ML20083A458

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Documents Results of 910915 Telcon in Which Util Requested Regional Temporary Waiver of Compliance from Tech Spec 3.8.1.1,action Statement a for Facility
ML20083A458
Person / Time
Site: Braidwood Constellation icon.png
Issue date: 09/16/1991
From: Kovach T
COMMONWEALTH EDISON CO.
To: Davis A
NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION III)
Shared Package
ML20083A431 List:
References
NUDOCS 9109240155
Download: ML20083A458 (34)
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{{#Wiki_filter:_ _ _ _ _ _ _ _ _ _ _ _ _ _ _. _ _ _ _ _. _ _ _ _ _ _ _ _ _ _ _ _ _ - [') C:'mm:nn:alth Edis:n 1400 Opus Piece 9 ,( C ] Downers Gron, lilinois 60515 \\g September 16, 1991 T W -its i n m.q fa V M, T-{(H %.g l f/. }" T ' :- - 'I / ~[ ~ Mr. A.B. Davin Regional Administrator ,l p "h-- C U.S. liuclear Regulatory Commission 7 Region Ill 799 Roosevelt Road Glen Ellyn, Illinois 60137

Subject:

Braldwood Station Unit A Request for Regional Temporary Walvor of Compliance to Technical Specification 3.8.1.1 IMC_Docke LNumber SO:4 R _ _ _ Dear Mr. Davis The purpose of thir letter is to document the results of a teleconference between Commonwealth Edison (Edison) and the tiRC Staff on September "L, 1991, in which Edison sequested a Regional Temporary Walvor of Comp 11ance from Technical Specification 3.8.1.1, Action Statement (a), for Draldwood Station Unit 1. At the time of the teleconference Unit One was in Mode 1 and Unit Two was In Mode 5. The normally allowed outage t.ime for Technical Specif(cation 3.8.1.1, Action (a), expired at 0422 hours on September 16, 1991. Prior to the action statement expiration Edison requested on September 15 that the requirement to restore the 1A Diesel Generator to operable status be extended Irom the current 72 hours to a total of 96 hours in order to complete the testing necessory to demons &. rate the effectiveness of the repair and the operability of the diesel. A Temporary Walvor of Compliance (TWOC) Irom the 72 hour requirement was verbally approved by the NRC Region III Staff at 8:35 PM on September 15, 1991. The basis for the request is provided in Attachment 1 and includes: A discussion of the requirements for which a waiver is requested. A discussion of the circumstances surrounding the situation, including the need for prompt action and a description of why the situation could not have been avoided. A discussion of compensatory actions taken. An evaluation of the safety significance and potential consequences of the proposed change. A discussion which justifies the duration of the request, r The basis for concluding that the request does not involve a significant hazards consideration. The basir. for concluding that t.he request does not involve irreversible environmental consequences. 9109240155 91091{ 6 SEP 17133] 1190:1 ADOCK0500Q PDR P

Mr. A.D. Davis September 16, 1991 1..tachments 2 and 3 contain excerpts from WCAP 10526 detalling the modelling of the D/G unavailability and the over all analysis results, respectively. This toquest for a Regional Temporary Waiver of Compliance has been teviewed and approved by Edia.on Senior Management, as well as the Braldwood Onsite Review Committee in becordance with Edison procedures. If the actions specified in this walver request are not accomplished by 0422 on September 17, 1991, Unit One will be placed in a Hot Standby within the next 6 hours r.nd cold shutdown within the following 30 hours in a timeframe cc.nsistent with the shutdown requirements of Technical Specification LCO 3.8.1.1. Edison sincerely appreclates the NRC staff's efforts and participation in ravlew of this TWOC. Please direct any questions or comments regarding this request to this office. Very truly yours, 6(k 6 T.J. Kovach Nuclear Licensing Manager cet S.G. Dupont, Hesident inspector - Bralduood a R.M. Pulsifer, NRR Project Manager - Draldwood W.D. Shafer, R111 Dranch Chief HRC Document Cont.rol Desk State of., ,_, County of I ( ~ $1000^ tiefo o me on this # # day I' 9/ &s or :,!Ci AL S E t t_ nyj/ s /c. 33#- b/; /* "A C.LARA Notary Public h A // s.~ +~ ~~ z,::W 1196:2 /

