ML20085J996

Ro:On 740313,tests of Feedwater Check Valves 3-220-58A & 3-220-62A Revealed Leakage Through Each Valve in Excess of Tech Spec Limit.Caused by Misaligned O-ring Which Seals Valve.Corrective Action Pending Review

ML20085J996
Person / Time
Site:	Dresden
Issue date:	03/22/1974
From:	Stephenson B COMMONWEALTH EDISON CO.
To:	Oleary J US ATOMIC ENERGY COMMISSION (AEC)
Shared Package
ML20085J993	List: ML20085J988 ML20085J996 ML20085J998 ML20085K002
References
212-74, NUDOCS 8310190301
Download: ML20085J996 (3)

Text

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w- _ C mm i Orts FirsWonal {7cith Edison Plaza. Chicago. Illinois Address Reply to: Post Office Box 767 Chicago, Illinois 60690 50-249

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350.Ltr.#212-74 Dresden Nuclear Power Station  ;

R. R. #1 Morris Illinois i3t March 22, 1974 ~~~

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- -- e Mr. J. F. O' Leary, Director -

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U. S. Atomic Energy Couunission g \q N

Washington, D. C. 20545 G

SUBJECT:

LICENSE DPR-25. DRESDEN NUCLEAR POWER STATION UNIT d3 REPORT OF UNUSUAL OCCURRENCE PER SECTION 6.6.B.2 0F THE TECHNICAL SPECIFICATIONS.

PRIMARY CONTAINMENT ISOLATION VALVE LEAKAGE.

References:

1) Notification of Region III of AEC Regulatory Operations Telephone: Mr. F. Maura, 1400 hours0.0162 days <br />0.389 hours <br />0.00231 weeks <br />5.327e-4 months <br /> on March 14,'1974 Telegram: Mr. J. Keppler,1510 hours0.0175 days <br />0.419 hours <br />0.0025 weeks <br />5.74555e-4 months <br /> on March 14, 1974

2) Dwgs: P&ID M-347

3) Letter to Mr. A. Giambusso fr m Mr. W. P. Worden (WPW Ltr.d468-73) dated June 20, 1973.

Dear Mr. O' Leary:

This letter is to report a condition relating to Local Leak Rate Testing while the unit was shutdown for refueling. The test was conducted on the day shift on March 13, 1974. The tests of feedwater check valves 3-220-58A & 3-220-62A determined that the leakage through each valve was in excess of the Technical Specification limit. This malfunction is contrary to Section 4.7.A.2.f. which specifies that the total leakage g

rate through any one isolation valve will not exceed 57. LTO (48) .

• PROBLEM At the time of the deviation, the unit was shutdown for refueling and LLRT was being conducted.

During testing of the Unit 3 "A" line feedwater check valves on March 13, 1974, excessive leakage was discovered from both tested volumes.

One of the tested volumes is bounded by valver 220-57A & 220-58A and the l other is bounded by valves. 220-57A & 220-62A. The leakage through 220-58A l was in excess of that which could be determined by the leak rate test i apparatus. The leakage through 220-62A was 2017 scfh, which is'above the -ll l'" $

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Mr. J. F. O'L h March 22, 1974 5%L' TO (48) or 29.381 scfh maximum leakage allowed through any one isolation valve. Both tests were also in excess of the maximum total allowable leakage (783.493 scfh).

INVESTIGATION The 18" dismeter swing type check valves (279-58A & 220-62A) were disassembled and inspected to determine the cause of the leakage.

Upon disassembly it was determined that the "0" ring which seals the valve seat to the valve body was no longer in its groove on either valve. The "0" rings were installed as a modification (M12-3-73-112) in June of 1973 to replace the original stainless steel trim seal ring. The stainless steel seal ring which was located on the periphery of the trim was replaced by a silicone "0" ring on the bottom of the trim.

The silicone "0" ring is 3/16" diameter by 16" I.D. and conforms to MILR-5847 Class 2 Grade 70; Military Specification Rubber, Silicone, Low and High Temperature and Tear Resistant. Class 2 has resistance to extreme high temperature ( 2 425 0F). The absence of this "O" ring is su'spected to be the cause of the excessive leakage.

CORRECTIVE ACTION The appropriate corrective action has not been determined at this time. The station has requested assistance from Commonwealth Edison's Mechanical & Structural Engineering Department. The appropriate corrective action, pending further review and investigation, will be completed prior to rasuming power operation. A follow-up letter, detailing the results of the review ano the corrective action, will be submitted following completion of action.

EVALUATIONS This occurrence did not endanger the safety of the public or of plant personnel. The particular valves in question serve to prevent

- excessive release of reactor water (vapor) into the reactor or turbine building should the feedwater line break in either of these areas. Should the highly improbable break have occurred, the release would have been minor since the leakage was through a circuitous path by the seal ring.

If the leakage was into the secondary containment, the Standby Gas Treatment System offers a sufficient barrier to keep offsite doses within 10CFR100 and station procedures protect plant personnel. If the leakage was into the turbine building, motor operated valves are available to effectively isolate the leak with the exception of two lengths of approximately 12 feet each between the MO valves in the turbine building and secondary containment. The probability of a failure of this piping is so remote -

as to be considered non credible. Should it have failed station emergency procedures would have been the only protection.

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• Mr. J. F. O'Le March 22, 1974

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Cumulative experience on these valves has been poor regarding leak rate tests. As mentioned above, the Unit 3 valves were inodified to produce a better seal at the low test pressure of 48 psig and retain equally effective sealing at high differential pressures.

In view of this occurrence and previous attempts to correct the problem, a review will be conducted to determine the appropriate corrective action. Following completion of the review, the check valves in the "B" feedwater line will be tested and repaired or revised in accordance with the review's determination of the appropriate corrective action.

Sincerely,, .,

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