ML18283B410
| ML18283B410 | |
| Person / Time | |
|---|---|
| Site: | Browns Ferry  |
| Issue date: | 03/22/1978 |
| From: | Fox H Tennessee Valley Authority |
| To: | O'Reilly J NRC/IE, NRC/RGN-II |
| References | |
| LER 1977-005-00 | |
| Download: ML18283B410 (24) | |
Text
~ Q o>y~~y<Q REGUL'ATQRY INFORMATION DISTRIBUTION SYSTEM (RIDS)
DISTRIBUTION FOR INCOMING MATERIAL 50-296 REC: OREILLY J P ORG: FOX H' DQCDATE: 03/22/78 MRC TN VALLEY AUTH DATE RCVD: 03/ 27/ 78 DOCTYPE: LETTER NQTAR IZED: NO COPIES RECEIVED
SUBJECT:
LICENSEE EVENT REPT (RO 50-296/77-005) ON 09/27/76 CONCERNING DURING LOSS OF LTR i ENCL i TURBO-GENERATOR AND OFF-SITE PWR TEST) RPS MG SETi A CONTINUED RUNNING AND MG SET B OUTPUT BREAKER DID NOT TRIP AND SCRAM DID NOT OCCUR WITHIN 5 SECONDS...
W/ATT ENCL 8. INFO.
PLANT NAME:BROWNS FERRY UNIT 3
++wss+++wss+esHI<sss++
REVIEWER 1NITIAL:
DISTRIBUTOR DISTRIBUTIQN OF THIS MATERIAL IS AS FOLLOWS
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X JM INITIAL:
INCIDENT REPORTS (DISTRlBUTIQN CODE A002)
FOR ACTION: BR CHIEF 44W/4 ENCI INTERNAL; ++W/E L NRC PDR+4W/ ENCL I 8. E++W/2 CL MIPC++W/3 ENCL SCHROEDER/ I PPOL I TO++M/ENCL HOUSTON~4 WfENCL NOVAK/CHECK~t+W/ENCL GR IMES++W/ENCL KNIGHT++W/ENCL BUTLER+~W/ENCL HANAUER++W/ENCL TEDESCO>+W/ENCL EISENHUT++WfENCL BAER4+W/ENCL SHAO++W/ENCL VOLLMER/BUNCH++W/ENCL K SEYFRIT/IE++W/ENCL f
KREGER/ J. COLL INST< W ENCL ROSA++WfENCL EXTERNAL: LPDR S ATHENS> AL+4 WfENCL TI C+>W/ENCL NSIC+4W/ ENCL ACRS CAT B+~W/ib ENCL COPIES NOT SUBMITTED PER REGULATORY GUIDE 10,1 DISTRIBUTION: LTR 45 ENCL 45 CONTROL NBR: 78087002i SIZE: iP+iP+iiP THE END 4 %4%% %%%%4 w%%%%%4%%%%%%%%%%%%%%%%%%
r.'; 1) 0 TENNESSEE VALLEY AUTHORITY CHATTANOOGA, TENNESSEE 37401 4LAR 32 i970 Mr. James Z. O'R lay, Director U.S. Huclear Re ulatory Commission Office of Insp ction and Enforcement Region II 230 Peachtre Street, Kf., Suite 1217 Atlanta, Geo gia 30303
Dear Mr. O'R illy:
TENNESSEE VALLEY AUTHORITY
- BROKVS FERE NUCIEQ PIANT UNIT 3-DOCKET XO. 50-296 FACILITY OPERATING LICENSE DPR-68 REPORTABLE OCCURRENCE REPORT BFRO-50-296/775 The enclosed report is a supplement to my letter dated, March 24~ 1977, concerning RPS K5 set A which continued running and MG set B output breaker which did not trip during startup test STX-31. This report is sulxnitted in accordance with Breams Ferry uni.t 3 Technical Specifi-cation 6.7.2.a.(9).
