Coordinating Meeting on R&D for Tritium and Safety Issues in Lead-Lithium Breeders (PbLi-T 2007)

1. Overview of Japanese PbLi-T Research Activities and Related Topics Takayuki Terai tera@n.t.u-tokyo.ac.jp University of Tokyo Coordinating Meeting on R&D forTritium and Safety Issues in Lead-Lithium Breeders (PbLi-T 2007)

2. Japanese PbLi-T Research Activitiesand Related Topics • Japan has not proposed a specific Pb-Li TBM design, but plans to contribute to TBM test by collaboration with other parties. • Tritium Behavior in Pb-Li - Diffusivity, Mass-transfer and Permeability by in-pile test (University of Tokyo) - T recovery by permeation window method (University of Tokyo) - Diffusivity and solubility of H and D (Kyushu University) - Permeability in a loop (Kyoto University) • Permeation Barrier Coating - Al2O3, Y2O3 coating (University of Tokyo) - Er2O3 coating (NIFS, University of Tokyo, JUPITER-II) • Related Topics - Advanced blanket concept based on PbLi – SiC – He combination with a LiPb-He dual coolant loop (Kyoto University) - Conceptual design of ICF reactor “KOYO-F” using PbLi as a coolant and breeder (Osaka University) - Q hehavior in SiC (Shizuoka University)

4. Silica gel Water Bubbler Gas supply System He + H2 (HT) He + H2 IC Polyethylene Blocks Reactor core Container with heater Schematic diagram of the irradiation apparatus Tritium Release Behavior from Liquid breeders under a Blanket -Simulated Condition (under Neutron Irradiation at High Temperature) (Tokyo) Pb-17Li, LiF-BeF2(Flibe), Sn-20Li 673-973 K Tritium chemical species (HT, HTO, TF, etc.) Tritium diffusivity Tritium release rate Tritium permeation through piping materials

5. Diffusion Coefficient of Tritium in Liquid Pb-17Li Under the condition of He-H2 (pH2 > 103 Pa) purge gas, Diffusion of T in liquid Pb-17Li is dominant, and D / m2s-1 = 2.50 x 10-7 exp ( -27.0 kJmol-1 / RT) (Terai et al., J. Nucl. Mater. 187 (1992), 247.) (Tokyo)

6. Mass-transfer Coefficient of Tritium from Liquid Pb-17Li to environmental gas Mass-transfer coefficient increases with pH2 in He-H2 purge gas, and at pH2 > 103 Pa, it is almost constant and given by KD / ms-1 = 2.5 x 10-3 exp ( -30.7 kJmol-1 / RT) This process is governed by the T diffusion in liquid-film, and the film thickness is 0.2 mm in this condition. (Terai et al., Fus. Engng. and Des. 17 (1991), 237) (Tokyo)

7. Tritium Permeation through Piping Materials Facing Liquid Pb-17Li In case of a-Fe, no stable oxide film cannot formed on the surface, and T permeation behavior is described by the T diffusion in a-Fe, while in case of SS316, a stable oxide film of Cr2O3 and FeCr2O4 decreases T permeation rate with a reduction factor of 30 – 300 depending on pH2. (e.g. Terai et al., J. Nucl. Mater. 191－194 (1992), 272) (Tokyo)

8. Experiments of recovery of hydrogen isotopes from Pb-17Li-Measurement of diffusivity, solubility and isotopic exchange rate constant- Li-Pb Fe Experimental apparatus for LiPb-H2(D2) system Comparison between experiment and calculation S. Fukada, Kyushu University group

9. Dependences of DH and SH on temperature for Pb-17Li-H system and comparison with previous researches Hydrogen solubility in Li0.17Pb0.83 Hydrogen diffusivity of Li0.17Pb0.83 S. Fukada, Kyushu University group

10. Li activity of LiXPb1-X-H2 system eutectic alloy Pb Pb • When xLi>0.5, electric charge of Li+ is not shielded by Pb atoms, and Li+-H- ionic binding is major in LiXPb1-X eutectic alloy. Activity of Li is higher. • When xLi<0.5, electric charge of Li+ is shielded by Pb atoms, and Li+ and H- ions are not combined directly. Activity of Li is the lowest. Li+ H- Pb Li+ Pb H- S. Fukada, Kyushu University group

