ML20084S136

Following Ro:On 730528,while Reactor in Startup Mode & Heatup in Progress Valve MO3-1501-22B Failed When Cycled for Diesel Generator Surveillance.Caused by Badly Worn Brake.Brake Assembly Replaced W/New Unit & Adjusted

ML20084S136
Person / Time
Site:	Dresden
Issue date:	06/14/1973
From:	Worden W COMMONWEALTH EDISON CO.
To:	Giambusso A US ATOMIC ENERGY COMMISSION (AEC)
Shared Package
ML20084S139	List: ML20084S136 ML20084S144
References
456-73, NUDOCS 8306160176
Download: ML20084S136 (2)

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-@ Comm ~lth Edis:n (j One First NeonM Ptm. Chicago. Uhnois qy3 N' -g;uy Address Reply Chicago, to Post Illinois 60690Office Box 767 50-249 WPW Ltr.#456-73 Dresden Nuclear Power Station R. R. #1 Morris, Illinois 60450 ,; 4 June 14, 1973 .-

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Q ;. . gI8g Mr. A. Giambusso ,

j Deputy Director for Reactor Projects -g , i, " M,q,7 A g' /

Directorate of Licensing U. S. Atomic Energy Commission g N g"f e Washington, D. C. 20545

SUBJECT:

_I,ICENSE DPR-2 5, DRESDEN NUCLEAR POWER STATION, UNIT #3,

_SECTION 6.6.C.1 0F THE TECHNICAL SFECIFICATIONS.

Reference:

Letter dated May 4,1973 from W. P. Worden to A. Giambusso concerning the failure of low pressure coolant injection valve 3-1501-22B.

Dear Mr. Giambusso:

This letter is to provide a followup report on the failure mode of motor operated valve 3-1501-22B and to report a subsequent failure of the valve which occurred on May 28, 1973. The failure on May 28 occurred before complete investigation into the cause of the failure could be ascertained. As was stated in the initial report, the inoperability of the valve was a result of a bent stem.

On May 28, 1973 at 2240 hours0.0259 days <br />0.622 hours <br />0.0037 weeks <br />8.5232e-4 months <br />, a subsequent failure of M.O.3-1501-22B occurred. At this time, the reactor was in the startup moue and a reactor heatup was in progress. The valve was being cycled for diesel generator surveillance. After the valve was opened, it would not close.

M.O 3-1501-22B was left open and M.O.3-1501-21B, a normally open valve in the injection line was closed. By opening M.O.3-1501-22B and using M.O.3-1501-21B as the isolation valve, the LPCI system remained in operation.

On a LPCI initiation signal, both M.O.3-1501-223 and M.O.3-1501-21B receive an open signal. Therefore, the failure of this valve is not considered to present any hazard to the public health and safety since the LPCI system was not degraded.

Investigation into the problem revealed that the failure was a result of a badly worn brake. The valve in question is designed to operate via a logic network, manually, or remotely from the Control Room. It is a normally closed motor operated valve with a Limitorque operator. The closing operation of the valve is controlled by the closing torque limit switch af ter the initial closing signal has been received. When the valve reaches A

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Mr. A. Giambusso O O June 14, 1973 its closed position, the valve seats with a predetermined amount of torque, dependent on the closing torque setting. When this value is reached, the closing torque limit switch opens and valve movement ceases. At this point, a friction brake engages and holds the valve in position. It was found that the brake had been improperly adjusted by the vendor and was engaged at all times. This caused excessive wear to the point where the brake was no longer serving its purpose. With the inoperative brake, and due to the gearing ratio of the operator, the valve would open slightly, af ter some time. This would allow the torque detecting device, (the Belleville spring washers) to relax, thus closing the close torque limit switch causing the valve to drive hard closed. This repeated " hammer effect" caused the valve. stem-to bend.

This is the first fsilure on Unit 2 and 3 which can be attributed to a faulty friction brake adjustment.

_ CORRECTIVE ACTION The brake assembly was replaced with a new unit and properly adjusted. The valve was tested satisfactorily and returned to service.

Sincerely,

.k As.cb W. P. Worden

. ' Superintendent WPW:do I

cc: File-AEC Corr./I i

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