply had failed open.

o An extended degraded power supply condition exists on that RPS bus.

o The RPS equipment being supplied the degraded power supply, failed to operate properly with the off normal condition.

o A valid RPS signal was present.

The probability of all of these conditions occuring simultaneously, considering the monitoring frequency discussed in Section 7, is felt to be remote.

5. Date on which the information of such a defect was obtained:

Failures of these breakers occurred at Peach Bottom on April 11, 1985; January 16, 1986; January 27, 1986; February 8, 1986 and April 23, 1986. The failure at Limerick occurred on November 9, 1984. The evaluation to determine reportability of this defect was completed on June 9, 1986.

6. The number and location of the basic component that contains a defect:

Twelve breake,rs of this type breakers are ,

utilized on Peach Bottom Units 2 and 3. They are arranged such that there are two breakers in series for each of the two normal RPS power supplies for each unit and two breakers in series in the single alternate RPS power supply.

The breakers are designated on each unit as follows: .

A=52-AC757A B=52-BC757B A Alt.=52-CC757A C=52-AC757C D=52-BC757D B Alt.=52-CC757B

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Dr. Thomas E. Murley Page 5 Four breakers of this type are utilized on -

Limerick Unit 1. They are arranged such that there are two breakers in series for each of the two RPS power supplies on Unit 1. They are designated as follows:

A=52-AY24801 B=52-BY24801 C=52-CY24801 D=52-DY24801

7. Corrective action that has been, is being, or will be taken; the name of the individual or organization responsible for the action; and the length of time that has been or will be taken to complete the action:

Steps have been taken at both Peach Bottom and Limerick to preclude future failures of this type. Operation aids (labels) have been affixed at the appropriate breakers instructing the operators to assure that tr'ip signals are not present when attempting to close the breakers.

The four Limerick Unit 1 RPS power supply breakers have been replaced with new breakers as of June 6, 1986. Utilizing a test procedure provided by Westinahouse, each of the replacement breakers was tested to determine if the breakers had a similar spin-over binding problem. The four installed breakers successfully passed this test procedure.

Additional modifications as described below have been made to the breaker shunt trip circuitry at Limerick and will be performed at Peach Bottom.,, ,

A circuit interlock was added to each of the RPS breaker shunt trip circuits. This interlock consists of wiring the second unused main contact of each breaker in series with its shunt trip coil and 'a' contact. The additional interlock contact will open the shunt trip coil circuit whenever the breaker i is opened or tripped, assuring that the shunt  :

trip coil is not energized beyond its momentary rating.

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Dr. Thomas E. Murley Page 6 The neon indicating lamps which are used to determine if a shunt trip signal is present will be replaced with multi-light emitting diode lamps during the first refueling outage currently scheduled for April 1987. These lamps have better visibility and, the'refore, will make it easier to determine if the trip signal is present.

These modifications will be installed on the Peach Bottom Unit 2 RPS power supply breakers during the next refueling outage scheduled for March 1987. The modifications to the Unit 3 breakers will be performed during the mid-cycle surveillance outage currently scheduled for January, 1987. ,

Until such time that the modifications are completed on Peach Bottom Unit 2 and 3,.

surveillance test ST 13.54 "M/G Set Breaker Coil Continuity Check" will be performed weekly and following any RPS breaker e operation. The purpose of this test is to check the continuity of the RPS breakers in order to verify that the shunt trip coil and

'a' contact are intact to ensure the operability of the breakers.

Since the circuit breaker interlock modifications have been completed at Limerick, this frequency of testing the breakers has been discontinued at Limerick. The surveillance interval will be returned to the Technical Specification requirement of once per 18 months.

Westinghouse has advised us that they are '

revising the Breaker manufacturing drawings to change the amount of spin-over on the handle post. They are also testing these breakers with the operating handle in the closed position to ensure that binding, which could cause shunt trip coil failures in this adverse operating condition, does not exist.

8. Notification: I 1

The industry was notified of these failures )

via an entry on INPO's NUCLEAR NETWORK on June 10, 1986.

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Dr. Thomas E. Murley Page 7 If you have any questions or require additional information, please do not hesitate to contact us.

Very truly yours,

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cc: Director, Office of Inspection & Enforcement (3)

E. M. Kelly, LGS Senior Resident Site Inspector T. P. Johnson, PB Resident Site Inspector See Attached Service List e

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cc: Troy B. Conner, Jr., Esq.

Ann P. Hodgdon, Esq.

Mr. Frank R. Romano l Mr. Robert L. Anthony j Ms. Phyllis Zitzer Charles W. Elliott, Esq.

Barry M. Hartman, Esq.

Mr. Thomas Gerusky Director, Penna. Emergency Management Agency Angus Love, Esq.

David Wersan, Esq.

Robert J. Sugarman, Esq.

Kathryn S. Lewis, Esq.

Spence W. Perry, Esq.

• Jay M. Gutierrez, Esq.

Atomic Safety & Licensing Appeal Board Atomic Safety & Licensing Board Panel Docket & Service Section (3 Copies) l E. M. Kelly l Timothy R. S. Campbell l

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1 February 4, 1986 i

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