ML19224A784

Preliminary Test Results,Semiscale Pressurizer Relief Valve Venting from TMI-Type Conditions

ML19224A784
Person / Time
Site:	Crane
Issue date:	03/31/1979
From:	Office of Nuclear Reactor Regulation
To:
References
NUDOCS 7905300288
Download: ML19224A784 (16)

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A.

SUMMARY

On Harch 30, 1979 NRC management personnel requested EG&G Idaho personnel to hulp evaluate alternattva courses of action for securing 4 the Three-Hile Island Plant (THI). We conducted our evaluation. Among several ret.canendations, we proposed conducting a venting test of the prianary rullef valve (PRV) in Senilscale from present THI condittor s to check the accuracy of calculations we performed on the response of THI to such a venting condt tion. We conducted the proposed test from 6:55 a.m. to 9:47 a.m. on March 31. 1979. Two-hundred forty channels of data were recorded. The test was success ful. We believe the test results may be of use to NRC in evaluating the probable TH! plant response if venting from present conditions is attempted. The remainder of this report is dividcd into three sections. Section 11 presents a comparison of THI and Semiscale significant paracters as best we know them. Section C provides the sequence of experim_ntel eventi and signt ficant pehnomena correlated with the time at which thef Occurred. Section D presents the Calculated THI plant response during venting from the PRV from the initial conditions provided by NHL. Section E presents our conclustons from pressurizer relluf valvo tests in Semiscale. n= ~,- +w . +..,-- ; : ^cc =. W.

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D. COMPARISON OF SEHISCALE AND THREE HILE ISLAND (THI) SIGNIFICANT PARAHETERS 1. VOLUME RATIOS ( f,"4' f" * ) 3g B&W Semiscale SS/0W Pressurizer 0.374 0.454 1.21 Cold Leg (one side) versus broken loop 0.118 0.255 2.16 llot Leg (one side) versus. broken loop 0.122 0.144 1.18 Total Loop (buth sidas) 0.974 1.596 1.639 2. ELEVATIONS (from G Nozzle HL) B&W Semiscale Top o f upper plenunt 14 f t - 6 i n. 13 f t 1/2 in. lup of cora g -2 f t - O f n. -5 f t - 0 in. Surge line connection to llL 6 ft 1/2 in. 4 ft - 0 in. Surge iIno verticai drop (not f run nozzle () 12 ft. - 8 in. 11 f t - 0 in. Piping vertical fielght (total) (including pump suctfun) 68 ft - 0 in. 51.3 ft (BL) 21.3 ft (IL) [ huzzle to top of tube (or pipe) 46 f t - 0 in. 41 ft (BL) 11 ft (IL) Surge lina below top of core 3 ft 1/2 in. 2f 01 4

i l 3. SIGNIFICAfiT DIffEftEflCES 1 B&W_ Scmtsraic Cold Leg 2 cold legs / side 1 cold l a g / e f (f. () s f *fe s r.n \\ mt for 3/4 flow) Hot Leg 1 per side I per si.f. Upper Plenum Vent Valves No vant valves Hot f.eg / Cold Leg Elevation Offference Hone 8-l/7 in. (llo t. Illnher) SG Elevations (difference) flone II. p 11 ft - o in. DL P 41 ft - O fn. i i 167 262 n

C. EXPERIl! ENTAL SEnUEr:CE AND SIGf!!TICANT EVEllT_S. A description of the initial conditions for the TifI plant sosponic I tes t and a table o f s f gnificant events follows. Also includad is a !I description of the signiff cant Sentscale system con f f gura t ion or opetatinq 1; conditions that may not be typical of the TitI plant. i l Initial Test Conditf ans f I l I H1trugen bubble initf ally established at a level o a. k r 43 f r ahnva hot leg pipe upper invert (about 0.5 f t ). The elevation o r tha 3 bubble is higher than expected for the full scale plant. r, No secondary s fde water war added to the steam gennrater. N b. Th15 j lack of water would cause a lesser armunt o f energy to be trans forred I to the pr f rna ry fl uid. Pressurtzer s team done was es tablished a t 307. o f. the c. pros e.o r lie r v o l "n a. It d. Leak ra te o f the sys tem was es tablished s ince the finw out the siinulated pressurf zer relief var ve flow was o f the r s ar c ragn i turla ( as possible leak rate. k e Systen was heated to 410'K utilizing the cora e. and an initial pressure . of 7.24 kPa was es tablIshed. lb7 263 l a

