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Document Sample
Tritium Extraction from a DCLL Blanket
Prepared by: Scott Willms (LANL)
Collaborators: Brad Merrill (INL), Siegfried Malang (Consultant),
Clement Wong (GA), Dai-Kai Sze (UCSD)
Presented by: Jim Coons (LANL)
Coordinating Meeting on R&D for
Tritium and Safety Issues in Lead-Lithium Breeders
11 June 2007
Idaho Falls, ID
LA-UR-05-1711
Outline
•DCLL process overview
•Conventional separator
•T removal via vacuum permeator
•Model
•Mass transfer coefficient
•Parametric study
•DEMO design
•Issues
•Conclusions
DCLL process overview
He Recover tritium
from He
T2
Permeator
He, T2
Breeder, T2, He
T2, He To Tritium
Use He to Plant
T2
Breeding strip T from
PbLi
Dual Coolant
Blanket To Tritium
T2/Breeder Plant
He
Separator
Heat
Exchanger
PbLi loop
Breeder Breeder, T2
He
He, T2
He loop
T permeation T2
thru HX tubes Heat
Exchanger
Permeator Recover tritium
from He
Avg. T2 breeding
rate: 0.024 sccm He
He loop
Pressure in T2 separator tank if all tritium is contained
(no permeation, no stripping, etc.)
14
12
Tritium Partial Pressure (atm)
10
8
6
4
2
0
0 20 40 60 80 100 120
Time (days)
Rough estimate for tritium removal pathways from PbLi
with both tank pump off and HX permeation
1
0.9
Total tritium
0.8
removed
0.7
Tritium Removed (gm)
0.6 Tritium removed by
permeation through HX
0.5 tubes
0.4
0.3
0.2
Tritium removed by
0.1 mass transfer (through
collection tank)
0
0 20 40 60 80 100 120
Time (days)
Evaluating the possibility of using a vacuum permeator
for tritium separation from Pb-Li
Recover tritium
from He
Use
Permeator
to recover
T from
PbLi
PbLi loop
He loop
T permeation
thru HX tubes
Recover tritium
from He
Avg. T2 breeding
rate: 0.024 sccm
He loop
Low Pressure Permeator Experimental Apparatus
66.0cm.
(26")
Retentate
Permeate (Inert)
(H2)
10.2cm. (4")
To Vacuum
Feed
(Inert/H 2)
27.7 cm (10.9") 0.635 cm
total length x (0.25") dia.
0.318 cm Stainless Steel
(0.125") dia. Tube
Pd/Ag Tube
Experimental Setup
P GC
F Vent
H2 FC
T
P P
Vent
Turbo Pump Backing Pump
Permeator
Ar or N2 FC
With 25 sccm H2, the retentate and permeate are
initially in agreement and ultimately breakthrough is
observed at about 375 sccm. at 450 C
25 sccm H /N Flow 2 2
o
0.1
0.09
0.08
0.07 Constant 25 sccm H2
Pressure (torr)
0.06 Increasing N2
0.05 450 C
0.04
0.03
Retentate Partial Pressure
0.02
0.01
Permeate Pressure
0
0 100 200 300 400 500 600
Total Feed Flowrate (sccm)
--Willms, R. Scott, Pamela R. Arzu, Kevin G. Honnell and Stephen A. Birdsell; "Initial
Testing Of A Low Pressure Permeator For Tritium Processing"; Fusion Engineering and
Design, 49-50, 963-970 (2000)
Mathematical model for PbLi/T permeator
• A component balance describes the tritium dx D MW G
mass fraction along the membrane length dz F
• Tritium transport to the membrane surface km
Ni xi x 0
is described by a mass transfer coefficient MW
2
• The effective tritium partial pressure at the x
pr 0
k
membrane surface is given by the solubility s
G kp
_
• Permeation depends on the permeability G pr p p
A l
Gtot
Membrane T2
F, Ci G F, Ci
Dz
PbLi, T PbLi, T
z
Mass Transfer Coefficient (m/s)
2.
W 1.
et Pl
te at
d e,
0.0000
0.0005
0.0010
0.0015
0.0020
0.0025
0.0030
0.0035
0.0040
Tu La
be m
/P in
l at ar
e,
La
m
3. /T
Pl u rb
4. at
W e,
La
et
te m
d /T
Tu ur
be b
,T
ur
bu
le
nt
6.
Pl 5.
at ?
e,
Tu
7. r bu
Tu le
be nt
,T
ur
8. bu
Tu le
be nt
,T
ur
9. bu
Tu le
10 be nt
.P ,T
ac ur
ke bu
d le
Be nt
Comparison of mass transfer coefficient results
d,
Tu
rb
ul
en
t
The mass transfer coefficient for this system was
estimated from general correlations
• 10 general correlations were considered
• The following correlation appeared to be
the most appropriate:
xi
x0 liq to solid
km D liq bulk-to- xfer
0.0096 Re 0.913 Sc 0.346 surface mass pr
D AB xfer
pp
permeation
--Harriott and Hamilton, Chem Engr Sci, 20, 1073, 1965 through membrane solid to gas
xfer
• However, this correlation was developed
with benzoic acid and glycerin-water
mixtures at room temperature—
considerably different from 700 C PbLi
and tritium
Values used to solve the model
Description Value Value in other units
Temperature 973.150 K 700 C
Permeate Pressure 1.32E-008 atm 1.E-5 torr
Membrane Diameter 0.01 m 1 cm
Membrane wall thickness 5.00E-4 m 500 microns
Area for flow of PbLi 7.85E-05 m2
Molecular weight of tritium 0.006 kg/mol 6 gm/mole
Tritium solubility in PbLi 0.162 mol T/m3/atm^0.5
Tritium solubility in PbLi 5.5E-8 kg T/kg PbLi/atm^0.5
Diffusivity of tritium in PbLi 8.87E-9 m2/s
Tritium solubility in Nb 6740 mol T/m3/atm^0.5
Tritium diffusivity in Nb 1.24E-8 m2/s
Permeability of tritium in Nb 4.16E-5 mol T2/m/s/atm^0.5
Viscosity of PbLi 7.4E-4 kg/m/s
Density of PbLi 8813 kg/m3
Flow velocity 5 m/s
Volumetric flowrate 3.93E-4 m3/s
Schmidt Number 9.47
Reynolds Number 595000.
