ML16341C704

Recommends That Board Notification on Semiscale Feed & Bleed Experiments Not Be Issued

ML16341C704
Person / Time
Site:	Crane
Issue date:	08/23/1982
From:	Bassett O NRC OFFICE OF NUCLEAR REGULATORY RESEARCH (RES)
To:	Speis T Office of Nuclear Reactor Regulation
Shared Package
ML16341C707	List: ML16341C704
References
NUDOCS 8210070035
Download: ML16341C704 (44)

Text

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c UNITED STATES NUCLEAR REGULATORY COMMlSSION WASHINGTON, D. C. 20555 AUG 23 1982 l>Et<ORANDUYI FOR:

Themis P. Speis, Assistant Director for Reactor Safety Division of Systems Integration FROM:

SUBJECT:

0.

E. Bassett, Director Division of Accident Evaluation Office of Nuclear Regulatory Research FEED AND BLEED EXPERIYIENTS IN SENISCALE As you are aware, RES has performed a Semiscale feed and bleed experiment (S-SR-2) at the request of HRR.

Results of this test indicate that difficulty was experienced in maintaining a steady-state feed and bleed condition without uncovering the heater rod bundles, Several members of your staff have had questions as to how this relates to the PWR feed and bleed operations being purposed for several plants.

These questions are now being addressed by EGSG Idaho, Inc., while taking into account the atypicalities of Semiscale, as they might affect the eed and bleed behavior.

As a start, EG8G have provided a letter report of se,eral steady-state calculations they have performed in an effort to help understand the Semiscale data (see enclosure).

These calculations included a study of the 'sensitivity of the results to core power, break flow quality, surge line and pressurizer

geometry, and availability of equipment, and were extended to parametric values typical of a commercial'MR.

The report concludes that there are large uncertainties in predicting the satisfactory performance of feed and bleed in the steady-state, but that the Semiscale experiment does not point to the existence of a definite problem regarding the satisfactory performance of feed and bleed in a PMR.

The Semiscale results still must be analyzed to determine the extent that the atypicalities effect the results and to put them in proper perspective..

This analysis work is currently in progress and should be completed in September 1982.

The Division of Accident Evaluation has concluded that. the Semiscale results have not produced new and unique results that indicate a

P11R would have a definite problem regarding feed and bleed.

Therefore, ere do not recommend a board notification.

hIe have concluded that the Semiscale results should be carefully analyzed to determine that relevance to PMR feed and bleed transients and this work is now in progress.

h'e

Themi s P.

Spei s should be able to provide you with a more complete answer to the relevance of the Semiscale experiment and our investigation into the feed and bleed'transient'in a

PMR by late September 1S82.

Enclosure:

Ltr fm North to Tiller dtd 08/06/82 cc w/encl:

L. H. Sullivan, EPB R.

R. Landry, EPB B. Sheron, NRR

. jQP-,y 0.

. Bassett, Director Division of Accident Evaluation Office of Nuclear Regulatory Research

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August 6, )982 Rr. R. E. Tf))er, Oirector Reactor Operations and Programs 0)v)sfcN Idaho Operations Office - DOE Idaho Falls, 19 83RlS PRIHARY COOLANT SYSTEM FEED hÃ0 KEN - FN-)37.-82 Dear Nr. Tii)er.

At the request of the nuclear Regu)atory Conarfssfon the semfsca)e Program recently conduct@et experiments cfeoigned to investigate the feasibility of primary coolant system (PCS) feed and bleed es e ee.ans of rejecting decay heat

$ n the absence of steam generator hmt. removal.

The results and preliminary analysis of the experiments evggesteO that.

8 reasonable uncertainty may exist

$n the ab5)it@ to effect stable PCS feed and b)eed.

Since current pressurizecf water reactor anergency operating guidel)nes call for primary feed and b1eed vnaer cortafn abnormal conditions, 4t was considered of scca importance tt-.at the

'neral subject ot feed and bleed bC studied 4n some depth +ad t4tt he Eeeisca)e results be carefully analyzed so that they might be inter-preted fn the proper perspective.

