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Design and Analysis of Nuclear Steam GeneratorComponents Using CFX-5

M. H. Hu

Westinghouse Electric Company

Madison, PAAbstract

A nuclear power plant U-Tube steam generator is a boiling heat exchanger with shell and tubes. Feed

water enters the generator as subcooled water and goes through a series of components to distribute into

tube bundle. In the tube bundle, the subcooled water boils, leaves the bundle as a mixture of steam andwater, and rises through moisture separation devices. Saturated water returns to a water pool where the

feed water enters and mixes with the saturated water. Steam continues rising up and leaves the steam

generator. Each component has its unique fluid conditions ranging from single phase to two-phase flowplus corrosion particles and solute. Modules of CFD analysis for various components are being developed

using the CFX-5 program. This paper presents four modules: (1) the lower tube bundle, (2) the sludge

collector in the water pool, (3) the steam flow through the last stage of moisture separation, and (4) the feedwater distribution ring. This paper presents results of the CFX-5 CFD analysis for these modules. The

paper demonstrates the CFX-5 role and its usefulness in the design and analysis of the nuclear steamgenerator. The continued module development will cover more components, in particular, in the tube

bundle where boiling takes place. For example, it is planned to evaluate steam and water flow through the

restricted passage of the tube support plate so that particulate deposition and solute precipitation in the

restricted passage can be examined and prevented.

Introduction

As a component of pressurized water reactor (PWR) power plant, a steam generator is a boiling heatexchanger that uses the reactor coolant as heat source to bring water into steam. Figure 1 illustrates a

nuclear steam generator that consists of thousands of U-shaped tubes through which the reactor coolant

passes and transfer heat to water outside the tubes. Within the tube bundle water boils and two-phase flow

results. Water is separated from the two-phase flow by the primary and secondary moisture separator.

Steam then leaves the steam nozzle and continues to the steam turbine. Feed water constantly supplies thewater mass to compensate the mass that evaporates and leaves the generator. Feed water brings with it thecorrosion products of either particulates or dissolved chemicals from upstream piping and components.

Therefore, water, vapor and corrosion products can form multiple phases in the tube bundle flow. In

summary, the steam generator thermal and hydraulic flow ranges from single phase to two-phase to

multiple phases. Depending on size of fluid domain in the tube bundle, fluid flow can be treated as eitherthe fluid flow with discrete solids or porous media flow.

It may be feasible to simulate the whole steam generator with just one model of computational fluid

dynamics (CFD). However, it is practical and flexible to approach the whole steam generator as a variety

of modules in setting up CFD analysis. After many years of searching and usage of different CFD codes,we finally settled on CFX CFD codes. In the beginning, we contracted the CFD analysis to outside firms.

For example, we had had ANSYS CFX to simulate flow in the upper, water pool, and the flow in the feedwater distribution ring. We finally convinced the management to use the CFD analysis and steadily build

up the in-house capability in applying the CFX-5 code. This paper is to present our successful modules ofthe CFX-5 CFD analysis for the nuclear steam generator.

Modules

We are continuing building CFD modules for a variety of needs in design and trouble shooting of the steam

generator. The paper will present four modules to date.

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Figure 1. Schematic of a Steam Generator

Module 1 Flow at Tube Sheet

Figure 2 depicts Module 1 to simulate flow at tube sheet of the steam generator. It consists of flow in the

downcomer and tube bundle. At the bottom end of the downcomer, a groove can relieve stress at the jointbetween the shell and the tube sheet. The design with the groove is new, and the designer wants to know

that such a groove will not compromise the fluid flow functions inside the tube bundle. For example, useof the groove should neither trigger the flow induced tube vibration, nor increase amount of settlement of

sludge particles on top of the tube sheet.

