ML17252A927

Letter Reporting a 01/16/1974 Occurrence Relating to the Failure of Relief Valve 3-203-3A to Operate - Dresden Unit 3

ML17252A927
Person / Time
Site:	Dresden
Issue date:	01/25/1974
From:	Worden W Commonwealth Edison Co
To:	O'Leary J US Atomic Energy Commission (AEC)
References
WPW Ltr. #57-74
Download: ML17252A927 (3)

Text

-

• One Common .....th Edison First Na--- Plaza, Chicago, Illinois ftegul atory

• Address Reply to: Post Office Box 767 Chicago, Illinois 60690 WPW Ltr.i/57-74 Dresden Nuclear Power*'station R. R. ill Morris, Illinois 60450 January 25, 1974 Mr. J. F. O'Leary, Director Directorate of Licensing U. s. Atomic Energy Connnission Washington, D. C. 20545

SUBJECT:

LICENSE DPR*25, DRESDEN NUCLEAR POWER STATION, UNIT #3, REPORT OF ABNORMAL OCCURRENCE PER SECTION 6.6.B.l OF THE TECHNICAL SPECIFICATIONS.

ELECTROMATIC 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 H-345

Dear Hr. 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 faiied to operate. This malfunction is contrary to Section 3.5.C.l of the Technical Specifica_tions 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 operi. 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.*

7 .

00

. **~ ... :*, Mr. J. F. O'Lear- January 25, 1974 INVESTIGATION Electromatic 3-203-JA 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 found that the threads were gone and the disc could be pulled out. It is thought that the threads were destroyed due to vibration as the disc retainer is made of a softer material 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.

CORRECTIVE ACTIONS The threads in the valve. body were cl.eaned 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*38 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. vaives were found with the disc reta~ne~ se~~r~ly in place.-:

• r

• EVALUATION .*.:.:

. . ~ '

• I. H',..

The relief valve.a. of the automatic pressure relief subsystem are a back-up to the HPCI subsystem. They enable the core spray or LPCI to provide protection against. th~* *smli' pipe break in the event of HPCI failure, by depresslill1;zing the reactor v~ssel rapidly enough to actuate the core sprays or LPCI. The core spray and/or LPCI provide sufficient flow of coolant to limit fuel clad teniperatures 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 problemand 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 wil~ 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, wJO~

W. P. Worden Superintendent WPW:do

\

I

--N-- ""'

• • N - ..,.Met* ln.<Dr-NNNOIN CD

.9

......... - "' ..., co -

,.j l . ., .

'* ~.