To th)s end, the Semisca)e tnqram is currently engaged

$ n an extensive ana3ysfs effort invo)H~ both full-scale plants and experimental results f$.e.,

Semiscale and L.OFT).

The purpose of this letter 5s to.provide n brief overview ef oar ana)y--

Sfs of feed and blee4 to date, 4sc)@ding the recent Seuisca)e results.

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0riaary coolant system feed arid b'teed 4n a pressurized +at~ rancor becomes a necessary decay heat reeoval eechanise in the unINe)y event that a)3 secondary heat removal capab$ )ity 4s )est.

Mhile %Stre exist numerous scenarios that could lead to thfs a4Natfon, the. foms: of

.. the present inalyset

.Cs.. the.feasibility ef ach$ eviag a FaveraMe coo%

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ant and energy ba3ance @ithunn the ~aar~ coo)ant system order condi-

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tQ pressure-operated rel4ef valvesM (PORVs) we oper 5.

prfaary rec)rculatfon peups are off Feed and bleed mv3ct ccemence ~n the PORV(s) ~e opened (Heed and high pressure infection began (&ed}.

The passage of'tean o~

%he Vts) provides for the ration eF decay heat vh$ fe the. fnf tfon of fCCS coo3arit provides eekeMp t'or the resultant coolant lo Yhe reeafnder ot'Ms 7ettet exanhnes the general aspects of pr$

feed and b)eel operation and the thecal-hydraulfc phenoca~ that gaverh ft. ~ predicted systee Wsponse fs butllned ffrat bed.tel effects of uncertainties are f))@strategy <6th an example Fmc acth plant phr&Rlcterc Next the key'h~ol-~jul fc phen~aa that 4

fluence the mcerta4nt$ es ore Recessed.

Ffaa)ly, the date fma See>scale experiments is br)ef)y presented to demonstrate syxtea tures end t.@~posse during w'ctual exper$ eant.

THEORETICAL FEC0 AHO SLEEb %'ERATJHS PRESSURE ROSE

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$~~JC. 0!9b.tressure 3Mect$ on system fKCCS).. fs.operant~

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h An upper pressure bound to the steady-state operating band $s def1 by a balance between the PORV average coolant ~va) rate ~ th<

NP1S coolant infection rate..

The average PORV coo1ant reuovA ra) 4s sfmp7y defined es the core ~r divided by the difference bet>

inlet and outlet enthalpfes:

Base case tond<tfons assess that )Mf gut)Sty steam 4s cfog char thr ough the PORV The affect of var ted quality is exaufse4 ly

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t at feeean4b 4s theoretice))g.yostkble v$th$ o o eerte4n band of pressure fuse f

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, IIeter am fmetfeiS'of prt@ig igcteYif j&s~." 'tb. 7~ ~St t'ai "ojorit$ng band ~reicp$i the mfn40e jc~are ak sihkchr the f can'pass enough stigma (with tbe ceo)ant

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poaiib>e. 'pe&tfoh:4t.a yresture above.'he f~ )&cia~

be eecceplfshed by eye)fng the FOR% opec end closed Kthfo a <es4c pressure band.

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Actually a coo)ant deficit exists at assures higher than the upper bound and 0, steady-state condition cannot exist due to a"continual loss of systaa coolant inventory.f Belier the upper bound the systea mass inventory can theorist,fez)ly bc maintained within a desired operating range by either throttling the HPlS or cyc3ing

$t on and off.

QNCERTAEHT)KS ASSQCIATKO MEATH STEADY-STATE CPCRATBlG PREMVRE'AND

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'he PORY is dependent on the fluid conditions at the top of the pres-surizer. If the pressurizer fs near liquid fuff the flow through the PORT vi33 he a elxture of liquid and Taper.

At a given systae pressure this rcsu)ts irs greater mass f3m than for saturated steam f)m through the PORT.

