ML20084F611
| ML20084F611 | |
| Person / Time | |
|---|---|
| Site: | Dresden  |
| Issue date: | 11/03/1972 |
| From: | Worden W COMMONWEALTH EDISON CO. |
| To: | Anthony Giambusso US ATOMIC ENERGY COMMISSION (AEC) |
| Shared Package | |
| ML20084F577 | List: |
| References | |
| 6091, NUDOCS 8304210188 | |
| Download: ML20084F611 (2) | |
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Commonwealth Edison Company 72 WEST ADAMS STREET
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'Mr. A. Giambusso Deputy Director for Reactor Projects Directorate of Licensing U. S. Atomic Energy Commission Washington, D. C.
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SUBJECT:
LICENSE DPR-19. DRESDEN NUrLEAR POWER STATION, UNIT #2,'SECTION 6.6.B.3 0F THE TECHNICAL SPECIFICATIONS.
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Dear Mr. Giambusso:
This is to report a condition relating to the operation of the unit in which, on October 25, 1972, the setpoints of two of the low pressure main steam line switches were found to have drif ted slightly below the value specified in table 3.2.1 pg. 38 of the Technical Specifications.
PROBLEM AND INVESTICATION On October 25, 1972, during routine calibration of the low pres-sure main steam line switches (required every three months by Technical Specifications), two of the switches were found to have setpoints drif ted below the Technical Specification value of > 850 psig.
The function of these pressure switches is to initiate a main steam isolation (Group 1) in the event of a break in the main steam line.
The subject switches, PS-2-261-30A and PS-2-261-30C, were found set at 849 psig and S47 paig respectively.
(Technical Specification > 850 psig). Both switches are Barksdale switches, model number B2T-A12SS, with a range of 15-1200 psig and an accuracy of +_ 1*/.. At the time of surveillance, the pressure setpoints on both PS-2-261-30A and PS-2-201-30C were corrected to 655 psig.
Although these two switches drifted from the Technical Specifi-cation Limits, the drift was not significant enough to cause a safety hazard. The electrical arrangement of the relays that operate from these pressure switches is such that isolation would have occurred at only one pound below the recommended trip point.
8304210188 721121
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F Mr. A. Gismbusco N:vemb::r 3,1972 CORRECTIVE ACTION The history of these switches for the past 30 months shows instrument drift in both the increasing and decreasing direction. To allow for this drift, the instrument setpoint on all main steam line low pressure switches, on both Unit 2 and Unit 3 will be raised from 860 psig to 866 psig. The previous setpoint of 860 psig allowed for only a 5 psig drif t from the lower limit of the setpoint band. The setpoint band determines when the instrument must be recalibrated.
The new eetpoint of 866 psig will allow a drift of 12 psig below the lower limit of the band.
The 12 psig value was used because the instrument has a + 1%
accuracy of a full scale reading of 1200 psig.
Also, surveillance of the instruments will be increased from once every three months to once every month, for the next quarter, to obtain further information on this drif t problem.
N,. Ob W. P. Worden Superintendent Dresden Nuclear Power Station WPW:do v
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