RS-13-007, Response to Request for Additional Information Regarding the Use of an Auxiliary Feedwater Cross-tie Between Units

Response to Request for Additional Information Regarding the Use of an Auxiliary Feedwater Cross-tie Between Units

ML13035A017
Person / Time
Site:	Byron, Braidwood
Issue date:	02/01/2013
From:	Gullott D Exelon Generation Co
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
RS-13-007
Download: ML13035A017 (10)

Text

4300 Winfield Roy 4300 Winfield R03dd Warrenville,I~I!60555 Warrenville, 60555 Exelon Exeton Generation 630 657 2000 Offc-e 6306552000 Offce RS-13-007 RS-13-007 10 10 CFR CFR 50.90 February 11,, 2013 February U. S. Nuclear Nuclear Regulatory Regulatory Commission Commission Document Control ATTN: Document Control Desk Desk Washington, DC Washington, DC 20555-001 Braidwood Station, Units 11 and Braidwood and 22 Facility Operating Facility Operating License Nos. NPF-72 and NPF-77 NRC Docket Nos.

NRC Nos. STN 50-456 and STN-50-457 Byron Station, Byron Station, Units Units 1 and 2 Facility Operating License Nos. NPF-37 and NPF-66 NRC Docket Nos. STN 50-454 and STN 50-455

Subject:

Response to Request for Additional Information Information Regarding the Use of of an AuxiliaryFeedwater Auxiliary Feedwater Cross-tie Cross- tie Between Units.

Units.

References:

1) Letter from from D.D. M.

M. Gullott Gullott (Exelon (Exelon Generation Generation Company, Company, LLC) LLC) to u. S.S.

to U.

Nuclear Regulatory Commission, "License Amendment Request Request for for the the use use of an Auxiliary of Feedwater Cross-tie Auxiliary Feedwater Cross-tie Between Between Units,"

Units," dated dated January January 31, 31, 2012

2) Email from Email from J.J. S. Wiebe (U. S. Nuclear Regulatory Regulatory Commission)

Commission) to to R.

R. W.W.

McIntosh (Exelon Mcintosh (Exelon Generation Generation Company, Company,LLC), LLC), "Preliminary "Preliminary RAls Related Related to to the Auxiliary Feedwater Cross Auxiliary Feedwater Cross Connect Amendment Request, Request,"II dateddated November 9, 2012 In Reference 1, 1, Exelon Exelon Generation Company, Company, LLC (EGC) submitted LLC (EGC) submitted aa license license amendment request request (LAR) to revise the Updated Final (LAR) to Final Safety Safety Analysis Report (UFSAR)(UFSAR) to to describe the use use of an Auxiliary Feedwater (AF)

Auxiliary Feedwater (AF)cross-tie cross-tie between between units.

units. The The LAR LAR described described the the intended intendeduse useofof the cross-tie cross-tie to support beyond design design basis basisevents eventsrelating relating toto total total loss loss of of secondary secondary heat heatsink.

sink.

In Reference Reference 2, 2, the the U.S.

U.S. Nuclear NuclearRegulatory RegulatoryCommission Commission (NRC) (NRC) requested requestedadditional additional information information to to complete complete its its review review ofofthe the proposed proposed license amendment amendment request.request.Clarification Clarificationofof the information information thethe NRC NRC needs needs to complete their review was requested review was requested in in discussions discussionsheld heldon on November 16, 16, and and December December4, 4,2012.

2012.EGCEGCis isproviding providingthetheattached attachedinformation information in in response response to the request.

request.

EGC hashasreviewed reviewed thetheinformation information supporting supportingaafinding finding ofof no no significant significant hazards hazardsconsideration consideration and and the the environmental environmentalconsideration considerationthat thatwere werepreviously previouslyprovided providedtotothe theNRC NRCininAttachment Attachment1 1 of Reference 1. 1. The Theadditional additionalinformation information provided provided in this submittal in this submittal doesdoes not affect affect the the bases bases for for concluding that the proposed license license amendments amendmentsdo donotnotinvolve involve aasignificant significant hazards hazards consideration.

consideration. InInaddition, addition,thetheadditional additionalinformation information provided provided in in this submittal does does not not affect affect

February 11,, 2013 February 2013 U. S.

U. S. Nuclear Nuclear Regulatory Commission Page 2 Page the bases the bases for for concluding concluding that neither an environmental environmental impact statement statement nor nor an an environmental environmental assessment needs assessment needsto tobe beprepared preparedininconnection connectionwith with the proposed proposed amendment.

amendment.

In accordance In accordance with CFR 50.91, "Notice with 10 CFR for public "Notice for publiccomment; comment;State State consultation,"

consultation," paragraph paragraph (b), aa copy (b), copy of of this this letter letter and and its its attachments are are being being provided provided to to the thedesignated designatedState StateofofIllinois Illinois official.

There are no no regulatory regulatory commitments commitments contained contained in in this this letter.

letter.

Should you Should you have any questions questions concerning concerning thisthis letter, letter, please pleasecontact contactRichard Richard W.

W. McIntosh Mcintosh at (630) 657-2816.

(630)

II declare declare under penalty of of perjury perjurythat thatthe the foregoing foregoingisistrue trueand and correct.

correct. Executed Executed onon the the 1st 1stdayday of of February 2013.

