ML20101B062

Responds to Generic Ltr 91-11, Resolution of Generic Issues 48, 'Lcos for Class 1E Vital Instrument Buses' & 49, 'Interlocks & LCOs for Class 1E Tie Breakers.' Evaluation Concluded That Controls in Place Are Satisfactory

ML20101B062
Person / Time
Site:	Browns Ferry
Issue date:	04/30/1992
From:	Zeringue O TENNESSEE VALLEY AUTHORITY
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
REF-GTECI-048, REF-GTECI-049, REF-GTECI-NI, TASK-048, TASK-049, TASK-48, TASK-49, TASK-OR GL-91-11, NUDOCS 9205050199
Download: ML20101B062 (10)

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Temessee Va4+y Authority. Post 0%ce Scd ?J)3 Decats Al2wN Ef.09 APR 3 01992 O L %e' Zeringue L;e Presukot, Bw rs Ferry Operahnns

U.S. Nuclear Regulatory Commission ATTN

Document Control Desk washington, D.C. 20555 o

'lentlemen:

Jn the'datter-of _ ) Docket Nos. 50-259 Tennessee Valley Authority ) 50-260 50-296 BROWNS FERRY NUCLEAR PLANT (BFN) - UNITS 1, 2, AND 3 - GENERIC LETTER (GL) 91-11, RESOLUTION OF GENERIC ISSUES (GIs) 48, "LCOs FOR CLASS lE VITAL INSTRIDiENT BUSES," AND 49, " INTERLOCKS AND LCOs FOR CLASS lE TIE BREAKERS"

[ Rhferences: 1. TVA to NRC letter dated January 29, 1992, same subject.

This letter provides NRC with BFN's response, pursuant to 10 CFR 50.54(f), to Generic Letter 91-11, R6 solution of Generic Issues 48,

'LCOn For Class lE Vital Instrument Buses,' and 49, ' Interlocks And LCOs For Class lE T.le Breakers," dated July 18, 1991. GL 91-1.1 directed

' licensees to evaluate the applicability of.GIs 4P and 49 to their plant and-to implement procedural centrols (or to provide justification that such controla are not necessary) to fulfill the following requirements:

l-L 1. Limit the time that a plant is in possible violation of the single-failure criterion with reLard to the Class 1E vital instrument buses and' tie-breakers,

2. Require surveillances of these components, and

3. Ensun that, except for the times covered in Item (1), the plant is operating in an electrical configuration consistent with the regulations and its design bases.

.DFh has completed its evaluation and-has concluded that the

. administrative controls in place satisfy the recommendations of the GL.

The bases for this conclusion are provided in the Enclosure.

9205050199 920430 PDP zADOCX. 05000239-(1037 ip-_

2 U.S. Nuclear Regulatory Commission April 30, 1992 If you have any questi s, please contact Raul R. Enron at (205) 729-7566.

Sincerely,

/

, i J. R. Rupe t Engineering and Modifications Manager In the absence of O. J. Zeringue Vice President, Browns Ferry Operations Enclosure cc (Enclosure):

NRC Resident Inspector Browns Ferry Nuclear Plant Route 12, Box 637 Athens, Alabama 35611 Mr. Thierry M. Ross, Project Manager U.S. Nuclear Regulatory Commission One White Flint, North 11555 Rockville Pike Rockville, Maryland 20852 Mr. B. W. Wilson Project Chief U.S. Nuclear Regulatory Commission Region II 101 Marietta Street, NW, Suite 2900 Atlanta, Georgia 30323 Subscribqd and sworn to before me on is f uth day of M(d 1992.

dAtU k. h h d q1 !.n u Notary Public gwei Waos WW^**

My Commission Expires g o. So _Ci Q

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e ENCLOSURE The following is the proposed resolution of Generic Issues (Gis) 48 and 49 for BFN Units 1, 2, and 3 utilizing the guidan e provided in Enclosure I cf Generic Letter (GL) 91-11.

