ML20084S267

Ro:On 730324,9 of 16 Main Steam Line High Temp Sensors Found to Operate Above Tech Spec Limit.Cause Unknown. Investigation Underway

ML20084S267
Person / Time
Site:	Dresden
Issue date:	04/04/1973
From:	Worden W COMMONWEALTH EDISON CO.
To:	Giambusso A US ATOMIC ENERGY COMMISSION (AEC)
Shared Package
ML20084S270	List: ML20084S267 ML20084S271
References
265-73, NUDOCS 8306160394
Download: ML20084S267 (2)

Text

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Commonwealth Edison Company 72 ' NEST ADAMS STREET

• C H I C A G O. BLLINOIS AM.an 8enly toe

.FOST O FFIC E BO X F4 7

• CHIC AGO, IL LIN OIS 40 69 0

-WFW Ltr.f265-73 Dresden Nuclear Power Station R. R. #1 Morris, Illinois 60450 April 4, 1973 s 50-249 Mr. A. Giambusso Deputy Director for Reactor Projects Directorate of Licensing U. S. Atomic Energy Convaission Washington, D. C. 20545

SUBJECT:

LICENSE DPR-25, DRESDEN NUCLEAR POWER STATION, UNIT #3, SECTION 6.6.B.3 OF THE TECHNICAL SPECIFICATIONS.

Dear Mr. Giambusso:

This is to report a condition relating to the operation of the unit in which on March 24, 1973, 9 of the 16 main steam line high temper-ature sensors were found to operate above the Technical Specification limit of 5 200 F.

PROBLEM AND I?NESTICATION The main steam line area temperature sensors are Fenwal series 17000 differential expansion thermoswitch units. The function of the switches is tc isolate the main steam lines in the event of a break in the steam piping. The switches were found with settings as follows:

switches TS3-261-18B and 18C at 2010 F, TS3-261-17B at 202 F, TS3-261-16B and 17D at 2030F, TS3-261-17C at 2040F, TS3-261-17A at 2050F, and TS3-261-18A and 18D at 2060F. All switches were insnediately recalibrated to trip at a temperature between 190-1940F.

The electrical arrangement of the contacts on these temperature sensors is a "one-out of-two-twice" logic. Analysis of the circuit reveals that in the event of a main steam line bresk, isolation would have occurred at 200 0F which is within the limit of the Technical Specifications. It is therefore concluded that system safety was not jeopardized by the setpoint variations of the temperature sensors.

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Mr. A. Giambucco O

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The tesperature sensors were last calibrated by electrical contractors at the time of installation in 1970. At that time the Tech-

. nical Specification limit of 9 2000F was ccasidered to be a nominal number, not an absolute limit. Original calibration records reveal that the electrical contractor set the majority of the Fenwal temperature sensors

• at exactly 2000F and in some cases as high as 2030F. *'hese a settings did not allow for the normal instrument repeatability error of + 30F or for errors in calibration technique.

The main steam line area temperature switches and the high pressure coolant injection (HPCI) area temperature sensors, a total of 64 switches, are the only Fenwal Series 17000 switches in use on safety system equipment. The Unit #2 main steam line and HPCI area temperature switches were last calibrated in March of 1912, at which time they were all found to be within the Technical Specification limits.

CORRECTIVE ACTION At the present time, an investigation is underway to determine the cause of this setpoint variance. The investigation was initiated as a result of a deviation involving the (HPCI) area temperature sensors reported in a letter dated March 26, 1973. This investigation includes a review of the calibration technique, and also additional testing of several sensors that have a history of drif ting. Additionally, the Unit #2 main steam line and HPCI high temperature switches will be checked at the next opportunity.

Sincerely,

% S . %D..

W. P. Worden Superintendent WPW:do cc: Ltr. Book File l

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