ML20084D673
| ML20084D673 | |
| Person / Time | |
|---|---|
| Site: | Dresden  |
| Issue date: | 04/14/1973 |
| From: | Worden W COMMONWEALTH EDISON CO. |
| To: | Anthony Giambusso US ATOMIC ENERGY COMMISSION (AEC) |
| Shared Package | |
| ML20084D675 | List: |
| References | |
| 2606, NUDOCS 8304120184 | |
| Download: ML20084D673 (2) | |
Text
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50-237
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Commonwealth Edison Company 72 WEST ADAMS STREET
- C H I C A G O.
ILLINOIS AM.en..e4 ter POST OPPICE 802 F41
- CHICAOO, ILLINOIS 40490 Dresden Nuclear Power Station s
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d Morris, Illinois 60450
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1 April 14, 1973 s-Aoq 9 bJ.-
Mr. A. Giambusso
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m Deputy Director for Reactor Frojects S
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Directorate of Licensing 4. n
's U. S. Atomic Energy Commission y
N ud Washington, D.C.
20545 c3
Subject:
License CRP-19 Dresden Muelnar Power Station. Unit f2, Section 0.0.C.1 of the Technical.5cecifications.
Dear Mr. Giambusso:
This is to report a condition relating to the operation of the unit in which on March 30, 1973, the containment cooling heat exchanger service water outlet valve, MO-2-1501-3A, failed to open during surveillance testing.
Problem and Investigation On March 30, 1973, at 0430 hours0.00498 days <br />0.119 hours <br />7.109788e-4 weeks <br />1.63615e-4 months <br /> while conducting a surveillance test on the containment cooling service water system, it was found that valve M0-2-1501-3A failed to open with a signal from the con-troller dPIC-2-1540-3A.
The subject valve is the outlet of the service water side of the 2A-1503 heat exchanger and is used to control the differential pressure between the service water side of the heat exchanger and the low pressure coolant injoction,LFCI, water side.
The valve is normally closed when both service water pumps are shutdown.
It is throttled to maintain the service water pressure 20 psig above LFCI system pressure whenever a service water pump is running.
The valve throttling is controlled bf a position modulator which re-ceives inputs from a differential pressure transmitter and valvo position sonsor.
The position modulator compares the differential j
pressure signal with the valve position signal and actuates a relay in the valve opening and closing control circuit to maintain 20 psig differential pressure.
The valve position signal is generated by a slide wire assembly located on the valve. The center tap of the slide wire is rotated by a geared shaft on the valve operator. The slide wire as embly p
b ese.12ese. 22e.1.
PDR ADOCK 05000237 g
PDR h
y 2-April 14, 1973 Mr.
ambusso is held in a position by a lock nut securing it to a mounting bracket.
When it was discovered that the valve would not operate from the control room, the valve was operated from the local manual station. After operating the valve manually, the system was again tested and found to operate satisfactorily from the control room.
The "B* containment cooling system was also tested satisfactorily.
The manual operation of the valve changed the conditions of the valve and thus hampered the determination of the exact cause of the failure. The investigation found the feedback resistor which feeds the position modulator tight and in the correct position. The valve limits were also checked and found to be correct.
A further investigation was conducted on April 5, 1973 A
simulated pump "on" and differential pressure signal to the transmitter were established.
The valve operated satisfactorily on four subsequent openings and closings.
At no time was there an indication that the slider arm had left the slide wire portion of the feedback resistor.
Although it cannot be conclusively determined, it is believed that the slide wire center tap rotated off the feedback resistor resulting in the input of a faulty signal to the controller and subsequent valve failure.
The failure of this valve to open would cause a partial loss of cooling to the LFCI injection water, but would have no effect on the injection of low pressure coolant into the vessel.
Failing closed would have no effect on the LFCI side and would insure high pressure on the service water side. Since the valve was manually operable and the required backup systems were avail-able, the failure was not considered to present any increased hazard to the public safety.
Corrective Action A similar failure occurred on the same valve on February 23, reported in our' letter dated March 23, 1973, and as a result an evaluation of the design was initiated and will be completed by June 1, 1973 The valve position feedback system will be modified as dictated by the evaluation.
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3AAtk 5.NoE W. P. Worden
- Superintendent Dresden Nuclear Power System WPW:CES:mlb
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