Respectfully, David M. M. Gullott Gullott Manager -- Licensing Manager Licensing Exelon Generation Company, Company, LLC LLC

Attachment:

1.. Response to Request 1 Request forfor Additional Additional Information Information cc: NRC Regional Regional Administrator, Administrator, Region RegionIII III NRC Senior Resident Resident Inspector, Inspector, Braidwood Braidwood StationStation NRC Senior Resident Inspector, Byron Byron Station NRC Project Manager, NRR - Braidwood Braidwood and and Byron Byron Stations Stations Illinois Emergency Management Illinois Emergency Management Agency AgencyDivision Division of of Nuclear Nuclear Safety Safety

ATTACHMENT ATTACHMENT 11 Response to Request for for Additional Information Information NRC Question RAI-1:

In aa staff In staff memorandum, memorandum, dated dated September September 18, 18, 1992, 1992, thetheU.S.

U.S.Nuclear NuclearRegulatory Regulatory Commission Commission (NRC) approved (NRC) approved the staff's position position that that the the General GeneralDesign DesignCriteria Criteria(GDC)

(GOC) will will not be applied applied to to plants receiving their construction construction permits prior prior to to 1971.

1971. Since Bryon and Braidwood Since Bryon and Braidwood received received construction permits prior their construction prior to to 1971, 1971, Exelon Exelon was was not required to adhere adhere strictly strictly to the GDCs.

GOCs.

However, Exelon However, Exelon is is required required to to state in their design bases basestheir theirinterpretation interpretation of of how how the the plants plants conform to the intent of GDCs.

conform GOCs.

Currently, sharing Currently, sharing of the auxiliary feedwater (AFW) auxiliary feedwater systems between (AFW) systems between the thetwo two units unitsisisnot notwithin within the licensing basis.

basis. The Theplant plantrecently recentlyphysically physicallymodified modified the theunits unitsto tocreate createthis thiscapability capabilityto to share AFW through the AFW through the train trainAAdischarge dischargeflow flowpath.path.When Whenaa sitesite shares shares systems, components, components, or structures, the staff uses uses guidance guidanceprovidedprovided in in 10 10 CFR CFR 50, 50, Appendix Appendix A, A, General Design Criterion (GOC)

Criterion (GDC)5,5,"Sharing "Sharingofofstructures, structures,systems, systems, and components," to to evaluate evaluateacceptability.

acceptability.

As stated above, since As since the the plants plants were were notnot licensed licensed to to GDCs, GOCs, then the the licensee licensee must mustexplain explain how thethe plants would would conform to the intent intent of the provisions in in 10 10 CFR CFR 50, 50, APP APP A, A, GDC GOC 5. 5.

In the In the Exelon's Exelon's January 31, 2012, letter, letter, Exelon proposes proposes revisions revisions to to the the Updated Updated FinalFinal Safety Safety Analysis Report Analysis Report (UFSAR)

(UFSAR)Sections Sections3.1.2.1.53.1.2.1.5and and3.1.2.4.5 3.1.2.4.5to toaddress address changes to to the plant plant design basis basis toto implement implement AFW AFW cross cross tietie operation.

operation. The licensee states: states:

The AF The AF [AFW]

[AFW] system is is designed designedwith with suitable redundancy redundancy to to offset offset thethe consequences consequences of any single single failure, failure, with with one exception exception duringduring AF [AFW] Train AA unit

[AFW] Train unit cross-tie cross-tie use.

use. Use Use of the Train A unit cross-tie results in unit cross-tie in aa temporary temporary relaxation relaxation of ofthe thesingle singlefailure failurecriterion criterion for the non-accident for non-accident unit, unit, which, consistent consistentwith with overall overall system systemreliability reliability considerations, considerations, provides a limited time to limited time to support support the the accident unit emergency emergency response, response,and andreturn returnthe the AF [AFW]

[AFW] Train A to an operable status.

In Exelon's In Exelon's evaluation evaluation of ofother othersystems systems that that share share structure, structure, system system and components (SSCs) (SSCs) in in UFSAR Section 3.1, UFSAR Section 3.1, Exelon Exelon finds finds that that the the shared shared systems systems can can sustain sustainaasingle singlefailure failureand andstill still accomplish the the safety safetyfunction function in in both both units.

units.

The staff finds finds by implementing implementing the the AFWAFWcrosscross tietie between between the units, the licensee licensee adversely adversely affects the non-accident non-accident unit's unit's AFW AFW system ability ability toto mitigate mitigate anan accident, because becauseitit cancanno no longer sustain aa single single failure failure and performperform its its safety function.

function. The staff finds finds the the licensee proposed change change to to the the UFSAR UFSAR unacceptable.

Provide justification justification why why thethe staff should not not deny deny the theapplication.

application.

EGC Response:

This request request does doesnot notchange changehow howthe theAuxiliary Auxiliary Feedwater Feedwater(AF) (AF) system systemdesign designcomplies complieswith with the 1010 CFR CFR 50,50, Appendix Appendix A, General Design DeSign Criteria Criteria (GDC),

(GOC), nor nor does does it change the the operation operation of of the AFAF system as asallowed allowed by bythe theplant plantTechnical TechnicalSpecifications Specifications(TS). (TS).