~ r ATTACitHr.HT 1 o 1. IlEQUIf EMENTSl0ILWillCILTilE TEMPORARLHAIVEILO11COMI'lel ANCE_IS_ REQUASTED This request for temporary relaxation of the allowed outege time for the Unit 1. A diesel generator will extend the permissible unavailability intoival from 72 houts to 96 f.oute on a one time basis. The current 72 hour action requirement is a part of *19chnical Specification 3.8.1.1, Action Statement (a), which in in force when an Emergency Diesel Generator la inoperable. The requested relief will empire at 0422 on September 17, 1991. If the 1A D/O has not been testored to operable status within that timeframe, t he unit. wlll-be brought t.o llot Standby within the next 6 hours, and to Cald Shutdown within the following 30 hours, consistent with the provisions of hCO 3.8.1.1. DESCRIPTIDH.Or_CURHCHT 04.REQUIREllENT: The Current Operating hicense requirement is to maintain two D/Us in an operable condillon while the affected unit is in Modes 1 through 4.- A 72 hout allowed outage time is granted for the purpose of restoring an inoperable D/G prior to taking action to place the unit in a mode where the requirement is no longer applicable. If at any time during the walver period it becomes obvious that sigt.lficont additional work is required such that the waiver period -becomes inadequat e to restore the diesel, actions will be taken at that time to shutdown the unit in a timelf manner. LiA S E S l0lLTilE_ Cult RCHT_ A RE0V I REM ENT : As required by 10 CFR $0, Appendix-A, GDC 17,, the design of the AC electrien1 power eystem provides Independence and redundancy to ensure an available source of power to the Engineered _Shfeguards Feature systems.- The Diesel Generators function to provide the necessary electrieni power for accident mitigation in the event the proforred, offsite electrical power supply is unavailable.- Decause the loss of tte offsite power sources la considered an initial condition in the' Chapter 15 pafety analyses, the Diesel Generators are rolled upon in all applicable analyses for safe chutdown and transient mitigallon. 1196t3 - l ? r ..m..------ +,me,-e.e a ,,,_,%,.-,-m..-. w e, , Em-. ._,m_,w .c,-.,_.e,,vE,n%-,,, ym,.v,--y,,,,c,vv,<-~-v.- -,v, ,,-w, y

i e 2. C IB CUM STANCE S lE ADllMlLTill.REQU E ST On Triday, September 13, 1991, at 0422 hours, the 1A Diesel Generatot was removed from service for planned lubrication. This caused entry into Action a of the subject specification. Following the lubricotton, the planned monthly operability surveillance was attempted. During this curveillance run the engine experlenced unexplained load swings. The engine was shut down and the cause was investigated. The problem was traced to a lack of f uel injection on cylinder nwnber 6R. Accordingly, the injection pwnp for that cylinder was replaced. During subsequent testing, slml,lar load swings were experienced. Further investigat.lon revealed that the lack of fuel injection was due to inadequate lubrication to the oush rod that actuates the injection pwnp for cyllnder number 6R due to a plugged fitting In the lubrication line. The cause of this plugging is under investigation. Additionally, all remaining cylaade a were examined to ensure that proper lubrication existed to the pushrod assemblies. No problemu were found with any other cylinders. Hepair work was completed'at approximately 2300 hours on September 15, 1991. The request for additional outage time was to complete operability testing on the engine. The testing began at approximately 0030 on September 16, 1991 and was completed by 1330 hours on Septembe 16, 1991. A testing schedule included a graduni loading of the engine, followed by a 4 hour loaded run. The run duration was extended for purposes of comparing the pertormance of the affected cylinder to several unaffected cylinders. Following the successful completion of the maintenance verification activities, the affected cam lobe was visually inspected to ensure that it has remained properly positioned. Upon completion of this activity, the work package was closed out, and an operability surveillance was performed. After successful completion of the operability surveillance, the 1A Eme:gency Diesel Generator was restored to operable status at 1409 on September 16, 1991. The circumstances leading to ths request for this waiver of compliance were unable to be foreseen and thus could not have been avoided. The nature of this problem la such that it will only manifest itself upon load!ng of the'dlesel. No mechanism currently exists at Braldwood that would have revealed this problem prior to a load being placed on the machine. .The purpose of.this request is to avoid the unnecessary cycling of the unit and the attendant increase in the risk of Inducing a transient on the degraded unit. This desire'is contingent on the satisfactory denonstration that the one-time A0T extension will not result in an unacceptable decrease in the health and safety of the public, or result in irreversible environmental consequences. Additionally, this request is made in order to ensure a continued reliable supply of electricity to the company's service territory. The time period covered by this requent falls into "dison's outage season, so the continued availability of Braidwood is important in ensuring that on ample supply of electricity is available. Currently, Edison has three large nuclear units in a refueling etage, representing over 3100 Megawatts of . generating capability. Several_ smaller fossil units are also in planned outages. The continued saft operation of Braidwood Unit I will ensure that the system load can be met in the most efficient and cost effective

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3. RISCUSSIGLOf1COMPENS ATORL ACT104S i The following compensatory measures will be in place for the duration of l the walver periodt No olectrical distribution equipment, either normal, standby or reserve, will be taken 4 ut of service on olther unit. This includes the remaining 3 Diesel Generators. '!h) switchyard activltles which could perturb the offsite power sources will be allowed. No Fire Protection activities which could result in a transformer-deluge actuation will be scheduled. The hoad Dispatcher has been notified to maximlre the availability of the offsite power lines servicing Draldwood. All upcoming Unit 2 outage actl-lties have been reviewed, end work on the 2A D/g and SX trains have been rescheduled to a timef rame outside that encompassed by this walver. The Shift Management will review all surveillances and out of services for impact prior to authorizing the initiatior. of the activity. Unit I will be removed from EGC for the durntlor of this walver. The avnllability of othar Unit 1 saf ety related equipment will b^ maximised. All operating personnel will be notified.vla Daily Order.to ensure these measures remain in effect for the duration of this walver. Southern Division OAD will be notified to refrain from work activities in the Broldwood swltchyard for the duration of this waiver. 1196:5 i,-__-..__a.-._,__.__ , _. - ~ - -.