The resvlt of having tvo-phase f3ov throvgh the PW Ss ttierefore to Imper the upper bound pressure.

tJncertaint) also arises 4n the RORY energy reeova3 curve cfue, to tm-phase flow.

Pith decreasing qua)ity the enercg removal per unit mass decreases while the mass discharge rate increases.

Eipondir3g. upon the quality the energy removal rate at a given pressure may ae tess than or greater than that for saturated stean.

Ae )ower hapl crf operat1nj bind mal'Varg.accepHig+

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0 Another significant variable that affects the Rdth of the opez at4ny bcmf concerns the actua) heat )oad that east be rejected t$mmQ the

,.j PORT.

Core decay heat decreases continually vith tice after'hutdovn.

Also, if some additiona) heat sink exists, such es environmate3 heat Toss or residua3 eater 4n the steam generator secondaries, the heat

'oad required to be re3ectcd through the l'ORV vill decree@.

Referriny to Figure 1, thks results

$ n levering the core power )inn ~ thus:-

3mcering the bottoe end of the operattng band and also 1~tny tht PQRV average aass f3'urve, thus ra4s$ ng the upper end of the operat-hg hang. ~vh vv~av& v~o apahg hf vva ~vahfvi

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. ~he final Uncertainty addressed heri

$ s the u~certa$ nty associated kith the HP15 injection curved.

The eff'erat.s here are rather c)ear i )cncer inject)on rate vil3 lower the upper end of the oper~Xfag ban~

"-e quantitative effects of the uncertainties andi'or variance>>

d)scvs Eed above are il)ustrated in f'insures 2 through 6.

~or these exmaples the curves kern q~n)rg'.eo using data obtains f'rom the Zio~.'rvclear generatino plant,

34) 1 RHL't) pressuriied eater reactor.

Figvr ShOWS a primary feed and bleed map fOr b 2X aeoay heat pCerir fere).

A steady-state operatin9 bard is seen to exist between 7.%'ve I4 RPa A decay heat level nf 2 of full @ewer is typical of the tive-period free about )0 min to 20 min after shutdown.

Figure 3 is, a siei)ar Curve, but herQ no alakevp pump infection 4e assvaed; on)y the HPlS pumps ~ere assumed to be operatic.

inc HPL5 yuri~ps are shee~ to deal head at abnut l0.3 Ni'a.

for this case no nperetin9 sand exists, sine ht the minimum pressure ahere the PORV can remove the energy t.here is 4 mass deficit between the PORV coolant re~oval and the R"'5 in)ec tion capacity.

Figure 4 chnus the pr4ary fae8 arid bleed map fear l-)/2$ fust praiser, a decay heat level typical of'he period fran )Z2 to l hr after shut-dom.

and for only 'HPlS 4n$ e.et(on.

Comparison to figure 3 sos that thy reduction in tore power and corresponding HARV average ~so t%ow

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hotb act to establish a steady-state operat,ing band.

The above curves are based upon the assumption that l00c quality stet exists at the PORV.

Figvre 5 sh~s the sensitivity of the ANGRY eneg reaeval curve to lower qua)ities os determined eath the HKR f$car eoa Since the energy removal per unit mass decreases awhile the ass f1m rate increases the energy removal rate initially decreases with deer>

ing qvalitp'.

HoweYer, s(nce the mass f)cec rate increases sabst.antial with decreasing quality the energy removal rate eventually Increases.

The effect on the lower operating bound pressure is not fares; hercv<

the large increase in

$'ORV mass f'to~ rapidly Icwers the oper end of the band.. As an example, for the conditions used

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'operatinj band cfoes not exist at oualities beloved approximately R5K (see Figure 5)i

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The foregoiny analysis 4s useful, in that 4t provides a basis for,.'

examining the feasibility of feed and bleed and ~or quant<t..C4ve'ly assessing the effects of uncertainties or variations in the bounding h

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3tnuever, tt dues nui 'address transient behaviour that may ave an itttpurtant bearintl un the ultixtate viaitility:fpr nary feed and b le'ed

. ln part3cular, it'hnutd be evident thai. there exists saute uncertainty reqardfng the abf)ity to safely bring the primary coolant System to ~)thin the "feasible" operating pressure band vft~ut. sustaii inq unacceptable coolant loss fn the process.'actors

~:hicb hear on this transient process include f.he primary coolant system state bt he )nftfation of hn attempt, to teed and bleed, and tbr nations of the Lvvfant, dfschar9ed through the f'OR%(s) sri aepressuriztn9 the system Co vkthin the operating band.