Ini tial Tes t Condi tions (Contd.) f. Pumps were coasted down and an Initial power of 7.rA W was c. i n t,1

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_ TABLE OF SIGNITICANT EVEt(TS, Time Event 0 Experiment inttf ated (pressurtzer s tem hehfile ventinu sinrt.ca' Ini tial clad tempera ture - 420*r. (295"I) Initial core outlet water temperature - 411"E (2n0"f) Inf tial pressurizer pressure - 7.6 Mpa (1100 ps!) Initial inert gas / vater interface at 1.33 m above ( G 3. l ". In.) cold leg cente. Ifne Initial heat flux 4.1 W/m2 (130f) O tu/hr-f t2) 0 - 1000 sec Nitrogen bubble in upper head expands downward. prenor f ree water level rises as steam 1s formed and ventc<f. pre unr a falls, temperatures rise slightly. 1000 sec Pressurizer wa ter level reachas vent connce t inn Clad temperature - 435"X ( 32 3 T ) Core outlet water temperature - 420'k ( 2 '!f. ' f ) Pressur12er pressure - 4,7 MPa (600 pc.1) Gas / water interface - 0.36 m (14.17 in.) nhove cold Icy centerline. 1000 - 3800 sec Nitrogen bubble continues downward expanston, puchinn watai-out pressurizer vent connection. Tempora horc e. inntinne increasing, pressures fall. 3800 see Nitrogen / water interface react'es top or hot ley opening 0.25 m (9.84 in.) above cold leg centerl f oe Clad temperature - 442*K (336'T) Cere outlet fluid temperature - 477"K (300"f) Pressurizer precsure - 2.6 Mpa (300 pst) 167 265

_ TABLE OF SIGrilFICANT EVEffTS_ ( Con til. ) Time Event '800 - 5000 sec Hitrogen expands into loop pf ptng. S team acnora t or Irn ins through cold leg and downcomer forcing r:oni water into lower part of core. Clad tempera tures nenern ily der.rea-a as well as pressure. 000 see Steam generator tubes empty completely. Peak clad temperature - 456'M (361*F) Core outlet flu f d tempera ture - 444*K (319"r) Pressurc - 2.2 HPa (319 psi) 000 - 7000 see Clad temperatures increase as core flew s t auna t es. finist temperatures rise as pressure continues to f3II. 000 sec Fluid temperature reaches saturation and bulF linillrio begins in core. Core outlet fluid temperature - 452"l. ( 3r1"f ) Peak clad temperature - 456*K (361"F) Pressure - 0.8 HPa (116 pst) 000 - 9000 see Low void fraction fluid rises in core, clad temperature t decrease, fluid temperatures remain at saturntlun as pressere falls. 000 sec T*st Shutdown. tif trogen has expanded into s team ynnera tor but pr essorlier a pp e a r.s to still be filled with i f quid or very low vo f 'l fraction fluid. Pressure - 0.34 HPa (49 psla) Clad temperature - 426'K (307"r) Fluid temperature - 423*K (302*r) fre bulk bofling occurred when saturation conditions were rear.berl. Max t l atl 'mpera ture - 456*K (361 *F)

TABLE OF SIG?llFICANT EVENTS, (Contd.) Time Event 3800 - 5000 sec Nitrogen expands into Toop pipino. Steam generator drnine. through cold leg and downcomer forcino e on1 water foto lower part of core. Clad temperaturcs nanerally.In c r e n - n as well as pressure. 5000 see Steam generator tubes empty completely. Peak clad temperature - 456*K (361*F) Core outlet fluid temperature - 444*K ( 11'V I ) Pressure - 2.2 HPa (319 psi) 5000 - 7000 sec Clad temperatures increase as core flew staunate'.. f l u t el temperatures rise as pressure continues to fall. 700'd see Fluid temperature reaches saturation and bu1F l'olling begins in core. Core outlet fluid tempera ture - 452"). ( 141"T ) Peak clad temperature - 456*K (361"r) Pressure - C.0 HPa (116 pst) 7000 - 9000 see Low void fraction fluid rises in core, clad te perature decrease, fluid te* aratures remain at saturat tun as pressure falls. 9000 sec Test Shutdown. Nitragen has expanded into steam generat.or fin t pvrunrlior appears to still be filled with 1Iquid or ve. y low vntd fraction fluid. Pressure - 0.34 MPa (49 psla) Clad temperature - 470*K (307"r) Fluid temperature - 423*K (302*r) Core bulk boiling occurred when saturation conditions were reached. Ma' clad temperature - 456*K (361 *F) 167 267 9