4. EVALUATION.Dr SAFETLSIGNIf1CANCEED_ POTENTIAL._ CONSEQUENCES OLTilE_EROPOSED_C11ANGE The proposed AOT extension will have no physical impact on unit _ operat.8 on. Approval will, however, result in the continued operation of the unit with an inoperable D/G for a time period in excess of the current 72 hours. The probability of an accident occurring =,,1 not be affected by the approval of this walver. This.egoest deals only with the allowed outage of equlpment assumed to operate for the mitigation of an accident. The availability of this equipment la unrelated to the sequence of events Iwading to the initiation of a trancient, and la thetofore unrelated to the probability of occurrence for a transient initiating evont. 1he consequences of an accident, in terms of offsite dose, will remain unchanged provided that the mitigative actions credited in the Chapter 15 annlyses are accomr; shed in accordance with_the-analysis assumptions. The .,1ynes annume that_all required mitigative equipment is operabit at the onset of the transient. No provisions are made for allowed outage times in the accident analyses. The currently permissible ellowed outage times represent a temporary relaxation of the single failure criterion. A probabilistic analysis was performed in 1984 for the Byron plant., applicable to Draldwood, for the purpose of extending the ellovtd outago time to seven days for the Diesel Generators and most of the safety related fluid systems. The results of this pHA Indicate that the overall impact on offsite dose is statistically insignificant. The consequences of a malfunction of equipment imporcant to safety will not be sigiificantly impacted. The basis foc this deteiminatlon 'Is the continued operability and availab.411ty of the 2A Diesel Generator to be crosstled to Unit 3. This would only be required if the plant were to experience a tranulent resulting.in or_ concurrent with a loss of offsite power, coupled with the-fallure of the ID Diesel Generator-to respond to the. demand. The allgrunent. of the 2A Diesel Generator must be manually accomplished at this time.. In this condition, the j' unit would be experiencing -a loss of all AC power, and the lr . mitigation and restoration = actions are directed by Draidwood Emergency Procedure _DwCA 0.0. There it no reduction in the design margin of safety. The AOT* extension represents additional relief from the slogie fallure criterion, not a reduction in the margin of safety. Sufficient compensatory measures, and reasonable operator action will ensure that the_ design complement of two l full-capacity Diesel Generators is available to Unit 1. This I la accomp11shed by etisuring that the 2A D/G is operable and capable of being_crosstled to Unit 1. Unit 2 is Mode 5, preparing for_a refueling outage. In this mode, only one Diesel Generator is required _for Unit 2, so credit can be taken for the 2A D/G being available to support Unit 1. 1196 6 .,..w.

4 4 - 5. JUSTI fl CAT 10!Lf 0.IL DURAT iotLorJ COVEST : As demonstrated in the attached evaluation of No i Significant flazards, the one-time extension to the ACT for the 1A Diesel Generator does constitute a significant increase in the risk to the health and safety of the public. The basis for this determination is contained in WCAP 10520, which sought. to justify a permanent increase in the A0Ts for the D/Gs and the major.f),uld systems from 3 days to 7 days. The results of this pHA Indicate a statie,tically insignificant increase in offsite dose. The contribution of the increased D/G unavailability represents a fraction of the increase due to all systems. The additional 24 hours is deemed sufficient to accomplish the desired testing and required operability demonst:ation in a safe and controlled manner. The 24 hour extension is deemed conservative for the following reasons: the total duration in less than the bounding seven days presented in the PRA, the PRA presents the dose information on a per-Reactor-year basis, and t.he full capacity 2A D/G la operable and available to support operation of Unit 1. Therefore the requested duration is justifiable, both on the bases of minirnsi risk and suf ficient time to execute the desired restoration plan. I l-I - 1196 7 _,__.,._,..._,._.._..-.-_,..,_..~._,m._,

e 6. DASIF_ TOR _COHCLUD1HG_ DIAT_ Tilt REQUEST DOES30LINVOLVE_ A.SIGNITICANT 11hEARE._CONSIDERATIQH Commonweal *.h Edlaon has evaluated this proposed Temporary Walver of Compliance and dete mined that. It involves no cignificant hazards considerations, j According to 10 CFR 50.92(c), a pr oposed mondment to an opernt.ing license involves no significant hazards considerations if operation of the faellity in 1 - accordance with the proposed amendment would not: 1. Involve a algnificant lucrease in the probability or consequences of an accident previously evaluatedl or 2. Create t.he possibility of a new or dif f er ent kind of accident f rom any accident previously evaluateds or 3. Involve a significant reduction in a margin of safety. The bl. sis for this determlnation of no signiticant hazards considerations lo presented below. Iden t i ti c nilo rto Lo tt e tt e d_ u nit, _ay at em_ e q ui emente nd_ App H c ableJiodc Lat Operation. tini t Iltaldwood Unit 1 Applicable Modes: 1, 2, 3, 4 System (s) affected: DG, Ap Equipment Name(s): 1A Diesel Generator EPN IDG01KA D e s cIl pti o n_o kt he_p r op o s e d_ ch ang e..nnd_ihed e nn on _to r_th e._ c ha ng e. This request for ternporary ralaxation of the allowed outage time for the Unit 1, A diesel generator will extend the permissible unavailability ir4terval (tom 72 hours to 96 hours on a one time basis. The requested relief will expire at-0422 on September 17, 1991. If the 1A D/0 has not teen restored to operable status within that. t.imef t ame, t.ho unit will be brought to llot Standby within the next 6 hours, and t o Cold Shutdown within the f o11owing130 hours, consist ent with the provisions of hCO 3.8.1.1. If at any time during the walver period it -becomes obylous that significant additional work is required such that the waiver period becomes inadequate to restore the diesel, actions will be taken at- . that time to shutdown the unit In a timely manner. 1196 8

