ML18039A741
| ML18039A741 | |
| Person / Time | |
|---|---|
| Site: | Browns Ferry  |
| Issue date: | 03/30/1999 |
| From: | Abney T TENNESSEE VALLEY AUTHORITY |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| TAC-M98205, TAC-M98206, NUDOCS 9904150024 | |
| Download: ML18039A741 (13) | |
Text
~ p CATEGORY 1 REGULAT RY INFORMATION DISTRIBUTIO SYSTEM (RIDS)
ACCESSION,NBR:9904150024 DOC.DATE: 99/03/30 NOTARIZED: NO FACIL:50-260 Browns Ferry Nuclear Power Station, Unit 2, Tennessee
,... 50"Q96 Browns Ferry Nuclear Power Station, Unit 3, Tennessee AUTH.NAMQ AUTHOR AFFILIATION ABNEY,T~ E.
Tennessee Valley Authority RECIP.NAME RECIPIENT AFFILIATION Records Management Branch (Document Control Desk)
DOCKET I 05000260 05000296
SUBJECT:
Provides partial response to NRC 981117 recpxest 376,proposing to extend current 14 days.
DISTRIBUTION CODE:
D030D COPIES RECEIVED:LTR TITLE: TVA Facilities - Routine Correspondence NOTES:
RAI re TS change 7-day AOT for EDG to ENCL SIZE:
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INTERNAL: ACRS OGC/HDS3 EXTERNAL: NOAC 1
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IIllIIIII'II.IIIIS NOTE TO ALL "RIDS" RECIPIENTS:
PLEASE HELP US TO REDUCE WASTE. TO HAVE YOUR NAME OR ORGANIZATION REMOVED FROM DISTRIBUTION LISTS OR REDUCE THE NUMBER OF COPIES RECEIVED BY YOU OR YOUR ORGANIZATION, CONTACT THE DOCUMENT CONTROL DESK (DCD)
ON EXTENSION 415-2083 TOTAL NUMBER OF COPIES REQUIRED:
LTTR 9
ENCL 8
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Tennessee Valley Authority, Post Office Box 2000. Decatur. Alabama 35609 March 30, 1999 U.S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, DC 20555 Gentlemen; In the Matter of Tennessee Valley Authority Docket Nos.
50-260 50-296 BROWNS FERRY NUCLEAR PLANT (BFN)
UNITS 2 AND 3
RESPONSE
TO REQUEST FOR INFORMATION REGARDING TECHNICAL SPECIFICATIONS CHANGE NO. 376 EXTENDED EMERGENCY DIESEL GENERATOR ALLOWED OUTAGE TIME (TAC NOS.
M98205 and M98206)
This is a partial response to the November 17,
- 1998, Request for Additional Information (RAI) regarding Technical Specifications (TS) change request 376.
TS-376, which was submitted on March 12,
- 1997, proposed changes to the Unit 2 and 3
TS to extend the current 7-day Allowed Outage Time for the Emergency Diesel Generators to 14 days.
Responses to Items 1,
2, and 3 from the RAI are provided in the Enclosure.
Item 4 of the RAI asked that TVA provide certain additional information in a manner consistent with the guidelines of Regulatory Guides (RG) 1.174 (An Approach for Using Probabilistic Risk Assessment in Risk-Informed Decisions on Plant-Specific Changes to the Licensing Basis, July 1998) and RG 1.177 (An Approach for Using Plant-Specific, Risk-Informed Decisionmaking:
Technical Specifications, August 1998).
These Regulatory Guides were issued subsequent to the TS-376 submittal and TVA is reviewing Item 4 in light of e90ea500a4 e90SS0 PDR ADQCK 05000260I' PDR,.i 'r
U.S. Nuclear Regulatory Commission Page 2
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March 30, 1999 these Regulatory Guides.
We expect to provide a response to Item 4 by the end of April, 1999.
This schedule was coordinated with BFN's Project Manager, L. Raghavan.
If you have any questions, please contact me at (256) 729-2636.
S'cerel
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Mana of Licen ing d Industry A fairs cc:
S age 3
U.S. Nuclear Regulatory Commission Page 3
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March 30, 1999 cc:'Enclosure):
Mr.,Albert W.
De Agazio, Senior Project Manager U.S. Nuclear Regulatory Commission One White Flint, North 11555 Rockville Pike Rockville, Maryland 20852 Mr. Paul Frederickson, Branch Chief U.S. Nuclear Regulatory Commission Region II 61 Forsyth Street, S.W.
