ML17252A919
| ML17252A919 | |
| Person / Time | |
|---|---|
| Site: | Dresden  |
| Issue date: | 03/22/1974 |
| From: | Stephenson B Commonwealth Edison Co |
| To: | O'Leary J US Atomic Energy Commission (AEC) |
| References | |
| BBS Ltr.#212-74 | |
| Download: ML17252A919 (3) | |
Text
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BBS Ltr.#212-74 Dresden Nuclear Power Station R. R. #1 U. ATOMIC HERBY flD1dlil ISSIOI le&nlatorJ
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SUBJECT:
LICENSE.DPR-25,DRESDEN NUCLEAR POWER.STATION, UNIT*il3, REPORT
- OF.. UNUSUAL-OCCURRENcE
- PER:SSCTION.6 ~ 6 ~ B~*2
- OF.m-* TECHNICAL * * *.
SPECIFICATIONS-. -.. *. :.
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- '-~- *-**,,.
-::.. PRIMARY-C:ONTAINHENT IS~LATION VALVE LEAKAGE,
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Refe~ences: l) Notification of Region Ill 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 from Mr. W. P. Worden (WPW Ltr.#468-73) 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 rate through any one isolation valve will not exceed 5% Lro (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 valves 220-57A & 220-58A and the other is bounded by valves 220-57A & 220-62A.
The leakage through 220-58A was in excess of that which could be determined by the leak rate test apparatus.
The leakage through 220-62A was 2017 scfh, which is above the
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.,.,J<.:-...** iMr. J. F. O'Leary March 22, 1974 5%- Lro-:::(48) -ot*--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" diameter swing type check valves (220-SSA*& 220-62A) were disassembled and inspected to determine the cause of the leakage *
. Upon disassembly it was determined that the "O"ring which seals the valve seat to the valve body was no longer-in its groove on either valve.
The "O"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 siiicone "O"ring on the bottom of the trim.
The silicone "O"ring is 3/16" diameter by 16" I.D. and conforms to MILR~S847 Class 2 Grade 70; Military Specification Rubber, Silicone, Low and High Temperature and Tear Resistant.
Class 2 has resistance to extreme high temperatur:e ( t:::: 425°F).
The absence-of this "O"ring is suspected to be the cause of the excessive leakage.
CORRECTIVE ACTION The appropriate corrective action bas not been.determined at this time.
The station has requested assistance from Couimonwealth Edison's Mechanical & Structural Engin~ering Department.
The appropriate corrective action, pending further review and investigation, will be completed prior to resuming power op~ration* A. foUo~-up *letter, detailing the results of the review and the*correcti,ve action, witi be submitted following completion of action.
EVALUATIONS Th~s 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 iinprobable break have occurred, the release would have been minor s'ince the leakage was through a circuitous path by the seal ring.
If the leakage was into the secondary containment, the Standby Gas Treatment
~Yli~~m offers a sufficient barrier to keep o~fsite doses_ within 10CFRlOO 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 l~ngths 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 be.en the only protection.
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- _.-*":._Mr. J. F. O'Leary March 22, 1974
- CU!iitiia_tiveuexp-er:ience on these. valves has. been poor re*garding leak rate tests. As mentioned above, the Unit 3 valves were modified to produce a bet'ter seal at the low test pressure of 48 psig and retain
- equally effective sealing at. high differential pressures.
In view ~f this. occurrence.a'nd*\\previous attempts to correct the problem, a :i::eview wUf *be ~co~duct~d to determine the appropriate corrective action.
Following completion of the review, the check _valves. in the "B" feedwater line wH.l;b~\\ test.ed 4n~. repail"ed or r~~ised.'in* accord.apce '_~ith the review's determination* of* the appropriate corrective acti~~
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Sincerely,
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BBS: JR: do
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