The GL recommended that each licensee " ensure that your plant has procedures that include tinie limitations and surveillance requirements for

1. Vital instrument buses (typically 120VAC buses),

2. Inverters or other onsite power sources to the vital instrument buses, and

3. Tie breakers that can connect redundant Class IE buses (AC or DC) at one unit or that can connect Class lE buses between units at the same site."

LMpfqnse To GI-48. "LCOs for Class 1E Vital Instrument. Buses" Two BFN electrical systems satisfy the definition of a " vital instrument bus" (VIB) provided in GL 91-11. These are 1) the 208/120VAC Instrument and Control Power System, and 2) the 120VAC Reactor Protection (RPS) System Power Supply. A brief description of each system along with TVA's rerponse to the GI for each system is provided below.

1, 208\1,20VAC Instrument and Control (I & C) Power System One [, air of I & C buses is provided for each unit. Each bus in the pair is energized by an indeliendent Class IE 480V shutdawn board source via a 480-208\l20VAC transformer in series with a 208\l20-208\l20VAC regulating transformer, and is ultimately backed by the shutdown board's associated diesel generator (DG). To increase the reliability of the system, the alternate supplies are frcm the same division of another unit. The following table summarizes the normal and alternate power supply arrangements for each bus:

BUS NORMAL ALTERNATE DIVISION 1&C Bus A (Ul) 480V Shutdown Bd la 480V Shutdown Bo 2A I I&C Bus B (Ul) 480V Shutdown Bd IB 480V Shutdown Bd 3B 11 I&C Bus A (U2) 480V Shutdown Bd 2A 480V Shutdown Bd 3A I I&C Bus B (U2) 480V Shutdown Bd 2B 480V Shutdown Bd IB II I&C Bus A (U3) 480V Shutdown Bd 3A 430V Shutdown Bd 1 A I I&C Bus B (U3) 480V Shutdown Bd 3B 480V Shutdown Bd 2B II An auto-transfer switch is provided on sch unit to transfer to the alternate supply after a three second time delay when the normal supply voltagefecreases to 70% of nominal bus voltage. Auto transfer back to the normal supplyjppfl occur when the l normal supply voltage increases to 90% of its nominal value.'Th61&C bas transfer scheme is shown pictorially on Figure 1.

Enclosure

• Page 2 of 3 The I&C transformer capabilities are adequate to supply normal ioads plus the additional I&C bus load from another unit. Transfer to the alternae supply (same division from another unit) maint? ins the divisional integrity of the I&C buses and does not expose the I & C t,uses to the potential for a violation of the single failure criterion. Therefore, no time limitations or additional utrols are recessary to ensure the reliability and avai'. ability of the 208\120VAC I & Tower System.

2. Desiption of the 120VAC RPS Power Supply Two redundant and electrically separated RPS channels, A and B, including power supplies, are provided on each unit. Each RPS power supply consists of a motor-generator (MG) set and two series circuit protectors. Each unit's RPS Channel A MG set is powered from that unit's 480V RMOV board A. Each unit's Channel B MG set ia powered from the corresponding 480V RMOV board B. The MG sets have no alternate power supplies. For Unit 2, the Unit Preferred Regulating trnasformer provides the capability for a common alternate power supply to both RPS channels' distribution buses from the Standby Auxii ary Power System. The Unit Preferred Transformer is a 4d0-240\120VAC stepdown transformer fed from the Unit 2 480V RMOV Board 2B. For Units 1 and 3 the kPS alternate supply capability for each bus is provided by each unit's RPS regulating transformer. The RPS Regulating Transformers are supplied from the Standby Auxiliary Power System via 480V Shutdown board IB for Unit 1 and 480V RMOV Board 3B for Unit 3. A switch is provided on each unit battery board to align a RPS channel to its alternate supply.

l The RPS bus transfer scheme is shown on Figure 7. Interlocks are provided to prevent the alterrate supply from supplying both channels simultaneously, and to prevent closing both the normal supply breaker and the alternate supply breaker to any one channel simultaneously. The design of the RPS is such that on a loss of normal or alternate power, components go to their fail-safe condition and a icactor scram occurs. The RPS bus must be manually re-energized following a loss of power.

