ML20009C158

LER 81-005/01T-0:on 810318,four Closure Studs on Reactor Coolant Pump 2A2 Had Corrosion Wastage in Pump Closure Area. Caused by Leakage from Pump Closure Gaskets.Stud 20 Replaced.Studs 1,2 & 3 Left in Place

ML20009C158
Person / Time
Site:	Oconee
Issue date:	03/04/1981
From:	Jackie Jones DUKE POWER CO.
To:	NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION II)
Shared Package
ML20009C157	List: ML20009C156 ML20009C158
References
LER-81-005-01T-01, LER-81-5-1T-1, NUDOCS 8107200332
Download: ML20009C158 (1)

Text

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' DUKE POWER COMPANY OCONEE UNIT 2 i

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! Report Number: 'RO-270/81-05 Report Date: April 1,.1981 Occurrence Date: March 18, 1981 i Facility: Oconee: Unit 2, Seneca, South Carolina Identification of Occurrence: Apparent Corrosion Wastage of Reacter Coolant Pump Closure Studs Conditions Prior to Occurrence: Cold Shutdown to Inspect and Repair 2B1 RCP i Motor Description of Occurrence:

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At approximately 1000 hours0.0116 days <br />0.278 hours <br />0.00165 weeks <br />3.805e-4 months <br /> on March 18, 1981, it was discovered that four closure studs on Reactor Coolant Pump (RCP) 2A2 had apparent corrosion wastage in the pump closure area. This pump is located in the Reactor Building inside the secondary shield wall area. This constitutes unusual degradation of the RC pressure boundary and is thus reportable pursuant to Technical Specification

6. 6. 2.1.a (3) .

The apparent corrosion wastage has been occurring due to closure gasket leakage.

! Since the unit was at cold shutdown at the., time of discovery, no immediate corrective action was necessary. The incident has been reviewed with regard to 10CFR 21, and it has been determined that this event is not reportable pursuant to 10CFR 21.

The corrosion wastage that has occurred.has been confine' f r tie most part to the closure studs within the closure area. This cerzosior, ir2 % lieved to be i caused by a slight amount of leakage from the pump's closure. - tets. .The leakage from the 2A2 pump was enough to visually observe. Fot. injection taps were installed into the casing. These were used to inject a material into the, annulus above the upper closure gasket to slow the leakage rate. This work was performed by the Furmanite Company.

The Unit 2 RCP's are manufactured by Bingham Willamette Company and are type RQV, size 28x28x41, single. stage quad volute pumps. The closure stads and nuts are made from a low alloy carbon steel. The pump casing is made frei 304 stain-less steel where the studs, thread into the pump. The motor stand. flange is made of forged carbon steel. The closure studs are tensioned using a Diamond Power stud tensioner to a pull of 440,000 pounds per stud. The studs are approximately 32 inches long and have 4"-8 threads. The unthreaded shank portion of the studs should be 3.836 to 3.846 inches in diameter.

The inspection that was accomplished on all studs for Unit 2 RCP's consisted of dimensional checks using an O. D. Micrometer and a U. T. measurement through the l

8107200332 810401 A V

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diameter of the stud. Because of the way the pump vas designed and built, a dimensional check utilizing an O. D. Micrometer could only be accomplished tangentially relative to the pump center line. Because an accurate dimen-sional check requires checking the diameter in at least two places, each stud was rechecked using a UT instrument. This was done in a normal direction relative to the pump centerline or looking in towards the center of the pump.

Apparent Cause of Occurrence:

The apparent cause of this incident is the result of a small enount of leakage from the pump's closure gaskets.

Analysis of Occurrence:

Evaluation revealed no stress concerns for continued operation by leaving stud numbers 1, 2, and 3 in place. Also, leakage is not considered a con-cern although it could change slightly, i.e. , gasket surfaces shot ld be un-affected. Based on Babcock & Wilcox's recommendation, continued operation of the unit poses no threat to the health and safety of the public.

Corrective Action:

Because Unit 2 was at cold shutdown at the time of the disco' ,ry of this incident, no immediate corrective action was required to lessen the con-sequences of the incident or to stabilize the prob?em.

Stud number 20 was removed and replaced. Stud number 3 was retensioned, and stud numbers 1 and 2 were to be left in place. The situation was evaluated, and it was determined to be acceptable to leave stud numbers 1, 2, and 3 in place.

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