ML20052F256
| ML20052F256 | |
| Person / Time | |
|---|---|
| Site: | 05000000, Browns Ferry |
| Issue date: | 02/28/1981 |
| From: | Panciera V Office of Nuclear Reactor Regulation |
| To: | Check P Office of Nuclear Reactor Regulation |
| Shared Package | |
| ML19219B002 | List: |
| References | |
| FOIA-81-417 NUDOCS 8205120289 | |
| Download: ML20052F256 (2) | |
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NUCLEAR REGULATORY COMMISSION J
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FEB 2 81981 MEMORANDUM FOR: Paul S. Check, Assistant Director for Plant Systems, DSI FROM:
V. W. Panciera, Section Leader Reactor Systems Branch, DSI THRU:
Themis P. Speis, Chief Reactor Systems Branch, DSI
SUBJECT:
INP0/NSAC REPORT - ANALYSIS OF INCDMPLETE CDNTROL ROD INSERTION AT BROWNS FERRY 3
)
I have reviewed the subject report for consistency with the accroach/ findings taken in our generic SER dated December 1,1930. The INP0/NSAC recort cre-sents a discussion concerning the possible causes of the failure to achieve full control rod insertion during the manual scram of Browns Ferry 3 on June 28, 1980. The report concludes that the partial failure to scram was due to water occupying a large part of the volume of the east scram discharge volume header. Other possible causes were investigated in the report sucn as an electrical failure, improper HCU valve lineup, lack of accumulator pressure, excessive CRD or scram discharge valve leakage and instrument air system failure. The recort presents good arguments that each of these oossible failure mechanisms should be discounted (NSAC intends to continue to investi-gate the control air system failure mechanism in its longer range generic study).
The report further discusses certain mechanisms that would exclain the pre-sence of water in the east SDV header. The mechanisms evaluated were:
a) an obstruction in the SDV drain line; b) a sub-atmospheric condition in the SDV caused by condensation of steam (entering through SDV vent path) or because of a loop seal in the SDV drain piping; c) a failed closed vent valve coupled with a partial or complete obstruction or trap in the SDV drain line.
The recort concludes that the exact mechanism that caused the accumulation of water in the east SDV header could not be detemined, and provides some general guidance concerning appropriate steps that should be taken to guard against the unintentional accumulation of water in the SDV.
The staff evaluation that was done to develop our generic SER considered the same mechanisms of failure as considered by INP0/NSAC. Our generic SER goes further in providing criteria and detailed guidance for correction of the SDV deficiencies.
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-s 8205120289 811103 PDR FOIA DIGNAN81-417 PDR
Paul S. Check pg;. : 4 In suninary the INP0/NSAC report is well written and covers the evaluation of the Browns Ferry 3 event of June 28, 1980, in an adequate manner. However, the scope of the report is within the scope of the staff evaluation done in developing our generic SER of December 1,1980.
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V. W. Panciera, Section Leader Reactor Systems Branch Division of Systems Integration cc:
D. Ross T. Novak l
e TENNESSEE VALLE't AUTMCR:7Y cra a'.cesa
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Mr. Harold 3. Danten. Directer Office of Nutlear Reactor Regulation p.-]
U.S. Nuclear 3egulatery Ocznissien
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In the Matter cf the
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Oceket Ncs. 50-259 Tenessee 7 alley Authority
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50-250 50-296 Inclosed fer your infersa*1en is a copy cf the significant cperating s
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experience report, Analysis cf Incercleta 0:ntrol Red :nsertien at 3rewns Ferry 3 (NSAC-20/OTPC-3), recently released by the Institute cf Nuclear ?cwer Oper tiens (CTPO) and the Nuclear Safety Analysis Center (NSAC) en the partial failurs :f :entrol reds to.^1117 insert at cur 3rewns 7erry Nuclear ?'_ ant.
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- 1. M..".111s, Mr. nager Nuclear Regulatien and Safety Incicau.9 cc:
Mr. *ames ?. O'Reill7, Oirector Office cf *.nspection and Intercoment U.S. Nucient Regulatcry Ocumission Regien : - Suite 31C0 101 Marietta Street CO/
Atlanta, Georgia 30303 3
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is 1980 Analysis of Inco1uplete CoutrolRodInsertion j
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Nuclear Safety Analysts Canter institute of Nuc! ear Power Ccerations
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Analysis of Incomplete Control Red Insertion at Browns Ferrf 3 NSAC-20/INPO4 Oecemcor 1980 Precaroc ey ir titute of Nuc! ear Pcwer Coerttiens a
Atlanta. Gecrga anc Nuc: ear Safety Anarysis Center Psic Aitc. Califernia
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CACERING INFCRMATICN I
Cocios of *nis reocrt may te orcered from AesearCn Aeocrts Canter (RPC). Scx 50490.
Psio Aito. CA 343C3 (415) 965-4C81.
(em Srcure 8WY 1 'MCorPtMete CarttrUt e d leserDOR. Nater WNOcp >R SCV. #N tACOe o
8suure of Scram Sveterns NCTICE N 4 # *ee Crecerad Cy '"e Nuc:eer $4rery Aperres Camer (N$AC operated h !Pe feC!PC %
a tu * 'rsutute. T. E.sel) acq gy 'Pe testitute of Nuc*eer % Ocoratuvis e NPCL Neeer NSAC. Leet c
.NPO. Serveers et W or iNPC. :trer corsors centreuerg is or aessang e ?e oreceranon of =e recort. -or acw corses act.rq ce to ceced st anw et mese cartes.as eases arv =erramy or 'eoreespranon. escrees or a CueiL mofft 'espect 'O ?e aCCW/. 33rPtretteese Or useN#ees Of '*e imCreaJort Cartteeped W9 **'t 'e00rt. 3r
?at '"4 use of anw *n80rmeDon. acDeraba. *etPc0 or Ofoceed @st:OteG in *ts re00rt *ew "Of PMe Cfwaterr Jweeg egftts' 2r'Of M any wtres adM 'eeDect 'O t"e use of. Or 'or carregos resueneg H=Jrft **e use of.
j ADV WTFOffPeDen accerttbt *eff900 or 3r0Cest GiaCJoseg A '"r8 i40lFT.
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l ABSTRA07
'he failure of 77 control recs in the Browns Ferry 3 reac:Or to scram c:meletely On June 23, 1980 has teen analyzed. It ts concluded that the cause of :Me
'ncident nas Mat one half of the scram disenar;e volume, nnien snculc Nave :een emety in creer to receive the nater from :ne centrei rod crtves, actually nas almes: 'ull of water.
a y :ne, er a c:meination, of several 9echanisms can c:ntetbuta :s ac:umulatf en of n
nater in :Se SOY uncer certain c:ncitions. It accears ;:cssttie that there nas an
- str'ac:10n er a trap in Me scram dischar*Je volume exit line antch iccecec its cratnage. 0:ndensaticn Of steam from other car *.s 3-
.ie clean rac maste crain system in :ne scram sischarge volume ay also have ::ntributec ic water ic:urula.
- ien.
- essite extensive investigation and analysis by T/A and others a unt:ue :ause 9as net :een esta:lisneo. Dessible says in enten the accve ci ed eenanisms :uld 9 ave teen ccerative are ::ointec Out, and suggested nays for guaref: q agains: :nem are given.
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Centents Analysts of
- ncemolete Centrol Red *nsertien at Browns Ferry 2 1.
- ntrocuction 2.
Executive Surinary 2.
Summary Cescriction of Incident 2
rincings anc C:nclusiens 4.1 2-+nc1:a1.:incings and Cenclusions 1.2 Cause Of tne :ncomclete Scram 1.3 Evicence 'er tse "Cbstraction dycetnesis" 4.1 Eneerce 'cr the" Vent Pycotnesis" 2.5 The *Stuc$ Valve Mycothesis" 2.5 Effect of Scram :n Fuel 1.7 C erater tes:ense 4.3
- cle of the Vent and Cetin 7alves 2.9 Ancillary Cuestions 4.10 Summary of Conclusions accendices SCE Secuences of Events CES System Cescri: tion and Coeratten CCN teacter les:ense anc Consequences CPS Ccerator Actions anc ?eccedures 8ederences Glossary 1
I analysis of Incomolete C ntrol Rod Insertion at 3rewns terry 3 1.
Intreduction This recort : resents the results of a study by NSAC and ;NPO of the June 29, 1980 incicent at the 3rewns Ferry Unit 3 reactor in anien 77 of the full c:nclement of 125 c:ntrol reds inserted only partially wnea a manual scram aas attemetec. The pur ose of this report is to present a escription of the incident, and seme
- ossible causes.
In :arrying out this analysis, NSAC and INPO :erdermeo a creliminary review at the site On.'uly 2, 4, ana 5.
Team briefings ano meetings were neld with 3aneral Ilectric and Tennessee 'talley Authority, and incividual censultatiens were 9 eld witn GE, T'lA, and several utilities. NSAC and INPO also :artietcated in several
'ncustry and NRC emetings on the incicent.
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NSAC/:NPO ::ntettut:rs to tnis evaluati:n ners:
- r. 4. 5. Baker l
- e. 3. L. G1111 scie Vr. W. M. Layman Dr. M. C. Leverett Mr. J. W. Power we. S. L. Resen
'Jtility recresentatives *no also contributed were:
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- r. 3. L. Clart, 2hilacelenta Electric w
Mr. 3. 3. Salagi, Corinonwealth idisen Mr. Jonn Stat:, Nortneast Utilities
2.
Executive Sumarv Event
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During a routine manual scram of the Browns Ferry 3 reactor, 77 coritrol reds failed to insert comoletely.
3ackereund On June 28, 1980, a manual scram of the Brewns Ferry 3 reactor
- was attemcted in conjuncticn with a planned shutdown for repair of a feedwater line in the turoine building. Aside from the need for this repair, plant conditions were normal.
The shutdcwn crecedure involved first icwering the reactor :cwer level to 25". by reducirrj the recirculation flow and inserting a numeer of centrol rods to cecrease the neutron chain reacticn; and secondly pushing the manual scram buttons to insert all centrol recs c:mpletely to terminate the neutron chain reaction.
C:molete control red insertien is normally accomplished in less than 3 secencs after both scram buttons are pushed.' In this incident, nor tal centrol red insertien did not occur when the scram buttons were pushed.
CescMotion of Event Of 185 control rods,10 wre fully inserted prior to the manual scram. 77 reds failed to insert fully upon manual scram, with insertien ranging fran position 02 (95% inserted) to position 46 (St inserted). Cbserving this, the operator reset the scram; this procedure allows recharging of nitrogen-pressurized accumulators and draining of the scram discharge instrument volume. Manual scram was receated. Insertion progressed somewhat, but 59 centrol rods remained only cartially inserted. After a third reset and manual scram, 47 remained partially i nserted.
Recharging and draining of the scram discharge instrument volume was receated and the scram instrumentation autcmetically initiated a fourth scram. All rods were now fully inserted, placing the reactor in normal shutdown c:ndition. This nas accomplished within about 14 minutes of the first scram.
- unit 3 is a 1067 %(e) net. General ElectMe boiling water reactor, in comercial coeration since Maren 1, 1977.
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The following caservations are signift: ant:
The first scram decreated the chain reaction so that the smeared average fission power level was aneut 2*. of full ;ower. The sec:nd scram teminated the Main 7 action so that the only remaining heat gener'ation-was 9ermal decay heat ;eneration.
i There were no indications that celay of full insertien untti the fourth scram caused any damage to fuel, to the reacter, or to any other ; art of tne plant.
Natural circulation core flow provided ere than acecuate Sverall cre
- cling.
1erecal Electric calculations indicata that no fuel Ocerating limits were exceeded.
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'his is *he Only kncwn instance of a large nuecer cf control r:ds failing to i nsert c:moletely :n comand. Because Of one :rucial imcortance :f being acle to snut tae reac cr :cwn :uickly and mitaoly wnen neeced, tne reacter Owner, the macter designer, the NRC, and a 'of nt NSAC-INPO team attemoted to detem1ne One causes af this failure to acnteve full insertion en the first scram.
