ML20203A928
| ML20203A928 | |
| Person / Time | |
|---|---|
| Site: | Browns Ferry  |
| Issue date: | 02/17/1998 |
| From: | Abney T TENNESSEE VALLEY AUTHORITY |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| TAC-M98305, TAC-M98306, TAC-M98307, NUDOCS 9802240158 | |
| Download: ML20203A928 (6) | |
Text
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Tevessee Vahey Authonty Post Oftce 80s 2000, Decatur Aiabama 35609 February 17, 1998 U.S.
Nuclear Regulatory Commission ATTN:
Document Control Desk Washington, D.C.
20555 G e n t l e. e n :
In the Matter of
)
Docket Nos.
50-259 Tennessee Valley Authority
)
50-260 50-296 BROWNS FERRY NUCLEAR PLANT (BFN) - UNITS 1, 2, AND 3 -
SUPPLEMENTAL INFORMATION ON A RESPONSE TO REQUEST FOR ADDITIONAL INFORMATION (RAI) REGARDING OFFSITE POWER SUPPLIES CONFORMANCE TO GENERAL DESIGN CRITERION (GDC) -17 (URI 97-03-01) (TAC NOS.
M98305, M98306, AND M98307)
This lettar responds to a NRC telephone request made on January 6 1998, for supplemental information regarding BFN's offsite power supplies conformance co GDC-17, Electric Power Systems.
TVA responded in a letter dated August 18, 1937, to a June 10, 1997, NRC RAI regarding BFN's offsite power and control power supplies.
Upon review of TVA's August 18, 1997, response, NRC had an additional question.
This question was discussed between TVA and NRC personnel in a telephone conversation on January 6, 1998.
At that time, NRC requested that TVA submit supplemental 4
information for the RAI to address the question.
The enclosure to this letter complies with that request.
k) 9802240158 980217 '
PDR ADOCK 05000259
.c f
n.
U.S.
Nuclear Regulatory Commissior.
Page 2 February 17, 1998.
There are no commitments described in this letter.
If you have any questions please call me at (205) 729-2636.
Sincerely 1
/
f8 T.
Nbtey Manager of Li nsi g and Indc.st y Affa'rs Enclosure cc: (Enclosure)
Mr. A. W.
DeAgazio, Project Manager U.S. Nuclear Regulatory Commission One White Flint, North 11555 Rockville Pike Rockville, Maryland 20852 Mr. Mark S.
Lesoer, Branch Chief U.S. Nuclear Regulatory Commission 61 Forsyth Street, SW Suite 23T85 Atlanta, Georgia 30303 NRC Resident Inspector Browns Ferry Nuclear Plant 10E33 Shaw Road Athens, Alabama 35611 1
ENCLOSURE TENNESSEE VALLEY AUTHORITY BROWNS FERRY NUCLEAR PLANT (BFN)
UNITS 1, 2, AND 3 SUPPLEMENTAL INFORMATION FOR OFFSITE POWER SUPPLIES CONFORMANCE TO GENERAL DESIGN CRITERION -17 BACKGROUND On March 5, 1997, BFN Unit 3 experienced a loss of offsite power.
This event is discussed in Licensee Event Report 50-296/97-001 and in NRC Inspection Report 50-259, 260, and 296/97-03.
In the Inspection Report on Page 3, it was noted that control power for all switchyard breakers (both 500 kV and 161 kV swithchyards) was supplied by a single battery board.
This resulted in an unresolved item that questioned whether a single control power source to all switchyard components satisfies 10 CFR 50, Appendix A, General Design Criterion (GDC)-17 requirements.
Based on this event, in a letter dated June 10,-1997, NRC requested additional ir. formation regarding BFN's offsite power supplies' conform:
,e to GDC-17, Electric Power Systems. -NRC requested TVA tr provide 4nformation of the following icsues:
_(1) For each offsite power circuit (immediately available and delayed access) to shutdown boards provide the control power source (which battery) for all the required breakers l
(including 500 kV, _61 kV, generator breaker, Unit Board ano l
Shutdown Board breakers)~, and (2) Discuss _the availability of l
offsite power '(immediately available and. delayed access)-to shutdown buses during a single event (i.e.,
less of a battery board or loss of unit station service transformer, etc.)
assuming that no onsite power is available. The discussion should i nclude how the tripping and closing of different breakers will be performed. Additionally _if delayed access offsite power is available, disauss the time delay involvea so that specified acceptable fuel design limits and design conditions of the reactor coolant pressure boundary are not exceeded.
After-reviewing TVA's response to the June 10, 1997, RAI, the NRC requested supplemental information in a telcphone conversation on January 6, 1998.
This response complies with the NRC's request for supplemental information as discussed in that conversation.
RESPONSE TO REQUEST FOR SUPPLEMENTAL INFORMATION NRC requested additional information to address the following question:
Provide the expected sequence of events to provide delayed off.:ite power (161-kV) to the shutdown boards given the loss of the immediate offsite source (500-kV) and the loss of control power for each unit, that is, Battery 5 for Unit 1, Battery 4 for Unit 2, and Battery 6 for Unit 3.
A concurrent problem with the respective unit generator should be included.
The control power for the 500-kV and the 161-kV switchyards is from control power distribution panel 9-24 which is located in l
the Unit 1/2 control room.
The distribution panel has a normal supply from Battery 4 ano an alternate supply from Battery 2.
When Battery 4 fuils, an alarm "BATT NO. 4 SYS AB"ORNAL" is received in the Control Room on panel 9-7, and the Alarm Response Procedure provides guidance for operator response.
