REGULATORYQIPORNATION DISTRIBUTION 0'lN (RIDE)
AOCESSION NBR: 8302070378 DOC 0 DATE: 83/02/01 . NOTARI'ZED: NO DOCKET FACIL:50-220BYNAME Nine Mile Point Nuclear Station< Uni;t 1E Niagara Powe 05000220 AUTH AUTHOR AFFILIATION MANGANzC ~ VS Niagara Mohawk Power Corp, YRGC IP NAME RECIPIENT AFFILIATION -VASSALLOtDBB~ Operating Reactors Branch 2
SUBJEOT: Forwards .results of 'App R safe shutdown analysis re 125 volt dc sys breaker coordination'o addi mods Yrequired, Revs,to administrative procedures necessary.
DI'STRIBUTION CODE: A006S,COPIES RECEIVED:LTR .f ENCL,f SIZE ~.. TITLE: OR Submittal': Fire Protection NOTES:
RECIPIENT -COPIES RECIPIENT COPIES ID,CODE/NAME LTTR ENCL ID CODE/NAME L'T.TR ENCL NRR ORB2 BC 01 3 '3
INTERNAL: ELD/HDS3 1 0 IE FILE 06 1 NRR F IORAVANT07 2 2 NRR HAMBACH 0 EB 09 2 2 NRR/DL DIR 1 FILE 04 1 RGN1 1
EXTERNAL0 ACRS 11 '3 LPDR 03 NRC PDR 02 1 NSIC 05 NTIS 1 1
:TOTAL NUMBER OF COPIES REQUIRED: LTTR 20 ENCL 18 1
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JS NIAGARAMOHAWKPOWER CORPORATION/300 ERIE BOULEVARDWEST, SYRACUSE, N.Y. 13202/TELEPHONE (315) 474-1511
february 1, 1983
Director of Nuclea'r Reactor Regulation Attention: Mr. Dominic B. Vassallo, Chief Operating Reactor Branch No. 2 Division of Licensing U.S. Nuclear Regulatory Commission Washington, D.C. 20555
Re: Nine Mile Point Unit 1 Docket No. 50-220 DPR-63
Dear Mr. Vassallo:
Our letter of December 30, 1982 indicated that the 125 volt DC system analysis for breaker fuse coordination would be completed by February 1, 1983. The results of this analysis are attached. While no additional modifications are required, revisions to administrative procedures will be necessary. Very truly yours,
C. V. Mangan Vice President Nuclear Engineering 5 Licensing JPB/djm Attachment
S30207037S S3020| PDR ADOCK 05000220 F PDR I
e f yr~g rl NIAGARA MOHAWK POWER CORPORATION
NINE MILE POINT UNIT 1
APPENDIX "R" SAFE SHUTDOWN ANALYSIS
125 VOLT DC SYSTEM BREAKER COORDINATION
INTRODUCTION
A breaker coordination study was made for the 125 volt DC power system which includes Battery Boards 11 and 12. The battery supply breaker on each power board is provided with long-time and short-time tripping characteristics. Most of the feeder breakers are provided with only a thermal trip unit. The remaining feeder breakers are provided with instantaneous magnetic trip units only, with the exception of one which is provided with long-time and short-time tripping characteristics similar to the supply breakers.
The DC power distribution system is ungrounded and is provided with a ground detection circuit which includes an alarm and indicating meters.
A single-conductor to ground fault provides only an alarm. A conductor-to-conductor fault is necessary to initiate an automatic breaker trip.
The results of the study indicate that we could experience a loss-of-coordination between a feeder breaker having only a thermal trip unit and the supply breaker for faults in the short-time current range of the supply breaker. This would result in the loss of the battery board and the associated loads.
However, for this to occur, calculations show that the fault would have to be located within eight feet of the power board for a No. 12 conductor feeder or within approximately 85 feet for a No. 2 conductor feeder. For this calculation, zero fault resistance was assumed. With any fault resistance, the fault would have to be located closer to the power board.
For feeder faults beyond the distances indicated above, the thermal characteristics of the feeder breakers coordinate with the long-time characteristics of the supply breakers. 4
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II SUMMARY OF RESULTS
The results of the 125 volt DC breaker coordination study were investigated to determine what impact they had on the Niagara Mohawk Power Corporation Appendix R Safe Shutdown Analysis. The impact was found to be minimal.
The lengths of cable which involve low resistance and could cause loss of coordination are contained within areas adjacent to the Battery Board Rooms. These locations are identified as Fire Areas 5 and 7 in the Appendix R Analysis. Due to the concerns already identified for these fire areas involving the potential loss of cold shutdown capability, corrective modifications and procedures were committed to. The concerns generated by the breaker coordination study wi 11 be incorporated into these corrective actions and will, therefore, not require additional modifications or procedures.
A description of the breaker coordination study impact on hot and cold shutdown capabilities is presented below.
Hot Shutdown Ca abi lit Hot shutdown will be obtained through use of the Emergency Condenser System, in all fire zones, sub-areas and areas with the exception of the Reactor Building Fire Sub-areas.. In these sub-areas, hot shutdown will be obtained by utilizing one of the low pressure systems associated with each diesel generator system (Reference Niagara Mohawk Power Corporation Appendix R Safe Shutdown Analysis submittal dated October 1, 1982).
The 125 volt DC breaker coordination analysis has shown that a fire-induced fault in the Reactor Building Sub-areas would be cleared by the Battery Board feeder breaker. This is due to the length of the feeder cable which provides ample cable resistance to limit the fault current and ensures tripping only of the feeder breaker.
Therefore, hot shutdown capabi lity is not affected and no corrective action is required.
Cold Shutdown Ca abi lit
Cold shutdown is obtained through use of the Shutdown Cooling System as described in our Appendix R submittal of October 1, 1982 and clarification letter of December 3, 1982.
The 125 volt DC breaker coordination analysis has determined that no additional fire areas, beyond those identified in our Appendix R submittal, would lose their cold shutdown capability as a result of fire-induced faults on DC feeder cables associated with Battery Boards 11 or 12. This is because outside of Fire Areas 5 and 7, the length of the feeder cables provide ample cable resistance, to limit the fault current and ensure tripping of only the battery board feeder breaker. A. Cold Shutdown Ca abilit (Continued)
In the Fire Area 7, which is adjacent to the Battery Board Rooms, there exists the potential for loss of both Battery Boards due to multiple fire-induced cable faults. To eliminate the potential loss of both Battery Boards, the alternate DC feeder breakers to Power Board 17 and 103 will be administratively locked out to prevent loss of both Battery Boards.
Fire Area 5, also adjacent to the Battery Board Rooms, has been previously identified as having the potential for loss of automatic cold shutdown capability due to damage to both AC and DC control and power cables (Reference Appendix R submittal dated October 1, 1982). Cold shutdown repair procedures are being developed and will incorporate corrective action to re-establish DC power in the event of the tripping of both Battery Board main supply breakers. '0 I
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