ML20084S148

Ro:On 730413,during Surveillance Testing,Two of Four Sustained High Reactor Pressure Switches Found Tripping Above Tech Spec Limit.Cause Not Stated.Pressure Switch Trip Points Reset.Investigation Underway

ML20084S148
Person / Time
Site:	Dresden
Issue date:	04/19/1973
From:	Worden W COMMONWEALTH EDISON CO.
To:	Giambusso A US ATOMIC ENERGY COMMISSION (AEC)
Shared Package
ML20084S151	List: ML20084S148 ML20084S159
References
320-73, NUDOCS 8306160184
Download: ML20084S148 (2)

Text

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( Commonwealth Edison Company ONE FIRST NATIONAL PLAZA 4 CHICAGO. ILLINOIS )

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Morris, Illinois 60450 ./,- t wi D April 19, 1973 s' h $

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Mr. A. Giambusso d 'f .,.r]. ,f$ .k/

Deputy Director for Reactor Projects -g 9 ,, . . , , . . ,

Directorate of Licensing .p y s.f .. .

e U. S. Atomic Energy Cocunission \

Washington, D. C. 20545 k[7'# M Y

SUBJECT:

LICENSE DPR-25. DRESDEN NUCLEAR POWER STATION, UNIT #3.

U. .- [ SECTION 6.6.3.3 OF tie T Cli:i1 CAL SPECIFICATIO :S..

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Dear Mr. Giambusso:

(\r' d This is to report a condition relating to the operation of the Aju unit in which, on April 13, 1973, two of four sustained high reactor

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pressure switches were found tripping at 1075 and 1073 psig during sur-

[. L ' s veillance testing. This is above the Technical Specification limit of q f 1070 psig for 15 seconds, as described in Table 3.2.2.

i PROBLEM AND INVESTICATION During a surveillance inspection of the sustained high reactor pressure switches, the setpoints for Heletron switches 3-263-53B and 53D were found to have drifted to 1075 and 1073 psig, respectively. The switches had previously been set at 1056 and 1058 psig, respectively. The purpore of these switches is to initiate use of the isolation condenser as a heat sink in the event that reactor pressure reaches 1070 psig or greater for at least 15 seconds. The isolation condenser was not required at the time the surveillance inspection was performed, since the reactor was being refueled.

Bad the isolation condenser been required prior to shutdown for refueling, it would have operated at a sustained reactor pressure of 1073 ,

psig, only slightly above the Technical Specifications limit of di 1070 psig. '

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Mr. A. Giambusso April 19, 1973 E e pressure switches are connected into a logic sequence of one out of two taken twice, so that overpressure trips on 263-53A or C, and 263-53B or D place the system in operation. Switches 53A and 53C were found set within Technical Specificatica limits, and 53B would have tripped at 1073 psig. Thus,

. the failure of switches 3-263-53B and 53D did not present a hazard to the

publicsafety.

CORRECTIVE ACTION The imediate corrective action was to reset the pressure switch trip points to 1052 psig for 53B and 1056 for 53D.

The Heletron model 372 pressura switch has shown a history of drif t in both the upward and downward direction. (Reference our letters dated August 1, 1972 and September 18, 1972). A spare switch of this type is presently being investigated under actual operating conlitions by the Station Instrument Department to determine the cause of setpoint drif t.

Findings of the investigation will dictate future corrective actions.

In addition, for the next 3 months, these pressure switches will be calibrated on a monthly basis. At that time, an evaluation will be made to determine frequency of future calibrations.

Sincerely, M.

W. P. Worden Superintendent WFW:do ec: WFW Ltr. File i

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