ML20084T538

Ro:On 721020,while Conducting Monthly Calibr Surveillance on Offgas Monitors,Offgas Monitor 1 Trip Point Found Out of Calibr.Caused by Drifting of Trip Setting.Calibr Surveillance Will Be Conducted Twice a Month

ML20084T538
Person / Time
Site:	Dresden
Issue date:	10/27/1972
From:	Worden W COMMONWEALTH EDISON CO.
To:	Giambusso A US ATOMIC ENERGY COMMISSION (AEC)
References
245-72, NUDOCS 8306230251
Download: ML20084T538 (2)

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50-249 Commonwealth Edison Company -

72 WEST ADAMS STREET

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• cnicAoo stainois soeve Nuclear Power Station R. R. #1 'g N Morris, Illinois 60450 October 27, 1972 N)

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Mr. A. Glanbusso s 'Q:,y .a.F, ^ , .,

'4" Deputy Director for Reacter Projects U.% -

Directorate of Licensing ~**""(.

U. S. Atomic Energy Commission Washington, D.C. 20545

Subject:

License DPR-25. Dresden Nuclear Power Station. Unit #3, Section 6.6.B.2 of the Technical Specifications

Dear Mr. Giaabusso:

This is to report a condition relating to the operation of the station, in which the #1 off-gas monitor trip point was found out of

, calibration, and in apparent conflict with section 3.2.D.1 of the Tech-nical Specifications.

PROBLEM AND INVESTICATION On October 20, 1972, while coaducting the monthly calibration surveillance on Unit #3 off-gas monitors, #1 monitor trip point was found to have drifted from the previously "as lef t" setting of 3500 units to 5000 units. Upon initial evaluation of the "as found" setting, based on a conservative calibration curve, it was concluded that the trip setting had drifted to a value which was equivalent to a release rate of LO Ci/sec.

(Technical Specification limit is 0.7 Ci/sec.) The trip was immediately reset to a value of 3500 units, which would be equivalent to approximately 0.65 Ci/sec. , based oihte above referenced conservative curve.

Subsequent evaluation, based upon a more reasonable calibration curve, indicates that the actual release rate, at a monitor setting of 5000 units was approximately 0.45 Ci/see and was well within Technical Specification requirements. However, the cause of the instrument " drift" is of concern.

There has been no history of calibration " drift" with the off-gas monitors to date.

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Mr. A. Gismbusso October 27, 1972 The monitors require a very high impedance for operation. This,in conjunction with the fact that the monitors contain electronic tubes that may 0 drift with age, may explain the drift of the trip point.

CORRECTIVE ACTION

. The calibration surveillance for the off-gas monitors will 'oe conducted twice this month to determine if the trip point is continuing to drift. Additionally, a calibration curve more representative of monitor reading versus actual release rate will be utilized.

Sincercly, k ,,n J. P. Worden

. Superintendent WPW:GJD:sdb 1

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