Fluid Dynamics Simulation in the Nuclear Industry - Ansys UK/staticassets/Fluid... · Fluid...

Fluid Dynamics Fluid Dynamics Simulation in the Simulation in the Nuclear IndustryNuclear Industry

Fluid Dynamics Fluid Dynamics Simulation in the Simulation in the Nuclear IndustryNuclear Industry

Phil StopfordPhil StopfordPhil StopfordPhil Stopford

© 2011 ANSYS, Inc. All rights reserved. 1 ANSYS, Inc. Proprietary© 2011 ANSYS, Inc. All rights reserved. 1 ANSYS, Inc. Proprietary

Phil StopfordPhil Stopford

ANSYS UKANSYS UK

Phil StopfordPhil Stopford

ANSYS UKANSYS UK

De Vere Milton Hill House

6th April 2011

Contents

• Multiphase model validation

– Vertical and horizontal pipe flow

– Bubbly flow around obstacle

• Case studies

– Fuel assemblies

© 2011 ANSYS, Inc. All rights reserved. 2 ANSYS, Inc. Proprietary

– Fuel assemblies

– Pressure vessels

– Steam generators

– Safety systems

– Radwaste

• Conclusions

ValidationCFD Exp.


CFD Exp.

Validation Test Cases

• Two-phase flows with lower

void fraction

– Vertically upward

– Vertically downward

– Horizontal, concurrent

– Horizontal countercurrent

• Free Surface Flows

– Horizontal concurrent


– Impinging Jets (Downcomer)

– Free Jets (ECCS)

• Flows with phase change



• Two-phase flows with higher

void fraction

– Vertically upward

– Vertically downward

– Horizontal, concurrent


• Bubbly flow around obstacle

• Flows with phase change

– Condensation

– Evaporation

– Flashing

– Boiling

Vertical Pipe Flows

• Experiments

– FZR

– MTLoop & TOPFLOW

Facility

• Modeling & Validation

– FZR


– FZR

– ANSYS CFX

• Target variables

– Volume fraction

– Gas velocity

– Water velocity

– Bubble size distributions

FZR-052

2.0

2.5

3.0

3.5

normalized volume fraction [-]

Experiment FZR-052

Antal W.L.F., Grid 2

Tomiyama W.L.F., Grid 2

Frank W.L.F., Grid 2


0.0

0.5

1.0

1.5

2.0

0.00 5.00 10.00 15.00 20.00 25.00

Radius [mm]


FZR-096

2.0

2.5

3.0

3.5


Experiment FZR-096

Antal W.L.F., Grid 2

Tomiyama W.L.F., Grid 2

Frank W.L.F., Grid 2


0.0

0.5

1.0

1.5

0.00 5.00 10.00 15.00 20.00 25.00

Radius [mm]


wire-mesh sensormovable diaphragm

movable diaphragm

TOPFLOW Test FacilityTOPFLOW Test Facility


gas injection

3d Bubbly Flow Around Obstacle

• Streamlines around the

obstacle

– Vortex system around the

edge of the obstacle

– Velocity component from left

to right along the


to right along the

vortex core

– Higher residence time in

vortex core close to the

straight edge


Water Velocity Comparison

• Comparison

CFD � Experiment

• Absolute water velocity

distribution in symmetry plane

• Import of exp. data

CFD Exp.


• Import of exp. data

into CFX-Post

• Pre-interpolation of exp. data

to ∆z=0.01m


Air Void Fraction Comparison

• Comparison

CFD � Experiment

• Air void fraction

distribution in symmetry

plane

CFD Exp.


Experimental Test Facilities

@ TU Munich

• Regular slug flow with defined inlet BC´s

Wire mesh sensor data

Air

time


time

By courtesy of

Edurne Carpintiero, TD, TUM

Slug Flow Simulation -

Mass Flow Boundary Condition

• Sinusoidal free surface perturbation (initialization and inlet BC’s)

• Transient simulation of 7.0s real time

• Slug formation after ~4.0s at x~4.0m

• Stable slug propagation; slug front/tail are continuously changing


Slug Flow Simulation -

Mass Flow BC’s (cont.)

First comparison with experimental data:

• Start of slug formation at ~4.0m from the inlet

• Difficult to reproduce experimental setup in CFD

– Inlet BC’s (e.g. phase mixing, inlet turbulence properties)

– Pressure outlet conditions (pipes & tanks downstream of test section)

• Quantitative comparison difficult for strong transient flow

– Small number of computed slugs


– Small number of computed slugs

– Slug length affected by limited pipe length and/or inlet conditions

numerical simulation experiment

slug period ~2.7m ~1.8m

slug transition velocity ~3.0 m/s ~2.7 m/s

pressure loss ~2000 - 2800 Pa on the last

4m, 2 slugs

� ~500 - 700 Pa/m

(strong transient)

~700 Pa/m

The Bartolomej Test Case

R = 7.7 mm

q=0.57MW/m

2

Variable Value

P 4.5MPa

R 7.7 mm


Z= 2 m

q=0.57MW/m

Gin=900 kg/(s m2)

R 7.7 mm

Gin 900 kg/(s m2)

0.57MW/m2

Subcooling 58.2 K

q&

Comparison to Experimental Data


Fuel Assemblies


Wall Boiling in a 3x3 Periodic

Fuel Rod Bundle

• 3×3 rod periodic section from a nuclear

reactor fuel assembly with guide vanes

• Periodic BC’s at all sides

• Wall heat flux of

qwall = 500 kW/m2

• Reference Pressure


• Reference Pressure

p = 15.7 MPa

• Water inlet velocity

vInlet=5.0m/s

• Water inlet temperature

TInlet= 607K

(= 12K water subcooling)