Efforts were also directed at identifying masures to prevent a recesition of this ce similar failures in this and any other totilng water reactor. The failure was of further interest to 'tSAC and INPO as a possible precur-sor to are sericus events.
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- 'adinos After the first scram attemot, the aceraters caserved that all but :ne :f the centrol rods wnich failed to insert sert en the east half of the nact:r.' 31s 5eftavior of the system led plant personnel and others to telieve that the east scram disenarge solume (:CV), a void into wnica react:r water is disslacec wnen The scram 'tydraulic system is snewn diagramatically in Fig.1. ~he ar-ingerrent Of the scram discnary voluce is snewn in Figs. 2 and 3.
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'e hign pressure water drives the east side c:ntrol rods into the reactor, was for j
some reason already almost filled with water ;rior to the scram. Thg SDV could l
not act:nnodate the additional water discharged into it during a normal scram and therefore insertion was impeded. *his conclusion has since been re-examined and stands generally accepted. Other ;ossible causes of the incomclete scram nave been analyzed and largely ruled out. *he origin of the water in the SCV and the cause of its accumulation have not teen firmly estaolished, but several ;ossible explanations have emerged. None individually can to confirmed, and a c:moination of them is also a ;ossibility:
There may have been an obstruction in the 170' long 2" ;1ce wnien connects the east scram discharge volume to the scram discharge instrument volune (SDIV). This line has nly a very slignt stoce f:r
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frainage, and a slight obstrJetien would h4Ve Deen sufficient t3 DaCX uG
=ater into the scram disenarge volume :rior to the scram. :: Nas teen theori:ed that such an costruction could have been disturtec ano
-elocated by the violent hydraulic action in the SCV after the miti;le scrams wnica teot ;14ce. It is not possible to state with assurance, thougn, that such an costraction actually did exist. It M.ss teen suggested that the costruction ::uld have been formed by the accueulation of solid crud. Solid crJd has been found in level switches :n the scram disenarge instrument volume. Mcwever, no ;ositive evidence af an costruction in the 170' long 2" line has been found.
A comoination of tracoing action in the east !DV vent line and in the east SDV !DIY 2" connector pipe, together with cendensation of steam in the east SDV, may have produced a partial vacuum. *he occurrence of such a ;ar:141 vacuum has been ceserved in the SDIV of Browns Ferry 1, wnich is very similar in ; icing configuration to 3rewns Ferry 3, and on at least two other !WRs. There is no :rcof, however, that this was the cause of the incident.
Elther of the foregoing may have been aggravated by momentary pressure er vacuum surges in the clean radweste (GW) drain systen caused by large influxes of water free sources cther than the !DIV. Both the SDV vent lines and the IDIV drain line disenarge into the GW drain system. *his nydraulically comolex system receives internittent drainage from accroximately 50 other sources. Scme Of that desinage is frecuently not water, wnien could increase ;ressure er suction surges, a
1 C nclusions Since it has teen incessible to determine wnether any of these ;ossibilities er comoinations of them were resocnsible for the incident, corrective ac* ton recem.
wndations shculd te comorehensive encugn to guard against 311 of them. It is concluded," therefore, that topreoriate steps should be taken by all ShR plants to guard against:
2n costruction in the SUV.!DIV ::nnection si:es.
A configuration of the SDV-!DIV c:nnecter or vent pices cacaole of 2 reducing a tras ce 1000 seal. Such a trac cr Icon seal could Ocssibly $4 the result Of *hermal GEOansiQn during 9st cCnditiens althougn 1:.ay eat :e ;rtsent in a cold envireneent.
- nterference my the DRW crain system with the :certtien of the 30Y.
!DIV system.
i Failurt Of the DV vent lire valves to :cen.
Teo slew :rsinage cf the SDIV :ue to inacecuate vent er desin
- acact:y.
The avview team also examined the precedures available to the coerater f r an event 7f this type, and the response of the coerators to those crocedures, sar.
- 1cularly 41th res ect to the criteria for deciding another to inject sodium pentaporate from the standby licuid control system. lt is concluded that these criteria should provide more exoticit guidance in deter 9 tining the need f:r sodiu.*
- entaborate injection.
The conclusiens outlined scove are intanced to acoly to all !WRs with nycraulic c:ntrol red drives Ocerating :r in construciton. It is rec:gni:ed that the scocific corrective nessurts voich should to taken will very frem plant to ;Iant because Of design variations and differing :recedurts.
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Surpary Cescrietien of incident On June 23, 1980, it was necessary to shut ecwn the 3rewes Ferry 3 (3F-3) reactor. This snutcown, whien had been planned fer a c:ucle Of days, was necessary in order to repaia a feedwater line in the vicinity of one of the fetcwater Dumes.
The shutdown was taking place according to normal precedure. Powr was first recuced to 390 "w (36% of rating) by decreasing -ecirculatten flow and inserting 10 control reds. The ocerator then initiated a manual scram to comolete the shut.
down. All centrol red drives received a scram signal as recorted by the ::erators and the shift technical advisor. All 92 of the withdrawn west bank control *eds inserted fully, ex,:ect red 30-23 which settled at position 02.*
(It is not unusual fer
- d to settle at position 32, i.e., ?S: inserted, and it is of little reactivity significance since practically all the reactivity effect :f the
- ntrol red is associated with the first 95% af its insertion.) 4cwever, :f the
!8 east bant rocs eitharswn, 76 failed to insert fully, c ming :s rest at <ardeus
- ositions in the etnge 46 (inserted 6") to 02 (inserted 138" with only 5" remaining to
- :molete insertien). The average ::rt 'ission ocwer nas recucto to less than 2% as -ecortec ey 32 (Ref.1) and as inferred frem recorcec '.?oM (iccal
- cwer range ment cr) readings after the first scram.
Ucon ooserving that many recs remained only partially inserted, the coerst:rs q-set the scram after 271 seconds, resulting in Ocentng the vent and drain valves *n the scram discharge system so that water could crain frem tt, and at 364 secencs receated the manual scram. All of the cartially inser ed recs moved inward, :ut scoe remained still :nly partially inserted. At 223 seconds the coeraters again re-set the scram, and at 476 seconds again receated the manual scram. Again, those control rods not yet fully inserted moved inward, but some remained only sartially inserted. At 682 seconds the coerators again reset the scrsm. Ucen removal of the scram direnarge volume by-cass the -eact:r scraemed aut:matica11y"
- n sign (50 gal.) volume in the scram cisenarge inst: ment volume. ~his -esulted in full insertion of all the centrol -eds nica had 9et already fully inserted.
"Gntroi red travel is ;AA".
Full in is csition 30. Full out is :csitten 18.
""anual and aut:matic scrims are functionally icentical, so the fact -hat it was an aut matic scram wnich finally insertec all recs is nct signtficant.
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J Following the fourth scram, a fifth confirmatory scrim was executed and, u:en ascertaining that the reacter was shut down and being cooled in a normal _ manner, numerous tests and observatiens were undertaken to ascertain the cause of the failure to achieve innediate and complete insertion of all centrol rods. The tests and observatiens included the following: (Ref.2)
Off gas and reactor cec 1&nt analyses Control Rod Drive Hydraulic Control Unit valve lineuJ Control Rod Drive Accumulator re-charge Exercising SDIV and SDV drain and vent valves Disassewely and inspection of vent and drain valves Vent system vacuum test SDIV level switch calibration Flushing !CIV level switch tsos and examinaticn for solid material Review of scram history at Browns Ferry (220 scrams successful except for a few instances of latening at ;ositien C2)
Control rod drive maintenance 'tistory review Review of Other maintenance and mccification wert en 3F-3 Verificatien of scram actuater de-grergizatien time Weasurement of c:ntrol red drive stall ficws and friction Review of CR0 temceraturs charts (hign temcerature c:uld signal excessive water leakage through the rives)
The 170' long 2* east connecter pipe was cut in six claces and redded with a metallic tace to detect any blockages System flushing with water (after cutting the nice)
SDV inspecticn with a $croscope (after cutting the pice)
Measurement of elevations at various coints on the east SCV connector pipe (after cutting and re-assemoling the pice)
Measurement of SDV slope Routing and c:nfiguration of air lines traced cut
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Unit 3 reacter butiding sumo (rtacter building eouipment drain tant, RSEDT) inscocted with an underwater ~V :amera and also raked fer solid objects Orainage times for the east and nest 50Vs, with and without the vent valves being coen onitoring of the ecutement (CRW) crain heacer for ::cssible vacuum w
i during the desinage time tests Individual scrams of all reds =nics failed to insert normally Manual and automatic scrams fran :cwer 10
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- hese tests and caservations failed to lead to a clear uncerstanding of tne cause of the incident. The drain aim tes*3 showed that both the east and =est $CVs would drain wnen the SCIV drain valve nas coened, wnether the SCV vent valves nere open er not. *he tim required to drain the entire system with the vent valves ocen aas teout 20 minutes. With the vent valves closed tne drainage time was estimated to te several hours, but drainage did occur. (*he postulated bicckage would not have been present during these tests.) With few excections these tests and ::servations indicated that the systan was at the tim of the tests :acaole of c:erating ncemally and as intenced. The principal exceptions aere that the low level (3 gal.) and rod stock (25 gal.) SCIV switenes did not ocerate curing the
'irst calibration fill, and the 50!Y wst vent valva ecerator was found to save a troxen air tute and an air leak. However, recorced data and ccerater recor*.s 19dicate that all of the SDIV level instrumefttation worted during at least : art Of tre incident. *he significance of tse $DIV west vent valve air leans 9as 9et :een estaolisned cut is cet Delieved to te scoreciaole. (Cn July 3 :ne mactor nas snut:cwn triefly because of a tent stem :n 53IV drain valve. :ut T/A states that this damage oc:urred after the incicent of June 23.)
Nese tests established that the rate Of crainage from t5e SCIV srsin valve :an exceed that fr'Om the east $UV 3ank. dence, tMe fact inat *he !CIV instaurents signal that little :r 9a =4ter is ; resent tnere furing crainage does 90: aecas-sarily mean that the east SCV has crained : moletely. However, ausent a teso or costructicn in the SCV connect:r pice, it neuld not :e excected that crainage Of the east SCV wuld significantly tag drainage of the SDIV.
- Fe reactor has coerated normally since being restar*.ed July 9, with 90 inci-cacions of damage to any equipment or the fuel. (See Appendix CON.)
11 l
4 Findings and conclusions 4.1 princioal Ffndings and Conclusions The review team's principal findings and conclusions are that:
a) the failure to acnieve complete insertion of 76 of the control rods in the east half of the Browns Ferry Unit 3 reactor wnen it was sanually scrassed on June 28 was due to water occupying a laqe part of the east bant of the scram discharge volume, and b) the source of this water and =ny it was present at this particular time has not been oositively determined and, cue to lack of evi-dence, may never be deter'sinacle with certainty. However, at least three plausible explanations have been developed from the availaole evidence, namely:
1.
There may nave been a solid costruction, at some ;oint between the lower end of the scram discharge volwe (SDV) and the scram discharge instrunent volume (SDIV), of sufficient si:e and strength to cause water to bact up in the east SDY. It has been calculated by GE (Ref.1) that, if the SDV sere 35-90:
full of water, the presence of this water plus the postulated costruction in the 2* connector pipe would be sufficient to account for the failure of 75 control rod drives (CRDs) to complete their strote. In order to hold up the water in the SDV the postulated costruction would have to se strong enougn
[
only te support a eclumn of water of acout 1/2' to 21/2' in l
height, depenoing on the location of the costruction in the 2" line. However, it would have had to be strong enougn largely to survive the first scram. The oostruction could suosequently have been aislodged and :ernaos disintegrated by the build up of pressure in the SDV anon the later scrams occurred. The j
source or sources of the water in the SDV could, in tais l
hypothesis, Mave been, at least in part, 1
Outlet scram valve leakage Normal water discharge during and following tae preceoing (June $) scram I
12 l
l l
The vent system (as licuid er as vapor which condensed in the SCV)
This hy;othesis nas been designated as the ":estruction hypoteesis".