The intent of the license amendment amendment request requestisisto todocument documentthe thedesign designdetails detailsofofthethecross-tie cross-tieinin the UFSAR, U FSAR, and how how the the AFAF system system design designcontinues continuestotocomplycomplywith with the the GDCs GOCs whilewhile the the system continues continues to to bebe operated operated in in accordance accordancewith with the approved approved TS. TS.

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ATTACHMENT ATTACHMENT 1 Response to Response to Request Request for for Additional Additional Information Information The proposed The proposed changes to the UFSAR UFSAR are intended to describe the function function and operation of the the AFcross-tie AF cross-tie between between the Unit Unit 1 andand Unit Unit 22 Train Train AAof ofthe theAF AFsystem.

system. As stated stated in in the the January 31,2012, January 31, 2012, letter, this AF AF cross-tie cross-tie piping piping does does not support or accomplish any AF system AF system safety function, safety function,design design basisbasis function, function, or or normal normaloperating operatingfunction.

function. The The cross-tie cross-tie may be used used in response in response to a total total loss loss ofof secondary secondary heat sink beyond design basis basis event event asasaamitigating mitigating strategy in strategy in accordance accordance with the functional with the functional restoration restoration procedures.

procedures. Similar Similar to other plant system functionalrestoration functional restorationstrategies strategies described described in in the the UFSAR, UFSAR, the the purpose of these these proposed proposed changes is changes is to describe describe the the cross-tie cross-tie capability capability and and operation operation in in the the UFSAR; UFSAR; not to change change the the AF system AF system designdesign related to GDC compliance, operation GOC compliance, operation of of the the system system in accordance accordance with with the TS, or TS, or any any of of the the AFAFsystem system safety safety functions.

functions. The purpose purpose of of the the Exelon Exelon Generation Generation Company, Company, LLC(EGC)

LLC (EGC)requestrequestisis not nottoto license license the the use of the cross-tie as asaacredited creditedsafety safetyfunction functionof ofthe the AF system.

AF system.

The AF system system design continues continues to meet requirements requirements of of GOC GDC 5 and GDC GOC 34:

• • With regard With regard to to GOC GDC5,5,there there areare nono normal normal operating, operating, abnormal abnormal operating occurrences, or design basis events that require events that require or creditor credit the sharing of AF AF system system components between the units. The Thedesign designand andcontrol control of of the the cross-tie cross-tie piping piping ensures ensures that thatthethe operation of one unit's A train of A train of AF AFdoesdoes not support or impact the operation of of the other other unit's A unifs A train train ofofAF AFduring duringan an event event or or condition condition wherewhere the the AFAF system safetysafety function function is is required. As As described in the January January 31, 2012, letter, 31,2012, letter, the the AFAF cross-tie cross-tie does doesnot notimpact impact AF system AF system compliance with with GOCGDC55since since thethe AF AFsystem system design design continues to be capable capable performing its of performing its required required safety safety functions functions on on its its unit unit during duringan an accident accident and is not required to required to support an orderly shutdown shutdown and cooldowncooldown of of the the other unit.

unit. In In the event event of of a beyond design basis basis accident accident on on one one unit, unit, which necessitates the use which necessitates use of of the the cross-tie, cross-tie, the non-accident non-accident unit unit remains capable capable of of an an orderly orderly shutdown since since plant plant design design does does not utilize its dedicated utilize its dedicated AF AF system system to support this normal, orderly shutdown. Therefore, Therefore, the use use ofof the cross-tie cross-tie between between units units does doesnot notconstitute constitute aasharing sharing of of components componentsin in conflict conflict with with GOC GDC 55 (Le.,(i.e., GOC GDC 55 continues continues to be be complied complied with). with).

• With With regard to GDC GOC 34, 34, each unit'sunit's AFAF system system continues continues to tobebecomprised comprisedofoftwo two redundant and and independent independenttrains, trains, eacheachcapable capableofofindividually individually performing performing the system'ssystem's required safety functions.functions. For For normal and design basis basis operation, operation, eacheachunit's unit1s AF AF system system design design remains remains capable capableof ofaccomplishing accomplishing its its safety safety functions functions assuming assuming aasingle singlefailure.

failure.

The cross-tie cross-tie from the other unit does does notnot support support any any redundancy redundancy requiredrequired to to comply comply with this GOC.

with this GDC. The use use ofof the the cross-tie cross-tie isis ananoperational operationalconditioncondition of of the AF AF system that that is governed by the unit's unit's TSTS asas discussed discussed below.below. The The cross-tie cross-tie operation operation is is not not a change change in in the the system systemdesigndesignthat thatprevents preventsthe theAFAFsystem systemfrom frommeeting meetingthe thesingle singlefailure failure assumptions assumptionsof of GDC GOC 34. 34.

Since there there are are nonoAF AF system system safety safetyfunctions functions thatthat require require sharing sharing of of components componentsbetween between units and safety safety functions can be be performed performed assumingassumingaasingle singlefailure, failure, the the AF AF system system designdesign remains compliant compliant with with thethe GOCs GDCs under under the the proposed change. change.

