ML20024C606

Summarizes Analysis Code Requirements & Verification Project,Action Item 5 on CRAFT2 Simulations of Small Break Transients

ML20024C606
Person / Time
Site:	Crane
Issue date:	09/04/1979
From:	Cullin J, Nirodh Shah BABCOCK & WILCOX CO.
To:	Morgan C BABCOCK & WILCOX CO.
References
TASK-07, TASK-7, TASK-GB GPU-2215, NUDOCS 8307120867
Download: ML20024C606 (4)

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l THE BABCOCK & WILCOX COMPANY hhh N

NUbii i. POWER GENERATION GROUP To l

C. D. Morgan. Manager. Tec M eni Staff

.cc:

C. E. Parks g

B. M. Duan-I From J

J. J. Cud.lin/3. B. Shah, LOCA Methods, Technical Staff gg g, File No.

Cust.

or Ref.

Date Sud. ANAT.YSIS CODE REOUIRD!ENTS A':D VERITICATION PROJECT:

9/4/19 I

ACTION ITIM 5 t

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A review of four frominent features of the B&W small break evaluation andel

-4=.s has been complaced as specified in Action Item 5 of the Analysis Code Eequire-Ig ~ {

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menta and Verific.ation. Project.. This review was aimed at the following af ain=a*=

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M$. ?c' [N._ "'$._ _.,. of CIAFT2 isimulatiods o.Y sma~11$reak trinsients:,,. (1) 'the d i

o a

._- m.

. - - -... ~..

" in vertically-stacked control vol.

-. y>'T '-,

43;-

. nique esplayed t.o prevent phase "p=~--W 9

tt.3 F_

--~..

.. ~.. ~. -....,:..

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unes', (2) the use of.'a multipliar in conjunction with' the Unaon bubble rise w

1. m.

-:- w

..;- r - :r.,.; r+:=:m-..

, v.....

'r

'd; ^ * ' " M8-modal to account for void distributions in large, verticany-orienced control -

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~

0;.. '

volumes, (3) sinalation of *stema generarv heat transfer particularly that

.{.

, ' attributable to -,~4hy feedwater, an: (4) pressurizar modeling within the 9.

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present capabilities of CIAFT2.. It was.riginally presumed that the investiga-h D

tion would establish the sensitiivity of tise small break evaluation model to

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t

.ceen.~.. -

P c-1.:-E -

these selected features. Early"on, however, it became obvious that the analysis'.. *

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results are strongly case-dependent." and that the emphasis should be shifted

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1. Dual riow Path Modeline..m small b.reak evaluation.model uti

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WW e

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nodes to anow for. counter enrrene flow and"also to reduce steam:" pancaking". ' _ ' '

t t.

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between verticany stackad nodes during phase separation In this model; a vertical flow path is divided into two equal area patihk staggered by about I

..T ;.

one foot and assigned opposite directions 'at the node interfa,ce. The pre-I i

.)

sent study ' indicates that the dual fluw path concept as.used adequately de.

3 However, a staggered length scribes the mixtura height in the top node.

i of about 0.5 feet was found to provide'optinun results in the test casa used

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• 3 9/4T/9

..r, Fici 2 C. D. NORCAN in this review.

l 2.

Bubble Risa velocity Multiolier

~

n a Wilson bubble rise velocity nodal is used to calculata phase separation

[.

rates in the reactor core and RCS piping. A factor of 2,38 is applied in L

the cora voluna to account for the effects of the nonuniform void fraction

. distribution largely attributable to tha. axial variation in cora power.

This approach is well-documented in ECCS Analysis --t~f ation films and is In other ves-supported by'%th 70AH2 analyses and level swell test data.

~

sal control.volunas a,'maltipliar of 2.0,is used, again to account for non-

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unifona void, distribut!sa,, p&-ily becauss of stana production af flashing..,..

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5. W*_~."_'a.e._ in conjunction

with. pr.im.ary metal ham't '.,In.this case, however, the suitipli...

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er has besa established also using FOAM 2 analyses whereis additional heat p.

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.1

.'c;99ft...

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sources were introduced. to approv4==e= the fh-W Trocesa. This procedura e

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T.h. i?h~,..***".=. (.aa equivalence between heat addition at" constant pressura,.and sa t.,g',',.,'

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..aexpansion.:: ::n.e gr'D. :...-,. e present stu.dy concentrated upon con irm p

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O.s"t*.dW.2.. s more defensible.. analysis, that the,v,a.lu.e used for the. bub.ble r.ise mu t -

_mu

a..

y

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i M U.-.M%N+':L. yliar is r==adia for its. intended application. -This objective ses met y..

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via GAFT2 de. pressurization casas in which the mixtura level behavior of a--

y r-e smvan

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2-

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single voinae.w. as compared to that of multinode model of equal' total volume.

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• Wilson bubbla rise amitipliers,of 2.2'and 1.6 applied to-the single voluna F.

vera found to "brachat" the' level behavior of the multinode modal in which

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v a.m.ana a..

smitipliara of 1.3 were used in each control volume.. nis indicatas that..