2.
Traos er loco seats may have existed in the system, :artica.
larly in the 2" connector sico connecting the !CV to the SCIV, which, in conjunc*1cn with a partial vacuum in the SCV, would be capable of Oreventing crainage of water from the SCV. A particular place wnere, it is ;ostulated, a trao could have existed is in the :ortion of the 2* If ne anich forms an ex:an-sien loco. This 1:co is in the steam tunnel. No cefinite evidence of the cresence of a trao in the 2" line is availaole since the line was cut acar: (Iceking fer an costruc*icn) befort ?easurements to detect a trac were mace. In this scenario the :artial vacuum could have :een c-tatac :y c:ncensatien Of steam in the east ICV Or its vent system.
~h e i
source of steam could be either the clean racwaste (CW) sumo Or ther-ally het discharges Of CW ints the 3" pi:ing to nien the SUV vent line is also connected. ~he scur e of the mater in the !CV could have been the same as in the *:tstruction hypothesis".
In particular, water may have teen f rted inte er sucked into the scram cischarge volume througn the SUV vent line as a result of cf. charges of water frem cther sources into the clean radwaste ersin system, and retained in the SUV by either an costructica in the 2" SCV.!CIY c:nnector si:e cr a trao er 1cco seal in that line, as in hycothesis 1.
~his ny;othesis nas been designated as the " vent nycethesis".
3.
The SUV <ent valve :ay have failed in the :lesed ;ositien at the time :f :Me June 5 scram, traccing water in Me SCV for the intervening 3 weet :eriod. Like the " vent nycothesis", this
- na :recaoly -ecuires that them to a trac :r costruction in the 170' icng 2" connec cr sice since it has been demonstratec l
that the east SUV tant will : rain (sicwly) even if the vent l
1
valve is closed. This hypothesis has ceen called the " stuck valve hypothesis".
It is cossible that a combination of these *hanisms were operative.
It is 00Vicus that a McManical obstruction in the 2" line could have essen.
tially the same effect as the hypothesized trap if the castruction mere big enougn comoletely to seal off the pice. Even if the obstruction were not big enough to seal off the pice it eculd still, in effect, reduce the diameter of the 3 ice, therecy decreasing the si:e of the dio er huce in the pice neces-sary to create the hypothesized trap. Thus, the benavice of the system is exclainaele by either a trap cr a mechanical obstruction in the 2" line.
Our crincipal conclusion regarding the cause of the cresence of water in a large cart of the !DV is thus that this water was cresent cue to either an costructicn or to a traccing and partial vacuum mechanism, or to scme ccmcin-atten of these which could include failure of the vent valve to coen after the June 5 scram.
These findings and conclusiens raise certain cuestions:
'ahy is it elieved that the inecmolete scram was due to the presence of water in the SDV?
'nhat is the evidence fer the cresence of an obstruction in the 2* connector pice?
What is the evidence for the cresence of a loop seal er trao in the 2" connector pipe?
' hat is the evidence for the existence of a partial vacuum in the east SUV?
What is the evidence for the
- stuck valve hypothesis *?
!s there any suestantial evidence wnich is clearly inconsistent with the three hypothesis cutlined acove?
M
Additionally the fo11cwing cuestions were addressed:
Oid the progress of the incemolete scram sucject the fuel to any unusual stress, and If so were any hazards c-eated?
Were the resconses of the o'oerating personnel accccoriate fcr tne situation, and were the precedures sceauate?
- hese questions are discussed in the folicwing subsee:1cns of this recort.
a.2 Cause of Me !ncerclete Scram
!: mas :een concluded that it was the cresence f a large amount of water in tae 50V anica caused incemalete insertien of 76 control recs Sy 9tncering tne
'ree :isenarge of aster fecm the east 30 units. The 'ault accears is have seen nydraulic in nature, not due to any electrical :r :neumatic mal'unct'on, and not due to any menanical malfunciten in a GO Or s Mycraulic c:ntrol unit (HCU). This conclusion has teen reacned :artly by eliminatien of etner causes and :artly by direct tvidence of the hycraulic nature of the :r:-
- lem.
- he evicence :earini; :n nis :enclusion is surmar :ec in :ne ':llcwieg d
- aragracns. Pef. :). all ine tests tra ceservations cited here are incse mace :y II cr *VA :ersennel.
Electrical ~ailure he electrical scram signal is acclied to four siscrete grouas of c:ntrol reds. Some rods in all groups moved inward :: ward full insertien. Bus the failure nas not one of 'ailure of the scram signal is reach one entire greus
. oreover, all 76 of the recs wnica did not insert c:mpletely
- f the rods.
w
-oved at least ene notch. In tests made after *he event the scram circuitry functioned normally and the electrical indeoendence af each rod scram group 4s verified. The :cerators recort that they CDserved that all the blue lignts On the reacter control :anel 11gnted uo. ~his ::o incicates that all the f ndivicual ma scram valves :cened, as recuired "Or a scram. 7ese
- eservttiens and tests shew tMat the preolem was not an electrical One c:ncerned atta the scram :tetuitry.
Se :ossibility Mat the react:r manual ::ntrol system, wnten c:nt-ols and
- rograms electrical ;cwor to salves in the 30 nycraulic system 'er nor-al insertion er withdrawal :f c:ntrol recs signt 9 ave interderred with the 13 1
e e
scram, possibly by introducing a falso withdrawal signal to multiple control rods, was considered. This could not cause control rod withdrawal or arrest since the insert force in a scram is sacut three times as large as the -
withdrawal force resulting from a sanual control signal. It is therefore concluded that the problem was not one connected with the reactor manual control systes.
)
HCU Valve t.ineup The possibility that there could have been an incorrect line up of the valves on the 76 individual hydraulic control units (HCUs) was consicered, since closing of the isolation valves on the HCUs could prevent rod notion. All valve lineups were reported to be found, in tw indeoendent oost-event inspections by 2 and TVA personnel, to be correct, so this was not the cause of the partial scram.
Lack of Acewulator Pressure The possibility that the nitrogen pressure in the scram accumulators might have been too low to get complete scran of all rods was investigated. The l
control room indications of accwulator pressure during and after the,inci-dont were normal. Even had the accumulator pressure been low, scra would have occurred since the cesign of the drives is such that reactor pressure also scrans the rods. Additionally, once cnarged, the accumufators are hydraulically isolated from ese. tother and the chance of so sany random failures occurring suddenly and simultaneously is very small.
Excessive CRO or Scrsu Valve Leakage Abnormal scram valve leakage could have supplied a significant quantity of water to the east SDV bank had it been present at the time of the incident.
The possibility that those drives wnica experienced only partial insertion had suddenly developed leakage of such size as to account for the inconclete insertion was investigated. !uch leakage would have had to be very large and would have been signaled oy recorded indications of aide screed high CR0 temperatures. Inspection of the pertinent recorder charts snows no such indications. Post-event tests indicated that leakage thru closed scram valves from all the drives comeined was about 2 gpn. Post-event individual stall flow tests indicated that seal conditions were normal in the 76 drives; leakage rates were in the 1.5 - 2.0 gpa range. These results show that
'individual drive seal leakage was normal, and scram valve lestage was small at the time of the post-event test.
15
i i
l pneumatic Unstroent Af r) System Failure The possibility of a pneumatic failure has been considered. Complete and detailed information on the layout of this systes is not yet available. The availacle information is that each air-operated scras valve is fed from the instruaent air systan with no valves intervening between the closest central,
point of instrument air sucoly and the individual scram valves except for the individual saintenance valves on each HCU. The design of the systas is such that each scram valve is nonna11y held closed by air pressure. Loss of air pressure, wnether intentional, by venting the scran pilot valve, or acci-dental, opens the scram valve causing the C2D to scram. Mditionally, back-un scram valves are located on the central instrument air supply to the 370
)
individual scrus valves. Opening of these bact-up scram valves removes air i
pressure from all the scran valves, allowing than to ocen if they nave not alreacy cone so. While the air sucoly to the east and west banks of HC'Js necessarily has east and nest branches, the availaole infornation ciscloses no way in enich the air pressure in the west bent could be released without I
releasing De air pressure in the east bant also.
"he possibility Mas been considered that some malfunction 21 gat have occurred on the east branch of the snematic systas only. For example, it signt be scecu'.ated that mater had been introduced into par
- of the instraent air systas througn a maintenance or modffication error, or that the cousson instrument air dryers had failed to dry the air adecuately, resulting in water being accumulated mort in the east than in the west branch of the HCU pne m atic systas. No evidence for such events has come to light.
'he possibility has been considered that the instroent air system pressure sight have d-1fted low enough to allow the scram valves to leak excessively; air pressure is recuired to keep the valves closed. Such leakage from a large tweer of drives could 'tave been large enougn in the aggregate *.o cause the east SDV partially to fill with ester, ever, if the 170' long 2" connector pipe had not been costructed. However, there is no record of a low instru-ment air syste pressure, and without more knowledge of the details of the instement air systas it is not clear how a pressure deficiency in that system could have affected only those scram valves on the east side of the reactor. In any event a deficiency in air pressure would have interferred with scrasuting only througn prenature filling of the SDV sith water since it is loss of air pressure wnich causes the scess valves to open.
"hus, there 17
5 is no evidence that the fault was a pnematic one. However, NSAC intends to investigate this possibility further in its longer range generic safety
~
studies.
presence of Vater in East SDY j
The po'ssibility that the failure to insert all the rods was due tc the pre-sence of a large amount of water in the east SDV was suggested almost inusediately by those wno were on the scene or were notified pecmotly. The principal points of evicence were:
All the control rods wnich failed tc insert completely discharged into the east SDY. Those on the west SDV all scrasuned completely, except for the one rod sentioned in section 3 of this report, wnich stooped at position 02.
The time to receipt of the 50 gallon level signal from the SDIY was about 18 seconds. The fill time for the 10 preceding scrams on unit 3 fell between 12 seconds and 54 seconos. It is thus imclied tnat a suestantial volume of water was alreacy present in tre SCVs at the time of the scram althougn it cannot be determined onwther this water was in the east Or west SUV or in both.
The scram was re-set and repeated three times after the initial scram. Each time the rods which were still not fully in moved toward and finally reached full insertion on the last scram. Thi s behavior is consistent with the pnysical picture that between each re-set and the next scram water was draining out of the east SDY at a slow rate, making room for more water to enter the east SDV from the east CRDs. Subsequent sessurements of water drainage rate from full SDYs indicated that the east bank drains in about 30 minutes with the vent valve open. The west aant crains in secut 10 sin-utes. The crain times between series were 93, 53 and 160 seconos.
Thus it would be exoected that the volme voided during the crain times between scrans would be sufficient to accesunodate the dis-charge from only a fraction of the still not inserted rods. (The discharge per full scrse is about 1 gallon ;er rod for drives enien are new or newly maintained. This is made un of 0.7 gallon dis-placement and 0.3 3allon leatage. With use this may be increased by seal near to 2.5 gal / red, full out to full in.
The subsequent 13
i l
testing showed that the 3F-3 drive seals were in good condition.)
It is evident that the time between scrans was insufficient to drain sore than a small fraction of the SDY volse particularly if the SDY connector pipe were sartially costructed. Since the first scram must have essentially filled both brancnes of the SDV it would not be expected that the succeeding scrues would necessarily be comolete if the postulated 00struction were still present.
General Electric has calculated (Ref.1) that the caserved senavior could be accounted for if (a) the east SDV already contained acout 35-70% of its volse filled with water at the time of the first scras and if (b) there were a partial costruction in the connector pipe. GE Dases these calculations on earlier tests on a single CRD and its accropriate disenarge volume in a full scale test accaratus, a.3 Evicence for tne *0bstruction Hvectnesis*
It 9as seen theorized that the presence of water in the east bank of the scrsn 31senarie volune was due to an costruction in the 2* senedule 150 pice
.nien has an !.D. of aDout 1.59 inenes and connects the IDV anc ce scram discharge ins #Jaent volume. Attemots to confim this taeory have not yielded :ositive results aither for or against the theory.
