ML20084T538
| ML20084T538 | |
| Person / Time | |
|---|---|
| Site: | Dresden  |
| Issue date: | 10/27/1972 |
| From: | Worden W COMMONWEALTH EDISON CO. |
| To: | Anthony Giambusso 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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October 27, 1972 WPA-D1,2,3
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gos Mr. A. Glanbusso
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Deputy Director for Reacter Projects
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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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