ML20084Q829

Ao:On 730904,setpoint of Pressure Switch in Reactor Protection Sys Exceeded Limiting Condition for Operation by 2 Psi.Caused by Instrument Drift.Investigation Continuing

ML20084Q829
Person / Time
Site:	Quad Cities
Issue date:	09/12/1973
From:	Stephenson B COMMONWEALTH EDISON CO.
To:	Oleary J US ATOMIC ENERGY COMMISSION (AEC)
Shared Package
ML20084Q832	List: ML20084Q829 ML20084Q833
References
NUDOCS 8306140275
Download: ML20084Q829 (2)

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Comm :lth Edison j[ 3 Ouad Citi;s G:ntrating Stat.on /['SI Wy !

N Post Othee Box 216 1

Cordova,Ithnois 61242 /(

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• ll5LTi? f September 12, 1973 J. F. O ' Leary, Di rector Directorate of Licensing Regulation U. S. Atomic Energy Commission Washington, D.C. 20545 Subj ect: Q,uad-Cities Nuclear Power Station, Unit i Docket No. 50-254: DPR-29 Appendix A, Section 1.0.A.2, 3.1, and 6.6.B.

Deer Mr. O ' Leary:

On September 4,1973 the setpoint of a pressure switch in the Reactor Protection systen was found to exceed the Limiting Condition for Oper-ation by 2 psi. This abnormal occurrence was previously reported to you by telegram on September 5, 1973.

PROBLEM AND INVESTIGATION Routine calibration surveillance was being conducted on the high reactor pressure scram instrumentation on September 4, 1973. At this time the "as found" setpoint of PS 1-263-55A was discovered to be 1074 psig.

This is equivalent to a reactor pressure of 1062 psig since the instru-ment has a 12 psi head correction. The remaining three switches were found to trip at less than 1072 psig in accordance with Technical Specification 3.1. The subject switch is a Barksdale Model B2T-Al2SS.

EVALUATIONS AND CORRECTIVE ACTIONS

a. Safety Imolications The safety significance of exceeding the LCO for this switch by 2 psi is negligible. In addition, since the other 3 switches were set within specifications, a scram would have been initiated at a reactor pressure less than 1060 psig. '

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Mr. J. F. O ' Leary September 12, 1973 l l

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b. Determination of Cause and Cnrrective Action

, The pressure switch in question was last calibrated on August 1,1973  ;

and was found to trip at 1064 psig. No adjustment was made at that l time. Previous experienco H th drift of these instruments led to an increase of the surveillanct frequency from quarterly to monthly in January of this year. At tnat time the calibration setpoint was also i reduced to 1066 (+0,-10) ps!g td provide a margin for drift.

Since a further lowering of the calibration setpoint will not affect normal plant operation, the setpoint will be changed again to further increase the margin to the LCO. As a long term corrective action the Com,vonwealth Edison Company is continuing its investigation on the problem of instrument setpoint drift.

c. Cummutative Ewoorlence The drif t tendency of these instrurients has been the subject of several previous abnormal occurrence reports. In spite of this however, the safety implications are not significant. The corrective action described above has greatly reduced the frequency of these occurrences and the margin by which the LCO is exceeded, as in this case, has also been reduced substentially.

Very truly yours, COMMONVEALTH EDISON COMPANY QUAD CITI ES NUCL_ EAR _ POWER STATION

,/ f*bb 4 B. B. Stephenson Station Superintendent BBS/Ik cc: Regional Director Directorate of Regulatory Operations - Region 111 f

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