6

-A. - J.-. <.

n-It-a:

g u::;;:saryp.t. the bubbla rise amitipliar used in small break analyses-is reasonable..

".. 'p-

:b,.l. should ba noted;e,.....however, that the. effects.of spatial variations in void

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s.--

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-m.. -

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i ly b a proximated.by %..this technique.. Accurate best estimata.,

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. g& g,.,,....,ract on,can on

,..e.presults will'.11kaly requir.e a finer discretization or, at laast,.a m S.l; O

af,.

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g.2 m;In Z

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• r ;,.r..,c.~,..1sticated method for phase. separation within large control volumes.

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Steam Cenerator Heat Transfer.-

.The evaluation' model uses, for each steam generator, one control volume to

a. mme..

represent the secondary sida and two contro1 volumes to represent the pri-

.w.

- c. g. ;

l t25 mary side.~ The top primary node generally comprises the hot leg,after the s.,.

r "U" ' bend, SC inlet plenum *'and half the tube lengths. The steady state heat I

load in each'senarator is* equally distributed betvean the two primary volumes.

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6 The ov.erall heat transfer conductance is c h ulated based on the M H.t

.w..

Ioad and the initial camperatura difference across the corresponding primary

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and. secondary volunas. The UA value thus calculated is generally kept con- -

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.n stant during the transient if =u14=ry feedvst...e is actuated and naintained.

m P.

Aa --=d anefaa of the Davis Bessa 1 natural circhlation data Ofesor2ndum E.

V. Winks to E. C. Jones, " Description of T.a*urni circulation Test conducted at Davis Besse 1", NSS-14/T3.5, January '15,1979.) fn,14eates that, subsequest.-

to reactor and RCP trip, the bulk of the heat tzar.sfer la the SC occurs with.

in the secondary mixtura height even when the sydiary TV is injected ne. air i

the top of the tube bundia. The conductanes val.ca for the botton noda during

. a low flow b 52 initial flow) drops to about 20: of the 4=4eM value..Ia f

the top half of the tuba hundia, the heat transfer would seem to taka pimem i

only 'in tubes naar tha outar periphery, cone =4afny about 10 to 15% of tha f

.g v. t:

tubes, which are directly impinged span by the ATV' spray. The primary fluid

.a c..

in the r--*=ia-tubes. vill only be cooled below the secondary mixture level.

f, waan ;..

A more accurate. s4=sf ation of this behavior would require that a =ifefehmanal p

- (;y M.

sed.

g

t..?..

c&.p,.....

SC model k.u... It.is at least clear, from the Davia Besse 1 data, thht g

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n

n.: -

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a..

tha ganarator heat deman.d assumed in-small break analyses is optimistia.

,Qh',.~. ; tW,%. O n & W.v.%-'.s -4

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Pressurizer Modeline in CitAFT2

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In. the ECCS ev=ta=E4a= andel, the pressurizar behavior is typically simm1stad.

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'niing's single equi 11srink con' tal volumi. ~Thus, during a transient..ths. -

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.staan and' liquid regions remain at equal'tamperaturas' corresponding to satof *

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~ ration stacas at tha, pressurizer pressure. - Obviously,,the effect of this *.

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• limitationuponresultsis.Watirelycase-dependen't;thedirection,andrata-N

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of surge flow, hen.ce the interattien between' the praissarizar voluna and the..

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...RCS, vi21 vary acc.ord'ing' to. both breik's' ze and location and tha. timeduring M

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ther tzansient.. :... t,'the d=Ff e4=ae4== associated with an'..equilibrisma '.

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volume....simula.tio.n~ of pres.s.urizar behav.ior eannot be concise.:ly datatsmined.' *

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Ms.M-.

For a: s---d a wr

.#C t:ransienti. say an insurgi so' sequent, 'to 53rW, th's shirt"comia'as... f.,.....'

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which are intuitively expected.are borne ou..t'.by a.,nalyses the equilibrium g

.,W, g._.m.. :pressurizar andal underpredic.ts. the r.i.se in systan pressure and'wi21 sitter. C.

W 17........

v..

p

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delay or.entiraly =iss ths itp -c of high pressure setpoints and} trips.;'.. '.

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- rr.. cartata.atine, this limit.ation; am be onreona br =.:ing a==1:1=1==e-(

model for tha, pressurizar as.in the DEI simulation performed'by ECCS Analy5iss.

P

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That case study was carried out wing both single equilibrium. volume and mi-f.

F tivolumepressurizermode~is.' Fre'dicted systen pressure and pressurizar level

're :ia.exeillene gree.dne, d.iff' r'ing, as would be.expdet.d',' i 'the'early. ',.

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6. D. HOW",AN Psee 4

,r DCAIID REstTLTS L

Specific casa studias and e='~'* cions performed for Action Itan.3 have been f

assembled in a e=' ~'= tion file retained by Loca Methods.

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