ML17252A989
| ML17252A989 | |
| Person / Time | |
|---|---|
| Site: | Dresden  |
| Issue date: | 04/04/1973 |
| From: | Worden W Commonwealth Edison Co |
| To: | Anthony Giambusso US Atomic Energy Commission (AEC) |
| References | |
| WPW Ltr. #265-73 | |
| Download: ML17252A989 (2) | |
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-"~i Commonwealth Edison Company 7 2 W E S T A D A M S S T R E.E T
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I L L I N 0 I S Addr.., Reply to, POST OFFICE BOX 767 *CHICAGO, ILLINOIS 60690 WPW Ltr.#265-73 Mr. A. Giambusso Deputy Director for Reactor Projects Directorate of Licensing U. s. Atomic Energy Commission Washington, D. C.
20545
SUBJECT:
Dear Mr. Giambusso:
D~esden Nuclear Power Station R. R*. #1 Illinois 60450 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 := 200°F.
PROBLEM AND INVESTIGATION The main steam line area temperature sensors are Fenwal series 17000 differential expansion thermoswitch units.
The function of the switches is to 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 l8C at 20l°F, TS3-261-17B at 202°F, TS3-261-16B and 17D at 203°F, TS3-261-17C at 204°F,.TS3-261-17A at 205°F, and TS3-261-18A and 18D at 206°F. All switches were immediately recalibrated to trip at a temperature between 190-194°F.
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 madtn steam line break, isolation would have occurred at 200°F 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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- April 4, 1973 The temperature sensors were last calibrated by electrical
- .. contractors a-t the time* of installation -in i97cf.
At that time the Tech-nical Specification limit of ~ 200°F was considered 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 2000p and in some cases as high as 203°F.
These settings did not allow for the normal instrument repeatability error of + 30p 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 112 main st~am line and HPCI 11rea temperature switches were last calibrated in March of 1972, at which time they were all found to be within tlte,.Technical Specification limits.
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CORRECTIVE AcTION At the. present time, an investigation is underway to determine the cause, of this setp.c;>int* variance.
The investigation was initiated as a result of a deviation involving the (HPCI) areatemperature 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 drifting. Additionally, the Unit 112 main steam line and.HPCI high temperature switches will be checked at the next opportunity.
WPW:do cc:
Ltr. Book File Sincerely,
- w. P. Worden Superintendent