Very tr~ yourss TENIQSSEE VALUE AUTHORITY j> fi I J~ f,'r )', >V>l/1
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- 3. S. Fox Director of Power Production Enc3,osure cc (Enclosure):
Director (3)
Office of Management Information d Program Control U.S. nuclear Regulatory Commission Lfashington, DC 20555 Director (40)
Office of Inspection and. Enforcement U.S. Nuclear Regulatory Commission Washington, DC 205)5 An Equal Opportunity Employer I )
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.'+Page 3 BFA85 fORM 368 UPDATE REPORT UTOUE REPORT DATE 3/24/77
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ao/5/77 LI.S.PJUCLEAR REGULATORY Cot/IhtlSSION P 77 I '
LICENSEE EVENT REPORT EXIRIBI I A CONTROL BLOCK:
I ss {PLEASE PRINT OR TYPE ALLREOUIREO INFORhIATIONI
~O A 1 B F 3Qs 0 0 0 00 00 " 00 Qs4 1 1 1Qs~Qs 7 8 9 LICENSf E CODE, 14 75 LICKtiSK NUASUKA Sas LICENSE TYPE A '5l CAT 53 CON'T
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)5 1~6I7 8 60 Qs 7 60 61 DOCKET NUAtefA Tsl 69 REPOAT DAZE EVENT OESCRIPTION ANO PROOAQLF CONSEOUENCES QIO foO~J During STX<<31(Loss of Turbo-Generator and Off-Site Power Test) RPS HG setIA
~Q3 continued running and hfG set B output breaker did not tr ip. Scram did not No significant occurrence took place. See the attached lettex with attach-ments 1-5 for an analysis of the event by the TVA Division of Engineering
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~8 LJS LJS 7 8 9 SYSTEM CAVSE CAUSE COI/IP. VAI.VE CODE COOK SUBCOOE CORI'PONEtlT CODK SUBCOOE SI'BCODE
~Os 8 9 10 II 12 12 16 La8 'MS 19 20 Sf OVENTIAL OCCL'AAENCE AEPOAT REVISION LER/AO sssoss EVENT YEAR
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~+'S Qa 21 22 23 26 2) 30 31 ACT!0M FVTVAE 6 FFECT SHUTDPY)N ATfACHMfsIT NSII~ PAISAECQVP. COL'IPONK!17 TAKEN ACT ICV ON PLANT L'IfTHOO HQUAS ~22 SUBRIITIED FQA!IILUD. SUPPI IKA AtsAtsVFACTVAfst MSLJS LIS LJS24 JS 26 3) 40 41 LJS LSS 44 Al CAUSE DESCRIPTION ANO CORRECTIVE ACTIONS Q27 FSAR description of system operation was not clear and is being revised.
GE CR2820B relays vere not set correctl and vere ad usted on all units.
GE TFK226Y225 breakers had dama ed undervoltage releases, possibl due to improper reset procedures; Damaged breakers vere replaced on all units and caution ta s vere added s ecif in reset methods.
'7 8 9 80 FACIUTY ~3P htETHOO QF STATUS '%POWER OTHER STATUS PJ QISCOVEstY DISCOVERY DESCRIPTION Q3? ~
5 8 Qs ~02 4 Q E/A ~CQ31 N/A 7 8 9 10 12 ACTIVITY CONTENT RKLEASKD Qf AKI.EASE AMOUNTOF ACTIVITYQSS LOCATION Of RELEASE Q38
~IS H O~HQ3.1 N A N/A 7 8 9 Iu It Pf ASONNE L f XPOSVAKS NUVDK'R TYPE DESCRIPTION Q39
~00 0 Qs'Qs E A 7 S 9 11 12 12 PEASO'INEL INJURIES I
~ 7 8 9 II 12 LOSS OF OR DAMACK TO FACILITY TYPE Of SCAIPTIQN Q43 9 ~P. N/A 89 Iu PVBLICITY 60
~2Q ISSVf Q
~NQIA Of SCAspTION Q N/A NRC USE ONLY I
7 ~ 9 IU 66 69 NAME OF PREPARFR PHONE:
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- Revision
@<re g,g Cc<7 I>> Oh<
P80 2'> 5 65 UNITI'O. ',TATES GOVIURN5IENT
'Memorandum TENNESSI<"I"'ALLI<Y AUTFIOHITY TO H. S. Fox, Direc or of Power product ion. , 7 16 EB-C (2)
PROM Roy H H. Dunnamam, Di,ector of ~ineering De si gn, W11A9 C-K .
