ML20133H461
| ML20133H461 | |
| Person / Time | |
|---|---|
| Site: | Byron, Braidwood, 05000000 |
| Issue date: | 10/04/1985 |
| From: | Miosi A COMMONWEALTH EDISON CO. |
| To: | James Keppler NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION III) |
| References | |
| 0739K, 7391C, 739K, 85-04(BY), 85-07(BW), 85-4(BY), 85-7(BW), NUDOCS 8510170374 | |
| Download: ML20133H461 (2) | |
Text
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v Chicago. Illinois 60690 ifM October 4, 1985 Mr. James Keppler Regional Administrator U.S. Nuclear Regulatory Commission 799 Roosevelt Road Glen Ellyn, IL. 60137
Subject:
Byron Station Units 1 and 2 Braidwood Station Units 1 and 2 10 CFR 50.55(e) Raport Nos. 85-04(BY) 85-07(BW)
Diesel Generator Faulty Tachometer Readings
Dear Mr. Keppler:
On September 5, 1985, Commonwealth Edison Comoany notified Mr. Robert Lerch of your office of a deficiency reportable pursuant to 10 CR 50.55(e) regarding faulty tachometer readings on emergency diesel generators.
This letter provides information to fulfill the thirty-day reporting requirement and is considered a final report.
Description of Deficiency The speed sensing tachometers associated with the subject diesels have, at times, indicated an rpm reading while the engines were in a standby mode.
These-erroneous indications were caused by
" noise" in the D.C. power supply to the tachometer circuit.
Analysis of Safety Implications When.the speed sensing tachometer indicates greater than 280 rpm, the starting air solenoid valves for the engine become de-energized.
With that condition present, the diesel engine-generator set would not start on receipt of an emergency start signal..This could result in the unavailability of the
" essential safety-related equipment" on the associated electric bus.
Corrective Action At the direction-of the tachometer manufacturer (Airpax Electronics), with concurrence from the diesel generator and control panel supplier (Cooper /Entronics), the DC to DC regulator supplied with the control panel was replaced with a DC to DC converter manufactured by Airpax.
The DC to DC converter provides isolation of the positive and negative leads to the power supply and prevents the " noise" from creating an. erroneous reading.
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'9 The revised configuration has been tested and found satisfactory.
Design documentation is presently being prepared and all Byron and Braidwood emergency diesel engine-generator sets' tachometer circuits will be revised.
Please address any questions that you or your staff may have concerning this matter to this office.
Very truly yours, J I s/a A.
D. Miosi Nuclear Licensing Administrator
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NRC Resident Inspector-Byron NRC Resident Inspector-Braidwood Director of Inspection & Enforcement 0739K l
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