The unit 3 reactor suilding ecutoment drain sumo, into whien the SDIV dis-enaries, was inspected. :t contained some sludge but no coject was found wnien could block a 2* pipe. The sume inspection did not include draining the suo comoletelyl Instead the bottom of the suso was razed, and insoected witn an under-water TV camers. The examination of the suum was thus incon-clusive and provided no support for the "costruction hypothesis".
After the incident the east connector pige was cut my TIA in six places and esca section of mice was roceed Out with a metal tape. No :ostruction was found. h east SDY was inspected by sating cuts at eacn connection between the 5* SDV volmes and their respective 1" vent lines. Fiber cotics and barescopes were used to inspect the SDV $* volmes. Small cuantities of silt
.ere observed but 90 larger objects were seen. It is conceivaale that me silt could 14ve accumulated and ;ernaos solidified at one point in me 2" line (say, at the excension 1000 in the steam tunnel) *o a :egree suca that c:molete or partial blockage of the line occurred. Ouring cost-incident 19 l
i
)
i l
examinations some silt or crud was observed in ifnes leading to the SDIY level measuring instruments, partially clogging these lines.
It has been theorized that an oostruction could have formed in the 2" con-nector pipe as a result of flushing of sitt from the SDV banks (this had been done only once) in orcer to reduce local ractation levels. The flushing did little more than to push the local hot soots fran the SDV 6* piping into the s:saller 2" line according to TIA outage personnel. The silt is theorized to have formed a soft plug, possibly fn the expansion loop in the 2' connector line. This loco is located in the steam tunnel wnere the hign temoerature may have hardened the soft plug into a Marc partial obstruction.
Presumably, if such an oestruction had been cresent, it could have been swoot out by the hign oressure differential resulting from the opening of the scram disenar;e valves and dispersed 50 that little if any evidence of it would Oe expected to te left after five scrams in rapid succession. :n any event, none has been found.
Curing the post-event investigation my TIA the SDY heacers.ere again flusned out wim water. Only a little silt was caserved in the discharge. It as coserved that the flushing procuced some movement of the previously existing radioactively hot spots in the heacers tcward their discharge enas, i.e., in the direction of the flushing flow. Presumanly the hot spots represented solid radioactive sacerials. However, these hot spots do not necessarily confire the presence of materials capable of clogging the connector pipe.
Also, earlier scrues, such as that on June 6, gave no hint of an oestruc-tion. Thus, wnile the presence of a nochanical obstruction cannot be ruled out, no direct evidence for it has been found.
Some indirect evidence for an obstruction may exist in the following. A mathematical nadal of the hydraulic aspects of the CRD-SDV-SDIY ccaclex has been devised 5y General Electric as earlier noted (Ref.1). Details of the model apoear in Ref. 3.
Thid model reproduces correctly the behavior of a single CRD and its ' share
- of the SDY in the San Jose test facility.
Accordingly the model has been used by GE to predict the behavior of the entire 3rowns Ferry 3 CRD-SDV-SDIY system. Wen this was cone it was fcund that in order to sake the model reproduce the behavior of the 3rowns Fern 3 system as caserved on June 23 it was necessary to assume that the east SDV
.as 35-9C% full of water and that the frictional loss coefficient of the 20 l
i
+
connec*Ar pipe was six times as large as would be expected from standard hydraulic correlations. Bis could be taken as indirect evidence of an costruction in that Dipe.
However, there are uncertainties weten make this conclusion cuestionaDie.
De tw aspects of observed Browns Fer y 3 benavior enich it.es cesired to make the model satch were I
al the fact that 76 rods on the east side inserted only partially or, 9ere precisely, that there was only 47*, average insertion of those east side control rods not alreacy fully inserted, and 3) ne recort that the 50 gallon SDIY signal mes received 13 secones (19 seconds by some accounts) after tne first scram. If the con-nector pipe Mad nad a nornal loss ccefficient the time to me 50 gallon signal would have been 3-10 seconds according to the mocel.
- t is not clear that either tee socal or the data am sufficiently etliaole to justify concluding that thert.as a meenanical.00struction present. De 30 -ity of the instrunentation used to measure the SDIY level to rescond caractly to very escid thanges in level, sucn as must have occurrto in tais case is.iot known. Also, the arrangement of the instrument piping is sucn as tc take it difficult to interpret level indications during the seriod of rapid filling of the SDIV, particularly if triert were some partial sinoing or blockage of them my crud, as was recorted.
4.4 Evidence for the " Vent Hveethesis*
De principal features of the
- vent hypotnesis" are taat:
De SDV, SDIY and c:nnected pioing, after eacn scrse, could become filled with steam drawn in trougn the SDV vents from tne comolex systas of drains into =nica other inan SDV vents and the SDIV train lines connect. (Some parts of this arsin sysam receive relatively hot water from various sources in the reactor building. Dis is any there is a cooler for the RBEDT into wnica all these drains dis-cnarge and this is any staae can te seen rising from tais tant wnen it is coen to the reactor building at:nosonert). Another :ossible mecnanise my anica the IDV could bec:me filled witn s*Jan is tne 21 l
i flashing of hot water, resulting frem a scram, upon draining the system. It is not kncd wnsther this occurred in this incicent.
Some of the steam drawn into the 50V vent may condense en the rela-tively cool walls of the 1* vent pice, the condensate ficwing by gravity to the SCV vent valve wnich is located in a heri: ental run of pice at a level about 5' below the hign point of the vent line and at that coint forming a seal or tao.
There is no direct evi-dance that this actually occurred at !F-3, but there is no way to I
have cetected it if it had Occurred. Therefore, its cccurnnce cannot be excluded.
x x 1
The connector pipe between the SCV and the EDIV has an cverall fall of abcut l'10* from end to end. (Ref. 5). This 21ce is senecule 150, having a ncminal I.D. cf 1.59".
If, at any point in the 1*C' run, them is either a Icw scot er hign spot differing more than about 1.59" in elevation from the inrediately adjacent ;1cing, such a spot will constitute a trao, sucn that if sucticn is maintained in the 31oing above it, a water column can te stably succertec in :nat pising even thougn the piping is Ocen anc free Of any meenanical costruction.
- 9as not been determined anothe'r the low :oint (or high point) in :ne connectcr 31pe and the traoping acticn of the vent valve necessary for this scenario were actually : resent. *he connector pipe c:ntains an excansion 1 coo about 13' long in a nominally horizontal plane. This loco is the rest j
precaole site for the hypothesi:ed hign point er low point to have existed.
- he slope of the piping in this Icoo at the time of the incident is unknown since the Dioing was cut apart for internal inspection before any measurt-M nts were made. *he I.D. of the elbows in the loop may be smaller than that ence a local Sign ;oint of 1.69" cc ;ossibly less would have of the 31ce. u sufficed :s form a trao. It Mas teen stated that pipe restraints are ; resent on the loco, but the extent to eich mice movement is prevented is not known. It may be significant that the loco is located in the steam tunnel, wnere amoient temperatures are usually high. Thermal expansicn c:uld :en-ceivably waro the 31 ping out of 1:s cold configuratien sufficiently to produce the necessary trac, even if the cold configuration were not such as to rocuce a trio. It is c ncluced tnat definite kncwledge Of the sic:es of 22
l l
t l
l parts of the 1000 at the time of the incident is lacking anc ;rebably can never te established.
Water can arrive in the CV frem CRC leakage as mell as by c:ndensation, and even ce 2 spn ieakage este threugn the scram discharge valves anich was reasured f:r all the 30s ::gether after the incident would :e sufficient essentially to fill the system in ueveral days if nere of it escaced. iia the IDIV drain valve.
L
~5f, as succosed in the vent hy:cthesis, it aos suo-at.-eseneric press'are * -
the SCV wnich permitted the SCV to fill :o aceut, !!-?C: cf 1:s volume eith mater, and if the trio in the connect:r pice aos iccated, as succosec, in ce steam tuore1 the sue:1cn would have had to be sufficient c succor: a column 3
- f aater of 9e'Sht ot -77re inan acout 2'.
det aatar enters :ne Or another
- ar :f the :!ean racwaste Orsin system frecuently, if 9et centinucusly.
Steam frem this mater aculd :e availaole to the CV vents since the CV vents
- nnect into the same C2W 2rsin system as : hose hatter streams. Visual ceservatten :f the RBEDT nas snown visitie currents :f steam ra sing fr:m 1:
at times.
A : molicatien in the analysis :f the systen <f s-a-vis the venting 9y c hesis ts the fact that there were several vents in the 3W :rsin system <nown to :e ccen to the at.wsonert. Scme of Oese vents aert Of 1/2" si:e, but it is also recorted by *VA that there is a 4* vent :o the at..os:nert at the reactor water clean go overf1cw. *hese vents art avenues Oy anicn air f4y enter the C2W system, creating an air / steam liixture wnich, if the C2W drain system aers at sun-atemscheric pressurt as hypothest:ed, 'aculd then tend to be drawn into the SCV and SDIV, finally filling than nith air to the point that inflow of the air / steam mixture duld cease. It would be thougnt that these vents aculd be sufficient :s Ortvent the c taticn f any suostantially sun-at.7cscneric :rtssurt in 2e 3W system and hence in the ICV Or CIV. Y et.
. nile :enoucting f ncividual r:c scram tests :n ht similar system at !F-1,
'e 3 gallon alar i en the CIV came in shcrtly after the sec:nc rea scranrod snd the ;rtsence :f natar in the SDIY was seriff ec.
~his incident :ccurred in 2rewns Fer y 1 :n 'uly ;9,1980. While c:ncucting sertm tests, ce 3 ; allen alarm :n the CIV ca o in sncrtly after the sec:nd red aas scranneo. *he IDIY crain valve and the CV vent valves aere totn
- cen as is nor al f:r incividual rec scram :1 ming tas:s. "1trascnic tasting 23 1
l l
I disclosed that about 7 gallons of water wa,s standing in the SDIY with no water indicated in the SDVs. Subsequently, a ? lug was removed fra :he bottom of the 3 gallon SDIY float switch assemoly. The' result was that air was drawn in to the open hole for several minutes, shcwing that a sun-
}
e stmosoneric pressure existed in the SDIV. Once the subat=osoneric pressure
~
was relieved, the water in the !DIY drained successfully. Several more rods were subsecuently scram-timed without recetition of the ;henomenon.
- NSAC and INPO have teen informed (Ref. 3) that aeditional incidents Itke that of July 19 have since been cDserved at EF-1 again. It is reported also that the July 19 incident symptoms (recei;t of the 3 gallon level signal) nave since been reproduced by the excedient of restricting the entry of cold water into the CRW drain system, admitting only relatively het water. It is recorted that =nen this is cone the 3 gallen !DIV level alarm can te received during normal cceraticn, and that :Me ccen Yf vents en the 565' level (acave referred to) nave been ceservec to enit steam. The cresence of a water column upstream from the !DIV drain valve has been detected altrasenically uncer these conditiens and accarently under more normal conditiens also.
(Ref. 3). No water was detectec in the 5* SUV headers, and no standing water has been detected in any of the testing done en all U.S. 3'n'Rs since One June 23 incident at 3rewns Ferry 3.
The 3F-1 coservations show that it is possible for a subatmosoneric pressure to occur in the SDIV (and presumably therefore in the !DV also) even thcugn the vent and drain valves are coen. Precise identification of the locations of the traps *nich permit this occurrence is not ;ossible withcut more detailed analysis of the system.
a.5 The ' Stuck Valve '4voothesis' It has been cointed out that, if the east vent valve had failed to ccen follcwing the June 5 scram, and if there ere a partial er ccmolete ecstruc-tion er a trao in the connector nice, water frem the June i scram could still have been in the east EDV on June 23.