TS TS 3.7.5 3.7.5 provides providesthe thelimiting limiting conditions conditions for for operation of of the the AFAF system, system, along alongwith with the the required required actions actions to to bebe taken taken whenwhen the the specified specified conditions conditions are not met. TS TS3.7.5 3.7.5presently presentlyallows allows 72 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> hours of of continued continued unit unit operation with with one AF system train inoperable inoperable (i.e., (Le., not not capable capableof of performing performing its specified function). function). EGC EGCwill will continue continueto tocomply complywith with this this TS TS inin the theunlikely unlikely event event that that thethe cross-tie cross-tie is is used used to to support support aabeyondbeyonddesigndesignbasisbasiseventeventon onthetheother otherunitunit(i.e.,

(Le.,accident accident unit).

unit). This This TS TS compliance complianceapplies appliestotothe thenon-accident non-accidentunit unitthat thatisisdonating donatingitsitsTrain TrainAAofofAF AFtoto the the accident accidentunit. unit. InInthis thiscondition, condition,the thedonated donatedtrain trainisisnot notcapable capableofofperforming performingits itsspecified specified 2 of 8 2of8

ATTACHMENT 11 ATTACHMENT Response to Request for Additional Information Information function of function of supplying supplying required required flow flowto tothethe unit's unit'ssteam steam generators and from from a TS standpoint standpoint is is considered inoperable. In In this this case casethe thedonating donatingunit's unit'sTS TSwill will be be complied complied with with such that the inoperable AF AF train trainmust must be be returned returned to to an an operable status status within within 72 hour8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br />shours or or the donating donating unitunit willbe will be shutdown.

shutdown. Use Useofofthe thecurrent current licensing licensingbasis basisrequiring requiring compliance compliancewith with thethe GDCGDC andand the the existing TS 3.7.53.7. 5 in in this this manner manner is appropriate and consistent consistentwith with the the application application of ofTS TSinin similar situations similar situations whenwhen a single single AF AF train train is inoperable due due toto equipment equipment failurefailure or or for planned maintenance.

The NRC issuedissued aa Regulatory Regulatory Information Information Summary (RIS) (RIS) 2005-20, "Revision"Revision to Guidance Formerly Contained in NRC Generic Letter 91-18, 'Information Formerly Contained 'Information to to Licensees Regarding Regarding Two Two NRC Inspection Manual NRC Inspection Manual Sections Sections on Resolution of Degraded and Nonconforming Resolution of Degraded and Nonconforming Conditions Conditions and on Operability',"

Operability'," dated dated September September 26,2005.26, 2005. Consistent Consistent with with the use use of of RIS RIS 2005-20, and as described described in in NRC NRC Inspection Inspection Manual Manual Part Part 9900, 9900, Appendix Appendix C, C, operation operation of of aa structure, structure, system, or component in accordance with with TS TS does not change change the the fact fact that that the system system design design compliant with remains compliant withthe the GDCs GDCs (e.g.,

(e.g., thethe design design remains capable capable of of withstanding a single failure with failure withone one train train inoperable).

inoperable). As As discussed discussedininPosition PositionC.1, C.1,the theGDCGDCand andthetheTS TSdiffer differin in that the GDC specify requirements for for thethe design of of nuclear power reactors, whereas whereas the the TSs TSs specify the specify the requirements for operation of of the the reactor.

reactor. Position Position C.1 C.1 further further elaborates elaborates on on the the relationship as follows:

as follows:

The GDC require redundancy redundancy of of function for for safety safety systems.

systems. This Thisisisnormally normally accomplished by incorporating incorporating at least two two redundant trains into the design of each safety system.

system. The TheTSs TSstypically typicallyallowallowaafacility facility to continue to operate operate for for aa specified specified time with with only onlyoneone train trainof ofaatwo-train two-trainsafety safetysystem systemoperable.

operable. In that case, the In that the GDC GDC areare met because because the the system system designdesign provides provides the necessary necessary redundancy.

redundancy. The TheTSs TSspermit permit the operation of of the system system withwith only a single train train based based on on anan evaluation evaluation of of the protection provided by the unique unique system systemlineup lineupfor for the the specified specifiedperiod.

period.

Application and Application and compliance with the unit's TS provides aa temporary with the temporary relaxation relaxation of of the the single single failure criterion failure criterion as as described described in Part 9900. 9900. Application Application of of the the TS TS in in this this manner manner does doesnot notallow allow or imply that the imply that the system designdesign isisnot notsingle singlefailure failure proof; proof; itit is simply simply an allowance allowance for for continued continued plant operation with with one of the redundantredundanttrains trainsinoperable inoperablefor foraalimited, limited, specified specifiedperiod periodof oftime.

time.

