ML20234B173

Summary of 870904 Telcon W/Util & Westinghouse Re Investigation of Facility Reactor Trip Breaker That Failed to Open on 870702

ML20234B173
Person / Time
Site:	McGuire, Mcguire
Issue date:	09/09/1987
From:	Hood D Office of Nuclear Reactor Regulation
To:	Office of Nuclear Reactor Regulation
References
NUDOCS 8709180291
Download: ML20234B173 (4)

Text

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jo, UNITED STATES NUCLEAR REGULATORY COMMISSION n

,E WASHINGTON, D. C. 20555

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SEP 0 91987 Docket Nos.:

50-369 l

and 50-370

-FACILITY:

McGuire Nuclear Station, Units 1 and 2

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1 LICENSEE:

Duke Power Company

SUBJECT:

RECORD OF TELEPHONE CONVERSATION SEPTEMBER 4, 1987 ON MCGUIRE REACTOR TRIP BREAKER TESTING On September 4, 1987, the NRC participated in a telephone call with membe s of Duke Power Company and Westinghouse regarding the investigation of the McGuire Unit 2 DS-416 reactor trip breaker (RTB) that failed to open July 2,1987.

Metallurgical examinations of the cracked center lever to pole shaft weld began August 25, 1987, and are continuing. Telephone call participants are listed in the Enclosure.

i l

Westinghouse provided a status report of the laboratory results obtained to date and preliminary answers to questions asked during earlier parts of the RTB testing program:

01. Load (high limit) transmitted to welds on the pole shaft during opening and closing A1.

10,000 pounds per square inch (closing force highest)

Q2. Strength of weld as designed (0.19 fillet, one side,180' length)

A2. 35,000 pounds per square inch

03. Safety factor in weld as designed A3.

3.5' Q4. Significance of cracked weld A4. Necessary for jaming to occur. Tolerances alone insufficient to cause jaming.

Q5. Tortional force welds can withstand A5.

2,030 inch pounds 1

06. Pole shaft / lever materials and coating A6.

1018/1010 plated with zinc 07.

Reason for weld failure A7. Due to fatigue fracture. Weld was undersized and short (120* length rather than 180 ).

Significant lack of fusion exhibited. Cold weld did not fuse to lever.

2500 cycles to failures (estimated).

Load cycle fatigue and eventual overload caused failure. Fatigue area is along the contour of the shaft.

Propagation was along the fusion line. Sudden final fracture was perpendicular to lever interface. The initiation point is not yet clear.

8709180291 870909 PDR ADOCK 05000369 P

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Reason for trip latch bearing damage A8. Polyester sleeve came apart due to lateral displacement.

This can not cause l

Jamming.

09. Westinghouse plans and actions A9. Westinghouse will issue a communication'to its customers for which the I

safety function of. the DS-416 breaker is to open requesting a visual-inspection of the center pole lever weld during the next periodic test.

i For the short term, if the weld is cracked or if the weld contains less than 90 of continuous good weld, then that breaker should not be used as a main breaker but may be used as a bypass breaker.

Westinghouse will also include an inspection criteria on the fillet weld size.

For the long term, during the plant's'next refueling outage, inspect the remaining pole shaft-welds.

Any pole shaft weld with less than 90 of continuous good l

weld should be repaired or the pole shaft replaced.

Also inspect roller-position on close cam to assure it does not contact the side plate.

For. DS-416 breakers for which the safety function is to close, the Westinghouse communication will call for visual inspection of each weld of each movable blade.

Westinghouse expects to issue the communication about September 11, 1987.

Metallurgical tests. should be completed September 9,1987.

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Darl S. Hood, Project Manager Project Directorate Il-3 Division of Reactor Projects, I/II

Enclosure:

As stated cc:

See next page 30 PO#1 -3/DRP-I/II PD#II-3/DRP-I/II DHood/mac LCrocker, Acting PD 09/y/87 09/q/87

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ENCLOSURE Participants

[,w Westinghouse

-Duke NRC C. Fezze.

U homas, et.al.

Dood i.

.J. Jelovich J. Richardson P. Morris E. Merschoff A.. Debs,-et.al.;

J. Stone K.-Naidu T. Peebles I

C. Y. Chan L. Crocker C. D. Sellers G. Toman (Franklin Research Center) l l

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1 u-

-- _ +

l TELEPHONE CONVERSATION

SUMMARY

DISTRIBUTION l

ff6dcket File. '

SEP 0 p 198 NRC Participants NRC POR D. Hood L POR J. Richardson NSIC E. fkrschoff PRC System J. Stone PD#I1-3 Rdg K. Naidu Project Manager D. Hood T. Peebles M. Duncan C. Y. Chan B. Kolostyak L. Crocker W. Troskoski (MNBB 6113)

C. D. Sellers OGC-Bethesda G. Toman l

ACRS (10)

(Franklin Research Center)

I A. Toalston W. Lanning C. Berlinger G. Lainas S. West OTHERS bec:

Licensee & Service List i

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