ML20009G095

Forwards Model Study of Reactor Containment Sump Flow Characteristics. Justification for Performing Tests at Ambient Temp Conditions & marked-up Revised Response to FSAR Question 211.132 Encl

ML20009G095
Person / Time
Site:	Summer
Issue date:	07/29/1981
From:	Nichols T SOUTH CAROLINA ELECTRIC & GAS CO.
To:	Harold Denton Office of Nuclear Reactor Regulation
Shared Package
ML20009G096	List: ML20009G095 ML20009G099
References
NUDOCS 8108030322
Download: ML20009G095 (15)

Text

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SoVTH CAROLINA ELECTRIC a GAS COMPANY post ornes som 7s4 COLUMBIA, SOUTH CAROUNA 29218 4

T. C. NicHO Ls, J R.

Vgg Patsiot=Y AND Gnova Extcurwr July 29, 1981 y NL.d a-o ~= =

t A UG 3 0 199 y,,,, ;

"DJE"*,

Mr. Harold R. Denton, Director Office of Nuclear Reactor Regulation

't?

g U. S. Nuclear Regulatory Commission m

Washington, D. C.

20555

Subject:

Virgil C. Summer Nuclear Station Docket No. 50/395 Model Study of Reactor Building Sump

Dear Mr Denton:

In response to FSAR question 211.132 South Carolina Electric and Gas Corapany agreed to conduct a model study of the flow characteristics of the reactor building sump following a postulated LOCA for the Virgil C. Summer Nuclear Station.

Ten (10) copies of that study, conducted by Alaen Research Laboratory are provided.

The report contained several minor errors which were hand corrected.

These appear on pages 3 and 17.

The report will be reissued in approximately two to three weeks to revise those pages and to provide better quality pictures.

It is being submitted now with the markerd pages to allow you to expedite your review.

The revised report will be sent to you when issued.

Also included in this letter as Attachment 1 is justification for performing the model tests at ambient temperature conditions.

As described in the report no signi'icant vortex phenomena ocurred in the model test program; therefore the existing sump design is acceptable and no modifications are required.

In the next FSAR amendment (#27) the response to question 211.132 will be revised to incorporate the results of the report. A marked up copy of that revised response is also included in this letter.

If you have any questions, please let us know.

Yours very truly, T. C. Nichol s, Jr.

l I d 8108030322 810729

' /

g7 PDR ADOCK 05000395 i

A PDR

RBC:TCN:1kb Attachments cc:

H: R. Denton (10)

i. C. Summer w/o attach.

G. H. Fischer w/o attach.

H. N. Cyrus w/o attach.

T. C. Nichols, Jr. w/o attach.

J. C. Ruoff D. A. *.'auman w.o attach.

W. A. Williams, Jr. w/o attach.

R. B. Clary w/o attach.

O. S. Bradham w/o attach.

A. R. Koon w/o attach M. N. Browne w/o attach.

B. A. Bursey J. L. Skolds w/o attach.

J. B. Knotts, Jr.

C. A. Price w/o attach.

G. M. Moffatt w/o attach.

H. E. Yocom w/o attach.

J. B. Cookinham w/o attach.

PRS w/o attach.

File w/o attach.

o 3

s ATTACHMENT I ALDEN RESEARCH LABORATORY WORCESTER POLYTECHNIC. INSTITUTE May 6, 1981 Mr. Gary Moffatt South Carolina Electric & Gas Company Post Office Box 764 Columbia, SC 29202 VCS/ SUMP-ARL-260E

Dear Mr. Moffatt:

~

With respect to the question of conducting high temperature tests as part of the ongoing reduced scale model study at the ARL for the Virgil C. Summer Station, we would like to provide a general review of model similitude con-4 siderations, a summary of tests on the scale model to date, and a review of

]

why high temperature tests will be conducted as part of the full scale para-metric sump study through Sandia for NRC-DOE.

This will be followed by our recommendation regarding the possible need to conduct high temperature Tests using the V.C. Summer model.

