ML20084T512

Ro:On 721119,during Instrument Calibr,Setpoints of Four of Main Steam Line Low Pressure Switches Found W/Trip Setting Slightly Below Tech Specs.Cause Under Investigation.Switch Trip Settings Adjusted

ML20084T512
Person / Time
Site:	Dresden
Issue date:	11/29/1972
From:	Worden W COMMONWEALTH EDISON CO.
To:	Giambusso A US ATOMIC ENERGY COMMISSION (AEC)
Shared Package
ML20084T513	List: ML20084T512 ML20084T515 ML20084T517
References
NUDOCS 8306230235
Download: ML20084T512 (2)

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Commonwealth Edison Company 72 WEST ADAMS STREET

• C H I C A G O. ALLINOls FOST OFFlCE BOX 767

• C M IC A G O. IL LlN OIS 6069 0 50-249 Dresden Nuclear Power Station R. R. #1 Morris, Illinois 60450 November 29, 1972 jgi1"rjh e - N h s ,.v

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e U Mr. A. Giambusso 5 DEC 41972 -

Deputy Director for Reactor Projects g, Directorate of Licensing C -

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U. S. Atomic Energy Cornission D Washington, D.C. 20545 ,; O

Subject:

License DPR-25, Dresden Nuclear Power Station, Unit #3, Section 6.6 3.2 of the Technical Soecifications

Reference:

Letter to A. Giambusso from W. P. Worden dated 11/13/72 regarding Main Steam Line Low Pressure Switch Calibration

Dear Mr. Giambusso:

'Ihis is to report a condition relating to the operacion of the unit in which, on November 19, 1972, during instrument calibration, the setpoints of four of the main steam line low pressure switches were found to have a trip setting slightly below the value specified in Table 3.2.1 of the Technical Specifications.

PROBI.EM AND INVESTIGATION Un November 19, 1972, as a result of previously experienced vari-ations in the calibration of the main steam line low pressure switcLes 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 Technicypecification value of E 850 psig. 'Ihe switches were promptly~ .

j reE lFr'sl:cd to trip at 866 psig. --

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The subject switches, PS-3-261-30A, PS-3-261-30B, PS-3-261-30C and PS-3-261-30D were found set it 847 piij~~848 psig, 849 psig and 848 1psig respectively.

(Technical Specification E 850 psig). Allfourswitchesf

, are Barksdale switches , model number 32T-A12SS, with a range of 15-1200 psig and a specified accuracy of 1 1%. The history of these switches shows  ;

slight setpoint change with time in both the increasing and decreasing l I

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 1) in the event of a break in the main steam line. The electrical arrangement of the relays that operate from these switches is such that a main steam line isolation, had it been required, would have been initiated at 2 psig below the value specified in the Technical Specifications. This l is an insignificant variance and the applicable transient analyses have  !

sufficient 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 psig, the corrective action specified in the reference. The new setpoint will allow a 12 psig drift below the lower limit of the setpoint band of 866 1 4 psig.

The 12 psig value was used because the instrument has specified accuracy of i 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. ,

Sincerely, W. P. Worden Superintendent WFW:sdb -

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