ML17252B010
| ML17252B010 | |
| Person / Time | |
|---|---|
| Site: | Dresden  |
| Issue date: | 11/29/1972 |
| From: | Worden W Commonwealth Edison Co |
| To: | Anthony Giambusso US Atomic Energy Commission (AEC) |
| References | |
| Download: ML17252B010 (2) | |
Text
~egulatory Fil
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- Commonwealth Edison Company 72 WEST ADAMS STREET
- CHICAGO, ILLINOIS Addreu Reply to, POST OFFICE BOX 767 *CHICAGO, ILLINOIS 60690 Mr. A. Giambusso Dresden Nuclear Power Station R. R. #1 Morris, Illinois 60450 November 29, 1972
-*Deputy Director ~or Reactor Projects Directora~e of Licensing
- u. s. Atomic Energy Conunission Washington, D.C.
20545
Subject:
License DPR-25, Dresden Nuclear Power Station, Unit #3, Section 6.6.:Q.* ~J of the Technical Specifications
Reference:
Letter to A. Giambusso from w. P. Worden dated 11/13/72 regarding Main Steam Line Low Pressure Switch Calibration
Dear Mr. Giambusso:
50-249 This* is to* report* a condition relating to the. operation of the unit
.*..in which, on November 19, 1972, during instrument calibration, the setpoints
.... of four of the main steam line low press"ut~ switches were found to have a trip setting slightly below the value specified in Table 3.2.1 of the Technical Specifications.
PROBLEM AND INVESTIGATION On November 19, 1972, as a result of previously experienced vari-ations in the calibration of the main steam line low pressure switches on' Dresden Units 2 and 3,.the trip settings were being adjusted to permit more variation in calibration without exceeding the values specified in the Technical Specifications. (See Reference) Prior to the adjustment, an "as.
found" check of the switches indicated that all four had trip settings below the Technical Specification value of? 850 psig.
The switches were promptly' recalibrated to trip at 866 psig.
- The subject switches, PS-3-261-30A, PS-3-261-30B, PS-3-261-30C and PS-3-261-30D were found set at 847 psig, 848 psig, 849 psig and 848 psig respectively.
(Technical Specification ~ 850 psig). All four switches are Barksdale switches, model number B2T-Al2SS, with a range of 15-1200 psig and a specified accuracy of +/- 1%.
'llle history of these switches shows slight setpoint change with time in both the increasing and decreasing direction.
The cause of this drift was being investigated at the time these switches were found to be out of the Technical Specifications.
The function of these pressure switches is to initiate a main steam isolation (Group l} in the event of a break in the main steam line.
The electrical arrangement of the relays that operate from th~se switches is such that a main st~am line isolation, had it been required, would have been initiated at 2 psig below the value specified in the Technical Specifications.
This is an insignificant variance and the applicable transient analyses have sufficment conservatism to cover such instrument inaccuracies.
Hence, it is concluded that no safety_ hazard to the public resulted from this slight deviation from Technical Specifications.
CORRECTIVE ACTION The trip setting of the switches was adjusted to 866 psig1 the corrective action specified in the reference.
'1.1].e new setpoint will allow a 12 psig drift below the lower limit of the setpoint band of 866 +/- 4 psig.
The 12 psig value was*used because the instrument has specified accuracy of +/- 1% of full scale reading of 1200 psig.
Also, as specified in the reference, surveillance of these switches has been increased from once every three months to once a month, for the next quarter, to obtain further information on the problem.
WPW:sdb Sincerely,
~.~-~-
- w. P. Worden Superintendent