Review of Model Scaling Considerations

~

General Models involving a free surface are constructed and operated using Froude similari+.y since the flow process is controlled by gravity and inertia forcer. The Froude number, representing the ratio of inertia to gravita-tional force, F = u/ h (1) where u = average velocity in the pipe g = gravitational acceleration s = submergence is, therefore, made equal in model and prototype F = F /F

=1 (2) r m p where m, p, and r der.ote nodel, prototype, and ratio between model and proto-type, respectively.

HOL DEN. MASSACHUSETTS 01520 + TELEPHONE 617-829-4323

r-7 Page 2 Mr. Gary Moffatt May 6, 1981 In modeling an intake sump, it is important to select a reasonably large geometric scale to achieve large Reynolds numbers and to reproduce the curved flow pattern in the vicinity of the intake (4).

An asymptotic be-havior of energy loss coefficients with Reynolds number is usually observed in similar flows (2).

Hence, with F7= 1, the basic Froudian scaling cri-terion, the Euler nunbers, E, will be equal in model and prototype.

This implies that the flow patterns and loss coefficients are equal in model and prototype.

Similarity of Vortex Motion

~

Fluid motions involving vortex formation in sumps have been studied by several investigators (1, 4, 5, 6).

In addition to the prLaary forces of gravity and inertia, viscous and surface tension forces could influence the formation and strength of vortices (1, 5).

The relative magnitude of these forces to the fluid inertia force is reflect-ed in the Reynolds and Weber numbers, respectively, which are defined as:

=^ u d/v (3)

R

~

(4)

~

W

=

(c/pr) where d = intake diameter r = characteristic radius of vortex o = surface tension force per unit length v = kinematic viscosity, a function of water temperature i

p = mass density per unit volume

~

It is important for a reduced scale model study to ascertain any deviations in similitude (scale effects) attributable to viscous and surface tension forces in the interpretation of model results. For large R and W, the ef-fects of viscous and surface tension are minimal, i.e., inertial forces pre-dominate. Surface tension effects are negligible when r is large, which will be true for weak vortices where the free surface is essentially flat.

Con-versely, only strong air core vortices are subject to surface tension scale effects. Moreover, an investigation using liquids of the same viscosity but 3

3 different surface tension coefficients (o = 4.9 x 10 lb/ft to 1.6 x 10 lb/ft) showed practically no effect of surface tension forces on vortices (1).

The vortex severity, S, is therefore mainly a function of the Froude number, but could also be influenced by the Reynolds number.

S=S (F, R)

(5)

y

+

7 Page 3 Mr. Gary Moffatt May 6, 1981 Anwar'(4) has shown by principles of dimensional analysis that the dynamic similarity of fluid motion at an intake is governed by the following dimen-sionless parameters 4Q u

j, and --

vs s

ud

/2gs g,

where Q = discharge through the outlet u = tangential velocity at a radius equal g

to that of outlet pipe The influence of viscous effects was defined by the parameter Q/(v s), known as a radial Reynolds number, R.

For ' similarity between the dimensions of a R

vortex of strengths up to and including a narrow air-core type, it was shown by experiments that the influence of RR becomes negligible if Q/(v s) was 4

greater than 3 x 10 (4).

For the prototype of this study, the value of R for the operating temperature range of 70' and above, and using the submer R 5

gence to the floor grating, was greater than 1.1 x 10.

In the scale model, 4

the value of RR for the RHR sumps was 2.6 x 10 for Froude velocity and 4.4 4

x 10 for prototype velocity, both for water temperatures of 50*F, Thus, vis-cous forces would have a negligible role in this model study.

Dynamic simi-2 larity is obtained by equalizing the parameters 4Q/ued, u//2gs, and d/2s in model and prototype.

A geometrically similar Froudian model satisfies this condition.