Suite 23T85
- Atlanta, Georgia 30303 NRC Resident Inspector Browns Ferry Nuclear Plant 10833 Shaw Road
- Athens, Alabama 35611
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ENCLOSURE TENNESSEE VALLEY AUTHORITY BROWNS FERRY NUCLEAR PLANT (BFN)
UNITS 2 AND 3 TECHNICAL SPECIFICATIONS (TS)
CHANGE 376 EXTENDED ALLOWED OUTAGE TIME (AOT)
EMERGENCY DIESEL GENERATORS (EDGs)
RESPONSE
TO REQUEST FOR ADDITIONAL INFORMATION (RAI)
DATED NOVEMBER 1 7 I 1 998 Below are responses to the first three of the four NRC items provided in the subject RAI on TS-376.
TS-376 was submitted on March 12,
- 1997, and proposes changes to the Units 2 and 3
TS to extend the current 7-day AOT for the EDGs to 14 days.
The NRC questions for Items 1,
2, and 3 are repeated below along with the TVA responses for each item.
NRC ITEM 1.a As stated in the Tennessee Valley Authority's (TVA's) March 22, 2997, letter, the purpose of the proposed amendment is to allow an increased outage time during plant power operation for performi ng emergency diesel-generator (EDG) preventi ve maintenance (PM), which would include disassembly of the EDG.
The staff is concerned that disassembly of an EDG would subsequently require pre-operational testing of'hat EDG (such as full load rejection tests) following this maintenance while the plant is operating instead of during shutdown, which has been the past practice.
To resolve this concern, the following should be addressed:
- a. What would be the typical and worse-case voltage transients on the 4260-V safety buses as a result of a full-load rejection?
TVA RESPONSE TO ITEM 1.a BFN TS do not require full load rejection tests, and these tests are not performed at BFN.
- Rather, TS 3.8.1.5 prescribes a
largest (single) post-accident load rejection surveillance test which is performed every 24 months.
The single largest load is a
Residual Heat Removal (RHR) pump.
Load rejection testing would also be performed if the EDG governor or voltage regulator was replaced or if major maintenance work was performed involving these devices.
Load rejection testing would typically not be
performed following mechanical preventive maintenance (PM)
,aCtivities such as the 12-year vendor recommended PM.
The EDG load rejection surveillance test is performed as part of the EDG Load Acceptance surveillance test (LAT).
During the EDG LATs, the 480-V Accident Load Shedding Logic is initiated which, for certain
- EDGs, adversely affects normal plant operations since various loads essential for continued plant operation are automatically shed.
Because of this, the B and D EDG LATs are not performed while Unit 2 is operating.
For Unit 3, the 3A and 3C EDG LATs have a similar effect and are, therefore, performed during Unit 3 refueling outages.
The B and D,
and 3A and 3C EDGs are the emergency power supplies for the divisionalized safety trains on Units 2 and 3 respectively.
The LATs (and associated load reject surveillance tests) for EDGs A, C,
3B, and 3D are performed with Units 2 and 3 in operation.
1 The single largest load reject surveillance tests are performed with their respective 4-kV Shutdown Board isolated from the offsite power system and must meet the operating response criteria of TS Surveillance Requirement (SR) 3.8.1.5 which is repeated below.
Specific EDG testing requirements for PM activities and corrective maintenance activities are defined by the TS and by the nature of the maintenance activity.
The ability.to conduct EDG tests while operating is based on plant systems
As noted
- above, for certain
If load rejection testing is required during operation, the EDG along with its associated 4-kV Shutdown Board can be isolated and the testing performed with minimal impact on plant electrical systems.
TS SR 3.8.1.5 Acce tance Criteria Verify each DG rejects a load greater than or equal to its associated single largest post-accident
- load, and:
a.
Following load rejection, the frequency is 6 66.75 Hz; and b.
Following load rejection, the steady state voltage recovers to 2 3940 V and 5 4400 V.
c.
Following load rejection, the steady state frequency recovers to 2 58.8 Hz and 5 61.2 Hz.
NRC ITEM 1.b
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- b. If a full-load rejection test is used to test the EDG governor after maintenance, what assurance would there be that an unsafe transient condition would not occur on the safety bus (i.e., load swing or voltage transient) due to improperly performed maintenance or repair of a governor?
TVA RESPONSE TO ITEM 1.b As discussed in item 1.a, full-load rejection tests are not used to test the EDG governors after maintenance.
If the single largest load reject test was necessary, testing would be performed with the EDG and associated 4-kV Shutdown Board isolated from the remainder of the plant electrical system and no transient condition could occur.
