Richard SchultzWilliam Wieselquist

2001 RELAP5 User’s SeminarSun Valley, IDSeptember 2001

Validation & Verification:Fluent/RELAP5-3D©

Coupled Code

The Idaho National Engineering and Environmental Laboratory

The Fluent RELAP5-3D Coupling..

• What we’re doing

• Why we’re doing it

• How we’ll make sure it is OK

• Our future plans

The Idaho National Engineering and Environmental Laboratory

Overall Perspective…• DOE’s Generation IV Roadmap effort is a part of national strategy

to gain public acceptance of nuclear power, and to encouragevendors and utilities to consider nuclear power as an optionagain.

• The roadmap program has received nearly a hundred reactorplant designs to evaluate including water-cooled, gas-cooled,liquid-metal cooled and other concepts.

• With the process underway to winnow the concept number downto 6 or so, a parallel effort is underway to evaluate ourinfrastructure:

o Analytical toolso Regulatory & licensing practices…etc.

The Idaho National Engineering and Environmental Laboratory

Analytical Tools for Advanced Systems

• Further development is needed—particularlyfor working fluids other than water.

• Recent developments—particularly in theCFD world—need to be considered and usedif advantageous.

The Idaho National Engineering and Environmental Laboratory

Fluent & RELAP5-3D Are BeingCoupled to…

• Enable an entire system tobe modeled using 1-Dfeatures of RELAP5

• While modeling somesections of systems in greatdetail using Fluent

The Idaho National Engineering and Environmental Laboratory

Development Underway UsingGas-Cooled Reactors as Basis

• PBMR is focus

• Working fluid: helium

• Work to couple codes is ongoingby Walt Weaver. He will use PVM& same techniques described inpapers by himself & Aumiller, et al.

The Idaho National Engineering and Environmental Laboratory

Once Coupling Is Completed…• Validation & Verfication* will be used to:

– Check that Fluent and RELAP5/ATHENA have been coupledproperly

– Examine the strengths and weaknesses of the coupled code• Important features that will be examined:

– Behavior at interfaces between Fluent and RELAP5/ATHENA– Using neutronics with Fluent– Modeling flow through packed beds____________________“Verification” is solving the equations right while “validation” is

solving the right equations.

7

The Idaho National Engineering and Environmental Laboratory

A Portion of V&V Matrix

Calis, H. P., et al,2001.

CoreFluent’s capability of calculating flowthrough portion of packed bed.

AirFlow through packed-bed

Stewart, W. T., etal, 1992.

Potential pipebreak andcountercurrentflow at break whennot choked

1. Mesh coupling between Fluent &RELAP52. Flow behavior calculated byFluent

Water &SF6

Countercurrent two-phaseflow

Bovalini, R., et al,2001 (used bypermission of Y.Hassan)

Core; althoughthis data set is forgeometry unlikePBMR,

RELAP5/ATHENA neutronicscoupling with Fluent mesh

WaterNeutronics-fluid Ineraction incore region(LWR)

Baughn, J. W., etal, 1984

PBMR inlet pipeand inlet plenum

1. Mesh coupling between Fluent &RELAP5

2. Flow profiile calculated by Fluent

AirTurbulent flow in backwardfacing step with heat transfer

Streeter, V., 1961PBMR inlet pipeMesh coupling between Fluent &RELAP5

HeliumTurbulent flow in pipesection

ReferencePBMR Regionof Interest

Phenomena of Interest orObjective

WorkingFluid

Experiment or Case

The Idaho National Engineering and Environmental Laboratory

Data (V&V Cases) Not Always Ideal• German data (AVR & THTR at Uentrop-Schmehausen)

not available to public• Currently:

– No neutronics-fluid interaction data for PBMRcore—but Fluent can’t model a packed-bed verywell yet anyway.

– Haven’t found countercurrent flow data moreapplicable (for CFD code) than Stewart, et al, 1992

• Working fluid and scaling usually not desirable.

The Idaho National Engineering and Environmental Laboratory

References• Streeter, V. L., Fluids Handbook, McGraw-Hill, 1961.• Baughn, J., M. A. Hoffman, R. K. Takahashi, and B. E. Launder, 1984,

“Local Heat Transfer Downstream of an Abrupt Expansion in a CircularChannel with Constant Wall Heat Flux,” Journal of Heat Transfer, Vol.106: 789-796, November 1984.

