ML19276G811

Responds to IE Bulletin 79-11, Faulty Overcurrent Trip Device in Circuit Breakers for Engineered Safety Sys. Neither Westinghouse Type DB-50 or DB-75 Circuit Breakers Are Used in safety-related Sys

ML19276G811
Person / Time
Site:	Zimmer
Issue date:	07/03/1979
From:	Borgmann E CINCINNATI GAS & ELECTRIC CO.
To:	James Keppler NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION III)
References
NUDOCS 7908270556
Download: ML19276G811 (1)

Text

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THE CINCINNATI GAS & ELECTRIC COMPANY sWE CIN CIN N ATI. OHIO 45201 July 3, 1979 E. A. BORGM AN N li.T."IiEc'i'EaI" Ye g ul a t o ry C ommi s s i o n Region III 799 Roosevelt Road Glen Ellyn, Illinois 60137 ATTN: Mr. James G. Keppler Regional Director RE: WM. H. ZIMMER NUCLEAR POWER STATION - UNIT 1 IE BULLETIN 79-11, WESTINGHOUSE DB-50 & 75 CIRCUIT BREAKERS, FAULTY OVERCURRENT TRIP DEVICE DOCKET 50-358, W.0. 57300, JOB E-5590, ITEM 956 Gentlemen:

We are not using any Westinghouse type DB-50 or 75 circuit breakers in the safety related systems of the WM. H. ZIMMER NUCLEAR POWER STATION - UNIT 1.

IE Bulletin 79-11 is therefore, not applicable to this facility.

Very truly yours, THE CINCINNATI GAS & ELECTRIC COMPANY e

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E.A. BORGMANN, SENIO ICE PRESIDENT WPC/kjd cc: NRC Office of Inspection and Enforcement Division of Reactor Inspection Programs Washington, D.C. 20555 R.F. Scheibel R.E. Cotta E.A. Borgmann C.W. Beringhaus H.C. Brinkmann W.W. Schwiers B.K. Culver J.R. Schott J.D. Flynn JUL s 1978 7908 2 7055G

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ATTN: Mr. Earl A. Borgmann  ;.  ! ,

Vice President Engineering Se.v:ces ._ , ,_

and Electric Production ,

139 East 4th Street *

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e. c Gentlemen:

Enclosed is IE Bulletin No. 79-11 which requires action by you with regard to your power reactor facility with an operating license or a construction permit.

aus-Should you have questions regarding this Bulletin or the actions -

required of you, please contact this office. r*,' -

Sincerely, M-

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p James G. Kepple

/ Director

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Enclosure:

IE Bulletin t;,,-

No. 79-11 >

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Mr. J. R. Schott, Plant Superintendent f,

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Director, NRR/DPM I.!d Director, NRR/ DOR j./

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Harold W. Kohn, Power b, J Siting Commission Citizens Against a Radioactive $'.'.-

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Helen W. Evans, State of Ohio 1r.

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U.S. NUCLEAR REGULATORY COMMISSION OFFICE OF INSPECTION AND EhTORCEMENT REGION III Ray 22, 1979 IE Bulletin No. 79-11 FAUI.TY OVERCURRENT TRIP DEVICE IN CIRCUIT BREAKERS FOR ENGINEERED SAFETY SYSTCiS Discussion:

We have received information from Westinghouse and an NRC licensee relating to the potential failure of a circuit breaker in an engineered safety syste=

of a nuclear power plant. This circuit breaker had a defect in one of its three time delay dashpots which resulted in a reduced time delay for over-current protection. The defect was a small hairline crack in 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 safety feature breakers also had similar defects. The circuit breaker is a Westinghouse type DB-75.

Westinghouse type DB-50 breakers 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 sa=e breakers.

Si=ilar make and model circuit breakers, when used for scra= 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 cause the breaker to trip inadvertently and thus prevent the motor start.

The defects reported by the licensee in April 1979, occurred in the replacement end caps which were provided to solve the problem described in IE Bulletin 73-1. The subject of Bulletin 73-1 was end caps made of a black phenolic material. As a result of that Bulletin, the black end caps were replaced with a new type made of fibre-filled polyester material called " navy-gray". Prior to th 2 April 1979 report, 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 crack nefects may be linked to a raw material batch problem. That is, the molding ingredient materials used may have neared the end of their shelf 31fe before use. It is not believed the end caps, after fabrication, have a significant shelf life limit, due to the low residual stress and low crack to a ation robabilities.

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