To c'ompensate for any possible excessive viscous energy dissipation (Reynolds number scale effect) and consequently less intense model vortex, various in-vestigators have proposed increasing the model flow and, therefore, the intake and approach velocity, since the submergence is maintained constant. Operating the medel at the prototype inlet velocity (pipe velocity) is believed by some researchers to achieve the desired results (1).

This is often referred to as the Equal Velocity Rule. The test procedure for the present study incorporat-ed testing the model at prototype pipe velociti es to achieve conservative pre-dictions.

ARL Vortex Activity Projection Technique ARL has conducted independent research to assure that no scale effect on vor-tex activity due to Reynclds number exists in models with weak vortices. A ced.alque was developed (9) to extrapolate model vortex activity to prototype Reynolds numbers by using elevated model water temperatures and varying model flow velocity (Froude ratio), and this has been applied to several studies (7, 8, 10, 11, 12).

Figure 1 illustrates the method.

The ordinate, F, is the

r s

l Page 4 Mr. Gary Moffatt May 6, 1981 ratio of model to prototype Froude number, while the abscissa is the inlet pipe Reynolds number, R.

The objective is to determine flow conditions at Fr = 1 at prototype R from tests at lower than prototype R.

Assume the model to operate at flow less than Froude scaling (Fr < 1) at point al. By increasing the discharge in the model while keeping the same submergence and water temperature, F and R are increased in increments, corresponding r

to a point, aN, where a vortex of type N is observed.

The model Reynolds number can also be changed by varying the kinematic viscosity with tempera-ture changes, and similar tests performed to locate b, another point on N

the locus of type N vortlees.

Extrapolation of the line of cons, tant vortex strength of type N can be made to a prototype Reynolds number at the proper Froude number (Fr = 1), Point P.

The locus could represent any expedient N

measure cf vortex severity, including inlet loss coefficient and inlet swirl angle. Any scale effects due to viscous forces would be evaluated and taken into account by such a projection procedure.

Figures 2, 3, and 4, and Tabla 1, iaou the effect of increasing Reynolds num-ber and increasing Froude ratio ror the final designs of four containment sump model studies conducted at ARL having scale ratios of 1 to 2.5 to 1 to 4.

The vortex types designated on these figures are shown in Figure 5.

In all_ cases, the data show no measurable changes in vortex strength, even for types 3 and 4, with Reynolds number at constant Froude ratio. This is reasonable since the Reynolds numbers are all above the limiting value (1, 4), a previously. des-cribed similitude requirement. Minor increases in vortex strength occur when the Froude ratio is increased. Other measurements, such as swirl in the inlet p,ipe, have also shown no measurable dependence on Reynolds number.

This indi-cates that reduced scale model tests ire e. direct indi, cation of prototype per-formance for weak vortices, particularly if vortex suppressors are part of the design, even at Froude scaled flow (i.e., Fr = 1).

Tests at higher than Froude scaled flow are seen to give conservative results, i.e.,

somewhat stronger vor-tices than expected in the prot ) type.

V.C. Summer - Test Results Approximately 50 conditions of varying approach flow distribution, and vari-ous combinations of blocking the bar racks and screens have been tested in the reduced scale model. Measurements include classification of vortex type, swirl in the inlet pipe, and inlet loss coefficient.

These tests show that no vortices stronger than type 1 (incoherent surface swirl) occurred for any combination of test variables, including operating the model at prototype inlet velocities as well as at Froude scaled velocity.

The only swirl ob-served is generated by obstructions in the approach flow, and these swirls are weak (type 1) and transient. Pipe Reynolds numbers are greater than 1.2 x 105 for the minimum flowrate modeled, the RB spray inlet.

This Rey-nolds number is comparable to the minimum for the previous studies which indicated no increase in vortex activity for increasing Reynolds numbers at constant Froude ratio.

The horizontal floor grating and the relatively deep submergence of the in-let pipes apparently act to suppress the formation of any coherent vortices above the reactor ~ floor.