DATi F bruary 24, 1978
.". UP.Sf'('T ZRGtJNS Fi2EX NUCLFJS,ÃMQ' - REACTOR PROTECTXON SXSTEN M-G SET OPERATXON REA r
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memorandums to you dated November 7 (hKB "(71104 021) and. December' (MEB 771207 0 037},
} 19(7 and a memorandum from D. R, Patterson to L. M. hhlls dated January 9, 197 Concerning the referenced, memoran um, we recently have been contacted morandum om both the Browns Ferry Nuclear Plan of Xnseection and EnforcementtRRegion the an~< ~
io XXDit "sis that was attached s itto th t f't e
and thee NRC office an di th mrs t,t referenced of s stated. in the second. re erenc to GE fo th i vi d. h i d th i concurrence. The analysis alsoo has been re een reviewed internally including TVA's Nuclear Safety Review Board.
Attached is the final version off thee analysis. ly Since it has been in TVA and by GE, it is ready for trans a o understand. that you intend, to do thi b supplementing reportable occurrence repo rt 96/
1$ .rch 24> 19"('f.
din the roposed revisions to the BFN FSAR included vith the a<<tach ed analysis, wc have rans mitted e these to the Regulatory B evisions i i f our staff by the third,d, re erence need memorandum. We requested be includ e d, n th e general update to the BFN FSAR S+< I r II C < < U<
rsenA1< hUc<<ga <<<I<I e <J is ear. Transmittal of the attached. analysis to the I C will notify the Regulatory Branchh that a thee revisions must be include int<Qe g<7 general FSAR update.
T. W. Bar-.I-alow iss handling o this matter for EN DES; arcb.n the analysxs, please have them contact if your staf Xf o staff h technical. aspects of the electrical bre ak th t d'hc BFRO-50-296/775, please have them contact H. E, McConne '
,2769 in Knoxville. Original SiIn>cd fly
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Roy H. Dunham ~<I<<< t>>CI.
F>> ~ Il< ~ ~ I>>ty Attachments H<>>< C>>>>.
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W. M. Bivens, 5100 MXB-K D. R. Patterson, WlOC126 C-K F. W. Chandler, WUC126 C-K Power, hhnager's File~ 73 J. P. Darling, 403 PRB-C M. M. Price, Brovns erry COAST (3)
MEDS, Z4337 C<<K E, F. Thomas, 818 PRB-C H." H. liullp E71324 C-K Buy U.S. Savings Bonds Regularly on the Payroll Savings Plan
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I~ httaclunent 1 JI'IhL1,"I OF TIIF, EFFECTS OF MCIGEBS )IPS P.-G SET CohSTDO;IN TlI:E hS OCCURRED DURDIG TIIE PEBFOHI!hHCE OF SThRTUP TEST STX 31 gn NBC X5E Report Nos. 50-259/76-20 and 50-260/76-20) 50-259/76-2II ~
50-260/76-2II, and 50-296/76-22; and, 50-259/77-18, 50-260/77-18, and 50-2r~5/77-18, appeared. discussiona regarding the perforrr" nco of strL'rbup teat ST1-31, "Loss of Turbine-Generator and 0 fsite Peter~"
on unit 3 of the Bro;cns Ferry Nuclear PLant on September 27, 3.977.