'lhese questions can only be addressed.

t)W'Cugh e~perirtlentatiun Ond the uSe Of Ceoput,er eOde dna)ySeS.

ACTORS ANECTfhlG PORU DISCHARGE P

Gf the hectors previously diuussod tno )orgest vnf.ertainty affecting the feed and bleed operating band arises From the influence of tm-phase PORV f3m.

The mass flat through the PNV's dependmt on up-stream fluid conditions at the top of the pyessurizer..Several factors contr(bute to'establ)shing pressurizer flufd conditions.

%he ones discussed here are:

transient vs steady-state

behavior, primary cool-ant system conditions, pressurfterAurqe linc geometry.

end surge line orientation.

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$ )nk the primary liquid smll ef 3) i'illthe p.e.surmiser end col-

)apse the steam bubble.

Several conditions ray form or su-..tairi a vapor hubble at the top of the pressurfzer.

A vapor bubble can be produced by )oss of pressurizer liquid fnventory, heating of the fbiid to saturn tfon, andlor depressurfrat$ on.. kn the present study the pressurizer

'eaters are assumed to be non-operitioriA and direct heatQq 4s there-fore grec)uded.

En b transient deprcssurizatforr

~ ligule flashing fn the p< essur izer ~i)3 tend to create a high cpiality region seer the top as long es the fluid 4n the pressurizer 4s the hottest

%n the system.

However, the 35quid s~3) that accompanies'u3k flu>Mng ~$ ))

tend to decrease the qua)sty at the top of the pressurizer.. for c.ither e ouasi-steady-state situatiori, or fn a transient once the origina) pressurizer inventory has been r'eplaced ~ith coolant from the hot lent.

the f'QRY fluid conditions are dependent upon the conditions ie the hot tey. If the coolant lost through the PORV 4s replaced by )ee qual' ty fluid the rttasS discharge out the pORV vilf reaain fair'ly h49h..

This vfll occur until the primary system inventory 4s reduced enou9h to cause significant voiding in the hot leg.. Once s59nif )cant hot

)eQ voiding occurs pressur$ zerg surge

)one geceetrg and ar~entatgon tree into p)oy 0s cfcscribe.d be3cat.

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.Ll F'r ik g3vei vapor volume a prissurizer eath 6 3arge'length-to-Comet tat)o would have b "tel)" void height re)atfvo tv o pre~sur$ zer s$ th a smal1er rat)o,

$ n addition to a1so having a seal)er cross sect)on.

A steam bubble of'reater height would tend to enhence severetion fr the vapor of liquid drop)ets created by hubbles brear$ ng thr'uqh tht

- liquid surfoce, due to the greater xa)) surface oree and re5iced potential for droplets being thrown upward into the hfgh vair veloc area near the PORV')ne entrance However. since vapor ue~~t by necessity pass thiwugh the pressurizer

) fqofd from the surge line ta the PORY a larae LZ0 mould %end to promote liquid s~Hl and droplet ent.rainmerit due tet the smal'er cross-sectional area.

in anv case.

the influence of the pressurizer geometry may be efninri hy the preclusion.af counter-current flm $ n the surge line.

Even i 0 lfqutdlvapor separation mechanism did exist in ttie pressurizer, typfca'I surge line velocities are ~ll above fkoodin9 limits.