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h I i The y,uipose of this requent tot telle! from the 72 hour allowed outage t,lme is to provide auf flcient time for the tirooly repolt and testing of the 1A Diesel Gentirator, wit hout. the concur r ent shutdown of the affected unit. l L,19LoLthe_cyplicable. SAIL senlons which descs ibc_the_ af f ected. systems, fa t.r uctur e s.. oL.cotaronent u _(SSCio L o t.ac tivities,..Jho S AILnccidenkanalyclu sac.tionsJ hich discusa...tbe.mtlected SSC's._ut their.OpetatioJw and_any_othet f.ontro11 AD2 Accwnents_Euch au S!;Ris 10CTR.JeguintotyJulden,. previous modiLicAtions.or_Salety3 valuations,_ote_116ted. hCO 3/4.8.1.1 and Bases WCAP 10b26 !!yron hCO Helaxation Prngram tlFSAR Chapters 8, 15 Draf t. H11HEU 1431 Westinghouse Hlandard Technlen! Speelficat.lons 10 CFR $0, Appendix A [ b Description _oLhow_the_ change _willof feckplankoperation. The proposed A0T entension will have no physical impact. on unit ope ation. -1 Approval will, however, result in the continued operation of the unit with an Anoporabin D/o for a tirm period in excess, of the -cur rent 72 hours. Deucilption_ol.howlhe_chango_W11Latieckteactivity management. The proposed walver will have no direct or indirect effect. on reactivity management. t ue n crip tio n.how_t hc ch a ng e _w i1La t f e ckequi ptna n Li a il u ra s. The proposed walver will not impact equipment failures.. This request deals with equipment sepalt times, not equipment operat ion. Na new system configurations are introduced, and no equipment is being operated in a now or different manner. Accordingly, no new or different. failure modes are being introduced. t Adentification_o L each_acciden kor_ anticipated _ transient The analyses of int.eiest are all at.-power transients addressed by Chapt.or 15 of-tho tirSAR.- One - initial aantunption of these analynes la that the preterred .offsite power source is unavailable at the initiation of the tranulent condition.,The Diesel Generators are relled upon for the power necessary for the safe r.hutdown of the affected unit and the oporation of required ECCS and ESF equipment.. Additionally,.the analyses also assume that the rnost limiting single active failure of required. equipment will occur upon demand by the plant's protective systems. For a large number of possibic s*:enarlos, this failure would be that of one of the two redundant, full capacity Diesel Generators. L 1196:9 ..__ _._ _ i i 1., ._._.-_.,..--_._,,.l..-,a -.u .. J -. - m,..,w. -

e Af f e ctedle chnic aLSperlilc ationLS AILSe cti onGcrldent s TECW'ICAL SPEC 1r1 CATION SECTION: 3/4.8.1.1, Action Statement (a) UrSAR Chapter 15 All at-power transients i . Hay _the probability _of_the_. accident.be_ increased? The. probability of an accident occurring will not be affected by the approval of this valver. This request deals only with the allowed outage of equipmen9 assumed to operate for the mitigation of an accident. The availab8lity of this equipment is unrelated to the sequence of events leading to t.he inftlation of a tranulent, and la therefore unrelated to the probability of occurrence for a transient initiating event. H ay_.the_c on s equenc eito Laito c c ide nt l o Ci s ite_do s e Lbe_i nc re a s e d? The consequences of an accident, in terms of offsite dose, will remain unchanged provided that the mitigative actions credited in the Chapter 15 analyses are accomplished in accordance with the analysis assumptions. The analyses assume that all required mitigative equipment is operable at the onset of the transient. No provisions are made for allowed outage times in the accident analyses. The currently permissible allowed outage times represent a temporary relaxation of the single tallure criterion. A probabilistic analysis was performed in 1984 for the Dyron plant, applicable to Braidwood, for the purpose of extending the allowed outage time to seven days for the Diesel Generators and most of the safety related fluid systems. Because of the supporting nature of the Diesel Generators in the ability of the other systems to perform-their # sign safety function, the Diesel Generator unavailability was a significant contalbutor in the offsite doce projections resulting from the proposed seven day A0T for all systems - evaluated. The results of this PRA-indicate that the overall Impact on offsite dose, however, is-statistically insignificant. Attached are the offsite dose projections for both a 72 hout and 7 day ADT for all analyzed systems. The contribution of the Diesel Generator unavailability is a significant percentage of the totel. The case for single unit operation is presented because Unit 2 is in a refueling outage. This is conservative because the 2A Diesel Generator is operable and asallable to. crosstle to Unit 1, and the 2A SX pump is operable. The~ referenced curves are included as Figures 1 and 2 for the 3 day and 7 day ACT, respectively. Hay _theJrobability_oLaSalf unction _oLequipment _lmpor. tant _.tois af uty_increasel ~ The extension of the allowed outage time for the 1A Diesel Generator on a one time basis will have no. affect or the crcbability of a malfunction of equipment'important to safety. Approval of this waiver will not result in more frequent demands-being placed on important equipment. Additionally, administrative actions are being taken to minimize the possibility of -porturbat3ons on the offsite systems, which will minimize the probabflity that a demand on the Diesel Generators will be necessary for the duration of this waiver. 1196:10 =es7 F -w v m'. Jr " ev 1e ee T-er'e'e-r++iy v ws eg y +y m-enm w g er m y.,,. +m+p gy Tr %=-T-gw +p my7pbMia-w gg ' q -'--gir gene ug-y-,*=g.g u.w e w feet-mem v w14-' 1m gp 4Pwway"%+w><up g w-,cy gy g'r'mN-gMt Fv7