11. He out LiPb in LiPb out He in Design of He-LiPb counter-current extraction towerfor tritium recovery • Material balance equation • Gas-phase mass-transfer coefficient • LiPb-phase mass-transfer coefficient • Tritium concentration profile in tritium extraction tower Cited from He-water system Cited from He-water system Example of calculation of tritium concentration in a counter-current extraction tower (Flibe case)S. Fukada et al., Fusion Science and Technology, 41 (2002) 1054.) S. Fukada, Kyushu University group

12. Ceramic Coating R&D for Pb-17Li Properties of ceramic coating for Pb-17Li blanket • Tritium permeation resistance • Electrical resistance • Corrosion resistance Fabrication and properties of ceramic coatings • Al2O3 coating fabricated by hot-dipping followed by oxidation (Tokyo) • Y2O3 coating fabricated by plasma spray (Tokyo) • Al2O3 and Y2O3 coating fabricated by plasma CVD (Tokyo) (Terai et al., Surf. Coat. Tech. 106 (1998), 18.) • Er2O3 coating fabricated by Arc-source deposition (NIFS, Tokyo, JUPITER-II)

13. Al2O3 Coating Fabricated by Hot-Dipping Followed by Oxidation (Tokyo) (Terai et al., SOFT-1994, p.1329) (Terai, J. Nucl. Mater. 248 (1997), 153)

14. Phase Change of the Coating Fabricated by Hot-dipping Followed by Oxidation

15. Er2O3 coating as tritium permeation barrier(NIFS, Tokyo) • Selection of Er2O3 coating as tritium permeation barrier • Thermodynamic stability, corrosion-resistance to liquid breeder, and high compatibility with structural materials • 　　　　→ permeation barrier at multi-conditions • Fabrication of Er2O3 coatings by several PVD methods Observation on characteristics of coating, （１）Surface observation for cracks and holes (microscope) （２）impurity (XPS, EDS) （３）density (weight change + SEM) （４）crystallinity (XRD) → Selection of coating methods and conditions Hydrogen permeation test （５）Coatings with different grain size and thickness → Evaluation of ability and mechanism for improvement on Er2O3 as a tritium permeation barrier.

16. Characteristics of coatings • The coating fabricated by arc-source method is considered to be sutable for tritium permeation barrier coatings. → Hydrogen permeation experiment for the coating fabricated by arc-source method.

17. 10Pa～105Pa Room temp. Hydrogen permeation rate coefficient (NIFS, Tokyo) • Permeation reduction factor to the vanadium substrate: 1/106～1/108 • PRF to iron or stainless steel : 1/100～1/10,000 (comparable with Al2O3 coatings) • Permeation rate coefficient was affected by the thickness of coatings than crystallinity or grain size Double layered coating

18. Institute of Advanced Energy, Kyoto University Activity in Kyoto University Objective Kyoto University pursues advanced blanket concept based on LiPb – SiC – He combination to be opearated at 900 degree or above. Research objective includes, -to Establish a possible advanced blanket concept with supporting technology -to Demonstrate the attractiveness of fusion energy with safety and effectiveness i.e. high temperature efficient generation and hydrogen production, minimal waste generation and tritium release, technical feasibility, adoptability to attractive reactor designs. Research Items Current researtch efforts are on the following tasks Conceptual design with neutronics and thermo-hydraulics, MHD LiPb-SiC-hydrogen system study: compatibility, solubility, permeability LiPb technology : Loop experiment, purity control, high temperature handling SiC component development : cooling panel, tubings, fittings and IHX Mockup development : heat transfer, tritium recovery and control - 9 -

19. Li-Pb Flow SiC-LiPb Blanket Concept Outer blanket calculation model • Module box temperature made of the RAFS must keep under 500 ºC. • Li-Pb outlet temperature target 900 ºC. • We propose the new model of active cooling in Li-Pb blanket. • This concept is equipped He coolant channels in SiC/SiC composite and provides more efficient isolation between the RAFS and high temperature Li-Pb. • We evaluate the feasibility of high temperature blanket in this model. 1.RAFS module box (~500ºC) 2.SiC/SiC active cooling panel 3.High temp. outlet (~900ºC)