og i In several instances the Semiscale sys tar conflyuration or onointing conditions wore not typir.41 of the TitI Plant. The nas t slont f tr ant l' instances include: i (1) Potential for structures to provide excessivo coni tnu o r t he lI fl ui d. 1 (2) 1.a c"( o f sinula tion o f the Pilft vent valves. i (3) Core elevation ef fects. (4) Possible atypicality of power operated rellaf valve flew l due to ef fects of size. I (5) Use of charging purps to account for leakayo fror: purp s o,1,. l (G) 1.ack of s team generator secondary wa ter. l The structures in the Semiscale Mod-3 sys tem have o ver*.e. t vc sur f a< n [ area which will cause atypical energy transfer during thn ct""se o r a r i u s.1 tenperature transient. During the simulation o f a proe.surl7c relie r i transinnt the structures will absorb excess energy which wonid tend to l 1 increase the depressurf za t1on rate and provida cooler watei in iha e 'o e { f region. An atterpt was nado to provide more typical fluid rondit lons by increasing the cors! pawnr level by about 35% above tbn scalo value i.hlrh was arrived at by determining the rate of energy transfer to the veu ni I structure and increasing the core power appropriately. The Seniscale syster.' cannot provide a particulncly good s trula t ino l of vent valve actuation du-inq a pressurizer rel f er draf n tes t hm ause of elevation di f ferences luitween the hot and cold lens. Itowever t h i r, inability does not strongly influence the Seniscale tes t r esnite, c in< n the influence of the vent valves on the Tlli plant cnid len bahnvlor is limited due to the cold leg geonetry. tin adverse ef fects on t e s t. t o. iil ' r. are expected in Semiscale pressurizer relief valve drain testino hacno,n ~ of the lack of a vent valve s trulation, j 6] 2hh 10 M_ m

p) 1 1 y 1e: A particulnrly e f on t rir,nt et t t rei rru c tic t u r e n t', t- .'ff' a 4 and the Ti!I Plant is related to the location o f the top o f the core Y rel a ti ve to tha vessel nozzles. In the Till plant the ton o r th. u r. le a p p ro m i ca n t a l y at the elevation of the v ess el now !.e. In t eia tamtecola Systert. h 0W e v e t*. the top of the core it approw trna t el y i l t ". rm t*anen t h j i M"."O!;l."U.L' ",';r;"",;M ; "' 3.,i", ;; :O;;m,'*,.'.;';7,T ;;, ' ; ' *. .a the Till plant than in the Semiscale Mod-3 syr. tem. . ) Flow through the Sentscale pressurizer relief valve strulat ten is h not expected to completely duplicate, on a scaled basis, that which nicht C occur in the Till Plant. Critical flow through small ort f le ns (c.o. the (., 1 0.030 in. diameter Samiscale flow area) has been shown to be 'f i r rer ent .W* ",j from that experienced in 2-in. diarieter pipes, so that vent. f low /pr a v o' c V, relief character 1stics mt ght reasonably be expected to di r rce tonnnhnt S l T between the two facilities. \\ ( Decause of consider.ible leakage of pump seals (and ot her miu rilancoue e, small leaks) it was necessary to provide nakeup lisiuld to t he s ys t em. Iha -t') HPIS punp was rur, for brief periods at fixed intervals thronobout t he t e* t N ) to supply the additional liquid necessary to account for the pump s en1 i .y leakage rate. Although the makeup rate was small comparcel in tha d f< discharge rate through the sinulated pressurtzer relief vnivr. tim t int I amount of IIPIS liquid in,lected into the sys trvn over the <f or n e t on o r i t, test was a r.ubstantial amount. Thus, considernbla n'ht i t lena l c olu nni t e 2 was added to the primary sys ten liquid inventory thtouch ur.n o' the F. I 'i jH pump. As a resul t, the core thermal respons e may have been Ic s evat a .um than would have otherwise occurred. T 11 r T 167 269 n. [' I? T., h_ -\\;.. .~ ; ?.:- : + pn s