May.-.the_ consequences _oLemalf unction _oLequipment important to safaty_ increase? The <:onsequences of a rnalf unction of equipment. Import. ant to anf ety will not be significant.ly impacted. The basis foi thin determination la the continuet operability and availabillt,y of the 2A Diesel Generator to be crosstled to Un t 1. Th19 would only be required if the plant were to experience a translent resulting in or concurient wlt.h a lour. of ofIait.e power, coupled the f allure of the IB Diesel Generator to respond to the demand. The alletnment of the 2A Diesel Generator must be manually accomplished at. this time. In this condition, the unit would be experiencing a losm of all AC power, and the m!',lgation and testoration actions are directed by Dialdwood t'.ergency procedute BwCA 0.0. Hey..the proposed._ change _ create-the_ possibility _oka _new..or_da f f erent..Aind 01 accidenki t oitt any_ accident _ pteviously_ ova'1ated? t The pos.nibility of new or dif ferent type of aceldent in not. introduced. The worst case scenario in thin situation is equivalent to or bounded by firaldwood's Station Blackout analysis. This ennlysis has been reviewed by the NRC, and the station wac found t.o be in comp 116nce wit.h the Stat.lon Ulackout Rule. Does._the_proposedaniver_oLevnpilonce_invoAve_a.319nifIcont reducLion_in_the I (tiatgin.o LsAfeLy1 The extenolon of the AOT la in a nonconsere ve direction, however, there is no teduction in the design. margin of safety. The ACT extension represents additional rellet from t.he single failure criterion, not. a.reduct.lon in the-margin of safety. Sufficient compensatory measures, and reni.onabic operator action will ensure that the design complement of two full-capacity Diesel Generators.As available to Unit 1. This is accomplished by ensuring that the 2A D/G is operable and capable of being crosst.iod to Unit 1. U ni t. 2 As Mode 5, preparing for a refue1Jng outage. In this mode, only one Diesel is required for Unit 2, so credit can be taken for the 2A D/G to support. Unit I without an unacceptable degradation to Unit 2. l L 1196:11-

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7. 11 ASIS TCR CONCLUDING.TilAT _ Tilt PEQUf;ST.POES NOT.!NYCLVfLIl< REVEL < SIDLE E!!Vll1HM01(TAL _._ CON G COVENC05 Commonwealth Edison has evaluat ed t he proposed TWOC against the c lterla for and identification of licensing and regulat ory actionn requiring environmental assessment in accoidance with 10 CTR $1.21. It has been determined that the proposed chenge meets the cilteria Ion a categorical exclusion as provided for under 10 CFR 51.22(c)(9). This detoimination in based on t.he fact that this change is being proposed as a temporary waiver to n license issued pursuant to 10 CrH 50, and the AUT extension represents a change in a requirement with respect to ti.e availabilaty of a faellity component located within the restricted area, and the change involves no significant hazards considerat.lons. Thoro is no change in the amount on type of releases made offsite, and there is no significant increase in in61vidual or cumulntive occupational radintion exposure. 1196:12

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3.2 ONSITE AC POE R SYSVEM 3.2.1 SYSTEM DESCRIPT1014 The onsite AC power system has two diesel generators per unit, supplying two redundant 4160 V busses. These busses in tu-n supply 480 Y essential AC to various loads and motor control centers throughout the plant. These vital sourtes are required for the supply of AC to equipment following design basis accidents and anticipated transients. The diesels auto-start on bus undervoltage, as 0: curs on a loss of of fsite AC power. The plant support state split f ractions are calculated in Section 4.1.2 and 4.2.2. f or the 3 day and 7 day LCO applications, respecti wly. A simplified one line diagram of the AC power distribution system is presented in Figure 3.2 1. The two diesel generators are physically and functionally separate, having separate start systems, fuel day-tanks, DC bus dependence, and service water cooling dependen:e. 3.2.2 FAULT TREE ANALYSIS The fault tree constructed to model the AC power sy* tem is presented in Figure 3.2-2. This section describes the analysis supporting the quantification of system unreliability. 3.2.2.1 SUCCESS CRITERI A Either diesel generator has the capacity to supply all necessary loads for mitigation of all analyzed ewnts. In order to address f ailures of other systems, this report probabilistically analyzes each state that the electric power system can be in, i.e., both busses energized, either bus 141 or 142 energized, and neither bus energized (f ailure of both diesel generators). 3.2-1

3.2.2.2 DEPENDENCE ON SUPPORT STATES The two diesels are supplied with cooling water flow from the Essential Service Water system header, the loss of which will cause a loss of the diesels. This phenomenon is modeled as support state 6, corcurrent with loss of offsite power. Refer to Sections 4.1.2 and 4.2.2. 3.2.2.3 RANDOM FAILURE MODEL The following assumptions were utilized in the development of the f ault tree for this analysis: 1. Diesel recowry is addressed in the Support State Model dewlopment, see Sections 4.1.2 and 4.2.2. 2. Loss of servite water causes a nonrecoverable failure of the diesels. This is conservative due to protecti ve instrumentation on the diesel. 3.2.2.4 COMMON CAUSE ANALYSIS The common cause of the AC diesel generators is modeled by simple application of the beta factor deried for diesels. The common dependerte on ESW is explicitly modeled. Refer to Appendix 3B f or deri vation of common cause treatment methodology and applicable beta f actors. Calculation: Occ = 82. P (FAIL to start and run) (.026)[2.42(-2)) = 6.3 (-4) = 3.2-2