'Ther fore, the liquid cou)d not drain'back to 'the loop and wouM "wtinue to be stored in the pressurfter u>>t.i) the PORP discharge quaffty sel Adjusted to acconm4ate removal of the eats..'t therefore appears necessary to have high qualltv steam supp) fed from the hot )e9 in o Co have high quality PARV discharge.

..S6r e Line OrientaUon 1f hot leg voiding does occur the orientation of the surpe 'kine x tnpluence the primary system )nrantory et mhiah high quality steam entered the pressurizer.

Surge line-to-hot leg connectfces of vari orientations, from horirontal side entrance to vertical top entranc are used in current PMR's.

Qith the top entrance line, and quiesce, leg conditfons, minimal hot leg voiding fs necessary tc e)2aac high

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kith a side entrance 1ine the hot key pipe liquid tnvst drop much 1&ear bef ore high quality fins begins.

1n either caI the Surge line f1~ may still be varfed significantly if non-qcr<escI condftfons exist that disrupt stratified fleet, sich as shen primary recirculation pocket are turned on, ar a trans>ent depressurizat.ion CcCur r)AQ.

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4 COhCLUS1NS SASEb Ob S1RPl O'IEO li'INlYSES Sased on the foregoing dkscussfon )t fs concluoed that a s)~)'.fied approach f.o chterminin9 the feasfbflity of primary ford and hJred 4n a ressurfzed sate>

reactor lies in the mapping of energy and mass flars.

oreover',

t.hfs ter,hn<que can be users to quent.$ f.at.fvely. assess.

the sensftfvfty of the. operating pressure oui>d to var)atfons in the boundary conditfons of ECCS flat, PORV

flower, and decay heat. it $ s evfdent that plausible variationS and uncertainties in these oarenettrs can lead to the r 3<efnatfon of i stea"y-state operating pressure range.

Prfncipol oblong these uncertafntfes

$ s t.he coolant discharge through the PORV.

The predictabflity of'hfs single parareter fs sK~ct, to much greater uncertafnty than esther decay heat, or Eccs firn.

frresoectfve of'hi exkstince of i theoretically feasib)e operating pre~sure band, there remains tne questfbn as to whet?:er

%he rector'ystem can be safe3y maneuvered into this pressure range.

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$ s cfear that a dependence mvst.be placed on camputer c"dc analyses

(~ith suitable verifkcitionl hand 88equate supportive@ experi-mental data.

Such analyses and or experiavrts whoufd exaefne 'ne plausfble scenarfos which lead the ooerator to ecmrnence primary feed and b)eed, sfnce the

$riftfal <ond5tfon of 'the primary coolant system iporticu)arly inventory) w)33 have i sfgn$ f4cant effect on :he outcome.

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/-ur'thermore, ft would appear to be a useful exercfse to erbmfne tb&

operating map that results for each set nf indivfdua).PPR pl-est para-..

meters.

The operating cap represents an u)finete statement as to whet.he fe~d and b)eel 5r. poss)b)e, and

$ s the startin9 point for e~min4ny specific design features that bear on the.,operating bounds.

RfSUl.T3 FRON SEHISCALE f;XPER?NE'ITS I

An experfment was conducted fn the Scmfsca)e Ho&2'A foi$3itj ko evaluate system behavior durfng primary feed and bleed operatfcns.

Figure 7 shms the primary feed and bleed ojerating map represent)ng boundary conditions used for the exper5mint.

Jt is seen that these parameters define a steady-state operating band between 7.3 and 8.2 NPa.

Several attempts were made to estabffsh steady. tate feed and bleed ~ithunn the operating hand.

Rhfle ft ~as possible to maintain pressure eoatro) by cycling the PORY, masurenents showed a continuous 7oss of yc.imary coolant inventory due to a lcm qua)sty discharge out the FORD The phenomena that led to this behavior ere described he)ur.

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At initial c'pnd<tioni the pressurizer heaters sere used t hontro) prbssuri breath 4 Orna)) steam bubb>e 4n the pressurizer.

Save iubcoo)fag existed kh parts yf the 'loops due to the lack of natural e$ rcu)ation resulting from having empty secondaries.

