ML20084D679
| ML20084D679 | |
| Person / Time | |
|---|---|
| Site: | Dresden  |
| Issue date: | 03/23/1973 |
| From: | Worden W COMMONWEALTH EDISON CO. |
| To: | Anthony Giambusso US ATOMIC ENERGY COMMISSION (AEC) |
| Shared Package | |
| ML20084D675 | List: |
| References | |
| 2027, 217-73, NUDOCS 8304120195 | |
| Download: ML20084D679 (2) | |
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O 50-237 Commonwealth Edison Company 72 WEST ADAMS 97REET
- C H I C A G O.
ILLINOIS Aaleiress A. ply for POST O F FIC E SOE F47
- C H I C A G O. IL LIN OIS 6049 0 Dresden Nuclear Power Statien R. R. #1 o-N.
Morris, Illinois 60450 J
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WP'd Ltr. #217-73 March 23, 1073 f8 f
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'"L' Mr. A. Gia=busso
. D. N y Deputy Director for Reactor Projects g
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Directorate of Licensing U. S. Atemic Energy Ccemission ij,g(Vd' Washington, D.C.
20545
SUBJECT:
LICENSE DPR-lo. DRFSDDI NUCL7AR PO*4ER STATION, UNIT #2, SECTION 6.6.c.1 of THE TECRJICAL SFECIFICATIONS.
Dear Mr. Giambusso:
This is to report a conditien relatin:: to the operation of the unit, in which, en February 23, 1973, during surveillance testine, the low pressure coolant injection (LPCI) centainment cooling heat exchanger service water cut-let valve failed to open.
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_PROBLDf AND INVESTIGATICN on February 23, 1973, at 0030 hours3.472222e-4 days <br />0.00833 hours <br />4.960317e-5 weeks <br />1.1415e-5 months <br /> while conducting surveillance tests, the containment cooling service water outlet valve,1501-3A, would not open.
The contairment ecoling heat exchancer service water outlet valve is normally closed when both service water pumps are shutdown. The valve is throttled automatically to maintain the service water pressure 20 psig above LPCI system pressure whenever a service water pumn is runninc. The valve throttling is centrolled by a positien modulator which receives inputs fren a differential p-essure tramitter and valve positien sensor. The position modulator ccmpares the di-
+ntial pressure signal with the valve position signal and actuates a relas, the valve crening and closing centrol circuit to maintain 20 psic different.al pressure.
The valve positien sienal is generated by a slide wire assembly located on the valve. The center tap of the slide wire is rotated by a Reared shaft en the valve operator. The slide wire assembly is held in a position by I
a lock nut securing it to a mounting bracket.
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The investigation revealed the lock nut securing the slide wire assembly had come loose allowing the entire assembly to rotate rather than only the center tap. As a result of this, a faulty signal was input to the position modulator which called for the 1501-3A valve to remain in the closed position.
The loosening of the lock nut is believed to be caused by over-travel of the slide wire center tap which exerts a torque en the entire assembly resulting in loosening of the lock nut and eventual faulty valve position signal. A similar problem has bee.n experienced with this and other slide wire assemblies on the containment cooling eervice water pressure control systems.
The failure of the containment cooling heat exchanger service water outlet valve would have slichtly reduced _the cooline _ capacity of the system; however, the valve was manu1117, operable and the required backup systems were tested.
CORRECTIVE ACTION The slide wire assembly was adjusted and the lock nut tightened.
We are evaluating modificatiens to the slide wire assembly which might minimize the pctential for recurrence of this type of failure. 'de expect to have our evaluation completed by June 1, lo73, and will make changes as dictated by that evaluation. Additionally, the slide wire assembly will be checked en valve 1501-3B en Unit 2, and valves 1501-3A and 3B on Unit 3, for tightness.
O W. P. L'orden Superintendent WPW:CES:jw cc: WFW Ltr. File 2027 j