' 3.2.2.5 TEST AND KAINVENANCE H0 DEL Testing of the diesel generators does not render them unavailable, and is therefore not modeled. Maintenance, however, is a significant contributor to overall diesel una vailability. The frequency of diese'l maintenance is taken f rom the ZPSS, Reference 7.1, Table 1.5.1-29; f 8.09 (-4) e vent / hour. 3.2.2.6 HU!%N ERROR ANALYS!$ No e.rors of omission or commission affecting diesel reliability are explicitly modeled due to the frequent testing and stringent requirements guiding diesel maintenance. 3.2.2.7 INPUT DATA An input listing of conponent identifiers and associated probabilities for analysis of the AC power system is presented in Table 3.21. Both 3 day and 7 day LC0 data are listed. 3.2.3 FAULT TREE QUANTIFICATION The following sections describe the results of the quantification of the AC power state split f ractions. 3.2.3.1 SYSTEM UNAVAILABILITY Ct.LCULATIONS The quantification of the AC power tree was accompl-shed with the WAMCUT C od e. The fractions for the power states are as follows: Power State 3 Day _tC0 7_ Day LCO 1 .9221 .9009 2 .038-048 6 3.2 3

. ~ Power State 3 Day LCO 7 Day LCO, 3 .038 .048 4 0019 .0025 The major contributors to system unreliability are, of course, the diesel generators' failing to start, f ailing to run, and maintenance. Here, the ~ ircrease in mean time of maintename results in a 26 pen:ent ircrease in each diesel's unreliability. 3.2.3.2 DOMINANT CUTSETS Diesel una vailabilit is comprised of the following modes and resulting percentages of overt train unavailability: Mode 3 Day 7 Day Dicael Fails to Start and Load 47 35 Diesel Fails' to Run (24 hours) 14 11 Diesel Maintenance 39 54 3.2-4

.m... .. _ - - -.. _ _.. _ _ _ - - - _.. _ - - - _ _ _, ~.. ~... - -.4m_. .m-.- -.-m..___. e N 5

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t r! cure 3.21 SIMPLIFIED ONE LINE DIAGRAM I O e> ee - J 4160V 4160V ] BUS 141 BUS 142 GJ GJ GJ GJ CQ ra CO CR 480V l 480V BUS 1312 BUS 132Z l MCC 13121 MCC 13221 480V BUS 480V DUS ~ 1 131X 132X _J MCC MCC 131X1 131X3 131XS 132X1 132X3 132X5 131X2 131X4 132x2 132X4 EXTRACTED FROM $TATION ONE LINE. OWG 1EO 4501 REV. F s 3.2-6 ..m ...,y, -...,..,n.... -y ~.e -w,-

_s.._ ..._2. . ~.. _ . e T.;.r :.... e......... m.. u.- T,'.,..

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. un -. ..ne. s wa .w.. . on.. . wn e o. .n l r ..u. w.. ..w i.a.n.... .an u.. = .m.we w l l ...s...w. ...u..n b no e :. t 4.sf.. a e w..# .t 940 t.3. A I.n.s... ..u.u... i... 1 a e. .u. Figure 3.2 5 AC Power System Fourt Tree 3 4 e-

~ i 1 NrIACIMf:NT 3 WCAP 10526 IIESULTS i l l l I i i l l l l l l i l l l l l l l 1196 11 _ _. -. _....,. _ _.. _. _. _ _. - _ -. - _ _.. _. ~ _, _,.

5.0 CONCLUSION

S AND DISCUSSION OF ANAlrSIS RESULTS This section presents the results of the analysis and provides a discussion of the major contributors to plant risk. A sensitivity analysis of risk to various system alignmer.ts is presented in Section 5.2. 5.1 RESULTS AND CONCLUSIONS The results of the analysis are presented in Figures 5-1 through 5-4, presenting 3-day and 7-day LCO consequence curves for comparison, the risk categories addressed are: 1. Early fatalities; 2. Latent fatalities; 3. Thyroid cancers; and 4. Early injuries. The results of the analysis show a statistically insignificant increase in the relative risk of the Byron f acility due to the projected increase in the LCO for all fluid systems. It is noted that the increase is well within the 10 and 90 percent confidence limits of previous risk assessments performed with the same techniques on similar Westinghouse NSSS reactor. The largest impact 4h on plant risk from a change in the LCO is noted, as expected, in the support -^ systems, _especially tlw diesel generators and the Essential Service Water System. The Component-Cooling Water System is not important due to the inclusion of a maintenance spare pump in the design. The increased outage time of the Auxiliary Feedwater System pumps does not lead to a noticeable increase in plant risk due to the overall reliability of the system and of backup feed and bleed function. Likewise, the reliability of the high pressure safety injection function, due to the design of four pumps (two HPSI and two charging), is not impacted by the change. The Residual Heat Removal System reliability is impacted by the proposed change, but there is a negligible totel' impact on plant risk. 5-1

