ML20149M883
| ML20149M883 | |
| Person / Time | |
|---|---|
| Site: | Cooper  |
| Issue date: | 02/19/1988 |
| From: | Trevors G NEBRASKA PUBLIC POWER DISTRICT |
| To: | NRC OFFICE OF ADMINISTRATION & RESOURCES MANAGEMENT (ARM) |
| References | |
| CNSS884010, NUDOCS 8802290206 | |
| Download: ML20149M883 (7) | |
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COOPER NUCLEAR STATION Nebraska Public Power District
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CNSS884010 February 19, 1988 l!.S.' Nuclear Regulatory Commission Document Control Desk Washington, DC 20535
Subject:
Containment Purge and Vent Valve Leak Testing Cooper Nuclear Station NRC Docket No. 50 - 298, DPR - 46
Reference:
- 1) Letter from W. O. Long to G. A. Trevors dated July 10, 1987, "Containment Purge and Vent Issues".
- 2) Letter from J. M. Pilant to D. B. Vassallo dated September 3, 1985, "Containment Purge and Vent Valve Leak Rate Testing".
Centlemen:
Reference 1 requested the District propose a program describing the testing intervals, acceptance criteria and reporting provisions for leak rate testing of the Containment Purge and Vent Isolation valves. The elements of this program were discussed with members of the NRC Staff during a September 29, 1987 meeting at Cooper Nuclear Station (CNS). This submittal provides a description of this program and additional information concerning the leak rate history of these valves.
There are four pairs of Containment Purge and Vent Isolation Valves with each pair consisting of an inboard motor operated (MV) valve, and an outboard air operated (AV) valve.
Each valve pair is located outside of primary containment and has a test connection between the valves to perform local leak rate testing. Beginning three months after startup from the 1988 refueling outage, the District will perform quarterly local leak tests on each valve pair. The measured leak rates from the four penetrations will then be added to the "as left" 1988 local leak rate test results for the other containment penetrations and compared with the value of L as defined in Section 4.7 of the Cooper Nuclear Station Technical Specifications. The maximum allowable leakage from the four penetrations will be L minus the total "as left" 1988 local leak rate results for the other contai*nment penetrations.
If a quarterly leak test for an individual penetration shows that the maximum allowable leakage has been exceeded, the leakage for each valve in that penetration will be quantified. The capability to ascertain the leakage through each valve in a pair will be achieved during the 1988 refueling outage.
If an individual valve leaks more than the maximum allowed as described above, containment integrity will be assured by tagging shut the other valve in that line.
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U.S. Nuciser Rsgulstory Commission February 19, 1988 Page 2 At the conclusion of one operating cycle, the containment purge and vent isolation valve leakage data will be submitted in a special report for NRC review.
If supported by the data, the valve leakage testing can then revert back to the 10CFR50 Appendix J interval for Type C Tests.
Reference 2 provided a leak rate and valve seal replacement history for the subject penetrations and valves for the period of 1975-1983.
An update to this history is attached and includes subsequent test results, as well as additional background on the testing history and frequency of valve operation.
The data demonstrates that in most cases where the penetration exceeded the CNS administrative leak rate limits, the majority of the leakage was due to one valve and that the other valve provided adequate containment integrity.
Our evaluation of the leak rate performance data indicates that the failures of the past were primarily related to the lack of proper lubrication of the valve seats. New seats were installed and lubricated in all eight valves during the most recent (1986) refueling outage. The preventive maintenance program has been amended to include replacement and lubrication of the seats at regular intervals.
In addition, steps are underway to reduce the number of valve operations that occur during the cycle in order to minimize the rechanical wear on the teats. The resulting improvement in the leakage performance of these valves is expected to be reflected in the quarterly leak rate test results.
Sincerely,
//h'kG
,, G.
revers Division Manager Nuclear Support GAT /sg Attachment cc:
U.S. Nuclear Regulatory Commission Region IV Arlington, TX NRC Resident Inspector Office Cooper Nuclear Station I
Attachaant CNSS884010 Page 1 of 1 CNS PURGE AND VENT VALVE LEAKAGE DATA X-25, Drywell Purge and Vent Supply This penetration is isolated by PC-232MV inboard and PC-238AV outboard.
Each valve is operated approximately 52 times a year. The penetration has failed local leak tests only twice.
In 1975, the initial leakage was determined to be 799.7 sefh.
Repairs were made to PC-238AV, reducing the leakage to 1.09 scfh.
Since no repairs were made to PC-232MV, the maximum "uncontained" penetration leakage could be assumed to have been 1.09 scfh.
In 1983, both valves were repaired. No record of leakage after the first repair is available. One-half of the initial leakage or 176.73 scfh must be assumed to have leaked from the penetration.
X-26, Drywell Purge and Vent Exhaust The inboard isolation valve, PC-231MV, is operated approximately 52 times a year and the outboard, PC-246AV, approxinately 100 times a year. Although local leak rate test failures have been reported for this penetration six times, the repair of a single valve has reduced the leakage to below the established limits in all but one case. The exception was in 1984, when both valves were repaired without recording the leakage after the first valse was repaired.
In this case, 50.14 scfh was assumed.
X-205, Torus Purge and Vent Supply The inboard and outboard valves, PC-233MV and PC-237AV respectively, are exercised approximately 52 times a year. The penetration has failed local leak tests only twice.
The 1978 leak rate test failure was attributed to leaking flange bolts.
After the bolts were tightened, the leakage was reduced to 1.93 scfh. No valve repairs were made.
In 1979, both valves were repaired without determining the leakage from each.
One-half of the total or 40.25 sefh was postulated to have been the maximum possible leakage from the penetration.
X-220, Torus Purge and Vent Exhaust The inboard valve PC-230MV, is operated approximately 52 times a year and the outboard, PC-245AV, is estimated to be operated 100 times annually. This penetration was failed local leak tests eight times. On five occasions, excessive leakage was reduced to below the limits after repairing one valve on the penetration.
In 1977 (568.98 scfh) and 1986 (29.59 scfh), one-half of the initial leakage was assumed, and in 1984, the leakage was quantified after repairing the ficst valve, indicating that the maximum penetration leakage was 11.85 scfh.
- l Although the containment purge and vent valves have been reported as having failed local leakage tests, a total of eighteen times, only on five occasions has the "uncontained" leakage from the penetrations exceeded the individual limits and only once has L been surpassed. Please note that these five leakage rates are conservaEively assumed to be one-half of the total for both valves on the penetrations. The CNS administrative leak rate limit for each valve pair, 7.5 sefh. The following charts diagram the "uncontained" penetratt.
ahage for the various penetrations.
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