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Review of Tritium Permeation Barrier Development for Fusion Application in the EU

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).

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Review of Tritium Permeation Barrier Development for Fusion Application in the EU

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  1. 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

  2. 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) • Thepreparation procedures and characterization of each coating were summarized in reportsuntil about end of 1998

  3. Introduction (2) 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   Nevertheless, this phase is not really finished!!

  4. Experimental (1) Hot-dip aluminizing process at FZK (simplified scheme) Steel sample (sheet or tube) Grinding Cleaning in acetone Coating, aq. flux-solution Pre-drying : 100°C Heat treatment (standard process) Glove-box (Ar-5%H2) Coated sample HIP-process (advanced process) Cleaning in water Hot-dip-aluminizing, 700°C

  5. Al2O3 - crucible Sample Steel tube Al-melt Furnace Experimental (2) Hot-Dipping Facility Glove-box Ar-5% H2 Coating conditions Temperature: 700°C Melt: Al or Al-Si Sample dimensions: up to 200 mm in length up to 40 mm in diameter Furnace

  6. Hot-Dip aluminizing process Parameters for hot dipping are: temperature at 700°C and dipping time of 30 s Microstructure of hot dipped surface Microstructure after heat treatment Al Fe2Al5 F82H-mod. FeAl HV 320 270 240 -Fe(Al) The alloyed surface layer consists of brittle Fe2Al5, covered by solidified Al Heat treatment at 1040°C/0.5 h + 750°C/1 h incorporates the solidified Al and transforms the brittle Fe2Al5-phase into the more ductile phases FeAl and -Fe(Al) F82H-mod. Experimental (3) HV 1000 230 Kirkendall pores

  7. Hot-Dip aluminizing process Parameters for hot dipping are: temperature at 700°C and dipping time of 30 s Microstructure of hot dipped surface Microstructure after heat treatment Al HV 320 270 240 FeAl HV 1000 230 Fe2Al5 -Fe(Al) F82H-mod. F82H-mod. The alloyed surface layer consists of brittle Fe2Al5, covered by solidified Al Heat treatment at 1040°C/0.5 h + 750°C/1 h and an applied pressure of >250 bar (HIPing) reduces porosity and transforms the brittle Fe2Al5-phase into the more ductile phases FeAland -Fe(Al) Experimental (3)

  8. Experimental (4) Main characteristics of the Hot-dip aluminizing coating • 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 permeationrate 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)

  9. 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 Al2O3 Fe-Al Experimental (5)

  10. Experimental (6) 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

  11. Results (1) Results of permeation testing in H2–gas in different facilitiesat ENEA Brasimone, Italy (PERI, CORELLI) Permeation Reduction Factors (PRF) pH2= 1 bar, steel: F82H-mod.

  12. Results (1) Results of permeation testing in H2–gas in different facilitiesat ENEA Brasimone, Italy (PERI, CORELLI), 1998-2000 Permeation Reduction Factors (PRF) cancelled pH2= 1 bar, steel: F82H-mod.

  13. Permeation data of HDA-coated FM-steels in H2 and Pb-17Li uncoated disk and tube PRF 2000 PRF  100 coated disk and tube Ispra Results (2)

  14. VIVALDI facility at ENEA, Brasimone, Italy, 2001-2003 Eurofer tube, one end closed Results (3)

  15. Results (4) 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.

  16. Results (5) Permeabilities of CVD-coated tubes in H2-gas PRF 6

  17. Results (6) Permeabilities of HDA-coated tubes in H2-gas PRF 140

  18. Results (7) Comparison of permeabilities of CVD-coated tubes in H2-gas and Pb-17Li PRF 15

  19. Results (8) Comparison of permeabilities of HDA-coated tubes in H2-gas and Pb-17Li T (K) Pb17Li PRF 15

  20. Results (9) Reasons for too low PRF’s in Pb-17Li CVD sample HDA sample cracks bad coating quality

  21. Conclusions (1) Conclusions • A large R&D activityregarding 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.

  22. Conclusions (2) 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.

  23. Contributions to this work FZK (Germany)J. Konys, H. Glasbrenner, K. Stein-Fechner, Z. Voss, O. WedemeyerCEA (France)C. Chabrol, A. TerlainENEA (Italy)G. Benamati, A. Aiello, I. RicapitoJRC Ispra (Italy)A. Perujo

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