ML17252A994
| ML17252A994 | |
| Person / Time | |
|---|---|
| Site: | Dresden  |
| Issue date: | 03/26/1973 |
| From: | Worden W Commonwealth Edison Co |
| To: | Anthony Giambusso US Atomic Energy Commission (AEC) |
| References | |
| WPW Ltr.#230-73 | |
| Download: ML17252A994 (2) | |
Text
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Commonwealth Edison Company DOCKETED USAEC 7 2
.W.E S T A D A M S. S T R E E T
- C H I C A G ~, TL L I N 0*1 s*
Addreu Reply fo, POST OFFICE BOX 767 *CHICAGO, ILLINOIS 60690 50-249 WPW Ltr.#230-73 Dresden Nuclear Power Station.
Mr. A. Giambusso Deputy Director for Reactor Projects Directorate of Licensing U. s. At0mic Energy Commission Washington, D. C.
29545 R. R. #1 Morris, Illinois 60450 March 26, 1973 Regulatory File Cy *.
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 16, 1973, 13 of the 16 high pressure coolant
~n~ection (HPCI) area temperature sensors were found to operate above the Technical Specification limit of~ 200~ as specified in Table 3.2.1.
- }?ROBLEM AND INVESTIGATION The HPCI area temperature sensors are Fenwal series 17000 differential expansion thermoswitch units.
The function 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 2030!, switch 2370D at 206°F, switch 2371C at 208°F, switches 2370A, 2373A, and 2373C at 210°F, switch 2370C at 212°F, and switches 2372B, 2372C, and 2371D did not trip at 212°F, which is the maximum temperature available from the calibration equipment. All switches were immediately recalibrated to trip at a temperature between 190-1950F.
The electrical arrangement of the contacts on these temperature 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 at 210°F.
Therefore, it i.s concluded that system safety was not jeopardized by the setpoint variations of the temperature sensors.
March 26, 1973 Mr.
A~* Giambusso.,,.
_ _ ___ The t~p~rature 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 ~2000F was considered to be a nomina! number, not an absolute limit.
Original calibration records reveal that the switches were normally set at exactly 200°F, and in some cases as high as 203°F.
These settings did not allow for the normal instrument repeatability error of + 3°F or for errors in calibration technique~
CORRECTIVE ACTION
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At this time it is not certain\\,ff this change _in temperature sensor setpoint was caused by calibration technique 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,
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W. P. Worden Superintendent WPW:do cc:-
Ltr.Book File
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