ML20085G046

AO BFAO-50-260/755W:on 750205,4-kv Shutdown Board D Emergency Control Bus 250-volt Dc Power Supply Lost.Caused by Inadequate Battery Discharge Surveillance Instruction. Changed Instruction Includes Transferance Step

ML20085G046
Person / Time
Site:	Browns Ferry
Issue date:	02/14/1975
From:	Eric Thomas TENNESSEE VALLEY AUTHORITY
To:	Case E US ATOMIC ENERGY COMMISSION (AEC)
References
NUDOCS 8308240205
Download: ML20085G046 (3)

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• i ABNORMAL OCCURRENCE REPORT Report No.: HFAO-50-260 755W j Report Date: Februar/ 1 , 1975 Occurrence Date: Februarf 5,1975 Facility: Browns Ferr/ Nuclear Plant units 1 and 2

, Identification of Occurrence Loss of 250-V d-c power supply to 4-kV shutdown board "D" emergency control bus.

Conditions Prior to Occurrence Unit 1 was in cold shutdown condition; unit 2 was at approximately 65-percent power. Unit 250-V batter / board 1 had been isolated from all plant loads for batter / discharge surveillance test as required by the technical specifications.

Description of Occurrence At approximately 0900 hours0.0104 days <br />0.25 hours <br />0.00149 weeks <br />3.4245e-4 months <br />, an undervoltage alarm was observed on the central diesel generator annunciator panel. Subsequent investigation revealed that the emergenc'/ control bus on 4-kV shutdown board "D" was deenergized. This negated autonstic starting capability of RER pu=ps 1D and 2D, core spray pu=ps 1D and 2D, RHRSW pump Dl, and diesel generator D (undervoltage initiation only).

Control voltage was i==ediately restored to the energency bus following the investigation.

Desirnation of Apparent Cause of Occurrence 2e battery discharge surveillance instruction did not contain a specific step for transferring the 250-V d-c power supply to 4-kV shutdown board "D" emergency control bus before the test.

3 Analysis of Occurrence As a result of the deenergised control bus, the afore=entioned equipment had

, no automatic starting capability for approximately 39 hours4.513889e-4 days <br />0.0108 hours <br />6.448413e-5 weeks <br />1.48395e-5 months <br />.

During the 39-hour period, each of the previously listed "D" pumps was capable of manual starting with the exception of PRR pu=p 1D which was out of service for maintenance. Diesel generator D was capable of automatic starting from b all initiating signals except undervoltage on 4-kV shutdown board "D." All

, other diesel cencrators and energency core cooling pu=ps on both units 1 and 2 were operable (execpt RER pu=p 13 which was out of service for maintenance) during the 39-hour period.

There was no dama6e to critical structures or components; and there were no adverse effects to the environment, public, or plant personnel.

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Corrective Action The battery discharge surveillance instruction has been changed to include l a step transferring the 250-V d-c power supply to the emergency bus. It will also be expanded to include verification of annunciations. A r.odificatio,1 chenge request has been initiated to install power-available indicating lights over the 4-kV shutdown board control bus selector switches.

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Failure Data ,

None

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TENNESSEE VALLEY AUTHORITY CHATTANCOGA. TENNESSEE 374o1 ,

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February 14, 1975 /*' '

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ht' Mr. Edson G. Case Acting Director of Licensing

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U.S. Nuclear Regulatory Co:stission ,g

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Washington, DC 20545 ,p t.j ;,j , ,3 ' , Q

Dear !*r. Case:

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TEICTESSEE VALLEY AUTHORITI - BROM!S FERRY NUCLEAR PLANT UNIT 2 -

DOCl3T UO. 50-E60 - FACILITY OPERATING LICENSE DPR ABNORMAL OCCURRENCEREPORTBFAO-50-260/755W The enclosed report is to provide details concerning loss of 250-V d-c power supply to 4-kV shutdown board "D" energency control bus and is submitted in e.ccordance with Appendix A to Regulatory Guide 1.16, Revision 1, October 1973. This event occurred on Browns Ferry Nuclear Plant units 1 and 2 on February 5, 1975.

Very truly yours, TENNESSEE VALLEY AUTHORITI

, x ... a O . rector of Power Production Enclosure CC (Enclosure):

Mr. Nornan C. Moseley, Director U.S. Nuclear Regulatory Cor: mission Regional Office 230 Peachtree Street,IN., Suite 818 Atlanta, Georgia 30303 hl 1745 gory sur REGION 4-' "

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