Special consideration to the Diesel Generators and the Essential Service Water System are being given. An analysis of past diesel generator maintenance events, presented in NUREG/CR-1362 (1990), with an assumption of 'g-normal distribution and categorical mean times to restore of 1, 4, 8 N and 12 hours for the discrete distributions of reported maintenance times, yields a mean tine to restore of about 7 hours, much less than the analyzed 19 and 34 hours. While not specifically addressing the frequency of this data set, the frequency used is justified by the Zion study, and some plant flexibility in control of the f requency of mainterance is noted, such that significant variation from that onalyzed would be an indicator of skewed component behavior, flagging the equipment for management ettention. The ESWS susceptibility.o maintenance is caused by the design of one pump per train, combined with the normally operating status of the system. In single unit operation, this becomes more dominant with the presence of only two (of two necessary) ultimate heat sink forced draft cooling tower fans, where the construction of the Unit 2 components have not been completed. Due to the shared nature of this system and the CCWS, the completion of the Unit 2 portion of the system will yield a noticeable increase in overall system reliability, with concommitant decrease in plant risk. The curves therefor; show that the proposed increase in the allowea maintenance outage time does not result,in a significant increase in plant risk. This result must be taken in the light of the conservative modeling assumptions used in the analysis, especially that:

1) mean maintenance duration is a function of LC0; and 2) main +enance frequency is a constant, I

independent nf changes in the LCO. Westinghouse belitves these resulti support the proposed changes to the Byron Technical Specifications. 5.2 SENSilt.VITY ANALYSIS This section presents the results of two analyses made to assess the dependence of plant risk on the dit rerences in particular systems' reliabilities. 5-2 i i l i__

Particular attention has been drawn to the Auxiliary feedwater System ( AfWS) since the Three Mile Island-2 incident. TI.< NRCs own assessment of the Byron AfWS showed that the system reliabi'ity just met their qualitative guidelines for the two-pump system. To bett-

ess the impact of maintenance, the analysis model used v?s developed to analyze a 7-day LCO on only the AfWS, learning all other plant fluid systems at 3 days.

This resulted in a change in internal core melt f requency f rcim 4.70(-5) to 4.86(-5), The risk curves for this analysis show no perceivable change on the given scale, but are nonthele.s presented in figures 5-5 through 5-8 for the four risk indices To better assess which systems impacted the plant risk to the largest extent, analysis was made of the support systems, i.e., Diesel Generators and Essential Service Water System. The support systems were maintained at the 3-day LCO, and all other plant system: were shifted to the 7-day reliability values. This resulted in a change in the internal core melt f requeixy f rom 4.78(-5) to 4.9)(-5). Again, the risk curves were superimposed, with no perceivable difference in results. Therefore, these curves have not been presented. This analysis supports the conclusions drawn above, in that the overall increase in plant risk due to the proposed LCO changes is dominated by the support systems. Since the magnitude of that change is statistically insignificant, the proposed changes are justified for all systems. e S-3

FIGURE 5-1 POINT ESilMATE RISK CURVE FOR EARLY FATAllTIES SUPPORT SYSTEMS FOR BOTH UNITS ARE MODELED INTERNAL RISK ONL Y . 0-5 '06 5.0 C J.0 6 2.u-6 i.0-6 7.0-7 5.0-7 3.0-7 2 0-7 w g.0-7 I 7.0-8 D 5.0-8 5 J.c s Y 2.0-8 W s !-8 0 4.;:: b i -3.0-9 d 2-0-9 9g e.0-9 a 7.0-10

  • ~5 0-.10 J.0-10 2.0-t0

-1.0 40 7.0 t1 $.0 1I 3 3-i1 2 0-)I \\ 1 0-11 - 4m W u' d oc odo oc dde no cod eo oco '"**2 28 8P8 88 888 88888 N9 ($ A O OO COC E ARL'

  • A' alt'iES. t

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FIGURE 5-2 POiNr g;tlMATE Risk CURVES FOR LATENT CANCERS SUPPORT $YSTEMS FOR BOTH UNIT 3 ARE MODELED INTERNAL RISK ONLY i .04 '.Q-? = 3.e J05 205 s.0-5 ' 0-6 E .5.0-6 3.0-6

k_

2.0-6 i.0-6 7.0-7 x J.0 ' ?<0-? 20' b' (, ) I ?.0-8 cc 5.0-9 o 3.0-0 k 2 0-8 m-i.0-8 m 7.0-9 g 5.0-9 a.0-9 2 0-9 d t.0-9 ?.0-10 m 5 0-10 S 3.0 10. '. 2.0-s0 p 0 10 ?.0-l1 5 0 11 3.0-11 ?.0 11 .04 11 7.0-62 5 0-12

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4 FIGURE 5-3 POINT ESTIMATE RISK CURVE FOR THYR 0iD CANCERS SUPPORT SYSTEMS FOR LOTH UNlTS ARE MODELED INTERNAL RISK ONL Y V.0 5 J 0 ', bs i.0 5 1.0.s >-0 a i.0-6 N x\\ ?.0 7 NN U 5.0-7 '('N N' J.D+7 C 2-0 7 La,* i.0-7 7.0-8 6-5 0-8 i r 3.0-8 d 2.C 8 T g 1 0-8 cr 7.0 9 5.0-9 I { 3.0-4 2 0,9 f r i.0-9 ?.0 40 k 5 0 10 1 'I I 3010 g 2.0 10 [ f i.0-10 \\ ^4 h O OO C00 OO 000 CO OCO C r. DOC <>C aC '"**'S REFfs 88 '!8 8 8 888 l2 8 98" - ~, .s c c o oce., n c2 0 - fHvR0ip CANCEDS, t' "