At )5000 secon (test tine) pressurfzer heaters mre turned off and the POHCY seas 3at Open.

P<9Vre S ShmS that the tySiem rapidly depreSSuriZed dOWn tO approximately 5 HPa.

Th)e corresponded closely to the saturation pr H the boldest f)Uid ]h the )oops.

~s seen fran the pressurizer co) liquid )eve) curve. flashing of the hot pressurizer fluid init'.ally t-esu4ted in substantia) voiding of the pressurizer.

Referring to F$

kt. Ss seen that th)4 is reflected fn the PORY mass disrharyp rate Vo))ming 5 brief initio) mass floe surge th& f)tN out the PURE agre tlosely with the predicted steam f)oM rata frr 100" qua)sty.

the st bubble depleted Ofter bpproximate>y 250 s tf'$9ure 8} and the PORV aa 0'fW t.ate increased to approximate)y 5 tines the steam f)~ rate IF'j.

As Seen in F)gure 9, the macs flee rate out the PORV appeared t ctependenh Upon the conditions in the hot )eg.

once swbstant$ al void of 4he hot )eg occurred the f>m out the PQRV began tD 0QMB, lfiUI th predicted stean flm rate,

<n Spite of the fact that the pressurizer l.ema$ ned nearly liquid fu)) (F<gUrt 8).

iThe pressurizer surge line 4n the Hod-2A system i4 connected to %he tide of the hot leg.]

At the:.time Mn juffickenh primary ate)ant inventory was fan@)y la to 44 to eood the hot ley the core a1as stroll adequately covered and cooled.

As teen tn Figure 10, there nss stl lle 's'nell def pelt tn t) amass

$n'ected into the s stem vith the Hf'fS relative to the PORY'Was r

discharge rate.

The result was then a very elm continued lass of Arch fed to event,ua) uncovers of the car~ at. about 37000 seconds.

fhh Qyortance bf'he 5emfsca)e results )ies

$ n demonstratfng the bf khe,PORV dischbrge tat8 on pr$ @bry Seed and bleed capability end dependence of the PORP discharge on hot )eo conditions, end consequ system inventor/ e The )nab))ity to eakntain system inventory once t POPV hbss f)W t.ate dropped to ref'tect steam f3oi is subject to ex bncerta)ntfes, since the steady-state operating band of f'ignore 7 4s tH,her narrow.

Uncertainties 8x)st

$ n the actual PORY orifice char ties>

HPlS fngect$ on rat& e>>d the measurement thereof. systea heat and Slu<d )eakaya.

thS observed NltV discharge relatfon ho hot leg conditions herever, outside the effects cd uncertainties discussed abave.

'the question that need to be addressed 4n interpreting bnd extrepo3atlng the res br'arge)y lelated to thk geometry effects.

The Had-2A system has short pressur(ter relative to the desired scaling of i./0.

The k./9 on )iqu$ d vapor separaiion fnust be analyzed.

The surge lire Meds evaluated also, tna$ n)y Hth regard to the. influence af the side en'he hot. leg as opposed to other desCgns.

hi Core pmer eds augmented to compensate for the best estimate s

heat lost.

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CO'lCLUSltlllS BASED Oll SEH1SCALE EtPEBlfKLTS

.n end of.the)selves

~'ihr tesv)KL.fr'om the imisca)e ey.;rLsriseats do not point to %be existence of a definitr pr'blue rcghrd>og frilIlaly feed and bleerl.

Svh they do tend to Support a concern about tht re'fat,tv@

t.t.nuousness of the process, further anr)>sos a.tanptfng to

~entify the potent(a) experieental distortions cr,d their effect on the results is now 5n progress.

These Bnalyses, a)ong xi 3: the resu) ts of annoy'sos of existent LOFT data, arid compvter er;ce calcvla-tiQn of the Seirrisca) e ex pcrirrrcnt an9 0 fvl)-seal cr plerrf l be do'cur.ien'.ed 5n Scptembei.

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