""1 Page 5 Mr. Gary Moffatt May 6, 1981 Full Scale Parametric Sump Study The generic study of full scale containment sumps being conducted at the ARL via Sandia Laboratories for the NRC-DOE addresses an unresolved safety issue (Task A-43) associated with ECCS systems.

As part of this general study, testing will be conducted using water heated to about 160*F to approach pro-totype operating conditions. Twc ump configurations will be selected for these tests, both configurations having been previously testing with normal water temperature, and showing evidence of intermittent air core vortices and air ingestion into the inlet pipes.

The basic reason for the high temperature tests are to determine the effects of decreased water viscosity and surface tension on two phase flow phenomena involving air and water.

The effects of increased vapor pressure per se' are expected to be negligible since the amount of air and water vapor released from the liquid phase is minimal compared to the ingestion of air by vorti-ces.

Also, the effects of increased Reynolds number on single phase flow parameters such as inlet loss coefficient and swirl angle (except due to change in vortex strength) are expected to be minimal since Reynolds numbers with normal water temperatures are already above any transitional values for changes in f ew patterns.

Basically, the high temperature tests are to deter-mine if a coherent but weak vortices (type 3 or 4) becomes an air core vortex,

.and if a weak air core vortex becomes stronger-and ingests more air (ise.,

will the void fraction increase).

Coherent vortices could become stronger with higher water temperature since vortex cores are regions of high shear (velocity gradients) and a decrease in viscosity could increase tangential velocities.

Based on work by others, the effects are expected to be small since the Reynolds number for all test conditions are well above suggested i

l minimum values relative to scale effects (1, 4).

All testing will be con-l ducted without any vortex suppressor such that the vortex can become stronger should that be the tendency.

l Evaluation and Conclusions Based on general similitude considerations, the results from the V.C. Summer sump reduced scale model testing program, and the intent of the high tempera-ture tests in the full scale sump facility, the following conclusions may be made regarding high temperature tests for the V.C. Summer model.

The V.C. Summer model was designed for minimal scale effects at Froude scale flow, but was also tested for conservatism at prototype velocities. No co-herent vortices were observed for any combination of test parameters. Past work at ARL with high temperature testing of scale models has shown that swirls and weak vortices are not subject to scale effects when Reynolds num-bers are above recommended minimum values.

The horizontal floor bar rack of the V.C. Summer sump acts as a vortex suppressor, which together with the i

I L

r-Page 6 Mr. Gary Moffatt May 6, 1981 lack of coherent vortices and scale effects, makes the question of how higher Reynolds may effect vortices a moot point. There is no technical reason that the observed weak swirls (type 1 vortices) will become ob-jectionable vortices for the V.C. Summer sump design, and tests at ele-vated water temperatures are, therefore, not warranted in this case.

Please contact us should you have any questions or if you would like any additional material.

Sincerely, h'/. 7'.

CL,

• L

' ~-

George E. Hecker Professor and Director GEH/nrb Enclosures P

e e

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A

f REFERENCES 1.

Daggett, L.L.,

and Keulegan, G.H., " Similitude Conditions in Free Surface Vortex Formations," Journal of Hydraulics Division, ASCE, Vol.'100, pp.

1565-1581, November 1974.

2.

Daily, J.W.,

and Harleman, D.R.F., Fluid Dynamics, Addison-Wesley Pub-lishing Company, 1965.

3.

Rouse, H.,

Handbook of Hydraulics, John Wiley & Sons, 1950.

4.

Anwar, H.O., Welle,r, J.A.,

and Amphlett, M.B.,

" Similarity of Free-Vortex at Horizontal Intake," Journal of Hydraulic Research, IAHR 16, No. 2, 1978.

5.

Hattersley, R.T.,

" Hydraulic Design of Pump Intakes," Journal of the Hydraulics Division, ASCE, pp. 233-249, March 1965.

6.

Reddy, Y.R.,

and Pickford, J., " Vortex Suppression in'Stil' ling Pond Over-flow," Journal of Hydraulics Division, ASCE, pp. 1685-1697, November 1974.

7.