- Also, as discussed in the next
- response, EDG testing following governor maintenance is performed in a graduated manner which reduces the likelihood of an unexpected transient on the EDG being tested.
The EDG would not be reconnected to the main electrical system until testing has verified proper governor operation.
NRC ITEM 1.c c.
Using maintenance and testing experience on the EDG, identify possible transient condi tions caused by improperly performed maintenance on the EDG governor and voltage regulator.
Predict the electrical system response to these transients.
- Also, TVA should provide information on the tests to be performed after PM to declare the EDG operable and provide justification for performing such tests at power.
TVA RESPONSE TO ITEM 1.c Improper operation of an EDG due to governor problems (or voltage regulator problems) would be corrected in a similar manner whether detected after a corrective maintenance activity or during routine surveillance tests.
Load rejection testing would be performed if the governor or voltage regulator was replaced or if major maintenance work was performed involving these
- devices, and would be completed while the EDG was isolated from the main plant electrical system.
If initial testing indicated that either device required adjustment, the EDG would be started and adjustments would be made prior to connecting to the 4-kV Shutdown Board.
The EDG would then be tied to the 4-kV Shutdown Board and gradually loaded and the responsiveness checked while closely monitoring E3
governor and voltage regulator performance.
Should the EDG
~becorhe'nstable during testing it would be promptly isolated.
Any instability should be identified at minimum EDG loading and isolation of the EDG would not result in significant syst: em perturbations.
Depending on the nature of a governor (or voltage regulator) malfunction, testing might also include the starting of an RHR pump motor (largest single load) and then disconnecting the RHR pump (largest load reject).
These tests are conducted with the 4-kV Shutdown Board isolated from offsite power.
Data obtained from this testing can then be compared to data obtained from previous similar EDG tests to confirm proper governor (or voltage regulator) operation.
This testing approach is straightforward and from past operating experience has proven to be a reliable means to assess EDG performance while avoiding possible transients.
In addition, required TS operability surveillance tests will be performed before the EDG is declared fully operable.
As noted previously, the above testing is performed with the respective 4-kV Shutdown Board isolated from its offsite power source.
Therefore, there will be no impact on electrical systems during the testing other than the RHR pump motor that is being started.
- Also, as discussed in the response to item 1.a, the ability to conduct EDG tests while operating is based on plant systems
NRC ITEM 2 TVA has stated that during Browns Ferry Nuclear Plant's 23 years of operation, there has never been a complete loss of offsi te power event.
However,'icensee Event Report 97-002-00 indicated that on March 5, 2997, Unit 3 lost offsi te power and EDGs started and tied to their respective buses.
It appears that at least once BFN experienced a loss of'ffsite power event.
Please comment.
TVA RESPONSE TO ITEM 2 The reference to BFN loss of offsite power history is provided on page E1-4 of the March 12,
- 1997, TS-376 submittal which discusses the diversity of TVA's offsite power system and that a complete loss of offsite power event had not been experienced in BFN's 23 years of operation (now 25 years of operation).
This section of the report focused on the low likelihood of a loss of power event being caused by the TVA's transmission system.
On March 5, 1997, Unit 3 was in a refueling outage with the prefer'red offsite power source from the 500-kV switchyard unavailable due to scheduled maintenance of the Unit 3 Main Bank 500-kV transformer.
This maintenance can only be performed when the Unit 3 generator is not in operation.
In this situation, offsite power was being provided to Unit 3 exclusively via the 161-kV system.
A loss of the 161-kV lines to Unit 3 were caused by a workmanship error on an unrelated piece of plant equipment
- and, thus, did not originate from the TVA transmission system.
Details are provided in Licensee Event Report 50-296/97001 dated April 4,
- 1997, which discusses that the event had minimal impact on Unit 3.
Unit 2 was at full power and was unaffected by the loss of the 161-kV supply.
Therefore, the event is not considered a complete loss of power event for BFN.
NRC ITEM 3 The Bases Section for TS 3.9.B.3 for Uni t 2 and TS 3.9.B.2 for Uni t 3 should be modified providing the basis for this change.
TVA RESPONSE TO ITEM 3 TS-376 was submitted in both custom and improved TS (ITS) format.
The TS Bases referenced above are from the custom TS (CTS).
In the CTS Bases, there was no discussion of EDG AOTs so no changes were deemed necessary for a change to a 14-day AOT.
Bases changes were appropriate for the ITS format and were provided.
BFN subsequently converted to ITS (Amendment Nos.
- 234, 253, and 212 for BFN 1, 2,
and 3 respectively) in July 1998.
Therefore, the proposed TS-376 changes in CTS format are no longer pertinent.
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