FNST Meeting UCLA, August 12th-14th, 2008

Brad Merrill1, Phil Sharpe1, Dai-Kai Sze2

1INL Fusion Safety Program2UCSD

Tritium Permeation in HCLL/DCLL

Presentation Overview

• This presentation examines Dual Cooled Lead Lithium (DCLL) and Helium Cooled Lead Lithium (HCLL) blanket tritium inventory and permeation rates as impacted by tritium:

Solubility in PbLi

First wall (FW) implantation

Reduced turbulent mass transport in PbLi

• The results are based on a TMAP model developed for the ARIES-CS DCLL design, with the model modified to give an intermediate helium cooling system to Rankine cycle in place of ARIES-CS Brayton cycle

• This TMAP model was also modified to simulate a HCLL blanket in ARIES-CS based on Melodie experimental results

• Conclude with a summary

ARIES-CS Design Parameters

Fusion Thermal Power in Blanket 2480 MW

Typical Module Dimensions ~4 m2 x 0.62 m

Tritium Breeding Rate ~400 g/d

PbLi Inlet/Outlet Temperatures 464/737°C

PbLi Inlet Pressure 1 MPa

Typical Inner Channel Dimensions 0.26 m x 0.24 m

Average PbLi Velocity in Inner Channel ~0.04 m/s

Fusion Thermal Power removed by PbLi 1323 MW

PbLi Total Mass Flow Rate 25,910 kg/s

Maximum PbLi/FS Temperature 472°C

He Inlet/Outlet Temperatures 385/460°C

He Inlet Pressure 10 MPa

Typical FW Channel Dimensions (poloidal x radial) 2 cm x 3 cm

He Velocity in First Wall Channel 46 m/s

He Inlet/Outlet Temperatures 385/460°C

Total Mass Flow Rate of Blanket He 3559 kg/s

Maximum Local ODS/RAFS Temperature at FW 654/550°C

Layout of ARIES-CS Power Core

ARIES-CS Power Parameters

ARIES-CS Tritium Extraction

• All PbLi component models (blanket gaps, pipes, permeator, and HTX) account for turbulent enhanced transport of tritium in the PbLi

• Correlationa proposed by Scott Willms used to model turbulent mass transport enhancement:

• Tritium solubility and diffusivity correlations developed by Reiterb and Teriac

Vacuum

QPb-17Li

CT,I

Niobium Membrane

T2

T2

Qvacuum

QPb-17Li

CT,O

Vacuum Permeator Concept

CT,Bulk

QPb-17Li

CT,S1

Or CT,S3 basedon molecularrecombination

CT,S2

Membrane diffusion

Pb-17Limass transport

( )S1T,BulkT,mT CC K −=Γ

x

CD- T

TT ∂∂

=Γ

2rT2 S3T,C α=Γ

0.3460.913

17LiPbT,

tubem ScRe 0.0096 D

DK=

−

17Li-PbS,

NbS,

S1T,

S2T,

K

K

C

C=

P KC sS3T,=

aHarriot and Hamilton, Chem Engr Sci, 20 (1965) 1073bReiter, FED 14 (1991) 207-211 cTeria, J. Nucl. Mater. 187 (1992) 247-253

s

m 27000/RT)exp(2.5x10D

Pam

T 1350/RT)exp(n2.32x10K

27

1/23PbLi8

s

−=

−−=

−

−

Schematic of ARIES-CS DCLL TMAP Model

Concentric pipesPbLi

Permeator

PbLi core

He/He FS HX

Non-Hartmann Gaps

Hartmann Gaps

First wall

Second wall

Rib walls

Back plate

Tritium cleanupsystem

Helium pipes

Shield Manifolds

IntermediateHelium Cycle

He/PbLi Nb HX

He/H2O Al HX

Tritium Inventory and Permeation Results For DCLL

• Based on TMAP results, increasing the solubility of tritium in PbLi by 100 increases the PbLi tritium inventory by ~12, but surprisingly reduces the reactor structural inventory and permeation rate

• This is due to the fact that the concentration jump at all PbLi/metal interfaces drops by 100 while the PbLi concentration increase of ~12 produces a balance between tritium production and extraction