The operator can cacess the equipment and transfer (generally in loss thaa 5 minutes) panel 9-24 to its alternate source.
Restoration at the switchyard control power will then allow the operator to make breaker alignment changes as necessary.
In the following scenarios the Emergency Diesel Generators are designed to automaticclly initiate upon the loss of voltage due to the loss of the immediate offsite power source.
However, for the purpose of this discussion, no credit is taken for this designed feature.
In addition, a noa-rafety-related battery failure does not prevent the safety-related battery from performing its design function.
UNIT 1 The Unit 1 generator breaker and Unit Boards 1A and 1B receive control power from non-safety related 250V DC Battery 5.
A concurrent loss of the 500-kV source and Battery 5 will result in-4-kV Shutdown Bus 1 automatically transferring, due to loss of voltage relaying, to 4-kV Unit Board 2B if voltage is available.
No transfers will occur at 4-kV Unit Boards lA or 1B.
250V DC control power can be re-established by manually transferring to the alternate source at the Turbine Building Distribution Board 2 located in the Turbine Building.
The Control Room Operator will then transfer to the-delayed source (161-kV) per an Operating Instruction (OI)-57-A
" Switchyard ad 4160 V Electrical System.
If the loss of tae 500-kV source has affected Unit 2, 4-kV Unit Boards 2A and 2B will automatically or by plant prccedure E-2
(0-OI-5'-A) be manually transferred to the 161-kV source from Control Room panel 9-8.
Unit Board 2A will supply power to 4-kV Sh'Itdown Bus 2 and Unit Board 2B will supply 4-kV Shutdown Bus 1.
The 4-kV Shutdown Buses feed the Unit 1/2 Shutdown Boards.
If the diesel generators are unavailable, HPCI and,'or RCIC will maintain reactor coolant inventory, since they are fed emergency power from a safety-related DC power supply, until manual transfer to the delayed offsite source is completed.
The manual transfer to the delayed offsite source (161-kV) can be completed in less than 30 minutes.
If the Unit 1 generator is required to trip, protective relaying will cause the 500-kV switchyard breaker to trip and isolate the Unit 1 generator.
The Shutdown Buses and Boards will automatically transfer to Unit 2 Unit Boards as described above.
UNIT 2 The Unit 2 generator breaker, Unit Soards 2A and 2B, and the 500-kV/161-kV switchyards receive control power from non-safety.. ated 250V DC Battery 4.
A concurrent loss of the 500-kV source and Battery 4 will result in 4-kV Shutdowa Bus 2 automatically transferring, due to loss of voltage relaying, to 4-kV Unit Board 1B, if voltage is available. No transfers will occur at 4-kV Unit Boards 2A or 2B due to lack of control power (Battery 4).
250V DC control power to the generator breaker and Unit boards can be re-established by manually transferring to the alternate source at the Turbine Building Distribution Board 2 located in the Turbine Building.
The Control Room Operator can then transfer to the delayed source per Operating Instruction (0-OI-57-A).
If the loss of the 500-kV s urce has also affected Unit 1, 4-kV Unit Boards 1A and 1B will automatically or the Control Room Operator from Control Room panel 9-8 can manually transfer to the 161-kV source because control power (Battery 5) is available.
Unit Board 1A will supply power to 4-kV Shutdown Bus 1 and Unit Board 1B will supply 4-kV Shutdown Bus 2.
The 4-kV Shutdown Buses feed the Unit 1/2 Shutdown Boards.
If the diesel generators are unavailable, HPCI and/or RCIC will be available, since they are fed emergency power from a safety-related DC supply, to maintain reacter coolant inventory until manual transfer to the de' ayed c 'fsite source (161-kV) is completed.
This transfer to the delayed source will take less than 30 minutes.
Should a problem occur with the Unit 2 generator with Unit 1 unaffected, protective relaying will cause offsite E-3 r
~
b
substation 500-kV breakers to trip and result in the isolation
.of the Unit 2 generator.
The Shutdown Buses and Boards will autonatically transfer to Unit 1 as described above.
UNIT 3
The Unit 3 generator breaker and Unit Boards 1A and 3B receive control power from non-safety related 250V DC Battery 6.
With a concurrent loss of the 500-kV source, Battery 6, and the diesel generators are unavailable, HPCI and RCIC will be available, since they are fed emergency power from a safety-related DC supply, to maintain reactor coolant inventory until manual transfer to the delayed offsite source (161-kV) is completed.
No transfer will occur at 4-kV Unit Boards 3A or 3B with the loss of control power (Battery 6). Operators must then transfer Turbine Building Distribution Board 3 located i. the Turbine Building to its alternate source (Battery 4) to restore control power to the Unit 3 Unit Boards.
The Control Room Operator can then manually transfer 4-kV Unit Boards 3A and 3B to the 161-kV source in accordance with operating instruction 0-OI-57-A.
This transfer to the delayed source will take less than 30 minutes.
Should a problem occur with the Unit 3 generator, protective relaying will cause the 500-kV switchyard breaker to trip and isolate the Unit 3 generator.
The Shutdown Boards will be manually transferred to the delay power source when control power is available at the Unit Boards as described above.
CONCLUSION 1
For the postulated event and the assumed concurrent multiple failures, delayed offsite power is available to the Shutdown Boards within 30 minutes.
During this time, HPCI and/or RCIC would be available to maintain reactor coolant inventory such that fuel design limits and reactor coolant pressure boundary design conditions are not exceeded.
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