The discussion being being added to to the TS 3.7 3.7.5.5 Bases Bases to torequire require thethe Train Train B to be OPERABLE OPERABLE as as a condition condition forfor making makingthe theTrain TrainAAinoperable inoperabletotosupport supportaabeyond beyonddesigndesign basis basis accident on the other unit unit ensures ensures that the cross-tiecross-tie isis not not toto be beput put intointo service serviceand andusedusedfor foroperational operational convenience. As As discussed discussedin in the the TSTS LCO 3.0.2 Bases, Bases,TS's TS'sRequired Required Actions Actions are are applicable applicable when aa system systemisisintentionally intentionally removedremoved from from service.

service. However,However,intentional intentionalentryentryinto into Actions Actions should not be be made for operational convenience, and alternatives that would not result in made for operational convenience, and alternatives that would not result in redundant equipment redundant equipment (e.g., (e.g., both both AF AF trains) trains)being beinginoperable inoperableshould shouldbe be used used instead. Doing Doingso so limits the time limits the time both both trains trains of of a safety safety function function are are inoperable.

inoperable. Avoiding Avoidingentry entryinto intoaacondition conditionforfor operational convenience is operational convenience is consistent consistentwith with thethe existing existing TS LCO LCO 3.0.2 Bases,Bases, and and the the added added detail in the detail in the TSTS 3.7.5 3.7.5 Bases Basesreflecting reflecting the existence existenceof of the the normally normally isolated cross-tie does does not not change change the the existing existingTS TSrequirements.

requirements.Furthermore,Furthermore,the thenuclear nuclearsafety safetybenefit benefitthat thatisisderived derived from from anan action action toto unisolate unisolate and and useuse the cross-cross-tie tie in such an an unlikely unlikely event (i.e., (Le., an eventevent not not expected expected to tooccur occurduring during the thelifetime lifetime of of the the station),

station), isisreasonably reasonablynot notconsidered consideredfor foroperational operational convenience. Therefore, Therefore, EGC EGC does does not not consider consider the the very very rare use use ofof the the cross cross-tie-tie and associated associatedinoperability inoperability of the Train Train A A and and use of the cross-tie cross-tie during during beyond design designbasis basis events events as asoperational operational convenience conveniencesince sincethe theoperability operabilityof ofTrain Train B B ofof AF ensures ensures the the safety safety function function cancan be performed performed and and thus thus this this approach approach does does not compromise safety.

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ATTACHMENT 11 Response to Request for Additional Information Note that in Note in the first first paragraph paragraph of RAI-1, RAI-1, thethe NRC NRC statesstates thatthat Byron Byron and and Braidwood Braidwood received received construction permits their construction permits prior prior to to 1971.

1971. For For purposes purposesof ofclarification, clarification, both Byron Byron and Braidwood's construction Braidwood's construction permitspermits werewere issued by the NRC NRC on December December31, 31, 1975.

1975.

NRC Question NRC Question RAI-2:RAI-2:

As described As described In In the UFSAR, UFSAR, both both AFW AFW trains actuate actuate automatically automaticallyon onthethesame sameinitiation initiation signals, except except thatthat train train A (motor-driven (motor-driven AFW AFWpump) pump)receives receives aa start signal on an undervoltageundervoltage on Division Division 11ESF ESFbus. bus. The staff requests the the licensee licensee evaluate evaluatethe theimpact impactof of the the loss loss of of this this function when function when AFW AFWtrain train AAisisunavailable unavailable during during cross cross tie tie operation.

EGC Response:

The design design of of the the Train Train A A and and B B AF AF pumps pumps differ differ in their motive force force toto drive drive thethe pump. The The Train B Train B AF AF pump pump is is driven driven by by its its own own independent independent diesel diesel engine, engine,while while the theTrain TrainAA AF AF pump pump isis driven by a motor that receives receives electric electric power powerfrom from the the 4160 4160volt volt Division Division 11 Engineered EngineeredSafety Safety Features (ESF)

(ESF) bus.

Upon a loss of power to the Division Upon Division 11 ESF bus, the undervoltage undervoltage relays relayswillwill open all all the feed feed breakers to the bus, bus, trip trip all the loads on the bus bus except exceptthe the4160/480 4160/480volt volt transformers, transformers, and and automatically start automatically start the the Division Division 11 Emergency Emergency Diesel Diesel Generator Generator (EDG). (EDG). Upon Upon loss lossof of voltage voltage to to the ESF bus, bus, the the ESF ESF loads loads mustmustbe besequentially sequentially loaded loadedonto ontothethebusbusto toprevent preventoverloading overloading the EDG.

EDG. The Thesequential sequentialloading loadingofofthetheEDG EDGisisautomatically automaticallyperformed performedwith with loads loadsrequired requiredfor for accident mitigation mitigation and and safe shutdown of of the reactor.

reactor.

To support this sequential loading loading requirement requirement of of the the Division Division 1 ESF bus bus when when fed fed from from thethe EDG, the EDG, the Train Train AAof ofAFAFhashasan an additional additional start start signal signal and and time time delay. Since Sincethe theTrain TrainBBof of AF AF does not does not receive receive power power fromfrom one of the ESF buses buses// EDGs, EDGs, there thereisisno norequirement requirementfor forthis this type type of additional additional start signal to sequentially sequentially load load thethe Train Train B B of of AF on to an an ESFESFbus.bus.

