ML20085K063

Ro:On 731208,during Routine Surveillance,Hpci High Flow Switch DPIS 3-2353 Operated at 25 Inches of Water Above Limit.Caused by Friction on Dial Indicator.Excess Slack of Wires Inside Switch Reduced

ML20085K063
Person / Time
Site:	Dresden, 05000000
Issue date:	12/27/1973
From:	Worden W COMMONWEALTH EDISON CO.
To:	Oleary J US ATOMIC ENERGY COMMISSION (AEC)
Shared Package
ML20085K054	List: ML20085K060 ML20085K063 ML20085K067 ML20085K070
References
934-73, NUDOCS 8310190359
Download: ML20085K063 (2)

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Chicago. Ilh 60690 ITPW Ltr.#934-73 Dresden N car Power Station

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December 27, 1973

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Hr. J. F. O' Leary, Director g

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Directorate of Licensing

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U. S. Atomic Energy Cc=sission NM@

Washington, D. C.

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SUBJECT:

LICENSE DPR-25. DRESDEN NUCLEAR FO'JER STATION, UNIT #3, REPORT OF Ub'JSCAL E'/EST PER S"CTICN 6.6.3.2 C7 T'.'E TECI;IC.\\L SPECI?!C\\TIO"3.

MALFUNCTION OF HICP PRESSURE CCOLAST INJECTION HIGH FLCW SWITC't.

References:

1) Dwgs: P & ID H-51

Dear Mr. O' Leary:

This letter is to report a condition relating to the operation of l

the unit at about 0400 hours0.00463 days <br />0.111 hours <br />6.613757e-4 weeks <br />1.522e-4 months <br /> on December 8, 1973. At this time the high pressure coolant injection high flow switch DPIS 3-2353 was found to cperate at 175 inches of water which is greater than the Technical Specification limit of 150 inches of water.

j PROBLEM At the time of the occurrence, Unit 3 was operating at a steady load of 680 F.Je.

During a routine surveillance it was found that HPCI high flow switch DPIS 3-2353 operated at a point 25 inches of water above the 150 inches of water limit. The switch was inspected and it was observed that the electrient wires inside the switch caused the high operating point.

INVESTICATION The switch cover was removed and the setpoint was' rechecked and found to be 145 inches of water which was within limits. The cause was determined to be friction on the dial indicator caused by the dial rubbing on the scale plate.

This friction was caused by an excess length of wire pushing on the scale plate.

Six #10 AWG wires are terminated inside the switch with the excess pushed up into the switch housing. The wires apparently worked free to a position in which they pushed on the scale plate.

This caused the dial to rub on the scale plate and thus require more differential pressure than normal to trip the switch. When the wires were pushed back into the housing, the scale plate pressure was removed, and the switch operated ac the required Technical Specification 1cvel.

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G310190359 740130 PDR ADOCK 05000249 COP ** 3FNT REGION _ '

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/Mr.J.F.oeary o

..Dacember 27, 1973 f-

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CORRECTIVE ACTION

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The irrediate corrective action was to pull the e:: cess slack out of the wires that terminate inside the switch. Additional action will be to notify Station Electrical Engineering of the problem and request a change in construction specifications to allow the use of smaller wire inside instruments.

In addition, a modification will be requested to remove the unused wires in all llPCI flow switches.

This will reduce the number of wires that must be terminated in the switch housing.

EVALUATIONS The failed switch was one of two switches that would isolate the llPCI steam line in the event of a high flow condition. The other switch DPIs 2352 was set at 144 inches of water and operated properly at that point.

Therefore, it is concluded that the safety of the plant personnel and of the general public was in no way compromised as a result of this switch failure.

This is the first malfunction of this type. This malfunction by itself does not reduce the safety of the unit's operation.

Sincerely,

,AsLcf NIc m d W. P. Worden Superintendent WFW:do e

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