Mass transfer coefficient 3.47E-3 m/s
Beta-Collection of constants 61200
Mass fraction of T in feed 2.E-10 1.E-2 torr partial pressure
Using these base conditions the tritium concentration
down the length of the permeator was determined
2.5E-10 1.E-02
Equilibrium partial p of T over PbLi (torr)
1.E-02
2.0E-10
Mass fraction of tritium in PbLi
8.E-03
1.5E-10
6.E-03
1.0E-10 Practical Length of Tube?
4.E-03
Exit Conc. Target
5.0E-11
2.E-03
0.0E+00 0.E+00
0 5 10 15
Distance along tube (m)
Performance depends strongly on the mass transfer
coefficient
2.5E-10
1.3 Pa (1x10-2 torr)
2.0E-10
Mass fraction of tritium in PbLi
0.00005 m/s
1.5E-10
0.0005 m/s
km=0.0035 m/s (base case)
1.0E-10
0.005 m/s
Exit Conc. Target
5.0E-11
0.05 m/s 0.0013 Pa (1x10-5 torr)
0.5 m/s
0.0E+00
0 2 4 6 8 10 12 14 16
Distance along membrane tube (m)
Wall thickness
2.50E-10
2.00E-10
Mass fraction of tritium in PbLi
1.50E-10
1.00E-10
Wall=0.0005 m
(base case)
Wall=0.005 m Exit Conc. Target
5.00E-11
Wall=0.00005
0.00E+00
0 2 4 6 8 10 12 14 16
Distance along tube (m)
Surface Concentration
2.50E-10
2.00E-10
Mass fraction of tritium in PbLi
1.50E-10
In bulk
1.00E-10
Exit Conc. Target
5.00E-11
At tube surface
0.00E+00
0 2 4 6 8 10 12 14 16
Distance along tube (m)
Permeability
2.50E-10
2.00E-10
Mass fraction of tritium in PbLi
1.50E-10 kp=Nb/1000
(like Fe)
kp=Nb/10
(like Pd)
1.00E-10
kp=Nb/100
Exit Conc. Target
5.00E-11
kp=Nb (base case)
0.00E+00
0 2 4 6 8 10 12 14 16
Distance along tube (m)
PbLi Flowrate
2.50E-10
2.00E-10
Mass fraction of tritium in PbLi
1.50E-10
v=50 m/s
1.00E-10 v=10 m/s
v=0.5 m/s
v=2.5 m/s
Exit Conc. Target
5.00E-11
v=5 m/s
(base case)
0.00E+00
0 2 4 6 8 10 12 14 16
Distance along tube (m)
Feed concentration
1.00E-08
1.00E-09
Mass fraction tritium in PbLi
x0=2x10-9
x0=2x10-10(base case) Exit Conc. Target
1.00E-10
1.00E-11
x0=2x10-11
1.00E-12
0 2 4 6 8 10 12 14 16
Distance along tube (m)
Tube diameter does significantly affect performance
2.50E-10
2.00E-10
Mass fraction of tritium in PbLi
Tube Diameter
1.50E-10
D=0.02 m
1.00E-10
Exit Conc. Target
5.00E-11
D=0.01 m (base case)
D=0.005
0.00E+00
0 2 4 6 8 10 12 14 16
Distance along tube (m)
Permeate pressure
2.50E-10
2.00E-10
Mass fraction tritium in PbLi
1.50E-10
1.00E-10 Pperm=1x10-5 torr (base case)
Exit Conc. Target
5.00E-11
Pperm=1x10-4 torr
Pperm=1x10-6 torr
0.00E+00
0 2 4 6 8 10 12 14 16
Distance along tube (m)
Considerations for a practical PbLi permeator
• PbLi flowrate for Demo: 26270 kg/s
• With 1 cm dia. tubes and 5 m/s flow velocity: 7592 tubes
• Total Nb required for 5 m tubes: 2.6 tons
• Total cost for Nb: ~$0.5M (?)
• Diameter of vessel to contain tube cross sections + twice that
area for space between tubes: 1.7 m
This permeator is a substantial vessel, but one that can
practically be constructed
While this initial analysis indicates that a PbLi permeator may be
feasible, there are many issues that must be resolved
• Measured mass transfer coefficients for the PbLi-T system
• Compatibility of PbLi with Nb at 700 C
• Additional resistances to tritium permeation such as surface
resistance?
• At the PbLi-membrane interface, is the effective partial pressure
exerted by tritium indeed given by the solubility equation? (this
may be a very different mechanism with a very different rate)
• What pressure can be practically maintained on the permeate
side of the membranes?
• Will Nb tubes degrade due to reactions such as oxidation? Will
a surface treatment be needed?
Conclusions
• Tritium permeation through the heat exchanger materials will be
substantial and cannot be neglected
• Tritium can be recovered from helium streams with gas
permeators and other technologies
• A reasonable plan for ITER TBM ancillary equipment is to
include a helium bubbler on the PbLi loop and permeators on
both He loops
• A potentially attractive option is a PbLi permeator to directly
remove tritium from PbLi. Based on present information such a
device might be practical.
• Whether or not it is actually practical would require considerable
R&D