Downcomer

Tube Sheet

Water Level &Water Pool

Outer Shell

Channel Head

Hot Leg:

Coolant

Inlet

Feed Water

Distribution Ring

Primary Separator

Tube Support Plate

Secondary Separator

Feed Water Flow

Wrapper

U-Tube

Cold Leg:

Coolant

Outlet

Sludge collector

Steam Nozzle

Downcomer

Tube Sheet

Water Level &Water Pool

Outer Shell

Channel Head

Hot Leg:

Coolant

Inlet

Feed Water

Distribution Ring

Downcomer

Tube Sheet

Water Level &Water Pool

Outer Shell

Channel Head

Hot Leg:

Coolant

Inlet

Feed Water

Distribution Ring

Primary Separator

Tube Support Plate

Secondary Separator

Feed Water Flow

Wrapper

U-Tube

Cold Leg:

Coolant

Outlet

Sludge collector

Primary Separator

Tube Support Plate

Secondary Separator

Feed Water Flow

Wrapper

U-Tube

Cold Leg:

Coolant

Outlet

Sludge collector

Steam NozzleSteam Nozzle

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Figure 2. Zone of CFD Simulation at the Tube Sheet with Groove (Dimension in mm)

A scoping assessment concludes that effect of the groove would be negligible to the fluid conditions insidethe wrapper where the tube bundle resides. The tube bundle consists of about 5800 tubes with 19 mm in

diameter, and 27 mm in tube pitch in square layout. As expected, flow perturbation due to the groove feeds

into the tube bundle. However, its effect should be quickly dissipated within 2 or 3 tube rows from theperiphery of the tube bundle because the flow resistance due to the tube bundle is orders of magnitude

higher than the flow resistance due to the groove.

To confirm this conclusion, we set up a CFD simulation over a fluid domain that covers from the top of the

tube sheet to the second tube support plate. An 180omodel was used with a tube lane that is relatively openwithout tubes as shown in Figure 2. Along the tube lane fluid flow is at relatively higher velocity than that

through the regions where tubes exist.

During normal operation, it is expected to see boiling in certain zone of the tube bundle because of heat

transfer from the reactor coolant to the secondary side water. However, we consider it adequate to simulatejust the hydraulic effect without heat transfer. Two simulations were done with and without the groove,

respectively. The boundary conditions are (1) uniform velocity at 4.36 m/s at the inlet of the downcomerand (2) uniform pressure at the top of the second tube support plate. The second boundary condition is

assumed according to a simulation of the whole tube bundle by ATHOS code (Reference 1) that showed a

fairly uniform pressure at the second tube support plate. Therefore, use of uniform pressure boundary

condition is sound for comparative evaluation between design with and without a groove. The built-in k-

turbulence model was used. The tube bundle was treated as an anisotropic porous medium with momentumsinks. The momentum sinks take the following expressions.

UUCS xxxRxM ,2, =

UUCS yyyRyM ,2, =

UUCS zzzRzM ,2, =

For the tube bundle in cross flow,

6030

3686

3506

LowerS

he

ll

Groove

Wrapper

Downcomer

1st Tube Support Plate

2nd Tube Support Plate

Hot Leg Cold Leg

Outlet Boundary

Inlet Inlet

56.20

50

200 Wrapper Opening Tu

be

Lane

2104

6030

3686

3506

LowerS

he

ll

Groove

Wrapper

Downcomer

1st Tube Support Plate

2nd Tube Support Plate

Hot Leg Cold Leg

Outlet Boundary

Inlet Inlet

56.20

50

200 Wrapper Opening Tu

be

Lane

2104

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=

DS

S

SgfC

oL

L

Lc

xR

2

,2

12

The coefficient CR2,yhas the same expression as the CR2,x. The friction factor (Ref. 2) is as below.

+=

+

D

DSSD

D

SDU

DS

Sf

o

oL

L

o

L

b

o

oT

T

o/13.143.0

15.008.0

044.0

In the above expression, the cross flow velocity Uis either Uxor Uy.