Therefore, the basis basis forfor the the additional additional start start signal signal for for thethe Train Train A A AFAF pump is to support sequential loading loading of the Division Division 11 ESF bus to protect the EDG. EDG. This Thisautomatic automaticfunction function isisnot not lost when the Train A A of of AFAFisisoperating operating during duringcross-tie cross-tie operation operation as as the relays and and actuation actuation circuitry remains circuitry remains capable of of tripping and sequentially sequentially loading loading the the Train Train A A AF AF pump motor motor on to to the Division Division 11 ESF bus. IfIf the the Division Division 1 ESF bus bus undervoltage undervoltagecondition condition occurs occursduring during cross-tie operation, the the donated donatedAF AF pump pumpmotormotorwouldwould trip trip and restart restart after after the the sequencing sequencingtime time delay as as designed.

designed.IfIfthe theundervoltage undervoltagecondition conditionon onthe thenon-accident non-accidentunit unitresulted resultedininaaloss lossofof the non-safety non-safety related related Feedwater FeedwaterSystem, System,the theTrain TrainBBAF AFpumppumpon onthe thenon-accident non-accidentunit unitwould would automatically start on a low steam generator generatorwater waterlevel,level, safety safetyinjection injection signal, signal, or or undervoltage undervoltage on the reactor coolant coolant pump pump buses.

buses. As As discussed discussedin in the the license license amendment amendmentrequest, request,the theTrain Train B of of AF AF provides provides sufficient sufficientfeedwater feedwater to to safely safely cool cool thethe unit unit toto temperatures temperatures at atwhich which thethe Residual HeatHeat Removal Removal (RH) (RH) system can can be beutilized.

utilized.

Question RAI-3:

NRC Question RAI-3:

The licensee licensee doesdoesnot notidentify identify aa surveillance surveillance or maintenance maintenance procedure procedurefor for demonstrating demonstrating that that the cross crosstie tieflow flow path path is is functional, functional, if needed, and if needed, andwillwill not not adversely adverselyimpactimpacteithereitherunit unitwhen whennot not in use. Since Sincethe theflow flow path path will will be credited in plantplant analyses analyses and and mitigating mitigating strategies, aa 4 of 8 4of8

ATTACHMENT 11 ATTACHMENT Response to Requestfor Response to Request forAdditional AdditionalInformation Information surveillance or maintenance surveillance maintenance procedure procedureshouldshouldbe beconsidered consideredororalternatively, alternatively,a ajustification justificationfor for not needing not needing it should be provided.

it should EGC Response:

EGC The AFAF Train Train AAunit unitcross-tie cross-tieflow flowpath pathisisnotnotcredited creditedininthe theaccident accident analyses analyses and the the design design function is function is entirely entirelypassive passive and and not an active active safety safety function.

function. The TheAF AFcross-tie cross-tieflow flow path path remains isolated remains isolated between between the the units units unless neededneeded for for an event event that is beyond design basis. basis.

EGC has EGC has appropriate appropriate surveillance surveillance and and maintenance maintenance procedures in in place to to ensure ensure the valves and piping's passive passive safety safety function.

function. Description Descriptionand andjustification justification isis provided providedin in the the balance balanceof of this this response.

Current surveillance Current surveillance requirements requirements are are unaffected unaffected by by this this license license amendment amendment request, and are are already inin place and continue to be be performed.

performed. These Theseinclude includethe thecurrent currentfull full flow flow Inservice Testing (IST) surveillance requirements, with (1ST) surveillance with an 18 month frequency in in which which AF AF is is discharged discharged directly to directly to all allfour foursteam steam generators, generators, and and aa quarterly quarterly surveillance surveillance in in which which the the AF AF pumps pumps discharge on recirculation recirculation to to their their respective respective condensate condensate storage storage tankstanks on on their their respective respective units.

units.

Neither surveillance requires unisolating unisolating the the AF AF Train Train A A unit cross-tie flow flow path betweenbetween the the units. The design design of of the the AFAF Train Train A unit cross-tie, and and the theconfiguration configuration of of this this flow flow path that remains isolated does doesnot notchallenge challengethe theflow flowcapability capability of of either either AFAF pump to provide feedwater unit's steam generators.

to its unit's generators. Therefore,Therefore,the theAF AFTrain TrainAAunit unit cross-tie cross-tie flow flow path does does not not require a new surveillance or maintenance require maintenance procedures proceduresto todemonstrate demonstratecontinuing continuingflow flow path path functionality.

fu nctionality.

Several activities activities ensure ensure that that the AF AF Train A unit cross-tie flow path remains unit cross-tie remains available availableififrequired required to mitigate theconsequences mitigate the consequences of a beyond beyond designdeSign basis basis event.

event. These Theseactivities activitiesare aresummarized summarized as as follows:

follows:

Periodic ASME

1. Periodic ASME Code, Code, VT-2 leakage examinations VT-2 leakage examinations are arerequired required for for this design deSign (once (once during during each inspection inspection period period required required by by the the Inservics InserviceInspection InspectionProgram, Program, approximately approximately every 3 years) at at normal normal operating pressures. pressures. The The VT-2 VT-2 leakage examinations examinations can can be beperformed performedininconjunction conjunction with with the the quarterly quarterly AF surveillance tests, tests, allowing allowing the pipingpiping between the two two manual manual isolation isolation valves, valves, (the (the1AF036 1AF036atatUnit Unit11andand 2AF036 2AF036 at at Unit Unit 2), to be be pressurized pressurizedto tonormal normal AF AF pressure pressureto toverify verify no no pressure pressure boundary leakage exists, boundary leakage exists, and and totoverify verify the valves valves can canbe besatisfactorily satisfactorily opened openedand and closed. Before Before an an AF AF Train A A unit cross -tie manual isolation valve would be unlocked unit cross-tie unlocked and opened opened to to perform perform a leakageleakageVT-2 VT-2 examination examination on on the the system systempiping,piping, the the other other unit's AF Train Train A unit cross-tie manual isolation valve would would be verified verified closed, closed, ensuring the the AF AF Train Train A unit cross-tie cross- tie flow path remains remains isolated isolatedfrom from the the other otherunit.

unit.

