Analysis on the amount of graphite dust deposited on steam generator of

HTGR

Wei Peng1, Tian-qi Zhang1, Su-yuan Yu2*

1Institute of Nuclear and new Energy Technology (INET), Tsinghua University, China

2Center for Combustion Energy, Tsinghua University, China

Background

Physical Model

Simulation model

Result

Conclusion

Outline

2

Background

3

Gen-IV aims: more efficiency and more safety

VHTGR: Very High Temperature Gas-cooled Reactor

Gen III/III+ units represent the current level of BAT (Best Available Techniques).

Background

4

Carbonaceous dust is suspected to be a hidden problem for HTGR. It comes from abrasion between pebbles/ pebbles and the fuel handling pipe.

Dusts finally deposit on the primary surface and influence the surface’s feature

5

Combined with FP (fission products) released by fuel elements Radioactive source of HTR in depressurization

accidents Hamper operation and maintenance in normal

operation. steam generator is an important component for the

dust deposition.

5

Physical Model

6

Heat transfer component between the hot helium and the cool water→ great temperature gradient→ thermophoretic deposition

Spiral heat exchange tube→complex flow field→ turbulent deposition

7

the amount of graphite dust coated on steam generator is the dynamic equilibrium between deposition of graphite dust and resuspension of deposited dust.

d r

d

dt

2amount of the graphite dust on surface (mg/m )

=deposition of graphite dust= ( )

=resuspension of graphite dust= ( )

d deposition

r resuspension

f V

f R

Deposition model

8

turbulent deposition thermophoretic deposition

2

12

2

2

2

2

2

1/(1 )

2 1

2 /3 1

1

1

+ ( 10) /32 +d d

1

(0.64 )2 0.01085(1 )1

0.0842

3.420.01085(1 )

0.037= [1 8 ] 0.14

1 (1 )0.037

0.14

L

g Ldk

LSc

g L

L

V e if Vg

L

otherwise

Model of Fan, F. G., & Ahmadi, G.

Model of Brock-Talbot

gs c t

p p

th

gm t

p p p

2

1 3 1 2 2

kC C C

k RK

kC CR k R

The total deposition mass depends on the deposition velocity

th

th

KV T

T

= ( )d depositionf V

Resuspension model

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The revised Rock’n’Roll model (Reeks and Hall, 2001) by Biasi et al. (2001)

Particle Resuspension: caused by the coupled effects of aerodynamic lift and drag; particles detach from the substrate when it receives enough energy from the turbulent flow.

2

2

2

( ) 1exp / 1 (( ) / 2

22a

a

f Fp n erf f F f

f

fa is the adhesive force which is assumed to be a log-normal distribution:

F is the aerodynamic force couple acting on the particle

1( )

2 L D

rF t F F

a

FL is the lift force and FD is the drag force on the particle

2' '

'' ' '

ln( / )1 1 1( ) ( ) exp( )

ln 2 ln2

a a

aa a a

f ff

f

= ( )r resuspensionf R

Conditions

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Name Unit Value

Inlet velocity of hot helium m/s 27.6Inlet temperature of hot

heliumK 973.15

Pressure MPa 3

Diameter of graphite dust m 0.1-10

Conductivity of graphite W/m.K 25

Density of graphite kg/m3 1720

Diameter of graphite dust

Velocity and temperature distribution

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The heat flux of the tube in steam generator can be divided into four parts:

heat flux distribution

friction velocity distribution

Distribution of temperature gradient

Collect bag

Vacuum tank

Link to the sonic nozzle

Deposition

the thermophoretic deposition velocity is larger than turbulent deposition velocity.

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0.0 0.5 1.0 1.5 2.00.0000

0.0004

0.0008

0.0012

0.0016

0.0020

x (m)

The

rmop

hore

tic v

eloc

ity(m

/s)

0.0 0.5 1.0 1.5 2.00.0000

0.0001

0.0002

0.0003

0.0004

0.0005

Tur

bule

nt d

epos

ition

vel

ocity

(m/s

)

x (m)

total d th= V V V

thermophoretic deposition turbulent deposition

0.0 0.5 1.0 1.5 2.00.0000

0.0005

0.0010

0.0015

0.0020

0.0025

0.0030

x (m)

The

rmop

hore

tic v

eloc

ity(m

/s)

total deposition velocityAverage deposition velocity is 0.0013m/s

Collect bag

Vacuum tank

Link to the sonic nozzle

Resuspension

The resuspension rate is associated with the time: in the beginning stage, the resuspension rate is high, it decreases rapidly as the time increasing, and then it decline slower. the resuspension rate after a long sufficient time is used

to analyze the graphite dust behavior in present study, is of about 10-5 s-1

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102 103 104 10510-6

10-5

10-4

10-3

10-2

t (s)

Res

uspe

nsio

n ra

te(1

/s)

resuspension rate

Vacuum tank

Distribution of dust in the steam generator

The result indicated that the amount of the graphite dust loading on the tube surface will tend to 6,760mg/m2.

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d r

d

dt

d totalV Nr R

total

dV N

dt

5106760(1 ) te

the amount of the graphite dust on the tube surface depends on the rate of the deposition and resuspension.

Collect bag

Vacuum tank

Link to the sonic nozzle

Conclusion

The deposition and resuspension of graphite dust in the steam generator was studied numerically:

(1) The turbulent deposition and thermophoretic deposition are the two mechanisms that make the graphite dust deposit on the heat transfer tube surface in SG, and thermophoretic deposition is the main depositional mechanism;

(2) The preliminary calculations result showed that the amount of the graphite dust loading on the tube surface will tend to 6,760mg/m2.

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Thanks for your attention ！

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