20. Institute of Advanced Energy, Kyoto University 15.12 mm 17.89 mm 6 mm Activity in Kyoto University LiPb loop operational for heat exchanger with SiC composite development Upgrading for LiPb-He dual coolant loop started in 2006. 900 degree He secondary loop will be added in 2007. LiPb loop was installed and started operation Major parameters: LiPb inventory : 6 liter flow rate : 0 – 5 liter /min temperature : 250 – 500 degree C (~900 deg C at SiC section) MHD , heat exchange, compatibility, hydrogen permeation studied. LiPb loop in Kyoto University SiC cooling panel structure channel structure unit with NITE composite developed for He-LiPb cooling panel. NITE SiC cooling panel channel

21. At Osaka University, brush up of conceptual design reactor KOYO-F and elemental experiments are continued with other universities collaborately Basic specifications Wall load at 200 MJ fusion yield Fast ignition KOYO-F

22. 1) Protection of beam ports 3) Tritium flow 2) Aerosols and particles Features of KOYO-F to deal with high a heating • Vertically off-set irradiation to simplify the protection scheme of ceiling • Cascade surface flow with mixing channelto enhance pumping by cryogenic effect. • Tilted first panels to make no stagnation point of ablated vapor Critical issues are: Target is enlarged by 150

23. Elemental study at ILE and collaborations with other universities • At ILE, Osaka • Ablation by alpha particles was experimentally simulated with punch-out targets driven by back lighted laser. • At Kyushu University • With Dr Y. Kajimura, beam port protection • With Dr. S. Fukada, tritium flow • At Kyoto University • With T. Kunugi, stability of cascade flow • With S. Konishi, ablation, aerosols, LiPb loop

24. Hydrogen isotope behavior in SiC for the insulator in Pb-Li blanket Si-D C-D Y. Oya and K. Okuno Shizuoka University Implantation temperature dependence on D retention in graphite, SiC and WC D2 TDS spectra for SiC at room temperature In the initial stage, D was trapped by C and after the saturation of C-D, D was trapped by Si. D retention in SiC is reached more than 0.7 D/SiC at room temperature.

25. He implantation effects on hydrogen isotope trapping in SiC Only D bound to Si was influenced by He+ implantation. By He+ implantation, the damaged structure would be introduced. In addition, He retention was observed, although D retention was decreased.

26. TITAN Task 1-2: Tritium Behavior in Blanket Systems Participants: T. Terai, A. Suzuki, H. Nishimura (U. Tokyo) S. Konishi, T. Kamei (Kyoto U.) S. Fukada, K. Munakata, K. Katayama (Kyushu U.) T. Nagasaka, M. Kondo, T. Uda, A. Sagara (NIFS) T. Norimatsu, K. Homma (Osaka U.) T. Sugiyama (Nagoya U.) P. Sharpe, P. Calderoni, D. Petti (INL) D-.K. Sze (UCSD) and others

27. Key technical items for tritium in liquid blanket systems • Solubility in Pb-Li • - typical measurements performed at relatively high hydrogenic partial pressure (~101-104 Pa) are extrapolated to much lower partial pressures required for tritium inventory control- deviance from Sievert’s Law is possible (based on other LM results, e.g. Li)- measurements at extremely low concentrations require tritium • Recovery methods from Pb-Li (and other liquid breeders) and He flows • - inadequate mass transport across liquid-vapor interface for vacuum disengagement or window permeators in PbLi- oxidation or cryogenic systems for He, with structural and power implications- ingenious techniques for high recovery efficiencies are needed • Transport barriers resistant to thermal cycling and irradiation • - minimum required PRF ~ 100, needs robustness or self-healing attributes- success (or lack thereof) greatly influences direction of blanket system design • Permeation behavior at very low partial pressures over metals • - linear vs. Sievert’s behavior? transport related to dissociation/recombination rates becomes non-equilibrium?- influence of surface characteristics and treatment

28. Proposed Research Project Areas for TITAN Task 1-2 Selected to provide the basis for the Tritium Behavior in Liquid Blanket Systems of interest to US and Japan • Solubility of T in Pb-Li at Blanket Conditions - Low pressure region of hydrogen isotopes using tritium - Confirmation of Sieverts’ Low, Phase diagram of Pb-Li and T system • Concentration Effects of T Permeation in Structural Materials and TPB Coating - Wide T pressure range covering several kinds of liquid breeders - Performance test on SM as well as TPB coating (to be developed in Japan) • Tritium Extraction from Pb-Li and Other Liquid Breeders at Blanket Conditions - Mass transfer kinetics - Permeation window, gas engager, etc. - Performance test on a loop which is constructed inside or outside the budget • Modeling and System Design for Tritium Behavior at Blanket Conditions