ML20084S276

Ro:On 730316,13 of 16 HPCI Area Temp Sensors Found Above Tech Spec Limit.Possible Causes Calibr Technique or Instrument Drift.Calibr Procedure Will Be Reviewed & Specific Recommendations Will Be Made to Assure Consistency

ML20084S276
Person / Time
Site:	Dresden
Issue date:	03/26/1973
From:	Worden W COMMONWEALTH EDISON CO.
To:	Giambusso A US ATOMIC ENERGY COMMISSION (AEC)
References
230-73, NUDOCS 8306160418
Download: ML20084S276 (2)

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Commonwealth Edison Company 71 WEST ADAMS STREET

• CHICAGO. ILLINOle Am ew, ,.,

Polf oP PICE SON 7 6 7

• C H IC A O o, I L L IN o I S 4 0 4, o 50-249 WPW Ltr.9230-73 Dresden Nuclear Power Station.

R. R. #1 Morris, Illin:iis 60450 [

March 26, 1973

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Mr. A. Giambusso t' , . .

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Deputy Director for Reactor Projects N f N ',*** s *-

Directorate of Licensing

' ,N. h, U. S. Atomic Energy Commission Q('-yh [

Washington, D. C. 20545  %.-c-

SUBJECT:

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

Dear Mr. Giambusso:

This is to report a condition relating to tae cperation of the unit in which on March 16, 1973, 13 of the 16 high pressure coolant injection (HPCI) area temperature sensors were found to operate above the Technical Specification limit of

• 2000F as specified in Table 3.2.1.

PROBLEM AND INVESTIGATION The HPCI area temperature sensors are Fenwal series 17000 \

differential expansion thermoswitch units. The lunction of the switches is to isolate the HPCI system in the event of a break in the HPCI steam supply piping. The switches were found with settings as follows:

, Switches 2371A, 2373B, and 2372D at 2020F, switch 2373D at 2030F, switch u d3 2370D at 2060F, switch 2371C at 2080F, switches 2370A, 2373A, and 2373C

/ f, at 2100F, switch 2370C at 2120F, and switches 2372B, 2372C, and 2371D did not trip at 2120F, which is the maximum temperature available from the

,' calibration equipment. All switches were icanediately recalibrated to

'h ) trip at a temperature between 190-1950F.

Qdn The electrical arrangement of the contacts on these temperature f'h sensors is a "one-out-of-two twice" logic. Analysis of the circuitry reveals that. in the event of a steam line break, HPCI isolation would have occurred

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at 2100F. Therefore, it is concluded that system safety was not jeopardized by the setpoint variations of the temperature sensors. , . ,

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8306160418 730326 PDR ADOCK 05000 S

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Mr. A. Giam$ is U March 26, 1973 The temperature sensors were calibrated only once previously, in August of 1970, by the electrical contractor who installed the system. At that time the Technical Specification limit of s 2000F was considered to be a nominal number, not an absolute limit. Original calibration records reveal that the switches were normally set at exactly 2000F, and in some cases as high as 2030F. These settings did not allow for the normal instrument repeatability error of + 3 F or for errors in calibration technique, i

CORRECTIVE ACTION At this time it is not certain if this change in temperature sensor setpoint was caused.by. calibration _techni_que or_ instrument drift.

In order to determine the cause, the calibration procedure will be reviewed and specific recommendations will be made to assure consistent and accurate sensor calibration. To determine if the problem is a result of setpoint drift, a calibration check will be conducted in approximately six months on four of the temperature sensors. The sensors checked will be the four found with setpoints farthest from the target setting.

Sincerely,

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

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