ML20084Q163

Ro:On 740218,annunciator Auto Blowdown Interlock Core Spray/ RHR Alarmed.Caused by Shorted Pressure Switch in RHR Logic Circuit.Defective Switch Replaced

ML20084Q163
Person / Time
Site:	Quad Cities
Issue date:	02/27/1974
From:	Stephenson B COMMONWEALTH EDISON CO.
To:	Oleary J US ATOMIC ENERGY COMMISSION (AEC)
Shared Package
ML20084Q166	List: ML20084Q163 ML20084Q178
References
BBS-74-43, NUDOCS 8306130151
Download: ML20084Q163 (2)

Text

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- -- z Comm ealth Edison Quid-Citi:s G:n: rating Station O*8 Post Office Box 216 Cordova,lilinois 61242 Telephone 309/654-2241 e *

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February 27, 1974  %

i Mr. John F. O' Leary, Director Directorate of Licensing Regulation U. S. Atomic Energy Commission Washington, D. C. 20545

Reference:

Quad-Cities Nuclear Power Station, Unit 2 Docket No. 50-265, DPR-30, Appendix A Table 3.2.2

Dear Mr. O' Leary:

The purpose of this letter is to inform you of the details concerning the instrument failure reported to you by tele-gram at 1030 on February 19, 1974. It was also reported by telephone at 0900 on the same day to Region III, Directorate of Regulatory Operations.

PROBLEM AND INVESTIGATION At 1100 on February 18, 1974, while operating at a steady state condition of 2321 MWt and 777 MWe, the annunciator " Auto Blowdown Interlock Core Spray /RHR" alarmed. No surveillance was being performed at the time. An investigation revealed the cause to be a shorted pressure switch in the RHR logic circuit. This switch, No. 2-1053D, closes when the discharge pressure of the 2D RHR pump gets to 85 psig. There are eight ,

of these switches which sense discharge pressure from the l RHR and Core Spray pumps. They serve a permissive function '

to delay initiation of Auto Blowdown until operation of one of the low pressure core cooling systems is verified.

PS-2-1053D shorted because of moisture collection in the case.

It is a Static "O" ring model 6N-L3 which operates by a piston pushing against a spring to actuate a microswitch. The work-  !

ing fluid is separated from the instrument case by a diaphragm "O" ring assembly.  ;

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O O Mr. John F. O' Leary February 27, 1974 Table 3.2.2 of the Technical Specifications requires that all instrument channels be operable or tripped; in this case the tripped condition would be open, not shorted. At 1700 on February 18, 1974 the faulty pressure switch was replaced with a new one and calibrated in accordance with station sur-veillance procedures.

EVALUATION AND CORRECTIVE ACTION SAFETY IMPLICATIONS The safety implications of this failure are minor since the ~

system is designed to tolerate a single' instrument failure.

Had the criteria for auto blowdown been satisfied, low low level and drywell pressure, the logic circuit would still have required a second pressure switch to be picked up by pump pressure before allowing actuation of Auto Blowdown.

DETERMINATION OF CAUSE AND CORRECTIVE ACTION The termination box adjacent to the instrument was opened to check for water and found dry. The defective pressure switch was replaced, disassembled and inspected. A frayed diaphragm was discovered in the switch which allowed water t.o enter. Since the failure was an isolated case and similar failures in the future will result in an alarm, no further corrective action is contemplated. In addition, the remaining seven Static "O" ring pressure switches in this subsystem were checked and found to be dry.

EVALUATION OF CU'4ULATIVE EXPERIENCE FOR SAFETY IMPLICATIONS This is the first failure of this type experienced at Quad-Cities. There are no safety implications due to cumulative experience.

Very truly yours, COMMONWEALTH EDISCN COMPANY QUAD CITIES NUCL R POWER STATION

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. . te enson Station perintendent BBS/lk cc: Regional Director Directorate of Regulatory Operations-Region III

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