ML20085K080

Ao:On 740114,during Routine Monthly Surveillance Testing, Condenser Low Vacuum Scram Switches PSL3-503A,B,C & D Actuated Below Tech Spec Setpoint.Cause Not Stated. Different Type of Switch Will Be Installed

ML20085K080
Person / Time
Site:	Dresden
Issue date:	01/22/1974
From:	Worden W COMMONWEALTH EDISON CO.
To:	Oleary J US ATOMIC ENERGY COMMISSION (AEC)
Shared Package
ML20085K085	List: ML20085K080 ML20085K087
References
51-74, NUDOCS 8310200063
Download: ML20085K080 (2)

Text

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x Commewcalth Edicon 3 ) One riri Acnat Plan. Chicago, t!bnois v.

' Adcress Heply to: Post Office Box 767 Chicago, lainois 00690 WFW Ltr.451-74 Dresden Nuclear Power Station R. R. #1

~'N 1: orris, Illinois 60450 m

,x January 22, 1974

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!!r. J. F. O' Leary, Direc tor

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Directorate of Licensing i, -

U. S. Ato : tic Energy Co::nission

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Uashington, D. C.

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SUBJECT:

_ LICENSE DPR-25. DRESDP!!_PUCLEAR TOWER STATION, itNIT #3, REFORT C / n:mo"AL OCCUEENCE PER SECTIC!I 6.6. B. l. A OF THE TECNICAL SN:CNfIC\\TIO"3.

CO'!DE 3ER LOW VisCUL"! SCRAM SWITCH DRIFT.

References:

1) Notification of Region III of AEC Regulatory Operations Telephone: !!r. I'. aura at 1400 hours0.0162 days <br />0.389 hours <br />0.00231 weeks <br />5.327e-4 months <br /> on 1/15/74.

Telegram: !!r.1:eppler at 1530 hours0.0177 days <br />0.425 hours <br />0.00253 weeks <br />5.82165e-4 months <br /> on 1/15/74.

2) Dwgs: P & ID !!-3t:6

Dear Mr. O' Leary:

This letter is to report a condition relating to the operation of the unit at about 1800 hours0.0208 days <br />0.5 hours <br />0.00298 weeks <br />6.849e-4 months <br /> on January 14, 1974. At this tire condenser low vacuum scram switch PSL 3-503C was found to operate at 22.35 inches of IIg.

This t-c1 function is centrary to Table 3.1.1 of the Technical Specifications which requires the condenser vacuum switches to be set at greater or equal to 23 inches Hg vacuum.

PR03LEM

. At the tice of the occurrence, Unit #3 was operating at a steady load of 620 1Me. The Instrument Department was conducting routine monthly curveillance testing on condenser low vacuum scram switches PSL3-503A, 3. C and D.

At thin time, PSL3-503C was found to actuate at 22.35 inches Itg vacuum, which is 0.65 inch Hg vacuum below the required setpoint. The switch was im=cdiately reset. to 23.75 inch Eg vacuum..

The function of PSL3-503C is to scram the unit in the event condenser vacuum falls below 23 inch Ug.

This vacuum level is necessary to assure adequate heat sink capability of the condenser.

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lir. J. F. O'Le January 22, 1974 TITVESTIC ATIO {

PSL3-503C is a Barksdalc !!odel DlT-lll8SS diaphraga pressure switch with a 0.4 to 18 psi range. The switch was found below the Technical Specification limit once in 1973 and in October of 1973 the switch was f ound set at 25.5 inch lig which was above the Dresden target band of 23.7 + 0.2 inches !!s.

!!o violations occurred in 1972.

The perfortance of the four switches as a group is somewhat unreliabic.

They seem to be susceptible to periodic changes in setpoint after periods of stable repeatability.

CORRECTTVE ACTION At this tima, PSL3-503A,B.C and D do net appear to have the repeatability necessary to consistently comply with the Technical Specifi-cations. To correct the problem, a different type of switch will be installed on Unit 3 for evaluation.

Vacuum switches manufactured by the Static-0-Ring Corporation have exhibited very good reliability on similar applications. The new switches will be installed as soon as Quality Assurance precedures and approvals can be completed, and the new switches received from the vendor.

}'NALUATION PSL3-503C and A both provide scram signals to scram channel "A".

Switch "A" was found to comply with the Technical Specification requirencnt and functioned properly when tested.

It is therefore concluded that the redundant circuit system functioned as designed and therefore the safety of the plant personnel or the general public was in no way jeopardized as a result of this occurrenca.

Sincercly, W. P. Worden Superintendent

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