• Tritium release is at or near allowable

  Ks-Reiter 100 x Ks-Reiter FW Implantation

Km/5

Tritium source ~400 g/d ~400 g/d ~940 g/d ~400 g/d

Inventory

Structure1 335 g 86 g 2500 g 1850 g

PbLi 1.0 g 11.5 g 2.6 g 3.0 g

Release2 0.9 g/a 0.03 g/a 3.4 g/a3 3.0 g/a3

Permeator overall efficiency 70% 7.7% 73% 26.5%

Tritium pressure

PbLi 0.17 Pa 1.3x10-3 Pa 0.86 Pa 1.1 Pa

Helium 1.4x10-2 Pa 9.0x10-4 Pa 0.9 Pa 0.5 Pa

Tritium global balance

Permeator 99.8% 99.9% 98.2% 96.7%

Helium cleanup system 0.15% 2.0x10-2% 1.7% 2.4%

Leaked 1.0x10-2% 2.0x10-3% 0.1% 0.2%

Permeates to VV 4.0x102% 8.0x10-3% 0% 0.7%

Permeation into Rankine cycle

Intermediate helium cycle 360 Ci/a5 93 Ci/a 2160 Ci/a5 1690 Ci/a5

Direct (required reduction)4/5 47/4.7x103

0/2

1.7x103

/1.7x105

1.1x103

/1.1x105

198% of this inventory is in the Nb alloy HTX and because reactor has 6 sectors only 1/6th is at risk during most accident

299% ventilation flow cleanup is assumed3Limit is < 1 g/a4Based on CANDU water concentration of ~1

Ci/kg (34,000 Ci/a allowed into Rankine cycle)5Based on US PWR water concentration of ~ 1

mCi/kg (340 Ci/a allowed into Rankine cycle)

Melodie* Results used to Investigate Extraction Column Tritium Removal for an ARIES-CS HCLL Blanket

*N. Alpy, et al., FED, 49-50 (2000) 775-780.Sulzer Column

(not a 750 Y series)

20 cm

Structured packing

80 cm

• The extractor column used in Melodie experiments was a Sulzer Mellapak 750 Y series

• The extraction column was 60 mm in diameter, 800 mm in height, and had an area packing of 750 m2/m3

Schematic of ARIES-CS HCLL TMAP Model

PbLi Pipes

PackedColumns

PbLi core PbLi/He HXPoloidalGaps

Radial Gaps

First wall

Second wall

Rib walls

Back plate

Helium pipes

Shield Manifolds

823 K

673 K

He/He FS HX

Tritium cleanupsystem

IntermediateHelium Cycle

He/H2O Al HX

Purgegas

Melodie Experimental Loop Results for Sulzer Extraction Column and Application to ARIES-CS

• Melodie measured extractor efficiencies were ~25%

based on concentration, i.e. • For this TMAP model, the reactor PbLi processing flow

rate is assumed to be 300 kg/s, giving a change out rate

of eight times per day• All external volumes (PbLi - manifolds, pipes, HTX) were

scaled to the 300 kg/s (from the DCLL 26,000 kg/s) and all

turbulent mass transport terms set to diffusion only• Extractor PbLi flow rate per column was set at 50 l/h• ARIES-CS will require ~2430 parallel extractor column

paths, and at an efficiency of ~25% will also need five

stages per path (i.e., 12150 Melodie type extractors) – an

occupational radiation exposure problem based in DCLL

TBM analyses• The counter flow gas rate per column set at 100 Ncm3/min• A film thickness of 0.2 mm was used to give an efficiency

of ~25% per stage in this TMAP

PbLi flow

PackingPlate

Gas flow

CT2 = PT2/kT

CT = Ks (PT2)1/2

Melodie Results

Schematic of TMAP Extractor Model

€

∝ pH2

Tritium Inventory and Permeation Results For HCLL

195% in of this inventory is in austenitic steel of extraction columns, and because there are 12,150 columns very little tritium is at risk in most accidents

299% ventilation flow cleanup is assumed399% of this permeation is from extraction

columns4Limit is < 1 g/a5Based on CANDU water concentration of ~1

Ci/kg (34,000 Ci/a allowed into Rankine cycle)6Based on US PWR water concentration of ~ 1

mCi/kg (340 Ci/a allowed into Rankine cycle)

• An increase in solubility by 100 increases the PbLi inventory by ~16 and increases HTX permeation, with the helium cleanup system now removing a large fraction of the tritium

• A tritium inventory of 0.9 kg for high Ks case could represent a radioactive release hazard for ex-vessel PbLi spills

• Tritium airborne releases are above allowable

• When implantation is considered, most of the implanted tritium remains in the helium cycles

Ks-Reiter 100 x Ks-Reiter FW Implantation

Tritium source ~400 g/d ~400 g/d ~910 g/d1

Inventory

Structure1 295 g 274 g 455 g

PbLi 60 g 864 g 60 g

Release2 130 g/a3,4 95 g/a3,4 145 g/a3,4

Extractor overall efficiency 80% 3.6% 80%

Tritium pressure

PbLi 2900 Pa 60 Pa 2925 Pa

Helium 2 Pa 14 Pa 130 Pa

Tritium global balance

Extraction columns 81.5% 55.5% 33%

Helium cleanup system 7.3% 30.0% 60%

Leaked 9.2% 6.5% 7.0%

Permeates to VV 2.3% 8.0% 0%

Permeation into Rankine cycle

Intermediate helium cycle 2890 Ci/a6 5930 Ci/a6 12,060 Ci/a6

Direct (required reduction)5/6 3.1x103

/3.1x105

1.3x104

/1.3x106

5.3x104

/5.3x106

Summary

• Based on the present models, an increase in tritium solubility above that measured by Reiter would increase the tritium inventory in the PbLi, decrease extraction efficiencies, but could reduce the structural tritium inventory and permeation rates in DEMO reactors