During t)ria tost the reactor die) not scram automatical3g- within ton seconds as was expected by the tost procedure but wraa scrammed manu<<U~
at approximately 18 seconds into the test. The fact thaC the reactor not scram automatically within 10 seconds waa attributed to t;ro 'Iid problems with tho reactor protection system (HPS) motor-generator (Il-G) aota. One problem wa that a time delay relay on the RPS I4-G set input breakers sras aot, to open the breakers at "6.5 and 5.2 seconds, reap ctivcly, for HPS N-G "cta A and. 13 for unit 3. Tais enabled. thc emergency ciicscl .
generators to start and. supply pcrirer to the RPS If-G set h before 6.5 seconds had elapsed. The second. pxoblem concerned the output brea)cora on the RPS I!-G sets ~rhich prevented. BPS N-G set 8 fxom triI'rping. This second problem has boon resolved.
I i Tho first problem has not been resolved with lIRC XSB since they required
! 'that 'TVA oa>alyzo the safety significance of the fact that the RPS II-G seta di<l not coast dcxrn within 3 to 5 seconds. There are two statements in the IIFN FShH that mention RPS II-G set coast dcmrntimes. One is in subsection 7.2.4 on page 7.2-10 which states'that "a comoleto, sustained loss of electrical po:rer to both motor-generator sots wou1d result in a acean, delayed by the motor-genorator set f2ywnoel inertia, in about three seconds." The other statement is part of the loss of aedliaxv pcrror transient analysis given in subsection 14.5.4.4 on pago 14 5-6 iIhich says that "Tho protection system M-G seta frere a..sumod. to coa Cd'n 5 seconds to the point where scram and, mxi.n steam iso-lation occurred." Tnosc two statements seem to imIx)y that the 3 to 5 second, coast dcmmtime is a requirement and that the RPS Ii-G set" are being relied upon to perform a scram function.
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'vT TVA's Division of Engineering Design (EH DES) has reviewed these FShR lb statements and. has contacted the General Electric Compo'GE) to clear'ify thc intent of the statements. GE has told. EH Dr8 in telephone discussions that thc times stated. in the FSAH wcx'e meant to be con-I servative values roprescnting the minimum coast downtimoa used by GE for analysis purposes. TVA requested GE in a'letter dated February 18, 1977, (attachment 2), to verify that 5 seconc'.a is the minimum coast docrn time assumed for ana'.Iysia purposes and that a longer coast do;rntimo c)oos not constitute a deficiency. GF, xepliod in a letter dated February 28, 1977~ (attachment 3) that 5 seconds is th" minimum coast dogntime,
<<ar;enod for <<nalysi.s puxposoa and that the efzocts of ionor coast darn times wore loss severe than those an~~mod in tho FSAH.;Due to some
inb . ganizational confusion over the resolution of thi'atter,
'Lysi" of GE'o information wao not completed. until rcccnb3y.
a
.rm:ation supplied. by GE has bc<<n analyzccl by TVA Ki DES. This
- s hao conc3uded that the tranoicnb ana3ys..s pre entecl in FSAH
.L,ion lil.g.>l.it io corxect, but has been vordecL ambiguously ancL 1 e xcvioecl. Atbachm nt, 4 io a proposed revision of FSAR
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- ~section 3A.5.>l.4, step (a) through (c). The statement in subsection
"(.2.ii on page 7.2-10 will bc revised. to read as fo.llcmrs, "a complete,
,::.uotaincd 3.ooo of electrical power to both motor-generator sets vill xcoulb in c:vcntual loss of HPS instnaventation po'rer as delayed by the.
t~cbcr-generator oct fly<wheel inertia. Loss of HPS instrumen ation pcarer w;.31 'nit. atc IVIV closure which will result in a reactor scram." Tnese pro~>>ocd revisions have been reviewed by GE ancl vi33. be included. in an YSAB amendment generally updating the FSAH ncrr being planneQ, for distri-brction in thc spring of 1978.
