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

T2/BreederSeparator

HeatExchanger

Breeder, T2, He

Breeder

T2

Breeding

He, T2

Breeder, T2

T2, He

He

Permeator

T2

He, T2

He

Permeator

To Tritium Plant

T2

To Tritium Plant

Dual CoolantBlanket

HeatExchanger

He

He

Use He to strip T from PbLi

T permeation thru HX tubes

Recover tritium from He

Recover tritium from He

He loop

He loop

PbLi loop

Avg. T2 breeding rate: 0.024 sccm

Pressure in T2 separator tank if all tritium is contained (no permeation, no stripping, etc.)

0

2

4

6

8

10

12

14

0 20 40 60 80 100 120

Time (days)

Tri

tiu

m P

arti

al P

ress

ure

(at

m)

Rough estimate for tritium removal pathways from PbLi with both tank pump off and HX permeation

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

0 20 40 60 80 100 120

Time (days)

Tri

tiu

m R

em

ov

ed

(g

m)

Total tritium removed

Tritium removed by permeation through HX tubes

Tritium removed by mass transfer (through collection tank)

Evaluating the possibility of using a vacuum permeator for tritium separation from Pb-Li

Use Permeator to recover T from PbLi

T permeation thru HX tubes

Recover tritium from He

Recover tritium from He

He loop

He loop

PbLi loop

Avg. T2 breeding rate: 0.024 sccm

Low Pressure Permeator Experimental Apparatus

66.0cm.

10.2cm.

Feed(Inert/H 2)

Retentate(Inert)Permeate

(H 2)

27.7 cm (10.9")

total length x

0.318 cm

(0.125") dia.

Pd/Ag Tube

0.635 cm

(0.25") dia.

Stainless Steel

Tube

To Vacuum

(26")

(4")

Experimental Setup

Permeator

Vent

Turbo Pump Backing Pump

VentF

P

GCP

TP

FC

FC

H2

Ar or N2

0

0.01

0.02

0.03

0.04

0.05

0.06

0.07

0.08

0.09

0.1

0 100 200 300 400 500 600

Total Feed Flowrate (sccm)

Pre

ss

ure

(to

rr)

Retentate Partial Pressure

Permeate Pressure

Constant 25 sccm H2

Increasing N2

450 C

With 25 sccm H2, the retentate and permeate are initially in agreement and ultimately breakthrough is observed at about 375 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 mass fraction along the membrane length

• Tritium transport to the membrane surface is described by a mass transfer coefficient

• The effective tritium partial pressure at the membrane surface is given by the solubility

• Permeation depends on the permeability

F, Ci F, Ci

Gtot

z

Dz

G

PbLi, T

T2

PbLi, T

Membrane

F

GMWD

dz

dx

0xxMW

kN i

mi

2

0

sr k

xp

prp pp

l

k

A

GG _

Comparison of mass transfer coefficient results

0.0000

0.0005

0.0010

0.0015

0.0020

0.0025

0.0030

0.0035

0.0040

1. P

late,

Lam

inar

2. W

ette

d Tub

e/Plat

e, L

am/T

urb

3. P

late,

Lam

/Tur

b

4. W

ette

d Tub

e, T

urbu

lent

5. ?

6. P

late,

Tur

bulen

t

7. T

ube,

Tur

bulen

t

8. T

ube,

Tur

bulen

t

9. T

ube,

Tur

bulen

t

10. P

acke

d Bed

, Tur

bulen

t

Mas

s T

ran

sfer

Co

effi

cien

t (m

/s)

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:

--Harriott and Hamilton, Chem Engr Sci, 20, 1073, 1965

• However, this correlation was developed with benzoic acid and glycerin-water mixtures at room temperature—considerably different from 700 C PbLi and tritium

346.0913.0Re0096.0 ScD

Dk

AB

m

xi

x0

pr

pp

permeation through membrane

liq bulk-to-surface mass xfer

liq to solid xfer

solid to gas xfer

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

0.0E+00

5.0E-11

1.0E-10

1.5E-10

2.0E-10

2.5E-10

0 5 10 15

Distance along tube (m)

Mas

s fr

acti

on

of

trit

ium

in

Pb

Li

0.E+00

2.E-03

4.E-03

6.E-03

8.E-03

1.E-02

1.E-02

Eq

uil

ibri

um

par

tial

p o

f T

ove

r P

bL

i (t

orr

)

Practical Length of Tube?

Exit Conc. Target

Performance depends strongly on the mass transfer coefficient

0.0E+00

5.0E-11

1.0E-10

1.5E-10

2.0E-10

2.5E-10

0 2 4 6 8 10 12 14 16

Distance along membrane tube (m)

Mas

s fr

acti

on

of

trit

ium

in

Pb

Li

0.05 m/s

0.005 m/s

0.0005 m/s

0.00005 m/s

km=0.0035 m/s (base case)

0.5 m/s

1.3 Pa (1x10-2 torr)

0.0013 Pa (1x10-5 torr)

Exit Conc. Target

Wall thickness

0.00E+00

5.00E-11

1.00E-10

1.50E-10

2.00E-10

2.50E-10

0 2 4 6 8 10 12 14 16

Distance along tube (m)

Mas

s fr

acti

on

of

trit

ium

in

Pb

Li

Wall=0.0005 m(base case)

Wall=0.005 m

Wall=0.00005

Exit Conc. Target

Surface Concentration

0.00E+00

5.00E-11

1.00E-10

1.50E-10

2.00E-10

2.50E-10

0 2 4 6 8 10 12 14 16

Distance along tube (m)

Mas

s fr

acti

on

of

trit

ium

in

Pb

Li

In bulk

At tube surface

Exit Conc. Target

Permeability

0.00E+00

5.00E-11

1.00E-10

1.50E-10

2.00E-10

2.50E-10

0 2 4 6 8 10 12 14 16

Distance along tube (m)

Mas

s fr

acti

on

of

trit

ium

in

Pb

Li

kp=Nb (base case)

kp=Nb/10 (like Pd)

kp=Nb/100

kp=Nb/1000 (like Fe)

Exit Conc. Target

PbLi Flowrate

0.00E+00

5.00E-11

1.00E-10

1.50E-10

2.00E-10

2.50E-10

0 2 4 6 8 10 12 14 16

Distance along tube (m)

Mas

s fr

acti

on

of

trit

ium

in

Pb

Li

v=0.5 m/s

v=2.5 m/s

v=5 m/s (base case)

v=10 m/s

v=50 m/s

Exit Conc. Target

Feed concentration

1.00E-12

1.00E-11

1.00E-10

1.00E-09

1.00E-08

0 2 4 6 8 10 12 14 16

Distance along tube (m)

Mas

s fr

acti

on

tri

tiu

m i

n P

bL

i

x0=2x10-11

x0=2x10-10(base case)

x0=2x10-9

Exit Conc. Target

Tube diameter does significantly affect performance

Tube Diameter

0.00E+00

5.00E-11

1.00E-10

1.50E-10

2.00E-10

2.50E-10

0 2 4 6 8 10 12 14 16

Distance along tube (m)

Mas

s fr

acti

on

of

trit

ium

in

Pb

Li

D=0.005 D=0.01 m (base case)

D=0.02 m

Exit Conc. Target

Permeate pressure

0.00E+00

5.00E-11

1.00E-10

1.50E-10

2.00E-10

2.50E-10

0 2 4 6 8 10 12 14 16

Distance along tube (m)

Mas

s fr

acti

on

tri

tiu

m i

n P

bL

i

Pperm=1x10-6 torr

Pperm=1x10-5 torr (base case)

Pperm=1x10-4 torr

Exit Conc. Target

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