2.

2. The manual manual isolation isolation valves were were addedaddedto tothetheLocked Locked Equipment Equipment program program for for each each unit.

unit. Therefore, they they will be maintained in the closed position will be position and and locked locked when when not not used used for for surveillance surveillance testing. testing. Additionally, Additionally, the the valves valves are areincluded includedinin the thelineup lineup procedures procedures as as locked locked closedclosed valves.

valves.

3. Preventive maintenance maintenance requires requireslubrication lubrication and and external external inspections inspections of of the the manual manual isolation valves in in the AF AF Train A unit cross-tie.

A unit cross-tie. This This periodic periodic preventive preventivevalve valve maintenance maintenance is is presently presently performed at least every ten years and ensures ensures the the manual manual isolation isolation valves can be manipulated as as necessary.

necessary.Additionally Additionally and and as aspreviously previously described, described, the theperiodic periodicVT-2 leakage examinations VT-2leakage examinationsthat thatare arerequired requiredby bythetheASMEASME 5 of 8 5of8

ATTACHMENT ATTACHMENT11

Response

Response to to Request Request for for Additional AdditionalInformation Information Code Code for for the the AFAF system system willwill also cycle both these these manual manualisolation isolation valves valvesmore more frequently frequently when system system surveillance surveillance testing testingpermits.

permits.

The The Train Train A A unit AF cross-tie feature will will remain available to the opposite opposite unitunit ifif needed neededto to support support aa beyond beyond design designbasis basisevent, event,whilewhilemaintaining maintainingeach eachAF AFpump pumpavailable availableto toits itsown own unit unit during all other plant operation. The TheTrain TrainAA unit unit AF AF cross-tie designdesign doesdoesnot notrequire requireadditional additional unavailability unavailability time time oror additional additional entryentry into into an an LCO LCO to to perform perform thesethese surveillances, maintenance maintenance or inspections inspections since since the thecross-tie cross-tieflow flow path pathbetween betweenthe theunits unitswillwill not not be beopened openedtotoperform performthe the activities.

activities.

Question RAI-4:

NRC Question RAI ..4:

The The licensee licenseeprovides providesthe therisk riskbenefit benefitfrom fromapplying applyingcredit creditfor forthe theability ability to to cross crosstietiethe theAFWAFW train A.A. The The licensee licenseeshowsshowsthat thatthetheLarge LargeEarlyEarlyRelease ReleaseFrequency Frequency(LERF) (LERF)reduction reductionfor for Bryon is 1%;  %, whereas, whereas, the the LERF LERF reduction reduction for for Braidwood Braidwood is is 2%.

2%.

a) Identify Identify thethe difference difference ininplantsplants that that accounts accounts for this this difference, difference, and and any impact on the use use of of the the AFW AFW crosscross tie.

tie.

b) Provide the increaseincrease in in risk risk to to the the operating operating unit unit (Core (Core Damage DamageFrequency Frequencyand andLERF)

LERF) when the the AFW AFW train train AA isis in in use use via via the the cross tie and comparecompareto tothe therisk risk reduction reduction noted.

EGC Response to RAI-4(a): RAI-4(a):

The license amendment amendment request request doesdoesnot notuse useaarisk riskinformed informed basis,basis,however, however,the therisk risk benefit benefit was quantified quantified for the original proposal by by evaluating evaluating the the internal internal events eventsprobabilistic probabilisticrisk risk assessment (PRA) assessment (PRA) model model for for the the Byron Byron and Braidwood Braidwood Stations. The ThePRA PRAresults resultsthatthatwere were used in in the license amendment amendmentrequest requestwere werederived derivedfromfrom Revision Revision 6F 6F ofof the the PRA PRA model.

model. The The current PRAPRA modelmodel is is Revision Revision BB011 BB011b.b.The The base base core damage frequency damage frequency (CDF) (CDF) and large large release frequency early release frequency (LERF)(LERF) results for for the current modelmodel still still support the basis basis of of gaining gaining risk reduction for risk for all all four four units units from fromthe the AF AF Train Train AAunit unitcross-tie cross-tie on on an an accident accident unit. With the unit. With the current PRA current PRA model, model, thethe table table previously previously provided providedininthe thelicense licenseamendment amendment request is revised as follows:

follows:

CDF and CDF and LERF LERF Benefits Benefits from AF Train Train A A Unit Cross -Tie -- PRA Unit Cross-Tie PRA Model Model BB011 BB011 b Unit 11 Un it 2 Unit2 Station CDF Reduction LERF CDF Reduction LERF

(%) Reduction (%) (%) Reduction (%)

Byron Byron 2.2 0.5 0.5 1.7 0.4 Braidwood Braidwood 2.4 0.5 0.5 2.0 0.4 As noted As noted in in the the question, question, there is a difference between the stations stations in in the the amount amount of of LERF LERF reduction. There reduction. There are are differences differences in in plant plant specific specific data data used used in in the the PRA PRA model model and and inin certain certain site site specific physical specific physical and and operational operational differences differences thatthat are are reflected reflected ininthe the modeling.

modeling. In In the the license amendment request, the values were amendment were rounded rounded to to 11 percent percent for for the Byron Station and Byron Station and 22 percent for the for the Braidwood Braidwood Station.