'Znc: transient anal.ysio in FSAR subsection 14 5.4.il xrao made under the a::svmrption thab the reactor vas at fuU. poorer when either all external p.i.:uib elecbrical connections are 3.ost or a fault occurs in the auxiliary po;,c:r syobem itself. The txansient analysis for the latter case con-b;;iuecl thc r t temcnt regarding the BPS H-G set coast downtime. Ef DES has rcvi<<;red t¹s parbicular tranoient analysis to determine the effects on it of longer HPS bI.-G oet coast downtime. Basecl on the information provided to TVA by GE in their February 28, 1977, letter, a simulation scqu'ncc similar to the onc in FSAH subsequence 1>l.5.4.4 was developed.
i'ni irnulation sequence is attached as attachmenb 5. GE stated in d
their 3.etber the;b "...the transient associated. with longer RPS M-G set co"'st clams is less severe than thab analyzecl in the FSAB due to longer bypas'o va3ve operati.on." The simulation sequence in attachment 5 supports this statement in that the turbine bypass valves will remain op n 3.onger than the two seconds assumed in the FSAH. This is assuming that the conclenser vacua continues to lose one inch of 'Hg per second, aX'ber the turbine bypass va3.ves open and. that the >SXV's do not go ful3y clo cd. until three seconds after initiation of NHXV c3.osure.
Eii DES also considered thc effect of a slower xate of loss of condenser vacuum. Xn thi case, a reoctor scram due to loss of condenser vacuum 1 >ro..l.d'not occur until later in the transient. Tne xeactor probab3y iu,S' voulcl be ocxos.~n d. first by another parameter such as low water level.
A" stated. in thc FSAB, the loss of auxiliary paperer txansi.ent in its f
initial. porbion is similar to the loss of feecbrater i(mr transient s
g an;;~g'zcd in FSAH subsection 14.$ .4.3 except, for the recirculation pump A
trip (which reduces the severity of the transient). After closure of thc 1$ IV's, the transient resembleo that caused by isolation of the main team lines. A slcwer rate of loss of condenser vacuum would change the sequence simulation, bub Bi DES feels that a scram would result from 3.mr water level. Turbine trip also could. scram the reactor, hmrcver, EN DES did nob determine xrhether this vould occur before,.a scram Que to lear ~rater level.
Thc transients in chaptbr 14 of the FSAR are performed. under very conservative
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assumptions and. represent thc most severe for the cases involved. The times given in the event sequences arc conservatively assum d values used for ano3ysis purooses. They arc not meant to be operating require-ments unless spccificaUy identified a" such in the FSAR or plant Tcchnical Specifications. Loss of auxiliary po:rcr produces a transient that is less revere than others studied (especially clo urc of a3'L V~Dr's) and faQure of tlic HPS II-G sets to co sMown to initiate 1$ XV clo ure xeduccs the severity of thc transient.
The startup test STX-33. Vas peyformcd arith the unit 3 reactor at 23.g power and the generator output at 193 l"/(e). These conditions were well below the. operating assimptions used. for the transient ana3ysis in FSAH subsection 14.5.4.4. The measured transient was belcrr the one given in the FSAR and was vrithin thc acceptance criteria for the test.
Sita relating to this is availablc at thc plant along with the test procedure, 'acceptance criteria, and detailed results.
Za the test the reactor was scrammed rwnually at approrizately 18 seconds into thc test. An auto~otic scram signal duc to low water 3.evcl was xeceived at 24.4 seconds into the test. The lowering of the to the scram setpoint may have been a result of the manm1 scram, .
reactox'ater however, Ef 3)LS feels that an automatic scram due to reactor low water levc3. >rould have resulted. eventually and that the manual scxam may only have hastened the autortatic scram signal. lt should be noted that the turbine bypa. s valve remained opened during this time providing a path for the steom to the condensers. Condenser vacuum during the test was not, measured, but its rate of loss ~ras slow enou+v that the reactor scram sctpoint was not reached during the time recorded. This is to bc expected at 3.ower power levels since the rate of steam production is below that o'f high power lcve3.s and loss of condenser vacuum primarily results from heat up of the condenser by the steam entering circulation has ceased.