  • 3 S.C, $f

1 l FIGURE 5-4 P0 INT ESilMATE RISK CURVE FOR E ARL Y I N JUR I E S UPPORf $TATES FOR BOTH UNITS ARE MODELED C INTERNAL RISK ONL Y . 3-4 ,9.S t 0-5 305

0-5

.3! '36 5 3-6 3 0-6 2 0-6 ^ l.0-6 Y 1.0 ? D 5.0 ' 3.o 7 { 2 0-7 m in0*f 7.0*B 5.0-8 E J.0-8 i 2.0-8 y y ? { cn i.0-8 O 7.0-9 4 5.3 9 J.0-9 J.0-9 1,0 9 7.0 10 t ?>. 0 - 10 I l t-

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4,0 iO 1,0-10 M n cio <, o coc o o doo c c roc a o DOC OC I s -, b ~ ( -o o n 00e c=co-(49(Y l4ddk l(E-f a ye

-0 FIGURE 5-5 u POINT ESilMATE RISK CURVE FOR EARLY FATALITIES SUPPORT SYSTEMS FOR BOTH UNITS ARE MODELED '-0 LCO COR FRONT tlNE SYSrEMS vs 3-D LCO CDR ALL SYSTEMS .05 '06 S.0 6 J.0-6 2 0-6 .06 7,0 7 5 0** 3.0-7 2.0-7 e.0-? IE '.0-9 [ 2 5.0-9 J.0-3 g 3 0-e u." 6.0-8 x ? 0 - 5 0-9 h J.C-9 d 2 0-9. ? g 4 0-9 m 7.04 10 5.0 10 3 0 to y 0-10 I.0-10 7.0-11 5 0-11 lr 3.0-11 i 2 0-Ii h i.0-11 - 4m dei d 6 5 odd 5 6 dds 5o oce oe oc5 - " ' ' 2 S E 82S ES SE8 SS SS$ N9 CAO OC OC FARLv F A T At i f i E e,. ( ~ ""9

5,,,s > 'sanhva :N34v' 88588 83s th E se 888 88 88888 888$~8 -85's 83 5~um at.c.i-1 ri c r i* ?t-C t i 71 - c +I g 21-C-i i tt-C'i \\ 1<-c e \\ st-C't g ti-c s tt-c't C' c's 01 c't Ot-c't g oi-o s m OI-c'4 s-c * ~ 6-C'E 6-c't t-C s ?n' 6-c'd m 8-0*i 3m 8 o e. g 8-0*C 8-c's S 8-0*4 y 4-c s m 5 \\ 4-o e + L-C't i-o 1 ~ 2-O's 9-Q't 9cr v" 9-c't 9-c s 9-c's 5-C f, + t ' t 5cC s-C s s,. c ' 4 m, c* SW31SAS ll'e 80s C]7 G-C SA SW315AS 3 Nil INGba bO..s US1 04 0373]CW 38V 511NO H108 603 SW31SA5 lbGddDS Sb3]NvJ IN31vl 803 53A803 NSIB 31vWliS3 1N10d 9-S 380913 e e

1 FIGURE 5-7 POINT ESTIMATE RISK CURVE FOR THYR 0iD CANCERS SUPP0gt gygTEMS FOR BOTH UNITS ARE MODELED -DAY LCO COR FRONT LINE svSrEMS VS 3-D AY LCO rog Att sv5fEMS ..o.4 , o.5 s.o.' 3 0<5 a.o.s e 0-5 ' 0<0 s. o. (, 3.o-6 206 y ..o-c .t.o.7 U 5 o-7 3.o-7 L 2 0-7 W" 1.07-7,0-8 L 5,0-8 t 3.o-e 2;o a \\ ~ ? \\ g 4 0-0 3 x ?.0-9 i s.o-9 t \\ + 3.0-4 j 2. -o l i.0-9 ' 0-t0 ?> 1 5,0-60 3.0-10 2 0-10' h 1 0-to 5 -5 vie o if ado ii 6co d a occ c o osc i = ti$ - '~' ""3 R 4 SE S 8 8, 888 8 8 888 !! S S E" - ~ r~c o o oc e _.c-fMYRoio CANCERS. O "" '" 3 9 $ Sf

s-FIGURE 5-8 PolNT ESTlMATE RISK CURVE FOR EARLY I N JUR I ES SUPPORT STATES FOR BOTH UNITS ARE MODELED -DAY t00 FOR rRONT LINE SYSTEMS /$ 3-DAY LCO FOR ALL SYSTEMS . 0-4

z

' 0*5 f 5.0-s t 3 0-s 2 0-5 0-5 ' 0-0 5 0-6 3.0 6 2.0-0 6 0-6 T t.0-7 I 5.0-7 E 3.0-7 { 207 w" 6.0-7 t.(-8 5.(-8 ,h 3.0 8 2 2.0-0 T g i.0 8 x 7.0-9 5.0-9 309 209 i.0-9 t,0-10 5.0-60 J 0-10 2 0-10 t.0-40 v~ N m WA C OC,000 00 00-FARLY INJURIES. (~ * " *" S 4M l -}}

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