ML20085K041
| ML20085K041 | |
| Person / Time | |
|---|---|
| Site: | Dresden  |
| Issue date: | 01/25/1974 |
| From: | Worden W COMMONWEALTH EDISON CO. |
| To: | Oleary J US ATOMIC ENERGY COMMISSION (AEC) |
| Shared Package | |
| ML20085K044 | List: |
| References | |
| 57-74, NUDOCS 8310190346 | |
| Download: ML20085K041 (3) | |
Text
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Add Reply to: Post Othcc Box 767 Chicago, liiinois 60690 WPW Ltr.#57-74 Dresden Nuclear Power Station
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6 January 25, 1974 5
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SUBJECI:
LICENSE DPR-25, DRESDEN NUCLEAR POWER STATION, UNIT #3, REPORT OF ABNORMAL OCCURRENCE PER SECTION 6.6.B.1 OF THE TECHNICAL SPECIFICATIONS.
ELECTRCMATIC 3-203-3A RELIEF VALVE FAILURE.
References:
- 1) Notification of Region III of AEC Regulatory Operations Telephone: F. Maura, 1415 hours0.0164 days <br />0.393 hours <br />0.00234 weeks <br />5.384075e-4 months <br /> on January 17, 1974 Telegram:
J. Keppler, 1520 hours0.0176 days <br />0.422 hours <br />0.00251 weeks <br />5.7836e-4 months <br /> on January 17, 1974
- 2) Dwgs: P & ID M-345
Dear Mr. O' Leary:
This letter is to report a condition relating to the operation of the unit at about 2300 hours0.0266 days <br />0.639 hours <br />0.0038 weeks <br />8.7515e-4 months <br /> on January 16, 1974. At this time, electromatic relief valve 3-203-3A failed to operate. This malfunction is contrary to Section 3.5.C.1 of the Technical Specifications which requires that the HPCI subsystem shall be operable whenever the reactor pressure is greater than 90 psig and irradiated fuel is in the reactor vessel.
PROBLEM At 2300 hours0.0266 days <br />0.639 hours <br />0.0038 weeks <br />8.7515e-4 months <br /> on January 16, 1974, the reactor mode switch was in run and the unit was at a power level of 2124 MWt and 622 MWe. Electromatic relief valve surveillance was being performed so that the HPCI system could be taken out of service for maintenance..Electromatic relief valve 3-203-3A failed to open. The down stream temperature element indicated that the pilot valve operated, but the valve failed to open.
The other four electromatics operated satisfactorily.
HPCI surveillance was then run to verify operability, but HPCI proved to be inoperable. A unit shutdown was then commenced and the unit was placed in shutdown at 1817 hours0.021 days <br />0.505 hours <br />0.003 weeks <br />6.913685e-4 months <br /> on January 17, 1974.
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- l INVESTIGATION Electromatic 3-203-3A was removed from the drywell and disassembled.
The disc retainer, see Part 6 of Figure 1, was found cocked and could not be unthreaded. Upon inspection, it was fcund that the threads were gone and the disc could be pulled out.
It is thought that the threads were destroyed due 4
to vibration as the disc retainer is made of a softer mat.erial than the valve body. Then when the pilot valve was opened, the steam leaking past the destroyed threads was sufficient to keep the valve closed.
l CORRECTIVE ACTIONS The threads in the valve body were cleaned and a new disc retainer installed. The valve was then returned to service.
The other four valves were checked for a similar failure. The disc on valve 3-203-3B could be moved approximately 1/8 to 1/4 turn. The disc was removed and the threads were found in good condition. The other three valves were found with the disc retainer securely in place.
EVALUATION The relief valves of the automatic pressure relief.su': system are j
a back-up to the HPCI subsystem. They enable the core spray or LPCI to provide protection against the small pipe break in the event of HPCI failure, by depressurizing the reactor vessel rapidly enough to actuate the core sprays or LPCI. The core spray and/or LPCI provide sufficient flow of t
coolant to limit fuel clad temperatures to well below clad melt and to assure that core geometry remains intact.
Redundancy has been provided in the automatic pressure relief function in that only 4 of the 5 valves are required to operate.
Because of this single valve failure there were no safety implications to plant personnel or the general public.
This type of valve failure has not been experienced at the plant before.
It is not considered a generic problem and no cumulative experience regarding this type of failure exists. Therefore, the failure is not expected to recur. However, during the next refueling outage on Unit #2 an inspection will be made on its electromatic relief valves to perform an already scheduled modification and also to examine for characteristics similar to what was found on Unit #3.
Sincerely,
@.!, bh; W. P. Worden Superintendent WPW:do l
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