ML20085K141

Ro:On 731120,during Local Leak Rate Testing,Excessive Leakage Discovered from Valves 3-1601-23,24,60,61,62 & 63. Caused by Worn Rubber Seats on Vent Valves.Seat Matl Changed

ML20085K141
Person / Time
Site:	Dresden
Issue date:	01/17/1974
From:	Worden W COMMONWEALTH EDISON CO.
To:	Oleary J US ATOMIC ENERGY COMMISSION (AEC)
Shared Package
ML20085K144	List: ML20085K141 ML20085K145
References
43-74, NUDOCS 8310200207
Download: ML20085K141 (2)

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-1 One Fits aational Ptara. Chicago. Ilkno.s Address Reply to: Post Othee Box 767 '

Chicago, !!!inois 60690 50-249 WFW Ltr.d43-74 Dresden Nuclear Power Station r is Illinois 60450

' January 17, 1974 ,'N -

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Mr. J. F. O' Leary, Director R:

c % l 4 3-l Directorate of Licensing  ; ,' k I

U. S. Atomic Energy Commission

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N J' g' Washington, D. C. 20545

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SUBJECT:

LICENSE DPR-25, DhESDEN NUf'f_-EAR POWER STATION, UNIT 43. REPORT OF UNUSUAL EVENT PER SECTION 6.6.B.2 OF THE TECHNICAL SPECIFICATIONS.

PRIMARY CONTAIEMENT ISOLATION VALVE LEAKAGE.

1

References:

1) Letter from Mr. W. P. Worden to Dr. P. A. Morris dated i May 18, 1972.

2) Dwg. P & ID M-356

3) Letter from Mr. W. P. Worden to Mr. J. F. O' Leary dated December 19, 1973.

Dear Mr. O' Leary:

Thistext The corrected ' letter is to below:

is given correct errors in the letter of Reference 3.

This letter is to report a condition relating to the operation of the unit at about 1100 hours0.0127 days <br />0.306 hours <br />0.00182 weeks <br />4.1855e-4 months <br /> on November 20, 1973. At this time, while conducting local leak rate testing of primary containment isolation vent valves on the drywell and torus, the test of the volume bounded by valves -

3-1601-23, 3-1601-24, 3-1601-60, 3-1601-61, 3-1601-62, and 3-1601-63 revealed excessive leakage. This malfunction is contrary to section 4.7.A.2.f which specified that the total leakage rate through any one isolation valve will not exceed 57. Leo (48). ,

PROBLEM, INVESTICATION, & CORRECTIVE ACTION During local leak rate testing of the Unit 3 drywell and torus vent valves on November 20, 1973, excessive leakage was discovered from .

the volume bounded by valves 3-1601-23, 3-1601-24, 3-1601-60, 3-1601-61, I 3-1601-62, and 3-1601-63. The leakage discovered was 435.29 scfh which is above the 57. Lea (48) (29.381 sefh) maximum leakage allowed through any one isolation valve, but below Lp(783.493 scfh) the maximum total allowable leakage.

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Nr. J. F. O' W e O Jntuary 17, 1974 During subsequent investigation to determine the leakage flow path, a blind flange was installed in front of the 3-1601-24 valva. This reduced the leakage to 254.12 scfh on November 21, 1973. Another blind flange was installed in front of the 3-1601-23 valve, which is in series l with the 3-1601-24 valve, on November 27, 1973. This reduced the total leakage to 4.69 scfh, which is within the limit specified above. Using this information, the leakage paths and rates are as follows:

3-1601-23 249.43 scf/hr.*

3-1601-24 181.17 scf/hr.*

Since the Technical Specifications do not require shutdown for leakage of this magnitude, Unit 3 has continued operation at power. These valves will be inspected during the next extended outage to determine the mode of failure. The blind flanges will remain in place until primary

! containment integrity is no longer required.

.i gvALUATIONS Combining the data from the above described tests and the local leak rate tests conducted during the Spring 1973 outage yields a total leakage of 281.80 scfh* which compares favorably with the maximum total allowable leakage (Lp - 783.493 scfh). (The leakage through two valves in series is not the sum of the individual leakages, but the smaller of the two leakages).

t Although there may have been some leakage from the drywell through the reactor building vent stack, the stack was continuously moni-tored and the leakage in no way represented an uncontrolled release. The leakage therefore rapresented no safety hazard to the plant or the public.

Leakage through the rubber seated butterfly vent valves has I 1

been a recurring problem on both Units 2 and 3. The problems have been related to the rubber seats. The recommended fix was to change the seat material from Buna-N rubber to "EPT", a rubber compound. See Reference (1).

The new rubber seats were installed in the two above mentioned valves during the Spring 1973 outage. It is not known whether the leakage is associated with the rubber seats or another unrelated problem. The valves will be inspected and repaired during the Spring 1974 outage. A followup letter will be submitted at that time.

• These numbers correct the errors made in the letter of Reference 3.

l Sincerely, W.P Wo W. P. Worden Superintendent WPW:do

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