After the June 23 incident the east vent valve was disassemoled. Nothing aDnormal was found. The ocerator has an indication in the control ecom of the status of this valve, derived frem valve stem position (not solenoid energi:stien). It is consicered cuite unlikely that the acerater nould have
' ailed to notice the light signifying that the valve was closed fer three 22
weeks. Thus it is considered unlikely that the " stuck valve hypothesis
- is valid.
A blockage at any coint in the vent line would have had the same affect as if the vent valve nad been closed. To investigate the question of wnether the vent line was ccen, the plant personnel c:nnected a small vacuum ;uma to the vent piping en the cownstreaI (RSEDT) side of the vent valve.
The results of the test acceared to show that there was no bicekage in :he cwever, :Me cenditions of the test were such that those cer.
vent line. w ferming them are reluctant to attach much significance to them, 4.6 Effect of Scrw on ruel
- he fact that all :Me reds wnich failed to insert fully we e in the same nalf of ne react:r could :e viewed as an out-of-secuence set of red movements,
- nus raising the cuestien of wnether any unusual stress was :ut en :ne fuel.
General Electric has : erd:r-ed an analysis o cetermine wnether :Me erttical
- ower ratio (CPR) of any Of the 'uel ent telew the licensed 1131 for :ne limiting euncle curing the transtent.
'*he :ritical :cwer ratic is :efired as fundle ecwer at anics transitten boiline star s s#*
Actual fuei : uncle ;cwor
- nitial ;cwor, flow and red ;ositions were the actual ones at the start of
At the end of the first scram the calculated minimum CPR.as 9.34 (Ref. 7) There are no indications against the assumption : hat the change in NPR frem 2.21 to 9.24 during the transient was monotenic. The recirculatten
- umes c:ntinued at constant s eed curing the transient and the -eactor
- ressure fell smcothly frem 920 :sig to 900 :sig with no recorced :ressure sotke nich signt cause a ;cwer spike.
i Core average fission :ower at Me end of the first scram was estimated, from Iccal :cwer range mniter (L?RM) readings, to te accut 2 Of rated :cwer.
Decay :cwer.4s also acoreximately 2*. Of rated :cwer. Ocolant flow througn
- he core was estimated to be accut 21*. of full rated ficw.
s
O 9
Recorded LPRM readings were examined in order to ascertain, if possible, wnether the red pattar9 resulting from the first scram had permitted the develocment cf any local regions in which there was a sufficient mis-match of power and flov to justify concern aoout potential fuel damage. While this concern ha: not been resolved in this specific case, further analysis is pl.anned to ex: fore the questien of wnether there are partial scram c:nditions which could carry the potential for fuel damage.
f
- he LPRM readings in the present case indicated that there may have been local regions w3ere neutron power was in the range of 10-15t of rated l
power. While gross core coolant flow is known, the ficw thr0ugn those channels in the locally high ;ower regicns is not known.
Rec:rded coolant and off gas radioactivity levels before and after the scram, as disolayed in Accendix CON, show no significant increase in released activity since June 23. It is thus implied that the fuel received no accreciable short term damage.
4.7 Ceerster aeseense Accendix CPS centains information On the pertinent ;recedures whien aere in effect at the ti:ne of the incident. The ;recedures were not written to incluce the possibility that a large numcer (not just a few) Of reds ould fail to insert comoletely since they called for the operat:r to scram each un-inserted red individually. It is possille that sequential individual ecd insertion could have been used in the June 23 event. However, if the oper-at:r (or shift engineer) regarded the situation anich he saw as one which was not covered by written precedure, it was reasonaole for him to do wnat he did, f.e., attempt receatedly to get a full scram of the rods en masse, rather than scransning each one individually. Under the circumstances crevailing at the time, the ccerators responded in an appropriate manner. In the present case it would 9 ave taken suostantially longer to carry out 76 individual red scrams than it actually teor to car y cut a en masse scrams, in soite of the fact that individual red scrams are carried cet alth the drain and vent valves ccen, thus facilitating drainage of the SCV and SDIV.
'he fact that it was necessary for the aceraters to deal with a situatien Of this type emchasi:es the desiracility of having procedures wnich have 3rcacer
- verage of ctential ccerating ;rcolems.
25
~he review team also discussed the matter of the acercoriateness of not injecting socium ;entaborate (the 'Stancey '.f auid Control" Or SLC) in :nis incicent. It is clear that, :ecause the react:r nas breught to a safe snut.
own condition without '1.0, SLC injection was r.ct necessary in this case.
Se crocedure governing SLC injection olaces the resconsibility for cecicing to inject (ce not to inject) cn the shift engineer er his assistant. In this case, using the information available, an accectable cecision was :r.aoe. So far as could be ascertained, no soecific criteria or quicelines fcr mating such tecisions have been set town. If One concition of the reac:Or (e.g.,
cwer level) at the time of the scram had been different than it was, and if
- ne scram had been one anf cn was necessary for a reason of safety, the !LC cecision 1ignt have had to be mace uncer 11ere adverse concitions than in this case. New crocecures governing this sucject are now in effect at 3rewns
~er y :ased on NUREG-0460, but their basis % net clearly cefinec in NUREG-C460.
a.3 1 ale of tse vent and Orsin Yalvas
~he ICV vent and the IDIV drain valves normally have Only the function af attaining aate* resulting frsn a scram. ano,.nen tre Ocerst:r sieets, :(
-eleasing Mat eter to the atact:r tuilding crain tanz. dewever, star-tng at a few see:rcs after the scram 1:self, tre vent and Crain valves :?ose anc
- ec me :ar: Of the :rimary :ressurt :cundary. If they should 'til : !cse they *cula create a small break LCCA with ::alant disenar;e cirectly :: the reacter building. If the coolant were nighly c:ntaminated, Derat:r ac:ess to vital equipment could :e imcaired. It is likewise necessary :nat the vent anc crain valves rot fail to coen anon recuired, since, in the event of a cartial scese it is necessary reliaely to ocen these valses in orcer to emoty the IDV in precarstion for a follow-on attemot to ccmclete the scram.
4.? Ancillarv Cuestions
- n :ne ecurse of *Me study of :ne 3F-3 incident it has :een accessary to icot
- r'efly at various ascects of the scram system not alreacy sc:ressec, sucn as ne :neumatic system, the assignment of the individual rocs to -Me two scram discharge headers, the reliability of ecuipment used for level incica:f on in the !DIV, and the interaction :etween the tur51ne/concenser system inc the esac:ce in the event of a cartial scram. So far as known these features of the slant played no adverse role in the event, but accisional ;ene-ic stucy accears to te naraantec. C:nsicerati:n of these ::cies will te su:;ec:
t later 15AC study anc *eoorting.
27 l
4.10 Summarv of Conclusions To summarize the fortgoing discussion, it is concluded that The June 28 partial failure to scram at Browns Fer y 3 was caused by water occupykng a large fraction of the volume of the east scram-discharge volume.
The origin of this water, how it got into the east SDV Dant and.ny it stayed there are and proosely will remain obscure, although several plausible explanations nave been advanced. None of these explanations is contradicted by the available evidence, but also none of them has a complete factual supporting 3 asis. The principal explanations are:
There may have been an costrue:1on in the 170' long 2" connector Dice frem tne SDV to the SDIV.
A comoination of trapping action in the vent line anc SCV-SDIV connector pige together lvith concensatten of steam in the SCY may have occurred.
Any of the foregoing causes may have been aggravated by nemen-tary pressure surges in the CRW drain system such as could be caused by large influxes of water from systems other than the SCV, particularly if that water were hot.
Incioental examination of various parts of *he 3WR scram system suggests further generic study of them by MSAC.
Re-examination of the ;rocedurts governing acticns *o be taken in the avent of a partial fatlure to scram, and of the Bases for deciding whether to inject sodium ;entacorate, suggests further study by eaca utility.
i
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- )llM l" T T WNI5 Sit elioWNS llidi'3~
~
Jutil ?!!, 19till Plasit 5t stas Prior to time $t as t of thee i va'nt.
lis owns f erry Unit 3 cemenenced a rout ine shutdown to perform aiaintenance oss a reactor feedwater laaemp discharge line. The inillai power reduction was perforened at a rate of ti anee/ min fruen titl2 wwe to 542 anse by reakscing recirculation flow, t
With time recirculation laanii operating at ininimies specil, 4 Littlunal power reiluction to 390 anse was accomplished by nornial insertion of selected control rods.
ihe plant conditions following this power reduction were as follows:
Power level 3t4 of kated 6
M Core Ilow 39 x 10 lies. Ier hr.
e,o Neactor Psessuie 920 isi
~
l Vessel level 35 ini.hes (203 inclies above the top of the act6ve fuel)
Generator Giatput 390 864 6
Steam flow 4.9 a 10 lbs. per 1.r.
Feedwater flow 4.9 m 118 lbs. per ler.
Control Hod pattern 151 cnntrol sods were fully withdrawei 10 rods were fully inserted lit roels wese at intersuediate loosition ($ce liefee ence 1)
Ilime I' vent kemasks askt keferences 01 31 Its A suasuaal sos am was f ailliated to causigileta-W6these several secosids af ter the scram, in accordance with 4
t
^1 4
line 1 vent keisarks asul Neferences the sliutdown. Ihis was a normal part ut sioimal procediares, tiie scr.am disclearge volume (SDV) bypass Llie Bs ows.s f erry sleutdown procedure, switc8 was placett in " bypass" posillosi, the reactor wode switch %s placcil is "sinst lown" posit tori, ased insertion of the souece rasigis selonitors (SkMs) and intermediate r'ange monitors (ikMs) were infilated.
Within several seconds (approximately 5 to 10) after this scrassi, operating personnel noted that:
lhe blue scram lights and the scrass accumulator lights were lit as expected.
A number of rs,ds on the east side of the reactor were indic.ted to te not fully inserted.
During this entire sequence of events, opes eting personnel seported that they observed that key thermal hydraulic par.smeters (pressure, level, temperatures and flows) wers*
,Q well within nosmal limits for ordinary scrams. Ilowever a A
seumber of control rods were not fully inserted.
Subsequently, a review of plant recorders and process computer printout showed:
A total of 11 rods did not tully" Insert. Of these, seven rods settled at either position 02 or 04.
lhe extent of insertion varied irtwa 5 percent of fully inserted to 95 percent cf fully inserted for these partially inserted rods. Ilic rod pattern at this time is shown by Fig. 50t~1.
Massy of Llie local pows:r rasigir seiosiltors (t pHMs) in the east side of fle reaClor and in the upper region (level C&D) Indicated above zero values (See i19 50[-2).
Ihe reddisigs of the fully inserted ikMs were dl1lll'oXilhately mid-rafigi! oil range five or stN.
e e
=
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lime tvent Hemarks asid lief eressces A review of IPlet readings leidicated tital fissinasi power in one or amare localized regions of the core could have been in the range of 10-15% of full rated power Joe to rods not being completeiy inserted in these regions.
During and after this scram, no other unusual or unesplained variations in plant parameters were observed.
Iotal isidicated steam flow droppeil sharply during this scr.sm to approntmately 10 to 15 percent of the pre-scram value.
Iteactor pressure decreased fram 920 to approximately 900 psi (this pressure rematoed approntmately cofisteelt tlirougliout tlie reliialader of tleeevent.)
fj Core flam decreased to 22 x 1816 lbs. per hr.
Ihis 4,
decrease was due to the loss of natural circulatiosa drivisig liend wisen reactor power was reduced, liasea os stemini fit. is sic.t tosi wiiscl. i.dr be inaccus ate at low scale values, tlic liest gesieration within the reactor was close to the local gestes'allon expected f rom decay heat alusic, line Isisertion of a
tlic rods had significantly realiaced power level.
01 31 24 t ow reactor-<, eater level trip occurs ed, lhe water level decrease was due to void collapse following (Ihn a.orsespanels to level 3 edikh is the scroisi. I riian plasit secorders it was later verifieil that it10.5 inches al;ove the top of the miniman water level reached during this event remained active fuel.)
above the level required for emergency core cooling system init iat ion.
