ML17252A936
| ML17252A936 | |
| Person / Time | |
|---|---|
| Site: | Dresden  |
| Issue date: | 12/19/1973 |
| From: | Worden W Commonwealth Edison Co |
| To: | O'Leary J US Atomic Energy Commission (AEC) |
| References | |
| WPW Ltr #918-73 | |
| Download: ML17252A936 (2) | |
Text
Dresden Nuclear Power Station R. R. #1
--__,.~
Mr. J
- F. 0 1 Leary, Director~;.;;._--
Directora te of Licensing U. S. Atomic Energy Commission Washington, D. C.
20545
SUBJECT:
Morris, Illinois 60 December 19, 1973
References:
- 1)
L~tter from Mr. W. P. Worden to Dr. P. A.. Morris dated May 18, 1972.
- 2) Dwg. P & ID M-356
Dear Mr. 0 1Lear.1:
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 5% Lt0 (48).
PROBLEM, INVESTIGATION, & 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, 3-1601-62, and 3-1601-63.
The leakage discovered was 435.29 scfh which is above the 5% Lt0 (48) (29.381 scfh) maximti.m leakage allowed through any one isolation valve, but below Lp(783.493 scfh) the maximum total allowable leakage.
During subsequent investigation to determine the leakage flow path, a blind flange was install,ed.in front of the 3-1601-24 valve.
This reduced the leak[ge to 254.i2 scfh on November 21, 1973. Another blind flange was installed in front of the 3-1601-23 valve,which is in series wi.th 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 infonnation, the leakage paths and rates are as follow:
3-1601-23 3-1601-24 176.48 scf/hr.
254.12 scf/hr.
Q1n5*<<.
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, *.1
- ,-,.;;:;r~J;f1'"~....../ Mr* J. F. O'Leary December 19, 1973 Since the Technical Specifications do not require shutdown for leak~ge_~f_ this magnitude, Unit 3 has continued operation at power.
Th,ese valves"will be inspected during the next extended outage to detennine the mode of failure. The blind flanges will remain in place until primary containment integrity-is no longer required.
EVALUATIONS 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 272.43 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).
Although there may have been some leakage from the drywe11 through the.. '.reactor building vent stack, the stack was continuously monitored and the leakage in no way represented an uncontrolled release.
The leakage th~refore r~presented no safety hazard to the plant or the public.
Leakage through the rubber seated butterfly vent valves has been a recurring problem on both Units 2 and J. The*problems have been related to the rubber seats. The recommE;inded fix was to change the seat material from Bi.uia.:.w* rubber to 11EPT", a. rubber compound.
See Reference (1).
The new rubber seats were installed in the two above.mentioned valves
- during the Spring 19,73 outage. It is not known whether the leakage is asso*ciated with the.ru.bber. seats or another unr~lated problem.
'!'he valves will be inspected and repaired *during"the Spring 1974 outage. A followup letter will be subinitted at that time.
~* *, -
_ Sincerely,
-7. l'. *$'471$ ~
$.~£/.
w.-P. Worden
_ Superintendent WPW:ls