For the tube bundle in parallel flow,

=

DSS

SS

DgfC

oTL

TL

ec

zR

2

2

,2

4

12

Where the friction factor (Ref. 3) is as below

=

DU

DSS

SSf ez

oTL

TL

2

2.0

4

046.0

For the tube support plate,

=

DSS

SS

Z

K

gC

oLT

LT

TSPc

zR2

2

,2

4

2

For present simulation, we have the following:

De 29.67 mm (Tube bundle hydraulic diameter)

Do 19.05 mm (Tube OD)

gc 1 g-cm/dyne-sec2

SL 27 mm (Tube pitch in longitudinal direction)

ST 27 mm (Tube pitch in transverse direction)

K 2.53 (Loss coefficient of tube support plate)

ZTSP 29 mm (Thickness of tube support plate)

778.6 kg/m3(Water density)

o 1.016E-04 Pa-sec (Dynamic viscosity of water)

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Using the above values, we have calculated the friction factors over a range of velocity (0.34 to 5 m/s). Of

course, the loss coefficient depends on velocity. However, their average value is a good approximation forsimplicity. The average is 0.0484 and 0.0032 for the cross and parallel flow, respectively. Finally, the

coefficient of the momentum sinks is calculated and results are shown below.

Coefficient Value, kg/m4 Remark

CR2,x 32185 Normal to Tube BundleCR2,y 32185 Normal to Tube Bundle

CR2,z 450 Parallel to Tube Bundle

CR2,z 142698 Normal to Tube Support Plate

Results of convergent solutions were obtained and analyzed. Figures 3a and 3b depict velocity contours ata plane 2.5 centimeters above the tube sheet that is perpendicular to the tube bundle. These velocity

contours represent magnitude of the cross flow velocity in meters per second. When the cross flow

velocity is smaller than a threshold of 0.3 m/s, the sludge particle will settle on the top of the tube sheet. Aclose comparison between Figure 3a with a groove and Figure 3b without a groove didnt show discernable

difference. Therefore, use of the groove will not increase amount of sludge settlement at the tube sheet.

Around 90o, the velocity contours penetrate much deeper because it is along the tube lane where no tubes

exist and thus flow resistance is much less, compared to the tube bundle zone. Such a flow behavior asshown in Figure 3b is also obtained by a special purpose code called ATHOS (Ref. 1) that uses different

approach in simulating the porosity of the tube bundle.

Figure 4 presents velocity components along two selective tubes for both simulations with and without the

groove. The difference in values of the velocity is negligible so that no difference in flow induced tube

vibration is expected. Results of CFD calculation confirm that effect of the groove is negligible to flow

conditions inside the tube bundle.

Figure 3a. Velocity Contours on the Plane 2.5 cm above Top of Tube Sheet with a Groove

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Figure 3b. Velocity Contours on the Plane 2.5 cm above Top of Tube Sheet without aGroove

0.00

0.20

0.40

0.60

0.80

1.00

1.20

1.40

1.60

0.00 0.50 1.00 1.50 2.00 2.50

Elevation, m

Velocity,m/s

Velocity, Non-G(180), T#1

Velocity,W/G(180), T#1

Velocity, Non-G(180), T#2

Velocity, W/G(180), T#2

Figure 4. Value of Velocity along Two Selective Tubes (Non-G (180): 180oModel without a

Groove, W/G (180): 180oModel with a Groove, T#1: Tube #1, and T#2: Tube #2)

Module 2 Steam Flow through Secondary Separator

Figure 5 depicts a CFX-5 CFD model for steam flow through the space from the exit of the primaryseparator, through the secondary separator to the steam nozzle. Purpose of this CFD simulation is to

estimate the range of transport time of sodium tracer through this space. The assumption is that the sodiumtracer would travel at the same velocity as steam does. A 45osector was modeled with steam flow entering

the fluid domain at the exits of the primary separator and leaving the domain at the steam nozzle (see

