ML20005A867

Forwards LER 81-005/01T-0.Detailed Event Analysis Encl

ML20005A867
Person / Time
Site:	Oconee
Issue date:	03/09/1981
From:	Parker W DUKE POWER CO.
To:	James O'Reilly NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION II)
Shared Package
ML20005A868	List: ML20005A867 ML20005A872
References
NUDOCS 8107010406
Download: ML20005A867 (6)

Text

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Duxz Pown COMPA,NY '

Pows Bintmswo 422 Soeta Cnuncu Stazzr, CaAntortz, N. C. sea 4a S/- o/ 6 ^

• 4 wi w m o. =aan ca s a.

,q s$$ 'n.'o*o'c','.'o. March 9, 1981 '" * *"* ' *!'/3,'.],3

' Mr. James.P. O'Reilly, Director U.S. Nuclear Regulatory Consnission ,

, '[Q, ,g Region II f 3Q ' ? Vj

', bi 101 Marietta Street, Suite 3100 ~~'" yN Atlanta, Ceorgia 30303.

st .'lO i33l

• j Re: Oconee Nuclear Station #3. <r u n uoAAtott -?)

• • "'" Q, Docket No. 50-269

Dear'Mr. O'Reilly:

y/t 1\'/

-6 i Please find attached Reportable Occurrence Report R0-269/81-5. This report is submitted pursuant to Oconee Nuclear Station Technical Specification 6.6.2.1.a(9), which concerns the discovery of a conditton that requires cor-rective action to prevent the existence of a potentially unsafe condition.

Very truly yours, j'/ f/krYL h- ,

William O. Parker, Jr. ,,

FTP:pv Attachment cc: Director Mr. Bill Lavallee Office of Management & Program Analysis Nuclear Safety Analysis Center U. S. Nuclear Regulatory Commission P. O. Box 10412 Washington, D. C. 20555 Palo Alto, California 94303 Director Office of Nuclear Reactor Regulation U. S. Nuclear Regulatory Commission Washington, D. C. 20555 l

l 4I I 810701 O VD(o S

DUKE POWER COMPANI OCONIE NUCLEAR STATION Report Number: R0-269/81-5 Report Date: " March 9, 1981 Occurrence Date: February 22, 1981 Facility: Oconee Unit 1, Seneca, South Caro)ina Identification of-Occurrence: Leaking LPI Check Valve

Conditions Prior'to Occurrence:- RCS Heatup (N300*F, 750 pois)

Description of Occurrence: At approximately 1800 hours0.0208 days <br />0.5 hours <br />0.00298 weeks <br />6.849e-4 months <br /> on February 22, 1981, a check valve in the Unit i Low Pressure Injection (LPI) System was discovered ,

to be leaking excessively.during the performance of an intersystem LOCA leak test. The' leaking valve was 1 CF-12, which is the final valve in LPI, loop "B" before reaching the reactor vessel (see Figure 1). The leakage of the valve is considered to constitute a condition that requires corrective action to prevent the existence of a potentially unsafe condicinn, and is thus re-portable pursuant to Technical Specification 6.6.2.1.a(9).

l Apparent Cause of Occurrence: 1 CF-12 is a 14-inch Crane Co. 1500 PSI Alloy Steel Swing Check Valve (design pressure of 2500 PSIG). Figure 2 provides some details about this type of valve. The disc *in this type of val *ve has a i '

j cylindrical " knob" on its back which is inserted through a hole in the hinge 4 arm and then has a retainer ring welded to it to hold the assembly together

! (see Figure 3). This method of assembly allows the valve disc to pivot to a certain extent on the hinge arm. By pivoting, the disc is allowed to find its seat properly should the mating surfaces become slightly altered. A

manufactured tolerance of. 3.co 11. mils between the dise " knob" and the hinge at the pivot prevents the disc from swaying too freely.

Exsmination of the valva disc-hinge assembly in ! CF-12 has shown that the

' disc had become frozen at the pivot in a cocked position. Consequently,

. only about half of the dise was seating. The " freezing" of the disc at the

]

pivot was apparently caused by a buildup of deposits in the gap between the hinge and the disc " knob" on the side of the knob closest to the hinge pin.

While there is flow through the valve, the disc is normally in a cocked i position, and it is postulated that the flow could carry deposits into the l_ pivot gap area, where they could accumulate. The accumulation of deposits could then cause the disc to remain slightly cocked when the flow was stopped.

During examination of the valve disc, the retaining ring was rencved and un-successful attempts were made to remove the disc from che hinge. Both the

hinge and disc are made of the same type of stainless steel (ASTM Spec.

No. A351 GR. CF8M) and under the high temperature of unit operation, some galling could have occurred. At the time of chis report, the disc is still j

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i connected to the hinge..

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Analysis of Occurrence: Prior to the testing of I CF-12, backup check valves 1 CF-11 and 1 LP-47 (see Figure 1) had been leak tested. and both had shown zero leskage. In addition, the LPI loop "B" motor operated valve 1 LP-18 was in its normal closed position during this period of time. Thus, the prevention of leakage from the RCS to the low prescure section of the LPI system was assured.

Examination of I CF-12 showed that although the disc was not seating properly, it remained capable of swinging up to its cocked position under LPI flow con-ditions. Additionally, all equipment required to mitigate the consequences of an accident at the conditions during the time of this incident were operable. Therefore, LPI flow through loop "B" was always available if needed.

1 CF-12 is the first valve, out of a total of 18 of the same type of valve leak tested-at Oconee, which has shown any leakage problem. During.the final preparation of this repart, another check valve of the same type was found to

., be leaking on Oconee Unit 3. The details of this incident will be provided in a separate report. Duke Power Company will be continuing its investigation into the leakage problems observed with these two valves to determine if generic implications exist. Duke will keep the NRC informed of any signifi-cant developments during this investigation.

Corrective Action: The unit was re.t;ned to cold sh;tdown conditions so that the valve could be repaire'd. The valve seat of 1 CF-12 was lapped and the internals (disc, hinge, and hinge pin) were replaced with new parts. The ,

valve was retested on March 2, 1981 and revealed zero leakage by the seat.

An analysis will be performed on the substance in the pivot gap of the valve to determine its origin. Extreme contamination of the 1 CF-12 internals, j however, has made examination of these parts undesirable at this point with a respect to personnel exposure. These parts remain in the Unit I reactor j

building. It is expected that examination of these it'.ernals will be feasible during the Unit l' refueling outage' scheduled for this summer. A report on the results of the analysis of the pivot gap substance in 1 CF-12 will be provided to tKe NRC when this information becomes available.

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