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Fabrication and performance of Li 4 SiO 4 pebbles by the melt spraying method

Fabrication and performance of Li 4 SiO 4 pebbles by the melt spraying method. Yongjin Feng. Southwestern Institute of Physics (SWIP ), Chengdu, Sichuan, China. Outlines. Background Fabrication Process and Results of Li 4 SiO 4 pebbles

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Fabrication and performance of Li 4 SiO 4 pebbles by the melt spraying method

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  1. Fabrication and performance of Li4SiO4pebbles by the melt spraying method YongjinFeng Southwestern Institute of Physics (SWIP), Chengdu, Sichuan, China

  2. Outlines • Background • Fabrication Process and Results of Li4SiO4 pebbles • Deuterium Retention and Desorption Behavior of Li4SiO4 • R&D Plans on Breeder Materials at SWIP • Summary

  3. 1. Background CN Helium Cooled Ceramic Breeder (HCCB) TBM designs based on the SB/He/FM concept. Explosive view of CN HCCB TBM Sub-module design 1-ton Ingot of CLF-1 Be pebbles by REP method

  4. The ceramic breeder material must satisfy the following requirements: • High tritium breeding capability; • Adequate mechanical properties; • Limited pebble fragmentation ; • Adequate pebble bed thermal conductivity; • Compatibility with ferritic steel and the purge gas; • Chemical stability to avoid mass transport and material restructuring; • Radiation resistance; • Low tritium residence time; • Low activation;

  5. The selection of fabrication process for the pebbles based on the following criteria: • Capability to meet the pebbles goal specifications adequate for the HCCB TBM; • Simplicity and economics; • Scalability to industrial range; • Sufficient production yield; • Conveniently recycling the unburned 6Li from the pebbles. The fabrication trials have been investigated, such as, Melt spraying method, Freezing-Sintering method, Extrusion-spheronization-sintering, Sol-gel. The pebbles produced by the melt-spraying method have several advantages: • Higher density; • Smooth surface; • Higher sphericity; • Less contamination source; • Simpler reprocessing.

  6. Melting pot Heating and insulation Gas jet sprayer Bottom feeder 2. Fabrication process and Results Raw materials: Li2CO3 (Purity:99.99%) SiO2 (Purity:99.99 ) Li/Si Molar ratio: 4 Melting Pot: Corundum Crucible The raw materials are melted at temperature of about 1400℃ . Gas pressure: 1.5 bar, Gas: Nitrogen, Falling distance: 3.5 m. Schematic drawing of fabrication setup Heat treatment condition: 1000℃, 2h Production: 100Kg/year pebbles with 1.0 mm diameter Fabrication facility

  7. Shape and surface structure • Broad size distribution. • Most of the pebbles are well spherically shaped, smooth surface. Optical micrographs and SEM Optical micrographs and SEM of the pebbles with 1mm diameter SEM of pebble’s surface

  8. Phase analysis Heat treatment atmosphere: Vacuum, air temperature: 1000℃ time: 2h XRD pattern of pebbles annealed at vacuum XRD pattern of pebbles annealed at air TG curve of Li4SiO4 at CO2 atmosphere The diffraction peaks of Li2CO3, Li2SiO3,Li4SiO4are observed. Carbon dioxide are easily absorbed by Li4SiO4 Li4SiO4as the major phase, Temp. <500℃ absorb rate very slow; 500℃< Temp.< 720℃ absorption obviously; 720℃ < Temp.< 900℃ CO2desorption Li2SiO3 as a second phase

  9. Thermal analysis • Physical properties Measurement of Density and porosity by Hg-porosimetry and He-pycnometry. Specific surface area measurement by a multipoint BET method. TG Mass change:-41.67% DSC 716.7℃ Thermoanalysis of mixed raw materials The weight loss of about 40% occurred between 550℃ and 800℃. the significant weight lost taking place at 720℃. The reaction is a endothermic reaction.

  10. Chemical Composition of pebbles • Behavior in air Pebbles were exposed to air for 50 days at room temperature. The influence of the exposed surface area on the rate of uptake was measured. The uptake of moisture was determined by the weight increase. Elements analysis by ICP-OES The amount of impurities are 0.116186% Li/Si molar ratio ≠ 4 Weight increase of initial state pebbles and after annealing pebbles.

  11. Mechanical properties Mechanical stability analysis by crush load tests. Single sphere was placed between two parallel plates. A continuously increasing load is imposed by a piston to a single pebble until it breaks. 40 pebbles with a diameter ~1.0 mm were tested, respectively. press pebble After heat treatment , the crush load increased. The value is scattered. The mechanical stability must be improved.