(this corresponds to level 2 editch is llG Intlies aliove the top of the active fuel.)
Ihe level variat lon, includisig entanimimis anil missimimi valises, was well within the espected resige during a norm.nl scram.
l e
b
6 Ilme Lvent Nessas Ls asul Neferences 01 31 34 The scr am discharge volume "high-high" This occurred 18 seconds after the manual scram. this level was reached.
.normally occurs approximately 40 seconds after a scram.
Subsequent investigation confirmed that all "high-high" lustrument volume level switches were properly calibrated asid f usiClloning.
n1 31 40 The main tusblue was tripped as part of normal psocedure.
01 32 01 the low seactor water level trip was During the interval between 01 32 01 asul 01 3h 43 storinal reset.
water level was achieved and one feedwater pump, two condensate lu2 ster pumps and one condensate pump were then secured.
01 35 43 The scrans was reset and the hydraulic tow pressure switch resets at approximately 950 psig, control unit accumulators were recharged Normal accumulator nitrogen pressure is 1150 psig.
until the lights cleared.
f$
01 31 20 A second scram was masiually inttisted for Within several seconds af ter this scram, operating i.
the purpose of' inserting the remaining personnel observed that:
i U rods.
All blue scram lights anal accussalator lights were lit asui scrain group pilot lights were out as eng=cted.
Hud movement was tsuficated, but sinut tosi appeared slower j
than normal.
Some rods were indicated to he snot fully inserted.
Subsequent review of plant recorders ased printouts
+
indicated that:
A total of 59 rods were still not fully inserted. the rod pattern at this line is shown by Fig. 50E-3. Major plant parasecters (steam flow, core flow, water level askl s edClos' pressure) remained essentially unclienged 4hroughoest the scram.
,p'
8 gen tvent Nemasss and kelerences lluctuatiosis ist ikH sensur reddisegs ptevent detersnination of actual ettects due to the scram.
01 38 19 line scram was reset asul the hydraulic control unit occameulators reclearged until the Ilijits cleased.
01 39 12 A third munual scram was initiateil.
Olerating per sosesiel c'eserved liial:
All blue scsam lights and.ccumulator lights were lit asui scram gringe pilot lights were out.
Rod movemesit was indicated.
Sonc rods were indicated to be not fully inserted.
Information obtained later tross plant recorders showed tinat :
E A total of 41 rods were still not fully inserted. Ihe rod pattersi at this t asm: is shown in figure 50[-4.
IpHH readirigs all leidicated *downscele" eacept 4041C wheth was f ailed.
All siajor parameters discussed above, remaisied approalmately constant througliunt this scram.
01 42 31 the scres was seset for the third time and the leydranslic control unit accomm:13 tors wese seclearged until tiie lights cleared.
01 4h 11 Ihe operator placed time screen discharge Operalistil lersunsiel observed that:
vuleme (SDV) bypass switch in *siosmal" whicle resulted ist a scram since the SIN Hod insce t ion rate appeared stormal for a scram.
was saut actosally fully de alswd. Ilo ts was tise fourth scram in this stepsence All blue scram liglets asid accessulator liglets were lit of events.
asul scr am gs'oiqi pilot liglets wese oest.
~
l l
lime fuent Ilensarks and Refereswys All rods we e indicated to be fully inserted as shown in figure 50E-5.
Plant parameters and cosulltions were as normally espected following a scram.
01 % 30 The operator initiated a manual scram (confirmatory).
01 46 43 line scrans was reset.
01 57 34 The discharge volume high water level trips (50 gallon scram trips) cleared.
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aPoENDIX CES SYST9 CE!C2!PTION CCNTRCL 4(X) CRIVE HYCRAULIC SYSG I.
SYSTDi FUNCTION Peneral - The control red drive system ukes enanges in core reactivity 4
a by incrementally ;:osittening neutron-abscroing control accs wt:af n Me reactor core in response to manual c:ntrol signals. The system is also cacaole of cuicx1y snutting dcun the reac::e (scram) in emergency situ-ations by rapidly inserting all withdrawn c:ntrol reda into the c:re in resconse to manual cr autcmatic signals.
3.
- he func:f ons of the system are to:
1.
wove the control accs in ei*her direction at c:ntrollec rates, latening the red stationary when cc: recuestec :o ove.
2.
Charge HC'J scram accumulat:rs.
2.
2rovide c oling ater to crive ecnaniscs.
II. *AJCR SY!Tei CCNPCNENTS (Refer to Fig. CES-1)
A.
Two 1C0". capacity, 5 stage, centrifugal aumes.
3.
Two 1C05 capacity drive water (discharge) fitters.
i r
1.
Darallel f nstalled, 50 sicren cartridge tyce.
- . Two :CC% :Joacity flew ::ntrol valves.
Air ccerated, balanceo trdm gloce valves :esitionec by automatic flew :entrol 1000 er lecal manual control stations.
2.
Nor-nally ::ntrollec in aut:matic xce to give accreximately ic
- m system flew.
OEI-1 r
D.
One drive water pressure c:atrol valve.
1.
Motor operated valve positioned by coeratcr to maintain approximately 250 psi differential ':etween drive water head and reactor pressure.
E.
One :coling eter pressure c:ntrol valve; 1.
Mater operated valve positioned by ocerator to maintain the c:oling water header accroxinately 20 psi above reacter pressure, to provice cooling ficw.
F.
Two sets of solenoid ocerated stab 11:ing valves.
G.
uyersulic centrol units (Fig. OES-2) 1.
Provide centrol interface between hydraulic system and incividual GCs.
h 2.
!even hydraulic picing Msers with manual snut-off valves at esca HCU proviced as fc11cws:
a.
Insert Mser - Line c:nnecting HCU directional c:ntrol manifold to representive GD under pisten area.
3.
Withdraw Mser - Line connecting HCU directional centrol manifold to respective GO over pisten area.
c.
Cooline water Mser - Line connecting hycraulic system
- cling header to GO inser*. line.
d.
Exnaust Mser - Line ::nnecting HCU directional centrol manifold and hydraulic systam return heacer.
e.
SMve 4ter Mser - Line c:nnecting system drive water header to HCU directional control manifold. Provices hydraulic ;ressure during insert, uniatch and withcraw medes of GD c erstion.
OES-2
t P
f.
Chareine water r4ser - Line connects hydraulic system charging "eacer to water sice of scram accumulater.
Yaf ntains scram accumulat:r at ;ueo cisenarge :ressure.
g.
Scram disenaree riser - Line connects the CRC over sisten area to the Scram Cischarge Volume via :ne witneraw riser and outlet scram valve.
3.
Oirectienal Centrel Vanf
- Id consists of a 4-.ay biccx ranifcic to scr: CRD nycraulic flows tetween :ne CRC ecnanism via the insert and nitacraw risers and the hydraulic system via :ne drive water sucaly and exhaust riser during normal roc fevement.
2 Scrim fec *en :ensists of :Me felicwing PC'J reuntac ::m:enects to allew escid inser: ten Of ne centrol - d in rescense :s signals frem the RPS.
3 icrim Valves - Sno. ncrmally cicsoc, air ::ertted 110:e valves. deid cicsec by instrurent air via two s lencic
- ersted scram silet valves, eacn :cwered frem :ne :f ne two 8PS tric cnannels anc ::nnectec :nysically suen :na:
cta solencics Tust ce-energi:e to vent air ' rem anc :s Ocen the scesa valves.
(1) !nlet !crim Yalve, wnen c en ::nnects the ater sice of the scram accumulator directly via the insert heacer to the CR0 uncer pist:n area.
(2) Cutlet !cetm Valve. nMen Ocen, :ennects Me CRC Over
[
sitten area, via the ni ndesw riser, to One scrim cisenarge volume.
3.
! cram accurulater ::nsists of ;isten tyce, ! gal ca:acity, accumulat:r connected to a crechargee '4; :yliacer a: :ne bott:m and the insert rdser via the inlet scram val <e a
- ne t00.
OES-3
4 c.
System Resoonse During Scram - When reactor scram is initiated by the reactor protection system (RPS) the inlet and outlet scram valves open to admit the pressure in the scram accumulator to the area below the drive piston and to vent the area above the piston *J the scram discharge headers. The scram discharge headers are maintained at
~
atmospheric pressure during nor,nal coerstion. The large differential pressures applied to the drive piston area produce a large uoward force on the index tube and control rod, giving the rod a nigh initial acceleration and providing a large margin of force to overcome possible friction or binding in the drive line. The characteristics of the CRD hydraulic system are such that the CRD index tuce rapidly accelerates to a scram velocity of approximately 5'/sec. As the incex tune closes off ports in the cylinder wall (i.e., buffer holes in the piston tuce), the increasing resistance to water ficw reduces the speed of the index tune. 3e numoer, sice, and scacing of Me buffer Moles in the CRD piston tuce enich are progressively closed are chosen to crovide a gradual deceleration of index tune movement.
Each CRD puts approximately 2.5 gallons of water inta the SDV for a maximum scram stroke; the water side of the scrse accumulator holds approximately 1.5 times this volume. There is adequate caoacity in the hydraulic system accumulator supplying each CRD to comalete a scram stroke in the required time at low reactor pressure. At nign reactor pressures, however, the accumulator provides l
the initial surge of water, but the normal acc:anulator discharge and line losses quickly reduce the pressure at the CRD to a level ecual to reactor ;ressure. This causes the ball check valve (built into the CR0 flange directly below *he under-piston water port) to shift its position and somit reactor water under the drive piston, thus l
admitting water from the accumulator and from the reactor vessel. Reactor pressure, therefore, sucolies the force required to ecmolete the scram stroke at higner reactor X3-4 l
l
l pressures, dile the accumulator alone suco11es the feres for low-pressure scrams.
III. SCRM JISCHARGE VCLL'PE (Fig. CES-3)
A.
General - Provided to receive and centain the water exnausted from all CRCs during scram. Curing a scram the CV becomes : art of the ;:Mmary -
system :ressure boundsry. Consists of header ::1oing dich connects to the c'CU scram discharge risers. *he east and west sectiens Of this
- f oi' g drain to a corinon instrument volume. The east and est Meacers n
are equipped with vent valves. Since a minimum 50V capacity is recuired to allow the water displaced during scram to accumulate in the GV 4
- series of level switches is provided en the instrument volume to warn of diminisning cacacity:
1 scram discharge volume not drained (3 gallens)
I rod 51ccx (25 gallens) 4 !DV Hi Hi scram (50 gallens) 3.
!CV Veat and Orsin - Air *o ::en, ner ally Ocen valves.nien taintain SCV drained and vented to at.:ossneMc :ressure curing ner tal ::er-scien. Valves are held ::en :y instrament air fron scram ::ilet air needer via a 3-way douele solenoid dume valve. Eacn solenoid is normally energi:ed from one of the :m react:r rotection systen tri; channels. When both solenoids are de-energi:ed (scram) the valve exhausts the air heacer downstream allowing the vents and crain to : lose by soring ;:ressure.
!ath the CV vent lines and the SIV drain If nw disenarse into the clean racwaste drain system. This is a c:molex ar*angement :f ;1steg anich
~
takes :ratnage frem secut 50 :oints in the reactor tuficing ric Ocliects it in :ne reacter building ecui: ment drain tanz. (Pef. 4) (Ref. 5), a lined stangular c:ncrete sumo of accut 6240 gallen capacity bottomed at elevation 5C9' in the reacter cutiding. Excect unen being ins:ected the Sco of the tank is closed with a :encrete plug.
- he RECT is ecuic:ed with cures fer removal :f the water and f:r
- assing the aatar througn 1 ::aler anen necassary. !everal ;otential OEI-5
4 sources of hot water drainage into this tank have been identified including:
Reactor Water Clean up System Leakage Fuel Pool Cooling System Leakage Steam Tunnel Picing or 'laive Crains Residual Heat Removal Feat Exenanger and Piping The CRW drain system collects drainage from ecuicment at several elevations in the reactor building as follows: (Ref. 4) 660'6" 521' 565'
. easurements of the
- he SCV-SCIV system is located on elevation 565'.
nor-al rate of CRW ficw rate into the REEDT are recorted by I'IA to have been ude, wits the result teing aceut 4-5 g;m. These Masurteents nave not :een documented to 'ISAC.