Durgin, W.W., Neale, L.C., and Churchill, R.L., " Hydrodynamics of Vortex Suppression in the Reactor Building Sump Decay Heat Removal System," ARL Report No. 46-77/M202FF, February 1977.

8.

Padmanabhan, M., " Hydraulic Model Studies of the Reactor Containment Building Sump, North Anna Nuclear Power Station, Unit 1," ARL Report No. 123-77/M250CF, 3 'y 1977.

9.

Durgin, W.W.,

and neu er, G.E., "The Modeling of Vortices at Intake Structures," Joint Symposium of Design and Operation of Fluid Machinery, Colorado State University, June 1978.

10. ' Padmanabhan, M., " Hydraulic Model Investigation of Vortexing and Swirl Within a Reactor Containment Recirculation Sump," D.C. Cook Nuclear Power Station, ARL Report No. lO8-78/M178FF.

11.

Padmanabhan, M., " Assessment of Flow Characteristics Within a Reactor Containment Recirculation Sump Using a Scale Model," McGuire Nuclear Power Station, ARL Report No. 29-78/M208JF.

~

12.

Padmanabhan, M., " Investigation of Vortexing and Swirl Within a Contain-ment Recirculation Sump Using a Hydraulic Model," Seabrook Nuclear Power Station, ARL Report No. 25-81/M296HF, 1981.

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MINIMUM WATER LEVEL MAXIMUM FLOW BOTH PIPES OPERATING (CASE 8)

BLOCKAGE SCHEME NO.12 NUMBERS WITHIN BRACKETS DENOTE MAXIMUM VORTEX TYPES OBSERVED T*F =

56 82 121 155 O

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g (2,3)

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REYNOLDS NUMBER, l

FIGURE 3 FROUDE NUMBER RATIO VERSUS REYNOLDS NUMBER SHOWING MAXIMUM OBSERVED VORTEX TYPES IN THE SUMP M

e CASE 1 PIPE 2 AT 9,500 GOM W.S. EL 602 FT 10 INCHES NOTE:

NUMBERS WITHIN BRACKETS WITH GRATING BLOCKAGE SCHEME 5 DENOTE VORTEX TYPES 2

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FIGURE 4 VORTEX TYPES OBSERVED DURING HIGH TEMPERATURE-

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HIGH VELOCITY TESTS (MODIFIED SUMP)

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m VORTEX TYPE INCOHERENT SURFACE SWIRL 1

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E SURFACE DIMPLE:

h COHERENT SWIRL AT SURFACE DYE CORE TO INTAKE:

3 COHERENT SWIRL THROUGHOUT WATER COLUMN e

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FIGURE 5 VORTEX STRENGTH SCALE FOR INTAKE STUDY

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TABLE 1 EXPERIMENTAL OBS,ERVATIONS OF VORTEX ACTIVITY IN THE SUMP PHASE 3 TEST SERIES: SCHEME 4 WITH SCREEN BLOCKAGE WATER MODEL 0

TEMPER ATUR E Hx 10 VORTIMETER READING k

• F INLET 2 REV/100 SEC.

REMARKS TEST NUMBER DATE 6-1 6/22/77 1.0 64 1.50 34, 35, 35 Surface swirls and dimples observed (Types 1-2) 6-2 6/22/77 1.4 65 2.10 49, 49 Surface swirls anif dimples observed (Types 1-2)

U 2.70 51, 51, 49 Surface swirls and dimples 6-3 6/22/77 1.8 65 observed (Types 1-2) 6-4 6/23/77 1.8 104 4.37 46,46 Surface swirls and dimples observed (Types 1-2) 6-5 6/23/77 1.4 107 3.40 45,45,46 Surface swirls and dimpics observed (Types 1-2) 6-6 6/23/77 1.0 103 2.43 15,15,15 Surface swirls and dimples observed (Types 1-2) 6-7 6/24/77 1.0 140 3.38 25, 25, 24 Surface swirls and dimples observed (Types 1-2) 6-8 6/24/77 1.4 143 4.73 47, 48, 45 Surface swirls and dimples observed (Types 1-2) 6-9 6/24/7

1.8 139 5.74 49, 50, 48 Surface swirls and dimples I

observed (Types 1-2)

Cther n-te

.a1 ble kage sources include:

l.

