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
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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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