- he GW drain system ciping ranges in si:e from a few 1/2" vents to 3" iron pice si:n downcomers. All discharges from that part of the system into unich the !DIV drains combine in a single 3" cowncomer. The design drawings for the system specify that it is to te air tight - no funnel drains permitted, but some of the 1/2" vents have acoarently been ocen for a long time. There is also a 4" vent at the RWCU ;recoat overflow line.
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apoENDIX CCN CON!ECUENGES CF WE E'/ENT *0
.'dE 4EAC CR
- he fact that the first scram resulted in an cut-of-secuence red configuration with the reactor still critical at a icw but not cre isely known :ower level nas raised the cuestion of wnether there could have been seme, cart of the react:r
.nich would nave been running at a :ower density nign enougn to Overstress the
'uel at the existing ecoling cenditions.
A Orsgrtatic answer to this cuestien lies in the cemeartsen cf :ef:re-and-after levels of radioac-1vity in the primary c:olant (Taele CCN-1) and tne of#-gas stream (Tacle CCN-2). It is seen that there is no systematic cnange in :ri.tary c:olant ;ress escicactivity r f: dine. 7e of'-gas activity snews a gererally increasing trend in June and August, :ut July levels cid ot snew sucn a t.7nc.
Also, July levels.ere not significantly cifferent than tnese of Jure.
Sese cata Oc not suggest any damage to the 'uel.
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TA8LE COM-1 PRI9ARY CCCLANT CHEMISTRY 9F-3 JUNE 1980 JULY 1980
's Gross Radioactivity (u C1/ml)
Hign 9.12!-03 3.53E-03 Solids Low 2.03E-04 2.37E-04 Avg.
1.27E-03 1.36 E-03 s
/
Hign 2.45E-01 1.48E-01 Filtrate Lew 2.54E-02 5.43E-03 Avg.
1.20E-01 5.35E-02 todine 131 (a C1/mi)
' lgn 1.55E-03 3.34E-04 i
3 Lcw 2.35E-05 0.75E-05 Avg.
7.46E-04 1.94E-04 l
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TABLE CON-2 OFT GAS SYSTEM 3ERFCRMANCE' 37-3 JUNE 1980 JULY 1980 AUGUST 1980 Off Gas Radiocctivity, cost-treat:nent mntter, a C1/cc Start of %nta 2E-03 3E-03 1.5E-03 End of wenth
!E-03 2E-03 3E-03 Maximum
!E-03 2E-03 3E-03 Off 3as Ficw Rata, SCFM, :crox. avg.
100 30-30 80-35
'The values given are the result of putting a straignt fine through the daily
.-eacings for the month and estimating the intercects. Hence the value at the end :f cne mnth :ces et accessarily agree with the value at tne beginning of the next month. Also,.n :ne case of July, values for accroximately the first half of the month were not used since the mactor as shut :cwn for acst of this time and the of* gas escioactivity readings were either Icw :r arcatic. However, no July nacings iigner than acout IE-02 wre recorced.
Additionally, GE Mas calculated that no fuel ccerating limits were exceeceo curing the transient. Cocy attacned. (Also Ref. 7.)
- n-3
l GENER ALh ELECTRIC
" " " ' ^ ^ '"
AND SERVICES GENEMAL ELECTRIC f.,CAdPANY,17s CURTNEM AVE., SAN.CSE. 0&L;PCANIA $$12s QlVl$8ON FPF-40-271 August 22, 1980 Or. Mil es Leverit:
Nuclear Safety Analysis Center 3a12 M111 view Palo Alto. 0A 943C3
- ear Or. Leveritt:
- he attacned serio sunnart:es the work performec by Generst Electric to evaluate tne concition of tne 3rewns Ferry-3 fuel following the ine:moleta red insertion on June 23.
- he results indicated suestantial sargins to any fuel limits existac. While inis wors has not reca1vec tne enginee' ring reviews wnica.e
.cula normally :erform as ; art of Our engineering evaluati:n eff:r s. :ne margins are so great inat we believe tne conclusions are ac:ursta.
If you nave any :uestions please :all me.
Very truly yours, d./.7% A.-
F. P. Felini, Manager Domestic 8eeduct Service M/C 380. 925-1257 FPF:ss COIL A
l NUCLEAR P0'uS SYSTE13 EC 2EPCS DEPARTLET ED 70; F.P. Felini OATE: August 22. '980 C?!D/80-237 4ECtJIMED AESPCNsE 84CM:
J.A. McGracy' OATE. n/a 8CR: ACT!CN C susaac7:
THE*."AL LIM!"3 r/All AT:CN CF 3RCWNS FIRAY 3 caestoN.
' AATIAL SCRAM CIE.'i7 INFC RMATICN {
l 2-0 3'AR si ulat:r cases wa-e ~Ja simu14:1 -<1, :ne c:re c:neitiens at Sr:wns terry 3 jus rior :s and just af*er :*e firs: :ar-1al scram.
' e actual red cattoms and :nemal-nyer aulic c:nditions :na: were a
- -otaati:n of me tes: availaste data fecm ne plant anc :es:
esti-ate (:v engineering ;uegement) values nore used in esse too cases.
!ased on :nese simula:ce :ases, tne themal limits at 3rewns Fer y 3 toth sofore anc after ce firs :artial scram, were not even :!:se is even :ne tecnnical s:ecifi:stien 3:erating 11m1:s en MC?'.
.*t -GR, anc GT' MR 'See 7431.e :el w).
- hus, as not even aor al ::erati g
- neral limt:s were violatec :uring ints event, eer-:41
- imt : c ola-
- . s are :f no ::ncern for ce ac:ual 3r:wns Terry 3 ;artial scram ev ea t.
eennteal i:ect:st en 2-0 2'4R ! % ;at:- :esu Ms The-a t '.49tt 3edere !:rts af e 's: St ati a i f e-tm s1.54(1.*3xy) 2.21 9.34 "C7R "uGR
< 13.4 G/ft 5.49 1.31 V71.itGR'
< 1.0 483
.137
( VApt%R
- APUiGA = (MAPt.nGR '...HT)
.nere MAPt.WGR limit varies wi:3 fuel r/ce and excesure.
3ese results nave not :een ve*1fied. Su: are believed :: te ecrtsentstw e of actual :cre :anct:1cns s ne extent -ecessary in justify :na: cer-:41 list:s were af no :encern :uring :nis event.
b-I Cancur-ence:
% m" 3,# "2.McG.,a Y 5 enter -nqineer ail.}:ce ! 0 - ut. :oi 55yst p esjjn 0:ert:ing 0:re Casign Manage ent.
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APOENDII CPS OPERATCR ACT'ONS AND PROCEDURES SURPOSE The Ourccse cf this secticn is to review the ;cssibly acplicacle precedures availacle at the tim of the event, the procedures and/cr mocifications to
- rececures as a result of the event, and :c cc:rinent on the performance of the
- erational staff curing the event.
- . 20SSISLI APOLICABLE CPERATION PROCEDURES AVAILABLE AT *HE !!!*E CF THE EVENT
- o0C. NO.
TI LE 35 Control 9ed Drive Hydraulic System Section IV (Abncrmal Oceratiens) 53 Stancty Licuid Contml System 1
0:erating 3recacure No. 35.
This was the only existing ;recedure at the time :f the event nica actually accressac :*.e situatien :f aces ' ailing to fully insert after a scram.
3asi:311y, the ::eraters scherec :s *his crecacure. It cces, newever, s:ecify scraming ne recs indivicually versus :er<cr-ting total c:re scrams. De original intent of the precesure did sct foresee sucn a large numcer of rods ict fully inserting and, therefore, it was reason-acle for the coerating :ersonnel c cet fer ::tal c:re scrams using the manual scran buttons.
As a result of this event, the :recedure has been.mccified t.c :e accife-acle wnen f:ur or less rods fail :s fully insert. Se 'silure of five or
-cre recs to fully insert is new accressed fn a new emegency Ocerating
'nstn etten wnien ts cata11ec under item (:!I) telcw.
3.
System 0:erating :nstruction No. 53, Stancby Licuid 0:ntml System
- his :recedure is accressed to shcw Only that it was availacle. ::
states that the shift engineer :r assistant shift engineer 9aa the authority s Order injecticn.
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In the case of this event, operations personnel acted in accordance with their judgment as provided in the then existing procecures. However, both the then existing and now existing procedures a?,cear to lack adequate criteria for making such judgments. Further review is advisable.
I!!. NEW PROCECURES PREPARED AS A RESULT OF THE EVENT The comolete text of these procedures is provided below.
1.
Control Rod Drive Hydraulic System Operating Instruction No. 35, Section m,_
5, Water in Discharge Header (By Ultrasenic Tests)
S.
Water in discharge header (by ultrasenic tests)
~ -
1.
Water level in scram discharge piping less than a.
Dispatch personnel to visually verify cpen positien of A
SDV vent and drain valves.
b.
Check for leaking scram disenarse valves.
1.
Check CRD tese recorder - hign drive temceratures may indicate leaking scram cutlet valves.
2.
Check temoerature of tne scram discharge riser at each hydraulic control unit.
3.
If any riser is found to be wann to the touch, verify scram discharge valve leakage according to GEX-9582.
2.
Water level in scram discharge pioing > 1 1/2" tut < 2".
a.
Innediately recuce 1 cad to 1rinimum and scram the reactor.
CPS.2 l
S
o 3.
' dater level in scram disenarge pioing ) 2".
a.
Initiate a controlled snutscwn to the cola snutscwn c:ndition.
2.
Failure of Control toes to Inser* Curing a Scram (Emergency Coerating Instruction No. 47)
I.
SvuorCus A.
Darameter enanges 1.
Failure of all control rods to fully insert acon scram signal 2.
LPRM's in'dicate the react:r is critical after scram 3.
3.
Al ar-s 1.
Reactor auto scram enannel A '3) 2.
Rod witacrawal 31cet 3.
Scram cisdharge volume not crained 4
Sequential events print.out would give additional annunctations II. SUTCMA!!C 4CTICNS Automatic actions airectly associated dita the event, causi1g the scram would occur (i.e., low water level, hign arywell pressure. turcogenerat:r trip and etc.)
CPS-3 i
i
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9 FAILURE CF ALL CCNTROL 2005 M INSERT III. !MWJf ATE CPrRATCR ACTIONS A.
Verify existing condition by.mitiple indications (i.e.,
alarms, charts, indicating Ilghts, gauges and other instruments).
S.
Verify all automatic actions have occurred. If not, place controls in manual and make corrective manipulations.
CAUTION: 00 NOT PLACE CCNTRCLS IN MANUAL, UNNECESSARY 'aHEN AUTCMATIC IS FUNCTIONING PRCPERLY UNLESS UNSAFE PLANT CCNDITICMS WILL RESULT.
C.
Trio reacter recircu14tien :umcr.
3.
Place moce switch in shutecwn. 31 ace scram discharge volume nign water level bypass switen to bypass. Verify scram discharge volume vent and craf n valves coen.
5 E.
Roset reactor scram and manually scram the reactor, reset and repeat if md motion is caserved until all control rods are fully inserted.
CAUTICN: CCMTINUOUSLY NMITCR NEUTRCN FLUX UNTIL ALL RCCS ARE "3tLY IN!ERTED.
F.
Notify supervisor of events and actions taken.
CPS 4
s 6
e s
a IV. !U85ECUE'tf CPTRATCR 1C.*T QS, A.
If all scram valve positten lights are not illuminated, isolate and sent the scram air header. Restere air enen all scram valves are open. ~
e I
S.
Individuelly, fran the auxiliary instrwnent room, scram those control rods not fully inserted. Roset esca red I
after it fully inser*.s and continue to stram rocs until all Fods are fully inserted. Select those rocs in areas of
^
l indicated hign reactivity to be scransned firs..
