ML19256B442
| ML19256B442 | |
| Person / Time | |
|---|---|
| Site: | McGuire, Mcguire  |
| Issue date: | 05/22/1979 |
| From: | James O'Reilly NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION II) |
| To: | Parker W DUKE POWER CO. |
| References | |
| NUDOCS 7907110091 | |
| Download: ML19256B442 (2) | |
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oq'o, UNITED STATES NUCLEAR REGULATORY COMMISSION 3
o k,'.\\/ [/ E REGION 11 b
101 MARIETT A ST., N.W., SUITE 3100 o
e" ATLANTA, G EoRGI A 30303 g
yay 2 ' 1979 In Reply Refer To:
RII:JPO 50-369 "x 50-370 y
Duke Power Company ATTN:
W. O. Parker, Jr.
Vice President, Steam Production P. O. Box 33189 Charlotte, NC 28242 Gentlemen:
Enclosed is IE Bulletin 79-11 which requires action by you with regard to your power reactor f acility(ies) with an operating license or a construction permit.
Should you have questions regarding this Bulletin or the actions required of you, please contact this office.
Sincerely.
f t
MVw q James P. O'Reilly Director
Enclosures:
1.
List of IE Bulleifns Issued in Last Twelve Months 835 132 s
. goo m Do9/
MAY 2 21979 s Duke Power Company cc w/ encl:
H. D. McIntosh, Plant Manager Post Office Box 488 Cornelius, North Carolina 28031 J. C. Rogers, Project Manager Post Office Box 33189 28242 Charlotte, North Carolina e
835 133
UNITED SIATES NUCLEAR REGULATORY COMMISSION OFFICE OF INSPECTION AND ENFORCEMENT WASHINGTON, D.C.
20555 May 22, 1979 IE Bulletin No. 79-11 FAULTY OVERCURRENT TRIP DEVICE IN CIRCUIT BREAKERS FOR ENGINEERED SAFETY SYSTEMS Discussion:
We have received infornation from Westinghouse and an NRC licensee relating to the potential failure of a circuit breaker in an engineered safety system of a nuclear pwer plant. This circuit breaker had a defect in one of its three time delay dashpots which resulted in a reduced time delay for over-The defect was a small hairline crack in the end cap of current protection.
Further investigation by this liczasee disclosed that 7 out of the dashpot.
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 DB-50 and -75 breakers are used extensively in PWR's, and some BWR's cap.
may also have the same breakers.
Eimilar make and model circuit breakers, when used for scram purposes, do net The end cap require the overcurrent trip feature and thus are not of concern.
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 providcd to solve the problem described in IE Bulletin The subject of Bulletin 73-1 was end caps made of a black phenolic 73-1.
As a result of that Bulletin, the black end caps were replaced with material.
a new type made of fibre-filled polyester material called " navy-gray".
Frior there have been no reports of suspect " navy-gray" to the April 1979 report, The and c.sps either from scheduled testing or unusual behavior in service.
minufacturer of the " navy-gray" and caps believes the crack defects may be linked to a raw material batch problem. That is, the molding ingredientIt is materials used may have neared the end of their shelf life before use.
not believed the end caps, after fabrication, have a significant shelf life limit, due to the low residual stress and low crack propagation probabilities.
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