Figure 5). The secondary separator consists of tortuous paths for capturing moisture. In addition, thoseblack bodies are solid cutouts where no fluid flow exists. Similar to the tube bundle in Module 1, the

secondary separator is treated as porous medium with the use of fluid sub-domain for introducing

momentum sinks. The steam inlet velocity from each orifice opening varies from 11.2 m/s to 13.3 m/s andthe outlet is at relative pressure of 0 Pa. The system pressure is 5.45 MPa, and reference temperature is

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269.3oC for this isothermal problem. Flow area of the outlet is so small compared to the dimension of the

fluid domain, and thus, use of 0 Pa at the outlet is practical and valid.

The built-in k-turbulence model was selected and convergent solution was obtained. Rigorous approach

of solving the transport time was instructed by ANSYS CFX Technical Support Center (Ref. 4), but was

not used in this analysis. Transport time of the sodium tracer is considered to be the time taken by steamalong the streamlines. Figure 6 depicts the transport time started at one of the orifice openings. As shown,

the transport time ranges from about 1.2 to 2.2 seconds. Use of the streamline yields quick, approximate

estimates of the transport time.

In fact, results of this CFD calculation is also of great use in understanding other mechanisms of moistureseparation. Granted, moisture droplets would travel paths other than those at the steam. However, as an

approximation, we can assume that moisture droplets travel with the steam at the same velocity. We seesome streamlines end up at the wall and never reach the steam nozzle. Therefore, the wall of the shell or

the solid cutout does serve the role of moisture separation. As depicted in Figure 7 for Orifice Inlet No. 2,

one of four streamlines reaches the steam nozzle, and the other three terminate on the wall and thus the

moisture droplets are separated by wall. Therefore, it appears that certain locations of the steam flow inletto the secondary separator may enhance the moisture separation, such as the Orifice Inlet No. 2 that is

directly below the bottom cover of the separator, and thus encourages the moisture droplets to divert to the

wall.

Figure 5. Geometry of Secondary Separator and CFX Model with Boundary Openings

Mid Deck Plate

Opening to Steam Nozzle

x

Sector I

Sector IISector III

Sector IV

y

81 23

4

5 6

7

8 Orifices on Mid Deck Plate

428 cm

420cm

Lower Tier of

Secondary

Separator

Upper Tier of

Secondary

Separator

Solid Cutout

Mid Deck Plate

Opening to Steam Nozzle

x

Sector I

Sector IISector III

Sector IV

y

81 23

4

5 6

7

8 Orifices on Mid Deck Plate

428 cm

420cm

Lower Tier of

Secondary

Separator

Upper Tier of

Secondary

Separator

Solid Cutout

Mid Deck Plate

Opening to Steam Nozzle

x

Sector I

Sector IISector III

Sector IV

y

81 23

4

5 6

7

8 Orifices on Mid Deck Plate

428 cm

420cm

Lower Tier of

Secondary

Separator

Upper Tier of

Secondary

Separator

Solid Cutout

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Figure 6. Steam Transit Time from Outer Orifice-Inlet (No. 8) to Steam Nozzle Outlet

Figure 7. Steam Transit Time from Inner Orifice-Inlet (No. 2) to Steam Nozzle Outlet

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Module 3 Flow inside and outside a Sludge Collector

Figure 8 shows a CFX-5 CFD model to simulate flow inside and outside a sludge collector. A sludge

collector is to trap the sludge particle. Sludge deposit on the tube wall could cause tube corrosion andreduce heat transfer. A sludge collector that sits in the water pool that is outside the tube bundle is a

desired device. The sludge collector had been verified and confirmed in field operation to capture sludge.

Purpose of a CFX-5 CFD analysis is to quantify and optimize the collector design.

Flow outside the collector is chaotic. It is critical to properly locate the inlet and outlet holes. Figure 8shows that the inlet holes draw the water into the collector and the outlet holes allow the water to leave.

