Forschungszentrum Karlsruhe in der Helmholtz-Gemeinschaft FUSION ITER TBM Project Meeting, February...

Forschungszentrum Karlsruhein der Helmholtz-GemeinschaftFUSION

ITER TBM Project Meeting, February 23-25, 2004, UCLA Jürgen Konys

Review of Tritium Permeation Barrier Development for Fusion Application in

the EU J. Konys

• Introduction• Experimental * Process parameters of HDA (FZK) and CVD (CEA) techniques

• Results * Permeation data of HDA and CVD barriers

• Conclusions



Introduction (1)

Why do we need TPB’s (Tritium Permeation Barriers)?

To reduce the Tritium release into the cooling water significantly (this was part of the WCLL blanket concept) EU Fusion Technology program selected Fe-Al-based coatings with Al2O3 as a thin top layer

First phase in EU (up to ca. 1998): 3 coating processes have been selected

Chemical vapour deposition (CVD) CEA Grenoble (F) Vacuum plasma spraying (VPS) JRC Ispra (I) Hot-dip aluminizing (HDA) FZK Karlsruhe (D)

The preparation procedures and characterization of each coating were summarized in reports until about end of 1998



Second phase in EU (up to ca. “2002”):

Several qualification tests were strongly required for the final

selection of a so-called “reference coating”!

Measurement of the hydrogen permeation rate in the gas

phase

Measurement of the hydrogen permeation rate in Pb-17Li ?

Self-healing tests in Pb-17Li

Irradiation experiments of the coatings

Compatibility studies of coatings in flowing Pb-17Li at relevant

temperatures

Introduction (2)

Nevertheless, this phase is not really finished!!



Experimental (1)

Hot-dip aluminizing process at FZK (simplified scheme)

Steel sample

(sheet or tube) Grinding Cleaning in

acetoneCoating, aq. flux-solutionPre-drying : 100°C

Glove-box (Ar-5%H2)

Hot-dip-aluminizing, 700°C

Cleaning in water

Heat treatment

(standard process)

HIP-process

(advanced process)

Coated sample



Experimental (2)

Al2O3 - crucible

Sample

Steel tube

Al-melt

Furnace

Coating conditions

Temperature: 700°CMelt: Al or Al-SiSample dimensions: up to 200 mm in length

up to 40 mm in diameter

Hot-Dipping Facility

Ar-5% H2Glove-box

Furnace



Experimental (3)

Hot-Dip aluminizing process

Parameters for hot dipping are: temperature at 700°C and dipping time of 30 s

Microstructure of hot dipped surface

The alloyed surface layer consists of brittle Fe2Al5, covered by solidified Al

Microstructure after heat treatment

Heat treatment at 1040°C/0.5 h + 750°C/1 hincorporates the solidified Al and transforms the brittle Fe2Al5-phase into the more ductile

phases FeAl and -Fe(Al)

FeAl

-Fe(Al)

F82H-mod.

HV 320

270

240F82H-mod.

Fe2Al5

AlHV 1000

230Kirkendall pores



FeAl

-Fe(Al)

F82H-mod.

HV 320

270

240

Hot-Dip aluminizing process

Parameters for hot dipping are: temperature at 700°C and dipping time of 30 s

Microstructure of hot dipped surface

The alloyed surface layer consists of brittle Fe2Al5, covered by solidified Al

Microstructure after heat treatment

Heat treatment at 1040°C/0.5 h + 750°C/1 hand an applied pressure of >250 bar (HIPing)reduces porosity and transforms the brittleFe2Al5-phase into the more ductile phases FeAland -Fe(Al)

F82H-mod.

Fe2Al5

AlHV 1000

230

Experimental (3)



Experimental (4)

The hot-dipping process is compatible with heat treatment of the steel, including HIP process (if required for densification of Kirkendall pores)

The oxidation process to form alumina is included in the heat treatment

The hot-dip coating is good adhering to the steel, is dense and ductile enough

A reduction of tritium permeation rate in H2 gas by more than 3 orders of

magnitude can be achieved

Corrosion attack by Pb-17Li ........ see presentation of tomorrow

Hot-dip aluminization is a well-established industrial technology (at least for low-alloyed carbon steels)

Main characteristics of the Hot-dip aluminizing coating



Chemical vapour deposition (CVD) by CEA

Industrial established 2-step process

Fe-Al coating

• Powder mixture: Fe-Al, NH4Cl and Al2O3

• T = 650-750°C, p < 10 mbar Ar, t = 1-5 hours

Al2O3 deposition

• MOCVD process (metalorganic precursor)

• T = 400-500°C, t = 1-2 hours

Experimental (5)

Al2O3

Fe-Al



Vacuum plasma spraying (VPS) by JRC Ispra

Industrial established process

Al coating

• Powder: Al 54 from Metco

• Sand blasting before coating, then final sputter cleaning in vacuum apparatus

• Tsubstrate = 230-250°C

• Pressure: < 10-4 Pa

• Spraying distance: 220 mm

• Heat treatment necessary to transform the sprayed Al-layer into iron-aluminide

Experimental (6)



T (°C) VPS HDA CVD

300 450 3100 3100

350 400 2800 2100

400 380 1500 1600

450 380 2400 1300

pH2= 1 bar, steel: F82H-mod.