Fifteen fibreus reinforced silicon rubber encl osure s (a ppr oxi-(

mat ely 4 square f eet each) which provide forced air cooling of equi pm en t inside the pressurizer cubicle,

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2.

Rubber e x pan si on joints in the ring header duct, and 3.

Eubber boots for reactor nozzel and support feet' ventilation (6 tctal at approximately 14 square feet each).

/

The blockage potential of the equi pa ent covers is subj ect to the s ame l oc at i en considerations as the Temp Mat inside the ' pressurizer cubicle.

In addition, the covers are located high in the cubicle and would have to cicar i ns t r umen t s, piping, and grating to reach the cubicle opening at the bottom.

The ductwork expansion joints are so removed f rom the s umps and pot enti al mis siles that their 23 bl ockage po t en t i al is very small.

The reactor nozzel and support ventilation boots are bol ted to the wall and clamped to the pipe.

(

However, if a boot became free due to its physical location, it would most likely remain in the i ncore i nstrument tunnel.

The potential for debris getting into the suction piping and causing or other components, is greately blockage or damage to the pumps reduced by the trash racks and screens.

For the components in the are the determin-ECCS flow path the Reactor Euilding Spray nozzles ing factor for sizing the smal l e s t strainer screens.

Strainer

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with 1/4 inch square openings will allow only those s creens

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particles smaller than 1/4 inch square to pass ccepletely through

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the system.

In order to perf orm a c ocpl e t e analysis, SCE6G her contracted Alden p e.e fo m y

a model study of the Vir gil C.

Kesearch Laboratories to Surmer Nuclear StationcECCS sumps and suction piping.

The study 4.Li h

211.132-7 AME v tI::' C2 2 7 b Vf UST iT, '?E1 e

investi fated.everal d e r : gre p.enomena incl uding swirling and vortex-i ing under full f l ew r.nd 50*. bl ock s t rai ner conditions, losses icad-wert ing to insufficient NPSH, and air entrainment.

Sc al ing f a c t or s rii:d,

'r m

also ar evaluated te ensure similarity between the model and proto-type operating under LOCAconditions,.jIf robler vitt the cr rent desi are

..cov. ed d ring

• ac s r.dy, d sign r idifi.tions,cill be r

adeq' ate s>1utio-is f<and.

ihese.esign

[

[

inv tiga ed u il a-e dific. ion < will

.hcr.'; mad to ti.

ful' scair s ump aes i gns.

RHR and RB Spray pur.p flow beyond rated runout is another condition which requires evaluation. Due to the different known and unknown conditions of operation, this evaluation i s more important for the RHR system.

Therefore, full scale tests of the RHR pumps were per-f omed at the Virgil C. Summer Nuclear Station for the different modes of injection and recirculation.

As a result of these tests, flow restricting orifices have been installed et the outlet of each 23 heat exchanger.

A retest of the RHR system will be perf omed to insure the adequacy of these orifices.

A full scale test of the RB Spray discharge ring headers and spray nozzles is not feasible. However, this system is only subjected to two worst case operating conditions, i nj ec ti on and recirculation, as i

its design basis.

Full scale tests have been perf omed using the suction and recirculati9n test returns to the RPST.

Test data on krs DseH the suction piping

--1;'. i compared to the results of the design calculations as a measure of their accuracy.

A detailed analysis f

wM a then iam perfomed of the Reactor Building Spray System's calc,u-possible M fIs lations to ensure that flow rates beyond runout are not 10segusaT fun p de,nay<,

[a do pi se reter o Stu lett_r to NR<

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~t' 211.132-8 AMENDMENT g 27 s-IcS1 AUf()$[

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