ML17252A474
| ML17252A474 | |
| Person / Time | |
|---|---|
| Site: | Dresden  |
| Issue date: | 12/16/1974 |
| From: | Stephenson B Commonwealth Edison Co |
| To: | James Keppler US Atomic Energy Commission (AEC) |
| References | |
| BBS Ltr. #894-74 | |
| Download: ML17252A474 (2) | |
Text
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Commonwea.dison One First National,
a, Chicago, Illinois Address Reply to: Post Office Box 767 Chicago, Illinois 60690 BBS Ltr. #894-74 Dresden Nuclear Power Station R. R. #1 Morris, Illinois 60450
-_ *** D~ceillbe~ 16, 1974 Mr. James G. Keppler, Regional Director*........
Directorate of Regulatory Operations"':'1'~g101L.'.i:II **
- u. s. Atomic Energy Commission 799 Roosevelt Road
-Glen Ellyn, Illinois 60137
~*
SUBJECT:
. REPORT OF UNUSUAL EVENT PER*SECTION-6.6.c OF THE TECHNICAL SPECIFICATIONS
... * *.*.,<. ~
DRESDEN UNIT 3, AEC DOCKET 5~249*.*_::, /
-~
Reference:
- 1) Regulatory Guide 1."16,fi~v ~,
- 1 App~ndix A
..*.. ~
- ~*: -~.:~.....-.
- 2)
Dresden Station Draw.{ng 356. -:.
Report Date:
December 16, 1974 Occurrence Date:
- November 22, 1974 Facility:
Dre*sden Nuclear Power Station, Morris'*~ I
.* -~
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IDENTIFICATION OF OCCURRENCE Failure of torus vent v~lve 3-1601-2PB toclo'se.
- CONDITIONS PRI0R TO OCCURRENCE Prior to the failure of AO --valve 3-1601-20B the Jmit Wa.s in the "Run" mode with a thermal power of 16o8 megwatts*.-Th.0 \\lliit was operating at a steady electrical load of 516 megwatts.
During the occurrence the instrument department was performing surveillance testing of. the. pres~e. switches which control*_
- A63-1601-20A and B.
No improper v8.lve position Wa.s noted prior to the surveillance test on 3-1601-20B.
DESCRIPTION OF OCCURRENCE On November 22, 1974 at about 1700 hours0.0197 days <br />0.472 hours <br />0.00281 weeks <br />6.4685e-4 months <br /> torus vent valve A0-3-16o1-20B failed to close after being opened.. No apparent cause of the failure could irmnediately be determined. Tpe valve was then manually blocked in the closed position and an investigation initiated.
/
- ~'**-'.-:.:--~;James G. Keppler.i.. ~.-
DESIGNATION OF APPARENT CAUSE OF OCCURRENCE From $e investigation it was' determined that the failure was due to settings on the pr..essure switch which causes the valve to fail safe on low instrument air pressure. The settings for~ -the switch were found to trip at 78 psi decreasing and 81 psi increasing~
- A review of the surveillance records indicates that the pressure switch was found to be 61 psi decreasing and 65 psi increasing at the last surveillance. Since the valve is spring assisted in the open direction the as-found settings had no effect on the open sequence~ However, when the valve control switch was placed in the "auto" position, which should close the valve, instrument air pressure dropped below the 78 psi trip setting of the pressure switch. The valve preformed as designed, as a resul_t of this apparent loss of control air signal, by utilizing the spring assist to return to the f_ull open position.
With the valve full open, instrument air pressure returned to about 90 psi which reset the.pressure switch. It is concluded that the valve malfunction can be partially attributed to the momentary decrease in instrument air
- pressure. This momentary decrease in instrument air pressure coupled with the as-found set point of the valve pressure switch caused the valve to remain open.
ANALYSIS -OF OCCURRENCE The failure of the 3-1601-20B valve to close did not.put the safety of the plant or public in jeopardy. The purpose of the 20B valve is to vent the torus if a vacuum build up occurrs. During the failure of the 20B valve a parallel vent line existed through the 20A valve.
CORREX;TIVE ACTIONS The immediate corrective taken was to block the 20B valve closed since it is only required to be open during a vacuum buildup in the torus. To correct the condition the trip and reset setting were changed from 78 psi decreasing and 81 psi increasing to 61 psi decreasing and 65 psi increasing. No additional corrective actions were taken because the problem was discovered
.during routine surveillance testing which is designed to detect this type of pressure set point drift.
FAILURE DATA There have been no failures of this type associated with the 1601, 20A, and B valves on either unit 2 or 3.
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