During the passage of the water through the collector, sludge particles will settle due to its being heavier

than water. It is desirable to draw adequate water to maximize the amount of sludge mass and yet to avoidre-entraining effect. If the flow rate through the collector is too high, the particle may not have time to

settle, and worse yet the settled particles can be picked up again (i.e. re-entrained into the water flow).

The overall fluid domain of the CFD model consists of boundary conditions, solid cutouts with velocity

boundaries, and thin plates to simulate the outer covers and inner floors for sludge to settle. This collectorhas three floors with the bottom one having largest floor area. There are four fluid flow inlets in the model.

Inlets 1 to 3 are for saturated water that is separated from steam and returned to the water pool at differentlocations. Such recirculated, saturated water is at 276.9oC and a flow rate of 283 kg/s with 10% via Inlets 1

and 3, each, and the remaining 80% via Inlet 2. Inlet 4 provides feed water at 227.3oC and a flow rate of

103 kg/s. The outlet is at a relative pressure of 0 Pa and the system pressure is 6.13 MPa. Flow area at the

outlet boundary is small compared to the dimension of the overall fluid domain, and thus use of zeropressure at the outlet is a practical approximation. The built-in k-turbulence model was selected and

convergent solution was obtained. Results of the convergent solution were captured through the userdefined surfaces for the eight inlet holes and outlet holes, respectively. Table 1 summarized the flow rate

through these eight inlet and outlet holes, respectively. Flow rate through the inlet holes is summed to 0.69kg/s, about equal to that through the outlet hole. The total flow through the model is 103 kg/s and thus the

collector flow of 0.69 kg/s is relatively small. Yet, the CFX-5 model is able to solve such a big contrast in

flow between the overall model and the collector. Of course, it took much effort in solution control to

finally obtain the convergent solution. It is considered that CFX-5 is a good CFD tool to produce result fora complicated problem like this.

Table 1. Flow Rate and Velocity through Inlet and Outlet Holes

Inlet Hole Flow Rate, kg/s Velocity, m/s Outlet Hole Flow Rate, kg/s Velocity, m/s

1 -0.046 -0.19 1 0.102 0.43

2 -0.022 -0.09 2 0.092 0.39

3 -0.060 -0.25 3 0.081 0.34

4 -0.115 -0.48 4 0.073 0.31

5 -0.046 -0.20 5 0.069 0.29

6 -0.126 -0.53 6 0.075 0.32

7 -0.151 -0.64 7 0.095 0.40

8 -0.118 -0.50 8 0.104 0.44

Average -0.086 -0.36 Average 0.086 0.36

Figure 9 plots temperature on wall of various components. The red color is at 276.9oC and the blue at227.3oC and those in between are due to mixing of saturated water and feed water. The cover of the

collector where the inlet holes are located is essentially in red that indicates that only the saturated water

enters the collector. The saturated water has a higher concentration of sludge particles than the feed water,and thus is desirable. Flow velocity through the sludge collector ranges from 0.05 to 0.10 m/s that are

below the re-entrainment velocity. Sludge particles entering with the water would settle on the three floors

in the collector. There is room for optimizing the amount of the sludge settlement in the collector. Thiscan be achieved by increasing the diameter of the inlet holes and increasing the floor space by extending

the radial edge toward the shell of the steam generator.

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Figure 8. Schematic and CFX CFD Model for Fluid Domain With Sludge Collector in theLower Left Corner

Figure 9. Temperatures on Wall of Various Components

Flow Outlet

Flow Intlet 1

FlowIntlet3

Flow Intlet 4

Flow

Intlet 2

Sludge

Collector

Solid Cutouts

CoverInlet Holes Outlet Holes

241 cm

218cm

Ou

tle

th

ole

sInletholes

Holes on Cover

(2 cm Diameter)