Taerefore, no single-failure exposure exists for the RPS power supply.

As described above, the concerns presented in the GL are not applicable to the 208/120V AC I&C Power System and the RPS Power Supply due to inherent design features. Therefore, we have concluded that GI-48 is resolved for the BFN VIBs.

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Enclosure Page 3 of 8 FIGURE 1 '

BFN I & C BUS TRANSFER SCHEME 4 80 S H U T DO'./N BOA RD 1 A 480 SHUTDOWN BOARD 2A 480 SHUTDOWN BOARD 3 A I

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UNIT 1 UNIT. 2 UNIT 3 480V SHUTDOWN BD 1B 480V RMOV- BD 2A 480V RMOV BD 1 A 480V RMOV BD 3A 4UOV RMOV BD 1B 480V RMOV BD 2P 480V RMOV BD 3B RPS REG. UNIT RPS TRANSFORMER P REF'D REG.

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e-Enclosure Page 5 of 8 B13ponse to GT-49. " Interlocks and 14 2s for Class IE Tle Breakers"

1. Standby At;xiliary Power System The Class IE standby AC electrical supply and distribution system for Units 1 and 2 consists of four DGs, four 4KV Shutdown Boards (Boards A, B, C, ud Dj, n,ar 480V Shutdown Boards, ten 480V Reactor Motor-operated Valve (RMOV) Boards

[i.e. Unit 1(2) 480V RMOV boards 1(2)A,1(2)B,1(2)C,1(2)D, and 1(2)E], eight MC sets, two DG 480V Auxiliary Boc.rds, and one 480V Control Bay Ventilation Board. The Class lE stanooy AC supply and distribution system for Unit 3 is separate from that of Units 1 and 2. It consists of four DGs, four 4KV Shutdown Boards (Poards 3EA,3EB,3EC, and 3ED), two 480V Shutdown Boards, five 480V RMOV Boards (3A,3B,3C,3D, and 3E), four MG sets, two DG 480V Auxiliary Boards, one 480V Standby Gas Trt.atment System Board, and one 480V Control Bay Ventilation Board.

Each 480V RMOV board has a normal and an alternate power supn . 'The n! ternate power supply is the other divisional 480V Shutdown Board in each uni: Electrical interlocks are provided to prevent the paralleling of the normal and alternate supplies.

Each unit's 480V RMOV Boards A, B, and C must be manually transferred to their alternate source. 480V RMOV Boards D and E are automatically transferred to their respective alternate saurce on a loss of vol Tge. 480V RMOV Boards D and E supply those valves necessary for Low Pressure Coolant Injection. These boards are connected to both the normal and alternate sources via MG sets to prevent fault propagation followmg an automatic transfer. Prior to the transfer of 480V RMOV boards l A, IB, IC,2A,2B, 3A,3B, and 3C to the alternate feeders, the following criteria must be adhered to:

A. While a unit is operating at power, transfer of the associated 480V RMOV Board to the alternate feeder is only p"missible when there is a failure of normal supply. Return to the normal supply shall be within twelve hours or the reactor shall be in cold shutdown within the n ~xt twenty four hoes. Indefinite operation on the alternate feeder'is permitted o.Jy during the shutdown condition.

B. The loading limitations shown on the 480V Shutdown and 480V RMO\ Board single line drawings shall not be exceeded.

C. Preventive maintenance on the ncrmal feeder breakers for the 480V RMOV Boards or their feeders is permitted only during the shutdown condition.

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Enclosure Page 6 of 8 D. When a 480V Shutdown Board is being fed from its emergency transformer

. the altemate feeder breaker to a RMOV Board fed from the Shutdown Board cannot be closed.-

These testrictions are also applicable to the Unit 3 DG 480V Auxiliary Boards when Unit 3 is in operation.

When a 480V Shutdown Board or Unit 1 or 2 DG 480V Auxiliary Board is placed on its alternate source, thJ board may be considered operable as long as the technical specification limiting condition for operation associated with the normal source 4KV

' Shutdown Board is adhered to.

