ML17252B016

Letter Reporting a 10/20/1972 Discovery of the #1 Off-Gas Monitor Trip Point to Be Out of Calibration and in Apparent Conflict with Section 3.2.D.1 of the Technical Specifications - Dresden Unit 3

ML17252B016
Person / Time
Site:	Dresden
Issue date:	10/27/1972
From:	Worden W Commonwealth Edison Co
To:	Giambusso A US Atomic Energy Commission (AEC)
References
Ltr. 3245-72, WPW-D1, 2, 3
Download: ML17252B016 (2)

Text

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• • ~11

• Commonwealth Edison Company 50-249 72 WEST ADAMS STREET

• CHICAGO, ILLINOIS.

Addr.,. llep/y fo, POST OFFICE BOX 767 *CHICAGO, ILLINOIS 60690 Dresden Nuclear .Power Station R. R. 1Fl Morris, Illinois 60450 October 27, 1972 WPW-Dl,2,3 Ltr. 11245-72 Mr. A. Giambusso Deputy Director for Reactor Projects Directorate of Licensing

• u. s. Atomic Energy Conunission Washington, D.C. 29545

Subject:

License DPR-25, Dresden*Nuclear Power Station, Un::i..t #3, Section 6.6.B.2 of the Technical Specifications

Dear Mr. Giambusso:

This. is .. to report a condition relat,ing to. the operation of the station, in which the 1F1 off-ga~ nio~itor trip* p.ofot. was found *O'l:lt .. of calibration, and in apparent conflict with section 3.2.~.l o( the ~ech nical Specifications*~

PROBLEM AND INVESTIGATION On October 20, 1972, while conducting the monthly calibration surveillance on Unit #3 off-gas monitors, #1 monitor trip point was found to have drifted from the previously "as left" 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 1.0 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 on the above referenced conservative curve.

Sub§equent 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/sec and was well within Technical

• Specification~

requireme.nts. 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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~ ~~ e Mr. A. Giambusso 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 drift with age, may explain the drift of the trip point.

CORRECTIVE ACTION The calibration surveillance for the off-gas monitors will be 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.

Sincerely,

w. P. Worden Superintendent WPW: GJD: sdb cC.:: WPW Ltr. File