• Bovalini, R., F. D’Auria, G. M. Galassi, A. Spadoni, & Y. Hassan, 2001,“TMI-1 MSLB Coupled 3-D Neutronics/Thermalhydraulics Analysis:Application of RELAP5-3D and Comparison with Different Codes,” 2001RELAP5 User’s Seminar, Sun Valley, ID., September.

• Stewart, W. A., A. T. Pieczynski, & V. Srinivas, 1992, Natural CirculationExperiments for PWR High Pressure Accidents, EPRI Project No.RP2177-5.

• Calis, H. P. A., J. Nijenhuis, B. C. Paikert, F. M. Dautzenberg, & C. M. vanden Bleek, “CFD Modeling and Experimental Validation of Pressure Dropand Flow Profile in a Novel Structured Catalytic Reactor Packing,”Chemical Engineering Science, (56), 1713-1720,

The Idaho National Engineering and Environmental Laboratory

Turbulent Flow in Straight Pipe• Purpose: Study mesh coupling between Fluent and

RELAP5/ATHENA. Determine factors which maydetrimentally influence flow

• Assume well-developed flow (left to right); study meshcouplings and influence on velocity profile atFluent/RELAP5 interface.

Fluent FluentRELAP5

Flow direction

The Idaho National Engineering and Environmental Laboratory

Backward-Facing Step: ExpandingFlow with Heat Transfer• Purpose: Study coupling between

Fluent—RELAP5/ATHENA and validate Fluent’scapability to model flow distribution downstream ofstep.

• Region of applicability: entrance flow into PBMR core.

The Idaho National Engineering and Environmental Laboratory

Backward-Facing Step (Cont-2)

The Idaho National Engineering and Environmental Laboratory

Backward-Facing Step (Cont-3)

0

0.5

1

1.5

2

2.5

3

3.5

4

4.5

5

0 10 20 30 40 50 60

x / H

Nu /

NuDB

1b2c3b5aBaughn

Ratio of local Nu to Nu for fully-developed flow as function of length for various turbulence models in Fluent—compared to Baughn data

The Idaho National Engineering and Environmental Laboratory

Backward-Facing Step (Cont-4)

Typical velocityprofiles calculatedby Fluent.

Study not yetcompleted

The Idaho National Engineering and Environmental Laboratory

Neutronics (RELAP5)-Fluent Coupling• Perhaps best approach

is to use OECD, CSNI-NSC PWR MSLBbenchmark.

• Approach not defined.Perhaps model onlyportion of core usingFluent.

0

5

10

15

20

25

V3

510

15

V15

10

15

V2

XY

Z

570565560555550545540535530525520515510505500495490

moderator temperature at 2nd power peak t=161.9s 03 Apr 2001 moderator temperature at 2nd power peak t=161.9s 03 Apr 2001

The Idaho National Engineering and Environmental Laboratory

Countercurrent Steam-Water Flow ModeledUsing Subcooled Water & SF6• Purpose: Examine capability of Fluent to model

countercurrent flow of two different fluids• Test performed by Westinghouse to study movement

of superheated steam into SG and return of saturatedwater to core

• SF6 (sulfur-hexafluoride) used to model superheatedsteam at high pressure.

• Virtue of these data are the nice temperaturedistribution measurements in leg, SG plenum, andcore

The Idaho National Engineering and Environmental Laboratory

Interim Plans: Use These DataUnless Better (More Applicable)Data Can Be Found

The Idaho National Engineering and Environmental Laboratory

Fluent Calculation of FlowThrough Pebble Bed• Calculation was

performed using CFX5• Ageement with data

within 10%.• Both laminar flow and

turbulent flow weremodeled.

The Idaho National Engineering and Environmental Laboratory

V&V Packed Bed Data-CFX5Comparison: Within 10%

The Idaho National Engineering and Environmental Laboratory

Summary• The Fluent-RELAP5 coupling is underway.• A preliminary V&V matrix has been constructed.• A search is underway for better data—but data are not

readily available