Geometry & Meshing

• Geometry preparation in ANSYS Design Modeler

• Extraction of periodic fluid domain



Geometry & Meshing

• Meshing in ANSYS Workbench

• Tet/Prism in lower part

• Extruded prism mesh in

upper part


upper part

• Mesh statistic

– Tetra: 1,752,320

– Hexa: 838,800

– Prism: 2,088,820


Fuel Rod Bundle


Vapour volume

fraction on

horizontal planes


Fuel Rod Bundle


Near wall

water

temperature


Fuel Rod Bundle


Streamlines &

water velocity in

horizontal planes

Reactor Pressure

Vessels


VVER-1000 Pressure Vessel Model


Courtesy of M. Böttcher, Institute of Reactor Safety (IRS)

Forschungszentrum Karlsruhe - KIT

RPV model – lower plenum

Flow through the perforated upper support columns:


Pressure loss obtained from a standalone full

detail model (3 Mio cells / column)Implementation of a pressure loss coefficient

in the coarser RPV model (5000 cells /

column)

Temperature Distribution and Flow

Patterns from the Loop Model


Influences on Mixing Coefficients


Swirl

Suppression

Asymmetric flow conditions at the RPV inlet affect the coolant mixing process !

The inlet conditions from the RPV models have to be revised.

Validation Case

• FZ Karlsruhe (Böttcher)

• VVER 1000– Unit 6, Kozloduy, Bulgaria

– OECD benchmark

• Geometry model


• Geometry model– Downcomer & core

– Upper & lower plenum

• Mesh– 13 million elements

• Simulation• ANSYS CFX & HPC

Validation Case

• Operating conditions

Loop # Cold leg

temperature,

°C

Mass flow

rate, kg/s

1 268.6 4737


2 268.7 4718

3 268.6 4682

4 268.6 4834

Validation Case

• Temperatures @ core exit


Steam

Generators


Design of Nuclear Steam Generator

• Duke Energy's nuclear power plant at

Oconee, South Carolina

• Babcock & Wilcox (Canada) unique

once-through steam generator


• Secondary-loop water is converted into

dry superheated steam

• Restrictor (7 venturis) added to outlets

• Need to check maximum ∆p

Design of Nuclear Steam Generator

Flow uniformly distributed


Design of Nuclear Steam

Generator

Pressure Velocity


Heat Exchangers

• Flow and heat transfer in shell and tube heat exchangers with three domains:

– Hot gas flow on shell side

– Conjugate HT through


– Conjugate HT through metal of tubes

– Process fluid flow inside tubes

• CFD used to optimise location of internal baffles and inlet and outlet location and deflectors

Porous Media HE Model

• Tube bundle geometry is often too

complex to model explicitly

• Represent shell-and-tube heat

exchanger by a porous domain

• Add 1-D additional variables to

represent the temperature and flow

Pressure Tube Temperature


represent the temperature and flow

velocity in the tubes

• Eulerian multiphase bulk boiling

model to predict steam production

• Add-on module to CFX

Steam Mass Fraction Shell Temperature

Containments


Containments

• LES of TH-20 test case

• 7 weeks @ 128 CPUs

• Time: 300 s

• Time step: 2.5 ms

• Mesh: 6 million hex Fan region

Helium

layer


• Mesh: 6 million hex elements

• Circumferential spatial averaging

• Monitor points = measurement locations

Fan casing

Fan region

Vessel

Containments


Safety

Systems


Vapor volume

fraction for a

simplified

Westinghouse

AP600 In-

Containment

Refueling

Water Storage

Tank

Courtesy Technical University of Aachen and

Center for Multiphase Research, RPI

Passive Safety Systems

Core Catcher:

• Hemisphere filled with steel

• Catches molten core

• Steel melts, then covers uranium

dioxide core material

• CFD shows progression of

fluid mechanics, phase

change, and heat transfer.


change, and heat transfer.



Vapor volume

fraction for a

simplified

Westinghouse

AP600 In-

Containment

Refueling

Water Storage

Tank

Benefits of CAE

– Gain physical insight about flow structures to guide safety system design

– Generate new parametric relationships to embed in system-level tools

– Extend behavior prediction from experimental to full scale conditions

Core Catcher


Deflagration/Explosion


Radwaste Storage




Drum Store

• Storage facility

– Inlet flow: 1 kg/s of air at 30°C

– Drum interior: thermal

conductivity 10 W/m/K with heat


conductivity 10 W/m/K with heat

source 16.5 kW

– Drum wall: thermal conductivity

25 W/m/K, wall emissivity 0.8

– outlet: fixed average pressure

Temperatures within

the Drums

Drum Storage Ventilation:

Inlet

Outlet


Temperature

Inlet

Flow

Diffuser

Symmetry

plane

Velocity

Dispersion: Hydrogen Build Up

Hydrogen build up in a

vault store with only

passive ventilation


Summary

• ANSYS CFD has well-validated turbulence and multi-

phase models suitable for nuclear industry

applications

• Both FLUENT and CFX were originally written with

nuclear industry applications in mind


• Long history of successful modelling cases

• Range of applications includes fuel assemblies,

primary and secondary circuit flows, containments,

safety and radwaste storage

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