ML19256B440
| ML19256B440 | |
| Person / Time | |
|---|---|
| Site: | Dresden  |
| Issue date: | 05/24/1979 |
| From: | Pappas H NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION III) |
| To: | COMMONWEALTH EDISON CO. |
| References | |
| NUDOCS 7907110068 | |
| Download: ML19256B440 (1) | |
Text
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NUCLEAR REGULATORY COMMISSION I,o i
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occ= cttyn. ittinois sois7 rg ( n 19/9 MEMORANDUM FOR: Those on Attached List FROM:
Helen Pappas, Chief, Administrative Branch
SUBJECT:
IE BULLETIN NO. 79-11 The attached IE Bulletin No. 79-11 titled " Faulty Overcurrent Trip Device in Circuit Breakers for Engineered Safety Systems" was sent to the following licensees on May 22, 1979, for action:
American Electric Power Service Corporation Indiana and Michigan Power Company D. C. Cook 1, 2 (50-315, 50-316)
Cincinnati Gas & Electric Company Zimmer (50-358)
Cleveland Electric Illuminating Company Perry 1, 2 (50-440, 50-441)
Commonwealth Edison Company Braidwood 1, 2 (50-456, 50-457)
Byron 1, 2 (50-454, 50-455)
Dresden 1, 2, 3 (50-10, 50-237, 50-249)
La Salle 1, 2 (50-373, 50-374)
Quad-Cities 1, 2 (50-254, 50-265)
Zion 1, 2 (50-295, 50-304)
Consumers Power Company Big Rock Point (50-155)
Midland 1, 2 (50-329, 50-330)
Palisades (50-255)
Dairyland Power Cooperative LACBWR (50-409)
Detroit Edison Company Fermi 2 (50-341) 35 119
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Addressees - Memorandum dated May 2'.,
1979 IE File.s MPA/DTS Central Files
-l Reproduction Unit NRC 20b
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Those on Attached List hUsi 2 41979 Illinois Power Company
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Clinton 1, 2 (50-461, 50-462) lowa Electric Light & Power Company Duane Arnold (50-331)
Northern Indiana Public Service Company Bailly (50-367)
Northern States Power Company Monticello (50-263)
Prairie Island 1, 2 (50-282, 50-306)
Tyrone Energy Park 1 (50-484)
Public Service of Indiana Marble Hill 1, 2 (50-546, 50-547)
Toledo Edison Company Davis-Besse 1 (50-346)
Union Electric Company Callaway 1, 2 (50-483, 50-486)
Visconsin Electric Power Compary Point Beach 1, 2 (50-266, 50-301)
Wisconsin Public Service Corporation Kewaunee (50-305)
Helen Pappas, Chief Administrative Branch
Attachment:
1835 12i RifI Pappas/bk 5/22/79
U.S. NUCLEAR REGULATORY COMMISSION OFFICE OF INSPECTION AND ENFORCEMENT REGION III
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b y 22, 1979 IE Bulletin No. 79-11 FAULTY OVERCURRENT TRIP DEVICE IN CIRCUIT BREAKERS FOR ENGINEERED SAFETY SYSTEMS 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 ene 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 cape 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 'ne 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 breakers.
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 prematu t tripping of the circuit breaker because of insifficient time delcy in overcurrent protection, i.e., the motor starting (inr4sh) 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 and caps made of a black phenolic material. As a result of that Bulletin, the black end caps were replaced with a new ty ae made of fibre-filled polyester material called " navy p' navy".
ray Prior to the Ap; 1979 report, there have been no reports of suspect gray" end caps either from scheduled testing or unusual behavior in service. The manufacturer of the " navy-gray" and caps believes the crack defects may be linked to a raw material batch problem. That is, the molding ingredient saterials used may have neared the end of their shelf life before use. It is not believed the end caps, after on, have a significant shelf life
. limit, due to the low residual at on robabilities.
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