Station. The underlying underlying calculations showed approximately approximately 1.3 1.3 to 1.41.4 percent percent 66of8 of 8

ATTACHMENT ATTACHMENT 11 Response to Request Request for Additional Information for Byron for Byron Station Station and and 1.5 to 1.6 percent percent for for the Braidwood Braidwood Station using Revision Revision 6F 6F of of the PRA PRA model. In model. In the table above, using the current PRA model revision, PRA model revision,these these values values areare revised.

revised. TheThe differences are, however, not as large as as the the rounded rounded values valueswould would indicate.

indicate.

The Braidwood and Byron Stations use use the thesame sameCAFTACAFTAsoftware softwaredeveloped developedfault faulttree treeforfortheir their PRA model.

PRA model. To account for physical physical differences differences between between the the stations (e.g., the essentialessential service water cooling towers at the Byron Byron Station), logic flags are used used to to turn turn on on or oroff off the the appropriate logic subtrees. To logic subtrees. Toaccount accountfor forplant plantoperating operatingexperience experiencedifferences differences(e.g.,(e.g.,failure failure data, maintenance maintenance unavailability, etc.), separate unavailability, etc.), separate databases databasesare aremaintained maintainedfor foreach eachstation stationtoto provide plant provide plant specific specificresults.

results. These These databases databases definedefine the the basic basic events eventsused usedininthe thePRA PRAmodel model including their including their associated associated plant-specific plant-specific probability probability values.

values.

The base base CDF CDF andand LERF LERF values values for for the the Byron Byron and Braidwood Braidwood Stations are different because different because the base base data dataused usedininthethequantification quantificationof of the therisk risk metrics metrics is is taken taken fromfrom the plants plants respective respective database. These database. Thesedifferences differencesininplant plantspecific specificdata datawill willalso alsobe bereflected reflectedininthetherelative relativebenefit benefit associated with associated with the theimplementation implementationof ofthe theTrain TrainAA unitunit AF AF cross-tie.

cross-tie.

EGG Response to RAI-4(b):

EGC RAI-4(b):

The NRC requests the following information: information:

Provide the b) Provide the increase in in risk to the operating unit (Core (Core Damage Frequency Frequency and and LERF)

LERF) when the AFW AFW traintrain AAisis ininuse use via via the the cross tie and compare compareto to the therisk risk reduction reduction noted.

There is aa negligible negligible increase increase in in unavailability unavailability that results on on thethe non-accident non-accidentunit unitfrom from considering the the AF AF Train A unit unit cross-tie cross-tie configuration.

configuration. That Thatincrease increaseininunavailability unavailabilityisisderived derived from considering from considering thethefollowing following impacts:

impacts:

• Likelihood of Likelihood of needing needing the AF Train A A unit unit cross-tie cross-tie on the the accident accidentunit unit

• Expected Duration for for the the donated train to be unavailableunavailable to to the the non-accident non-accidentunit unit EGG considered the EGC the impact impactof of the the above aboveitemsitemson onquantifying quantifyingthe theadditional additionalunavailability unavailabilityto tothe the AF Train AF Train AA current current configuration, configuration, and determined determined that thatthe theadditional additionalunavailability unavailabilityresulting resultingfromfrom the AF Train A A unit unit cross-tie cross-tie configuration configuration was was negligible. Specifically, Specifically, the the additional additional unavailabilityfrom unavailability fromthetheAF AFTrain TrainAAunit unitcross-tie cross-tieisisnegligible negligiblebecause because itit waswas approximated to to be be at least least five five orders of magnitude below below the the baseline baselineunavailability unavailability that that is is averaged averagedfor for the the current AF Train Train AA configuration.

configuration. The resultingresulting negligible negligible impact on unavailability unavailability results in no discernible increase increase in in risk risk for the proposed proposed AF AF Train Train A unit unit cross-tie cross-tie configuration.

configuration. This This conclusion is valid valid for forthe the current current model model as as well well as the model model in in use useat atthe thetime timeof of the theoriginal original submittal.

7of8 7 of 8

ATTACHMENT 11 Response to Request for Additional Information

References:

Letter from D.1)M. Letter Gullott from (Exelon D. M. GullottGeneration Company, (Exelon Generation Company, LLC)LLC) to u.

U. S. Nuclear Regulatory Commission, Regulatory Commission, "License Amendment Request for the use uLicense Amendment use ofof an an Auxiliary Cross -tie Between Units,"

Feedwater Cross-tie Units," dated January 31,2012.

dated January 31, 2012.

Email(U.

Email from J. S.2)Wiebe fromJ.S.Wiebe(U.S.NuclearRegulatoryCommission)toR S. Nuclear Regulatory Commission) to R. W....McIntosh V.Mclntosh (Exelon Generation Company,LLC),

Generation Company, LLC), "Preliminary npreliminary RAIs RAls Related Related to tothe theAuxiliary Auxiliary Feedwater Cross Connect Connect Amendment Request," November 9, 2012.

Request, II dated November 8 of 8 8of8