These restrictions have been incorporated into Operr, ting Instruction 0-01-57B, 480V/240V AC Electrical System. The alignment c.f the 480V RMOV and Shttdown Boards for system operability is performed in accordance with 0-OI-57B and is independently verified. Board alignment is then monitored by the BFN System Status Control Program.

2, 4KV Shur awn Board Tie-breakers Each of the 4KV Shutdown Boards _on Units 1 and 2 (Board A, B, C, and D) may be connected to its respective (same division) Unit 3 4KV Shutdown Board (Boards 3EA, 3EB, 3EC, and 3ED, respectivelyY via cross-tie breakers. This A.gn feature enables a Unit 1 or a Unit 2 Diesel Ger.erator (DG) to be operated in parallel with its respective Unit 3 DG. For example, DG A can be paralleled only with DG 3A.These

-interconnections are through manrally_ controlled circuit breakers which are

- electrically interlocked to prevent the tie-breaker from being closed when the normal upply breaker is closed. Additionalinterlocks are provided to ensure that the DGs are properly synchromzed prior to interconnection. The alignment of the 4KV LShutdown ~Boacds is monitored in accordance with the System Status Control Program.

Parallel operation of two DGs is administratively limited to a condition where an

. accident signal is present in any unit and offsite power is not available and 10 minutes have elapsed since the accident began.' Parallel DG operation is controlled by Abnormal Operating Instruction 0-AOI-57-1 A, Loss .of Offsite Power.

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Enclosure Page 7 of 8

3. Maintenance Tie-Breakers for the 480V RMOY Boards D and E As described above, the normal / alternate power supplies to each uait's 480V RMOV Baards D (Division I) and E (Division II) are MG sets. A third power source, a maintenance feeder, from 480V RMOV board C (non-Divisional)is also available for supplying 480V RMOV boards D and E. Use of this feeder allows maintenance to be performed on th^ MG sets.

The use of the maintenance feeders from each unit's 480V RMOV board C to 480V RMOV boards D and E is administratively controlled by BFN Operating Instcuction 0-01-57B,480V/240VAC Electrical System, and may be used only during periods of reactor shutdown. During reactor operation, the maintenance feeder breakeii are controlled by the System Status Control Program.

4. 250V DC Power System Tie-Breakers The 250V DC Power System is consists of two subsystems:

A. The 250V plant DC system, which consists of four 120-cell lead-acid batteries (on'. Class 1E unit battery and battery charger per unit, one non-Class lE statica battery and battery charger, and one Class lE spare charger). 250V plant DC system power is distributed to its safety-related loads via three 250V DC battery boards and nine (three per unit) divisionalized DC RMOV boards.

An alternate power supply for each DC RMOV Board is provided ,, another unit's 250V DC battery.

B. The 250V DC Control power system (250V DC control power supplies A, B, C, D, and 3EB for 4KV Shutdown Boards A, B, C, D, and 3EB, and 480V Shutdown Boards I A, 2A, iB and 2B, respectively), which consists of five lead-acid baueries (one battery and battery charger for each Hutdown board, and one spare battery charger). Alternate power sources are provided by the 250V plant LC system. Electrical interlocks prevent paralleling the normal and alternate power supplies.

The use of alterna*: supplies for the 4KV Shutdown Boards,480V Shutdown Boards, and tne DC kMOV Wards are administratively controlled by 0-OI-57D, DC Electrical System Operating Instruction and BFN Technical Specifications, Section 3.9, Auxiliary Electrical Systems. During the use of alternate control power sources for the 4KV Shutdown Boards and the 480V Sbutdown Boards, continued reactor operation is permissible during the succeeding the days. During the use of the

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s Enclosure Page 8 of 8 alternate feeders to the DC RMOV Boards continued po_wer operation is permissible during the succeeding seven days. The ^]ignment of the 250V DC Power Systerr is controlled by 0-OI-57D, DC Electrical System Operating Instruction and is monitored by the System Status Control Program, BFN . has evaluated the use of Class IE tie-breakers against the NRC staff's recommendations contained in the GL and has determined that the existing controls are sufficient to resolve the GI-49 concern.

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