1,2

3,4

,5

6,7,

8

1,2

,3,4,5,6,7,8

Flow Outlet

Flow Intlet 1

FlowIntlet3

Flow Intlet 4

Flow

Intlet 2

Sludge

Collector

Solid Cutouts

CoverInlet Holes Outlet Holes

241 cm

218cm

Flow Outlet

Flow Intlet 1

FlowIntlet3

Flow Intlet 4

Flow

Intlet 2

Sludge

Collector

Solid Cutouts

CoverInlet Holes Outlet Holes

241 cm

218cm

Ou

tle

th

ole

sInletholes

Holes on Cover

(2 cm Diameter)

1,2

3,4

,5

6,7,

8

1,2

,3,4,5,6,7,8

Ou

tle

th

ole

sInletholes

Holes on Cover

(2 cm Diameter)

1,2

3,4

,5

6,7,

8

1,2

,3,4,5,6,7,8

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Module 4 Distribution of Feed Water Flow

Figure 10 illustrates a schematic of a feed water distribution system into a steam generator. It is desirable

to have a uniform distribution of feed water via the top-mounted spray tubes into the water pool in thesteam generator. In addition, local velocity distribution for each spray tube would be of great use in

assessing the erosion-corrosion potential. The feed water distribution system consists of an inlet pipe, a

Tee, a reducer and a ring with constant diameter. There are two tubes on top of the Tee. There are 31

tubes on the ring with a tube pitch of 4.7o.

The boundary conditions are (1) uniform inlet velocity at the pipe inlet, and (2) constant pressure at exit

windows of spray tubes. The built-in k-turbulence model is used in the simulation. Result of convergent

solution was captured for each discharging window of each spray tube. Table 2 tabulates the average

velocity and mass flow rate through each spray tube. Discharge flow is not uniform among all 33 spray

tubes. The first two spray tubes have the highest discharge rate this is because the feed water flowimpinges on the back side of the Tee and turns, and thus flow slows down and kinetic energy transform into

potential energy. Therefore, the pressure differential from the inlet to the outlet of the spray tube is highest

for the 1stand 2

ndspray tube (see Figure 11). When feed water flow leaves the reducer and gets into the

ring, the flow speeds up at the expense of the pressure. Therefore, the pressure differential for the spray

tubes in this portion of the ring is low, and the discharge rate or velocity is relatively small. When the feed

water flow approaches the end of the ring, it slows down and thus pressure increases. Therefore, thedischarge rate and velocity is relatively high within the rear portion of the feed ring.

Table 2. Flow Rate and Velocity through Each Spray Tube

Spray Tube No. Flow Rate,kg/s

% of TotalFlow

Spray TubeNo.

Flow Rate,kg/s

% of TotalFlow

1 18.67 6.18 18 5.02 1.66

2 16.96 5.61 19 4.96 1.64

3 3.94 1.30 20 11.91 3.94

4 3.41 1.13 21 11.08 3.67

5 2.89 0.96 22 13.20 4.37

6 3.07 1.02 23 13.81 4.57

7 2.90 0.96 24 13.94 4.62

8 2.90 0.96 25 14.83 4.919 3.61 1.20 26 14.92 4.94

10 3.39 1.12 27 15.65 5.18

11 3.66 1.21 28 15.93 5.27

12 4.46 1.48 29 15.95 5.28

13 3.67 1.21 30 16.30 5.40

14 3.33 1.10 31 16.05 5.31

15 4.44 1.47 32 13.01 4.31

16 4.15 1.37 33 12.56 4.16

17 7.48 2.48

Figure 12 depicts velocity vector on the symmetry plane of the inlet pipe and outlets of certain spray tubes,

and velocity contours on the symmetry plane in the Tee and reducer. Each spray tube has differentdischarge flow pattern, and it shows circumferential and axial variation within each spray tube. The

difference in flow conditions among spray tubes may be responsible for whether erosion-corrosion may

occur in specific tube. Figure 12 indicates that Spray Tube Nos. 1 and 2 can have velocity as high as 11m/s. A velocity of 11 m/s could lead to erosion-corrosion for carbon steel tube. However, current design

of alloy 600 spray tube should have no concern of erosion-corrosion for a velocity of 11 m/s.