• Most of the tritium in a DCLL concept will be in the PbLi/helium HTX tube walls, and because Nb is a getter accidents that result in HTX cooling will not release significant quantities of tritium

• For the HCLL concept, the majority of the tritium inventory and permeation is associated with the extractor columns, which could be reduced by a better design or selection of column materials. In addition, the HCLL has a much higher PbLi tritium inventory, making ex-vessel PbLi spills a tritium release concern

• Tritium permeation into a simulated Rankine power cycle was compared against equilibrium tritium concentrations in CANDU and US PWRs, it appears to be difficult to maintain an equilibrium concentration of 1 mCi/kg (PWR concentrations) by permeation barriers and/or material heat exchanger choice

• Regardless of the blanket concept employed, FW tritium implantation represents a significant problem for a Rankine cycle; a FW coating is need on the plasma side

• However, these result are based on the assumption that a sufficient understanding of tritium behavior in the PbLi, at PbLi/metal or PbLi/gaseous interfaces is presently known. Based on present experimental information this is clearly not the case

• What can be inferred from these results is that fusion reactors tritium inventories and permeation rates are highly dependent on this information, and thereby the ability to predict accidental and routine release of tritium from fusion reactors

Postscript On Melodie Results

• If the simple TMAP extractor model is correct, then data from Melodie can be used directly to determine if Reiter’s solubility coefficient is reasonable for Melodie conditions, at least based on simple conservation equations

PbLi flow

PackingPlate

Gas flow

CH2 = PH2/kT

CH = Ks (PH2)1/2

Schematic of TMAP Extractor Model• Conservation of mass between phases:

( )

2

2

11

2

Hgs

s

lHl

Hl

Hl

Hl

Hll

Hl

Hl

Hls

ois

s

ois

oi

kTCKDA

QCC

Cfor solving

CCQCCCDA

=⎥⎥⎦

⎤

⎢⎢⎣

⎡⎟⎟⎠

⎞⎜⎜⎝

⎛ δ+η−=

−=⎟⎟

⎠

⎞

⎜⎜

⎝

⎛−

+

δ

• Conservation of mass in liquid and diffusion:

2

2

121

1

Hsats

Hl

gHl

ls

l

s

pKC where

QC

kTQK

Q

DA

i

i

=

⎥⎥

⎦

⎤

⎢⎢

⎣

⎡−

⎟⎟

⎠

⎞

⎜⎜

⎝

⎛ η−

η=δ

• Substituting the above and solving for film thickness:

Postscript On Melodie Results (cont.)

• Given the volume of the Melodie column (V=2.26x10-3 m3), a packing fraction of 80%, and a packing area density of 750 m2/m3, the packing (film) surface area is ~ 1.4 m2

PbLi flow

PackingPlate

Gas flow

CH2 = PH2/kT

CH = Ks (PH2)1/2

Schematic of TMAP Extractor Model

K 673T @ s

m3.76x10

min

Ncm 100Q

s

m1.39x10

hr

l50Q

s

m 2.0x10 D

K 673T

36

3

g

35

l

29-

===

==

=

=

−

−

• Given the other parameters of

where, Ks-max is the largest solubility that still results in

a film for the TMAP extractor model, which is found by setting the term in brackets in the film thickness equation to zero => Reiter Ks fits Melodie results

and using Melodie saturation pressures and efficiencies gives:

PH2sat

(Pa) η δ (mm)

Ks-max

/Ks-Reiter

Ks-δ=0.15 mm

/Ks-Reiter

1100 0.31 0.149 1.37 0.998

475 0.25 0.156 1.28 1.010

230 0.25 0.046 1.07 0.843

Schematic of ARIES-CS HCLL TMAP Model

PbLi Pipes

PackedColumns

PbLi corePbLi/He HX

PoloidalGaps

Radial Gaps

First wall

Second wall

Rib walls

Back plate

Tritium cleanupsystem

Helium pipes

Shield

Inter-cooler

Pressure boundary

Manifolds

BraytonCycle

823 K

673 K

Purgegas

Concentric pipesPbLi

Permeator

PbLi core

PbLi/He Nb HX

Non-Hartmann Gaps

Hartmann Gaps

First wall

Second wall

Rib walls

Back plate

Tritium cleanupsystem

Helium pipes

Shield

Inter-cooler

Pressure boundary

Manifolds

BraytonCycle

Schematic of ARIES-CS DCLL TMAP Model