The secondary side of the steam generator was dry, I.n., no mot.lva fluid for heat trans fer. This condition rintnfzed the i n fl ue nt o nr secondary heat trans fer on the course o f the PP.V trans f ont in Semle.cnie. If ths temperature on the secondary stife of the steam opnerator Ic lower than the prinary system temperature the subcoolino on the inre un'fon leg will be increased, thereby increasing the subcnoling in the enro. Conversely, if the secondary side torperature is h ighar t.ha n tbc prinney side temperature the purnp suction dansity will be reiluce<! t hri nbv rc<forino the tore inlet subcooling. For a PP.V transi ent the r econdni y 'Idc terperature should be less than or equal to the prinary e.ide t er onr a t.n rc. Based on previous experiments contlucted in Samiscain, s t enr-einon r n 'o r beat trans fer is not expected to have a signi ficant in fluence on the er c. ur line relief drain tests. b 167 270 12

D. PRELI?ilflARY ASSESSMEtif or Tile Tiil PLAT 41 Resp 0il5E DURIllG VErlilflG Analysis Simpli fied calcula tions were perfortied to evaluate e xper tc<f i ce. pone.o First, the heatun of Tft1 to the PRV release rrode of depressurtration. no circulatton rate of the core fluid was calculated to be 400*F/hr 1( if the total occurred (heating the core liquid volume only) and 170'F/hr reactor vessel fluid volume ware tu be heated. (flai ther i nl e nis t ion included fuel or rretal mass heat capacity). from this it vas concludeI is v ecin vert that makeup should be providad to asture core coverage as beat inte to r'ect by steaming. About r>0 gpm was calculated as the rnquir ed 1 the steam generation needs. The expansion of the (then n t s red ) I r,no r t t o s cae.h ihn of gas to fill the hot leg, steam generator, and pressurf ree point of gas venting and norr rapid depressurization would reu h thfi a n.I point at about 300 ps1. At assuc'ed liquid relief rr te o f r.no upm steam rate of 110,000 #1hr, this was calculated to taka abnut unn bour. F 0 est The Semiscale systen depressurized slower; reachino ahnut in one hour with a smaller relative gas volume. Intparatino tba hInb velocity " gas" relief showed that the bot liquid in the pi cuoriier flashed to steam and separated yielding a larger total vn19ma of stonn to be re",leved prior to the time of liquid relief. The data al+.n showed that the pressurizer and surue line remained itquid full, thus T h e r. a fastusas not making that volume availahin for gas expansion. are being added to a more conplex model. Initial Indiu ttons nra that a reasonable description of the pressura transient and volune chanon will result from this model, and it should be applicable to Titi. 167 271 u r

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E. CONCLUSI0!Is (1) The Seniscale sys ten can be depressurized via tha p ropos o.1 r c t ho<l to a 1evel at wh!ch the RilR pumps can be activa ted anel usc I tn renove res idual hea t from the cora. (2) In the Seniscalo systen n'incondensible gas did not vent eas il y or uni fornly wl th the prorosed method. The noncondansthic nas linble i n entered the hot leg at approximately 3000 teconds. (3) Core uncovery in the Seniscale facility did not ncror unt fl a f ter a point in time at which the RllR pumps cottid have bann ar t f vat o,i ir da-5 d I,thus prevonting core uncovery). (4) The Seniscale results sugges t that if ECC fluid is injar t e I Into the systen at ra te comparable to tha t a t which the a s ve. t en is being vented, i signi ricant bene rits in the overall s ys ten res tense and core cooling may be real1zod. I i L (5) The heater rods in the Sentscale test remained 4 i a neule o r nooel l cnoling during the proposed trans lant and rod tonnera ture rises were minimal, t t (6) Depressuriza tion from 1050 psia to 49 ps f a was accomplishnel in the Sentscale tes t in approxinately 3 hours. 00111nu in thn corn did not occur until approxinately 6000 seconds a f t er i fin van' relief transient was int tf ated. i 167 272 h 14 I i!

(7) Sentscale results arc de rf n1tely influence <1 by such cralina <lis tort tons as geometr1c size, one-dinensional1ty, s tructura l hea t transfar nrca, and elevation in fl uences. Caution s hould be ex tirc it o,I i n t h. Infor-pretation and extrapolation o f these resul ts to any othe, stia rar l11 t y, e

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