Generally, the feed water ring is made of carbon steel. Therefore, junction of the carbon steel feed ring to

the alloy 600 spray tube may be subject to erosion-corrosion if velocity is high. Figure 13 shows velocitydistribution among junctions for all 33 spray tubes. As shown, the junction of Spray Tube Nos. 3 to 8 may

experience velocity ranging from 7 to 9 m/s. For carbon steel without a trace of chromium content,

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erosion-corrosion may take place at the junction with velocity as high as 7 to 9 m/s. Therefore, it may be

desirable to relocate Spray Tube Nos. 3 to 8 to other locations, such as the reducer and other part of thefeed ring. To relocate to other part of the feed ring, one can use a tube pitch smaller than 4.7o.

Spray Tubes of Nos. 3 to 8 have the lowest discharge flow rate among 33 tubes, and yet have the highest

velocity near their junction to the feed ring. Non-uniformity in discharge flow is due to non-uniformpressure distribution as shown in Figure 11. We have considered that all 33 discharge windows on spray

tubes are at same pressure. In reality, pressure at the discharge windows may vary, and thus amount of

non-uniformity in discharge flow can change. However, it is considered that pressure variation among 33discharge windows is small compared to the pressure differential between the inlet and outlet of each spraytube. Therefore, use of constant pressure for all 33 discharge windows is a good approximation. If desired,

the uncertainty of constant pressure boundary condition can be removed if we consider a fluid domain to

include water pool outside the feed ring. Such a model is to be simulated in the continued CFD analysis fornuclear steam generator design.

Figure 10. Schematic of Feed Water Distribution System

152.4 133.108

5.9

14

.93

24.88

R58

.432

35

38.1

35o

Note: Unit is cm Z

Y

58.483 118.178

Flow

Ou

tlet

Flow

Ou

tlet

Flow

In

let

133.1

08

152.4

=3

2o

1 2 34

56

7

89

10

11

12

13

14

15

16

17

18

19

20

21

2223

2425

2627

282930

313233Spray Tube No. =

Z

X

176.6

61

Flow Inlet

152.4 133.108

5.9

14

.93

24.88

R58

.432

35

38.1

35o

Note: Unit is cm Z

Y

58.483 118.178

Flow

Ou

tlet

Flow

Ou

tlet

Flow

In

let

152.4 133.108

5.9

14

.93

24.88

R58

.432

35

38.1

35o

Note: Unit is cm Z

Y

58.483 118.178

Flow

Ou

tlet

Flow

Ou

tlet

Flow

In

let

133.1

08

152.4

=3

2o

1 2 34

56

7

89

10

11

12

13

14

15

16

17

18

19

20

21

2223

2425

2627

282930

313233Spray Tube No. =

Z

X

176.6

61

Flow Inlet

133.1

08

152.4

=3

2o

=3

2o

1 2 34

56

7

89

10

11

12

13

14

15

16

17

18

19

20

21

2223

2425

2627

282930

313233Spray Tube No. =

Z

X

176.6

61

Flow Inlet

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Figure 11. Pressure Distribution on the Inner Wall of Feed Water Distribution System

Figure 12. Velocity Vector on Symmetry Plane and Spray Tube Outlets, and VelocityContours

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Figure 13. Velocity on a Plane Normal to Spray Tubes and 1.6 cm below Top of the FeedRing

Discussions

CFX-5 offers a wide range of capability in simulating fluid flow. Four modules presented above of course

cover just a small area of the CFX-5 capability. Modules 1, 2 and 4 consider single phase flow withoutheat transfer, and Module 3 again deals only single phase flow, but with energy transfer due to hot and cold

water mixing. All four modules are models at important areas in the PWR steam generator, the modules

demonstrate that CFX-5 can be used to verify and optimize the design. These capabilities are important in

view that flow tests are now generally out of the reach.