I C.
Select the control rods that did not fully insert and manually insert as 4SC3 permits; bypass the %M; 314ce the l
RSC3, secuence w e selector, in :ne insert :csition anc select the red group to se inserted. Frem :ne auxiliary instrweent ecom, bypass all reds to full in sost:1cn, inen manually drive ne rods in one at a time.
i 3.
If the control H system is unable to maintain :te mact:r in a suecritical c:ndition, u:cn snift engineer's accroval, initiate stancby licuid control (!I.C) and continue to inject until tre entire contents of the stancby licuid contro1 tank is injected.
l 0P5-5
s 1
CAUTICN: IF AT ANYTIME THE FCLLCWIfG CCNDITICMS EXIST, SLC
!?OECTICN !$ MMDATCRY:
1.
Five (5) or more adjacent rods not inserted below C6 position and either reactor water level cannot be maintained, or succression pcol water temperature limit of 110*F is reached.
2.
Thirty (30) er are rods not inserted below C6 position and either reactor water level cannot be maintained or suppressien ;ool water temcerature limit of 110*F is reached.
E.
Confirm the react:r water cleanuo system (RWCU) isolates or manually isolate the RWCU system.
F.
Restart the reactor recirculation ; ump (s) at minimum ficw to aid in mixing of neutren ansorcer.
4 "2.
'lerify Mutron flux decreases as !LC solutten is injected into the core.
4.
Log events and actions taken in daily journal.
l CPS-6 l
,0 REFERENCES 1.
Evaluation of Ine:molete Centrol tod Insertion Event at 3rewns Ferry 3.
Recort NECC-24276, General Electric Co., Cet:eer 1980.
2.
Reoort and Safety Evaluation of the Browns Ferry Unit 3 2artial Scram Failure of June 28, 1980.
T. 3. Knignt, Tennessee valley Autnority, Rev.1 July 10, 1980.
3.
Scram Discharge System !aecial test 3F STEAR No. 30-13. Tennessee Valley Authority, Mercer: Abercremeie, August 3, 1980.
4 TVA Crawing 4T=852-2 Ficw Diagram, Clean 9adweste anc Cec:n Orainage Browns Ferry Units 1-3.
5.
VA Orswing 47W481-7 *ecnantcal - Orains anc E.t.cecced 3teing Stage !"! anc
- V.
Browns Ferry Units 1-3.
n i.
TVA Orawt99 C::F-5-0028 CR0 ! cram Otsenarse -eacer :semetric. 3r:wns ~erry Nuclear slant. (Unit 3).
IE '.atter, J. A. *cGescy to :. 8 Feltni, August 22, 19P.O. ' Thermal L*mits Evaluatten of 3rewns Ferry 3 aartial Scram Event * (C::y in Aapenctx 00N).
3.
Internal GE report, " Analytical Studies to Simulate the Incomolete 0:ntrol lod Insertion Event at 3rewns Ferry 3 Using a Transient Mccel". OPE-0820.
3.
C. Rennels, August 1980.
s s GLOSSARY APRM Average 3cwer Range Scnitor Each APRM gives :ne average of 3 strings of L7RMs. Diert are 6 APRM channels CPR Critical sewer Ratio. Suncle power at nich transition toiling would start divicea by actual fuel tundle :cwor CR0 Control acd 3rfves. *%chnical & Hycraulic 81ston :evices anien insert /witheraw c:ntrol rods (insta11ec cirectly ancer reactor vessel) 02W C1 san Racwaste Waste. huicment leakage is collected directly at source anc sent tact to storage price to receatec usage AP 31fferential rtssurt MCU Hycraulic Control Units. Hycraulic, Pneumatic electrical devices nich control insert / withdraw Of C20's (located Outside containment) deacer 3ank
- he 1 ci;es, 6* in I.O. atout 50' teng nich are ao i CV.
- here are 2 heacer Danus - east and nest lNPO Institute of Nuclear 3cwer :eratiens (Atlanta, Gecrgia) lRM
- ntermediate Dewer Range wonit:r. Neutren detect:rs :a:aole Of
- eing insertec into mact:r :s measure :cwer at inte. ect ate levels. C.CC01". to 20*. Of full :cwer. React:r has 3 lRMs L?8M L: cal 2:wer 3ange wentt:r a aeutr:n mentt:r f:r ase in :.9e
- ower Ocerating range. *he ::rt contains U2 L;RMs arranged in 13 vertical strings ef'i eacn wC?R Lowest value cf CPR in reactor NSAC Muc! ear Safety analysis Canter (Palo Alto, California)
SC3AM Insertien of control recs at maximan s:eed to terminate ensin reaction aeruotly. Insertion time usually 2 3 seconcs SDIV
! cram Discharge Instrumentation Volume. Incleces tants and Ofoing, fixtures and instruments nica mniter water level SCV
! cram 31senarge Volume. includes cising fixtures frem individual MCU disenarge lines :nru to :isenarse int: IDIV SAM Source range :ower (9eutren monit:r). Source to accut 2*.
- f full Ocwer. Reacter was 1 IRPs.
T/A Tennessee Valley Authcrity
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$1GNIFIC CPERATING EXPERIENCE REFCRT 30-4 DECE!3ER 19.1980 PARTIAL PAILCRI CF CONTROL ROCS TO INSERT
~
R.'IRINCI: UNIT - BROWNS FIRRY 3 CCC NO/LIR NO: 50-296/30-24 DATI: 6/"S/80 NSSS/AI - GI/TVA NSAC 30/INPO 3 Analysis of Incomplete Centrol Red !nsertien at 3rowns Fer./ 3 CISCRIPT:ON:
Whde in the process of performing a norma 1 shutdown for maintenance, a manual scram resulted in s partial fanure to insert of 76 contrei reds, asscetated with the east Scism Disenarge Volume (SDV). Two additional manual scisms fcCowed by an automatic scism were required ;rter to attaining au reds in.
- he details cf 2is event are descr: bed in me INPC/NSAC repcrt referenced scove.
SIGNIFICANCE:
~he potential exists for water to accumulate wicin de Scism Dischar;e Volume ISCV)
- ipmg h suen a way as to remain uncetected
- y the Scrsm Discharge hstru:nent Volume (SCIV) instrumentation.
This water accumulatien may, in turn. result in premature ;rtssur::atien of the SDV sad thus affect centrel red motion upon a scram.
RICCM3tINDACONS:
Since desig.s and eend!tions vary from plant to plant. It is reccgnized Sat any :ne set of specific recommendations can not apply to an BWR plants.
- heretcre, dese recommendatiens are presented as cojectives whfen should :e attained, with examples of ;cssible ways to achieve these cojectives. It is understecd these examples do not necessartly represent au the acceptable ways of achieving me cojectives. It should :e noted that many of the examples are the same as specific fixes whien have been preposed y others in the fonowing documents:
NRC II 3CLLIT:N NC. 30-17 SUPPLDtINT1 SUPPLDIINT3 SUPPLEtIN* 3 GINIRAL ILIC*RIC SIL NO. 331 SUPPLDtI.V"4 CT:L"TY SC3COMSti""II RICOM3tINDACCNS
'Lang-Term Evaluation of Scrsm !!senarge System" RECElygg a h
JAN g (egy
" RID
- 2. MICIAII A INICN g
j Y ILI.O W - PROMPT A.. NCCN QQ l RE%LATORY STAFF 0* I#
~ N 0 * ' A L ^^~~I*~'0 N
r.. o e
1.
< card Arains: Ace.:mulatien of Undeteced Tater In the SCV The SDIV instrumentaten can indicate :he absence of water in the SDV; wnen, in fact, :ne 3DV is essentially fuu. The SDIV water deteci:n instrumenta:icn should provide reliable, direc incicanen Of water in the SDV.
2.
?.nsure Adecancv ef P ecedur-s :n Detee-ion of Tater Lisure that adecuate procedures exist regarding acten :o be :sken if water is deteced in :he SCV system wnen it should be free cf water.
3.
Guard Aeainst Chstruc :en Cr Tescetne !n The SDV-SDIV C:nnee er ci:e.
Any costructon of the SDV-SDIV line, whetner by solid ma::er er by a water trap, snculd be guarded against. Pcssible ways of guarding against a sciid ecstruc.icn er water trap in the !!ne include:
F.nlarge the diameter f the line connecting the 3DV :: me SDN as c!cse as practcal to :ne internal diameter of :ne SDV heacers and reci e with care to eliminate !ccations wnere sciids would be expecec to ac' cumulate sucn as dies er humes in me line, m:ernal roug ness a: weid peints, dameter enanges, etc. C nsseer re! caten of me 3DIV :s a cwer level in
-cr-
~
'nstali separate 5DIVs for :ne two heacer banks, so mat the line fr m eaca heacer bank to its SDIV win be relatvely sner, stratznt, anc as :!:se as practcal to tne same internal iameter as me SCV heace.s memselves.
4 Guard Artins: Trancine *.n The Vent !.ine Any locatien er c:nfiguration favorable to trapping water in me ven:!ine secuic de avoided. Possihie ways =f doing so include:
Put vent valves in vertical, not heri:=ntal pipe runs, and ensure :nat all hori: ental pertions of vent lines ac:ually have sufficient sicpe :o assure crainage witneut trapping.
5.
Guard Aesinst !nte 'erece :-em CRT Crain Svstem De ;cssibility mat steam er water from other drsins into me CRT crain system c:ula interfere wi:n :peranen :f me SDV-5DIV system by incuc:ng a scenen :r precucing a pressure saccid be guarced agains*. A pcssible way of teing mis is :::
Isolate me vent and crain lines from each :ther and from other CRT cramage, by running them as dedicatec lines direc-!y is :ne reac cr budding eg.apment crain. sump.
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i 5.
Guard Acains: The cessibility Of The vont Not 0:ening l
Failure of the SOV vent valve to open should be guarced against since such failure could interfere with the SUV draining freely. ?:ssible. ways of doing :nis include:
Install a redundant vent valve
-o r-Cross 03nnect the vents on the two header system 7.
Guard Acainst Excessively Slow SOV Crainace Excessively slow drainage of the SOY should be guarded against since, if suc:essive and close-spaced scrams are necessary as in the 3r0wns Ferry 3
~
case, it may be difficult to achieve enem if the SDVs are essentially full of water from the preceding scram. After One scram has been attemoted, ne readiness of the system for a possibly needed next scram snould not be limited by the 50V-SDIY crain time..One way of acnieving thi: :cjective is:
i Ensure that the 50V vent valves open when the scram is re<?at by installing redundant valves and ensure that the SCV vent lines are : lear.
Ensure that the 50!V drain line capacity is si:ed := allcw cremot drainage and install redundan: SDIV drain valves.
3.
Guard Acains: Trseeino In Individual Feaders In some :lants esca SUV header bank consists of 2 or mort hencer mi:es
- nnectac ::ge:ner, in :arallel, :: f0nn :ne desired v0!ume. The ;ossibility Mat one neacer c:uld fail to drain even :nougn the etner :arallel header nas drained snculd be guarded against. Ways of acnieving :nis incluce:
Ensure that :he design provides an adecuate slo:e for all heacers in each bank.
9.
Ensure That r ilure To Scram P-ecedures Are Adecuate a
Procedures, adecuate for guidance of c:ers:ces and shift engineers in :ne event of failure to scram, should be provided. These :recedures shculd scecify under wnat circumstances scacific measures saculd be taken in the even of delayed scrams or incemalete scrams.
10.
Guard Against Uncentrolled Release Of Reactor C:clant To the 2eacter Buildinc Failure to close en sienal of a single vent valve or single crain valve can result in loss of reactor ::alant to the reacter building sumo. Recuncant reans to close off :Me drain and vent pathways during a scram sacula te
- nsicered, s
INFORMAT*CN CONTACT:
Dick 3aker (IMPO) (10:1953-7515
-o r.
Miles Leverst: (NSAC) (115)355-2925 i
h