it once the cooling water Operational transients at la~a power levels are less severe than those analyzed in the FSAR since thc xeactor thermal potrer level and steam production rates are lower. The times given for annlgtico1 purposes in chapter 14 are based on conservative assumptions in order to postulate the most severe transient. These times may notcox'respond to those actually measured in tests. This is espcc9.a13g true at U' 3owcr power levels where it msy tahe longer to get to a x'eactor scram setpoint (such a" lcw water level), but the other applicable parameters
,T V are also lower and/or longer (such as rate of temperature riseinside A the fuel elements). Therefore, a delay past the automatic scram times assuiaed Cn chapter 14 is mitigated, by the lower poser leve1 of the reactox core.
The FSAR statements which gave rise to the conccxn avex this issue vill be revised as indicated earlier. These revisions should clarify that the five-second. coast do~mtime is assumed for analysis purposes, Thc RPS H-G sets axe not being relied upon to provide an initiation for reactor scram within a given time. The function of the RPS M-G sets is to protect the RPS instx~entation from rapigmomentary fLuctuation" and,to reduce spurious reactor scram" that could result from such momentary fluctu tions. The initiation of a reactor scram
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reslQ.ting from )>017 closure is an indirect result of the BPS.Y.-G.
Xt is noL a safety system, is not meant to be onc, and. there sets'oncl;ion.
nol; a present requirement for it to 'be one.
A4'l:er consideration of the aforemcnl;loncd matte-:.s, TVA ha., conc1udeiI g;"l; thc fact that the I<PD H-G sets did. not coast dcrmwithin five seconds during the performance of STX-31 on unit 3 >ms an cceptablc evuit that d:i.d not reduce thc safel;y of the p1ant.
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Genera.L Electric Con~pal ~ ~
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Knoxville, 'ennessee 37919 ~ ~
Gent1men: Attention: )h. H. N.
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l>~<JOB EQUMI~2iT PACKAGE AUD I'fSSS CO'i'JMCT 66CoO 9O74jr 18rD 67CGO 91750 liPITEt HO. >11-5>l, If2 5'~t~ -I'D 3-B~I28 PROI'ECTXOM STSTBf If>>G SETS IP34-1+3+ ~).h JQS TQl)- COO. ~ - .A 'EACI.'OR 0
l Paragraph 14.~>.4.4(b) of the BF TSAR indicates GF.'s loss of,aurQ1axy ~ 'k
.. yo.rcr enosis assu."aed that, a~on less of aux11iary peter, the SPS lg j
sets ~rD3. coast down in 5 seconds to the point vrhere sere an@ rain
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stcam isolation ir&1 occur. Please confim tha 5 seconds ia the 'a longer Nrinham coast Gosm time assed for missis purposes an@ that coast Go~m tine docs not constitute a reportable deficiency please
.proi<Ge this confination by? hrch. 4~ 1977.
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5MNESSEE VAL'lZX AUTHOKPzf ~ ~
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'.'enness."e Va'lley f) thority 400 Co-.:.erce f)Yet (!
Ynoxville, Tenn.- ssee 37002 c l
SUB JI:CT: BROiii'!S F="t!RY lllIIf5 1-3 R)EftCf0,", I'PO'fECI IO'I S't'STEtl tl-G S"=TS Be-,"erence: TYh'Letter llos. lIll-b6, 'HZ-5~'nd 3-8022 ~ ~
D ar <'ir. Patterson: V
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. Tl)is letter con i)-s ttlat ~ sccot>ds ls th. mtnjmuiA co/st (0' till-tnalysis purposes.. Th effects'of .long r coas'o';:n tom s c)) e Qssu;"1"(I'or tilltigllc(l
~ by.tire loss of I.'i"1 con(lenser vacuum as (lescl ib d jn ti)e )Sf'LR, v)
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condertser vacuum loss, whicl) results fro~i loss of pou r to'n~ circulating
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)tater p:tmps, is conservatively estitiated at 1 inch Hg per 'secot'.d; attaciled
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tab'le sho;ts the trip setpo'ints associated <>ith loss of condenser vacuum, B,.s d on this data, reactor scram and turbine. trip would occur at 5 s cotlds and 6 second:;.
