ML20137B778
| ML20137B778 | |
| Person / Time | |
|---|---|
| Site: | Nine Mile Point  |
| Issue date: | 12/16/1985 |
| From: | Mangan C NIAGARA MOHAWK POWER CORP. |
| To: | Starostecki R NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION I) |
| References | |
| (55(E)85-27), (55(E)85-27)), (NMP-2L-560), (NMP2L-0560), (NMP2L-560), NUDOCS 8601160074 | |
| Download: ML20137B778 (3) | |
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'c-i M YNIAGARA R UMOHAWK NINE ISILE POINT-UNIT 2.PO. BOX 63. LYCOMING, NY 13093/ TELEPHONE (315) 343-2110 December 16, 1985-(NMP2L 0560)
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Mr. R. W. Starostecki, Director U.S. Nuclear Regulatory Comission Region I Division of Reactor Projects 631 Park Avenue King of Prussia, PA 19406 Re: Nine Mile Point - Unit 2 Docket No. 50-410
Dear Mr. Starostecki:
Enclosed is a final report in accordance with 10CFR50.55(e) for the problem concerning standby diesel generator unsuccessful starting during preliminary testing. This problem was reported via tel-con to L. Dorflin of your staff on-Septe:2er 4, 1985 Very truly yours, C. V. Mangan Senior Vice President CVM/GG/cla (0471P)
Enclosure xc: Director of Inspection and Enforcement U.S. Nuclear Regulatory Commission Washington, DC 20555 R. A. Gram, NRC Senior Resident Inspector -
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NIAGARA M0 HAWK POWER CORPORATION NINE MILE POINT - UNIT 2 DOCKET NO. 50-410 Final Report for a Problea Concerning Standby Diesel Generator Unsuccessful Starting During Preliminary Testing (55(e)(85-27)
Description of the Problem During preliminary testing a system anomaly was observed wherein the Division II standby diesel generator failed to start when given an emergency start signal. This was due to the circuit's engine speed sensing relay picking up a false speed indication through its 125 V dc ' control power source.
The 125 V de power supply was apoarently receiving " noise" from the Division II uninterruptible power supply, which receives its 125 V dc power from a-comon source under loss of offsite power and during testing of uninter-ruptible power supply circuits.
This " noise" was interpreted as engine speed by the two speed sensing relays and the start permissive for the engine was already disabled when the emergency start signal was given.
The speed sensing relays that operate from the Division II 125 V de power source (reduced to 24 V dc) are designed for reference dc (-) to " ground" when connected in accordance with manufacturer's drawings.
At Nine Mile Point. Unit 2, the Division II 125 V de system employs a ground detection scheme which effec-tively references to dc(+) and dc(-) at 65 V dc (+) from gmund. _Because of this, the installed system operates improperly when " noise" is introduced on the 125 V de system.
l This problem also pertains to the identical Division I standby diesel generator.
Analysis of Safety Implication It is determined that if this problem had not been discovered th' rough testing and remained uncorrected, the safety of the plant could have been adversely affected during an accident condition due-to the inability of Division I and II standby diesel generators to start.
Corrective Actions The following corrective actions will be taken:
1.
The signal sensor input will be modified by running the cable input directly to the speed sensing relay -and reterminating the _ cable's shield directly to the cabinet ground bus.
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.t 2.
The magnetic pickups will be checked to ensure correct installation and to ensure that the cable's shield is isolated from signal input and ground.
The above corrective actions will be completed in accordance with Engineering and Design Coordination Reports No. C46,280 and C46,281.
All permanent modifications will be completed prior to fuel load.
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