Results of permeation testing in H2–gas in different facilities

at ENEA Brasimone, Italy (PERI, CORELLI)

Permeation Reduction Factors (PRF)

Results (1)



T (°C) VPS HDA CVD

300 450 3100 3100

350 400 2800 2100

400 380 1500 1600

450 380 2400 1300

Results of permeation testing in H2–gas in different facilities

at ENEA Brasimone, Italy (PERI, CORELLI), 1998-2000

Permeation Reduction Factors (PRF)

pH2= 1 bar, steel: F82H-mod.

cancelled

Results (1)



Results (2)

Permeation data of HDA-coated FM-steels in H2 and Pb-17Li

Ispra

uncoated disk and tube

coated disk and tube

PRF 2000

PRF 100



Results (3)

VIVALDI facility at ENEA, Brasimone, Italy, 2001-2003

Eurofer tube, one end closed



Permeation tests in VIVALDI facility

The coated samples were tested in sequence and compared with the bare sample, both placed together in the permeation chamber.

Hydrogen gas at a known fixed pressure of 1 bar was released into the permeation chamber. The gas permeated through the samples and caused a pressure rise in the inner calibrated volumes.

This pressure rise could be converted into an amount of moles of gas permeating per unit area of the samples.

By comparing the steady state fluxes of the coated and bare samples, one could calculate the Permeation Reduction Factor PRF.

Results (4)



Permeabilities of CVD-coated tubes in H2-gas

Results (5)

1,3 1,4 1,5 1,6 1,7 1,8

1E-12

1E-11

CVD 1 T increase CVD 2 T increase CVD 1 T decrease CVD 2 T decrease Reference specimen Disk shaped sample

(m

ol m

-1s-1

Pa-1

/2)

1000/T (1/K)

750 700 650 600 550

T (K)

PRF 6



Results (6)

Permeabilities of HDA-coated tubes in H2-gas

1,3 1,4 1,5 1,6 1,7 1,8

1E-14

1E-13

1E-12

1E-11

1E-10

(

mol

m-1 s

-1 P

a-1/2)

HD T increase HD T decrease Reference Disk shaped sample

1000/T (1/K)

750 700 650 600 550

T (K)

PRF 140



Results (7)

Comparison of permeabilities of CVD-coated tubes in H2-gas and Pb-17Li

1,35 1,40 1,45 1,50 1,55 1,60 1,65 1,70 1,75

1E-13

1E-12

1E-11

1E-10 CVD 2 gas phase CVD 2 liquid metal T increase CVD 2 liquid metal T decrease Reference in gas phase Reference in liquid metal phase Disk shaped sample in gas phase

(m

ol m

-1s-1

Pa-1

/2)

1000/T (K-1)

450 400 350 300

T (°C)

PRF 15



Results (8)

Pb17Li

Comparison of permeabilities of HDA-coated tubes in H2-gas and Pb-17Li

1,3 1,4 1,5 1,6 1,7 1,81E-14

1E-13

1E-12

1E-11

1E-10

HD T increase HD T decrease HD T increase 2 Ref T increase Ref T decrease Disk shaped sample HD in gas phase

(m

ol m

-1s-1

Pa-1

/2)

1000/T(1/K)

700 650 600 550T (K)

PRF 15



Results (9)

Reasons for too low PRF’s in Pb-17Li

HDA sample

CVD sample

cracks

bad coating quality



Conclusions

Conclusions (1)

A large R&D activity regarding the development of coating techniques for TPB‘s was launched in the EU during the last 10 years.

Fe-Al-type coatings were identified as potential materials for TPB‘s and partly qualified in the gas phase. They fulfill the requirement of PRF 1000. CVD and HDA process were selected as possible candidates for being the “reference coating“ for TPB‘s. A final selection between both coatings has not yet been made.

The low PRF‘s in Pb-17Li (required was a PRF 75) obtained in the VIVALDI experiments, demonstrated a distinct sensitivity of PRF to the coating quality.

Nevertheless, the reason for the too low PRF‘s in the presence of Pb-17Li is not really known or understood. A reaction of Al2O3 to form LiAlO2 is discussed in literature, but not believed to explain the current results.



Conclusions

Since 2001/2002, no further development regarding coating techniques was made, (either at CEA nor at FZK) because “design people“ decided to live without TPB‘s in the (at that time) existing WCLL blanket concept.

Therefore, no more funding from the EU was available. Only a small budget for the permeation measurements at ENEA Brasimone, Italy, was launched.

In 2003, a change from WCLL to HCLL blanket concept was made, due to budget restrictions in the EU.

In the new HCLL concept, temperatures up to 550°C (or maybe higher) are envisaged in the “Pb-17Li area“ of the blanket structure. This was or is the return of the necessity of coatings for the reduction of tritium permeation into the coolant (He) and also for so-called“ corrosion barriers“, because of the increasing dissolution corrosion of structural steels in high-temperature Pb-17Li.

Nevertheless, a new programme for the continuation of the TPB/corrosion barrier development is not decided for funding in the EU at the moment.

Conclusions (2)



Contributions to this work

FZK (Germany)J. Konys, H. Glasbrenner, K. Stein-Fechner, Z. Voss, O. Wedemeyer

CEA (France)C. Chabrol, A. Terlain ENEA (Italy)G. Benamati, A. Aiello, I. Ricapito

JRC Ispra (Italy)A. Perujo

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