) esp'ctively, fo'liow)ng loss. of auxiliary power,. Hain steam isolation do s not
'occur prior to th turbin trip, as assum d.it) .the FSf)R, clAd th" bypass valves U )iill be op'n long. r titan two seconds. Hain steam 'isolation will occur >::hen tile c~
'pPS ll-G sets coast down to the isolation setpoint or tl:e con(l. nser v cu.tm r .cl s U
f it" iSOlat;iOn SetpOint. TilerefOre, the tranSient aSSOCiated With longer RPS c'I-8 A spt co:1st dowt)s is less severe than that analyzed in the FSiNR d(le to I otlger bypass Yal Ye operation.
r Because tltese conditions are already discussed in Lhe FSf('R an(l your letter.do s l)ot rcaise any new issues, we have not.ref'erred this for: potentic~ I ly reportable
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Rex<so(l 7'">A!'J)escrintion for 3 oss o." Auxili..",a.v'o:rer
( } 5 L L 'plvf';ps ar(: 'vr.i.'Apt "4 a'4 't L'> e Oo ~'<ox'lM L co8st Q~ Win tib'.Gs x.'a~re
'< ..';cQ for.'hc r(.~. Yell.tact.LOQ an(l:(.<<<<ii'.:.'.t:cr pip'p.'.
>.,') Pi )m -' s".co;1c sp rca< or 'r '~l'; "s UI"<<Qv. to bc inici tc<.
t" 1>!'hc lod c(intel)scr vaculEl vrlp s(.'i'ilail'Lg (loss ofthe 1pJA5 n co:Kl(,nscr circula ing 'LlK Qx'lllQj)s 3'1;ls est'r5zDt(.d to c u e condenser vacuum to drop to the reactor scram trip setting by 5 seconds). 'Xhe reactor.protect'ion system?l-G sets also axe assumed to coastdo;m to the point that RPS instrumentation po:ver is lost. Tigris initiates closure of the 5SXV's which also produces a scram signal after the va1ves have moved 10$ of their total nevement.
(c) The condcriser vacuum eras assumed to continue dropping and xeaches the tu bine trip setting by 6 seconds'he turbine bypass va1ves open for a short period (about 2 seconds), then they close due to the loss of pressure 9n the main steam lines do;rnstream of the htSD"s once the i~tSIV's complete their closure
.at time = 8 seconds, U
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~0 3anper RPS W-0 Set Poastc3o>m T'm>>
('g A'.1 p'3.'>c'4 ".iYippcci r ':ime =- 0 >'ioxr>al coast <ko; ntimes 1rere
.>>-:;,d I'oz thc::".>':irn>'xc.l:i cn <<nc. fceck.rater. puri>i>s.
(b) '>;hc 'J.~>;; o';!cr to tl>c: circut.atinz~ archer I>u>>ys results;i.n a 3.c>ss of.'on".'user vacuum xrhich i" conservatively estimated at 1:in'h )fan pcr second. The condenser vacuum dxops to the reacto" scram trip sctpoint afl;cr 5 seconds. A reactor scram is initiated..
ot this point.
"(c) The conden"er vacuum continu s to drop and. reaches the turbine trip setting by 6 seconds. The-'bypass valves open until either the main stcam line is isolated or, the condenser vacuum reaches the bypass valve closure setpoint. Yogin steam line isolation wil3. occur when the RPS N-6 sets coast de to the point where RPB instrumentation power is lost and, tSIV closure is initiated or the condenser vacuum reaches theYSIV closure setpoint'.
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