Steam generator involves a wide range of thermal and hydraulics. Four modules will not cover the whole

range. For example, there are water and steam flow that are of two-phase. A simulation of two-phase flow

through the opening of the tube support plate was made at Rensselaer Polytechnic Institute (Ref 5) via a

contract from Westinghouse, and not included in this paper. Module 1 demonstrates the flexibility of theCFX-5 code in simulating tube bundle flow through the use of porous media. Module 2 also involves the

use of porous media for the tortuous passage through the moisture separation device. The porous media

modeling works well for both cases. As of now, Module 3 considered only water flow, and results ofwater flow are used together with the empirical correlation of sludge particle settlement. Module 3 for the

sludge collector can include sludge particles with water flow, and the amount of settlement of the sludge

particle could be directly estimated without using the empirical correlation. Continued moduledevelopment will include simulation of two-phase flow, such as steam and water flow, and water with solid

particle in the above mentioned sludge collector. Module 4 encountered certain difficulty in building thesolid. The code cannot accept the projection of the half circle arc from the upstream pipe into the Tee

pipe when both pipes have equal diameter. However at the advice of the CFX Technical Center, a

reduction of the upstream pipe diameter from 38.100 cm to 38.092 cm solves the difficulty. Compared to

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Module 3, solution of Model 4 is relatively easier, and results of the pipe flow like Module 4 offers a lot for

properly locating the layout of the spray tubes.

CFX-5 provides excellent means to post processing the results of the CFD calculation. For example,graphical representation itself can be adequate to confirm the design requirement. Figure 9 is such an

example, temperature distribution on wall of various components clearly depicts that the sludge collectordraws just the recirculated water, not the feed water. As the recirculated water has a higher concentration

of sludge particles than the feed water, thus a collector will be more efficient to draw the recirculated water

only. Module 2 demonstrates again that CFX-5s graphical option provides a quick estimate of range ofsteam transport time through a complicated, 3-D domain. If the numeric is important the user-definedsurface can serve the user well. For instance, we defined user surfaces through eight inlet and eight outlet

holes on top of the collector, and obtained flow rates through them.

Conclusions

It appears practical and useful to divide the whole steam generator into modules when adapting CFX-5 for

CFD analysis. The CFX-5 CFD code apparently offers a wide spectrum of capability in evaluating thermal

and hydraulics of engineering equipments. Current paper emphasizes in one aspect: simple, practicalcapability as a CFD analysis tool. The presented modules of four have successfully demonstrated the

capability of the CFX-5 in verifying or optimizing the component designs of the PWR steam generator.

Acknowledgements

The author would like to acknowledge that the presented Modules 1, 3 and 4 were supported through two

contracts granted by Mitsubishi Heavy Industries, Ltd for design and analysis of Tsuruga Nuclear Power

Plant Units 3 and 4 in Japan. In addition, excellent support from the ANSYS CFX Technical Center isgratefully acknowledged.

References

1) Keeton, L. W., and Singhal, A. K., ATHOS3: A Computer Program for Thermal-HydraulicAnalysis of Steam generators, EPRI NP-4604-CCM, Electric Power Research Institute, July

1986.

2) Kreith, F., Principles of Heat Transfer, 3rdEd., Intext Educational Publishers, New York, p.482.

3) Kays, W. M., Convective Heat and Mass Transfer, McGraw-Hill, New York, 1966, p. 73.

4) Mi, J., Pordal, H., and Svihla, C. K., Calculating Residence time in CFX-5, ANSYS CFX, Feb.

8, 2001.

5) Podowski, M.Z., Antal, S. and Hu, M.H., CFD Analysis of Two-Phase Flow Around Tube

Support Plates in U-Tube Steam Generators, Proc. International Conference on IndustrialApplications of Two-Phase flow, Milan, Italy, October 1998.