  12. 3. Deuterium Retention and Desorption Behavior • The elucidation of tritium recovery from Li4SiO4 is one of key issues of TBM design. The study of hydrogen isotopes behavior in solid breeder materials is a important subject in the design for D-T fusion blanket module. • D2 irradiation has been applied as a technique of hydrogen isotopes implantation. Deuterium ion implantation was used to induce hydrogen isotopes and other irradiation defects into the surface of irradiated breeder material. • Desorption of hydrogen isotopes as water forms and hydrogen molecular forms might be due to the existence states of hydrogen isotopes on the surface of irradiated breeder material. • In Shizuoka University of Japan, the X-ray Photoelectron Spectroscopy (XPS) and Thermal Desorption Spectroscopy (TDS)apparatuses can be utilized for the elucidation of D2 desorption behavior in solid breeding materials.

  13. Temperature: 1173 K Heating time: 3 h Sintering Heating temperature: 1000 K Heating time: 10 min Heating treatment X-ray source: K α of Al XPS Ion energy: 3.0 keV D2+ Ion fluence : (0.4, 0.6, 0.8, 1.0)× 1022 D+ m-2 Ion flux: 2.0×1018 D+ m-2 s-1 Implantation temperature: R.T. D2+ Imp. XPS Heating rate: 5 K min-1 Heating region: R.T. - 1000 K TDS Experimental procedures of D2+ implantation 13

  14. XPS results • Comparision of before implanation and after implanation O-1s XPS spectra Li-1s XPS spectra Si-2p XPS spectra Atom Li: 55.6 eV Li-O- : 53.3 eV Si-O- : 107.1 eV Si-O-D : 105.2 eV O-Si: 536.1eV D-O-D: 533.8eV -O-D: 531.3eV

  15. Comparision of before implanation and after implanation O-1s XPS spectra Li-1s XPS spectra Si-2p XPS spectra After TDS, the BE of electron for Li-1s,O-1s and Si-2p shift back to before implantation. The irradiated influence for the chemical state of Li-1s,O-1s and Si-2p in Li4SiO4 will be recovered after TDS.

  16. TDS results D2 retention of Li4SiO4 at different fluence Peak analysis for TDS spectrum at the fluence1.0×1022D m-2 TDS spectra of D2 for Li4SiO4 at different fluence The D2 TDS spectrum of Li4SiO4 can be divided into 3 peaks. The first is due to the material surface adsorption, the second could be from the defects caused by D2+ implantation, and the third would be from O-D bond. Peak 1 (400 K) → Surface adsorption Peak 2 (500 K) → Defect Peak 3 (650 K) → -O-D- bond • D2 desorption rate and the total D2 retention increase with the increasing of implantation fluence. • All of D+ are trapped by oxygen vacancy to form –OD bond.

  17. 4. R&D Plans on Breeder Materials • For Fabrication: • LiOH and SiO2 will be used as raw materials, and compared with the current raw materials, the heat treatment will be optimized; • The reprocessing of Li4SiO4 pebbles will be considered by remelting; • Li2TiO3 pebbles shall be produced using Extrusion-spheronization-sintering method. • For the properties of pebbles: • Long-term annealing experiments under ITER TBM (DEMO blanket) relevant temperature and atmosphere; (Li content of the pebbles, Phase composition, microstructure, density, etc) • Mechanical stability analysis will be tested as heat cycle test. After the tests, the amount of broken particles are determined. • (Temperature : 200-600℃, number of cycles: ~100 cycle (~1cycle/h) ).

  18. Irradiation properties of pebbles: • Tritium behavior in thermal neutron irradiated Li4SiO4will be considered to carry out in this year; • (Temp. : < 353 K, T. N. flux: 5.5×1012cm2 s-1, T. N. fluence: 3.3×1015cm2) • Effect of implantation temperature on retention behavior of deuterium in Li4SiO4 will plan to investigate. • Thermo-mechanical of pebble bed • Uniaxial compression tests at temperatures up to 900℃ to determine the mechanical characteristics of pebble beds will be performed. • (Stress-strain dependence during stress increase and decrease, thermal • creep strain at constant stress levels. ) • Thermal conductivity measurements of pebbles bed and the effect of thermal creep on the thermal conductivity will be performed. • (Tests in helium and air atmosphere and temperatures up to 900℃ )

  19. 5. Summary • A melt-spraying fabrication process for Li4SiO4 pebbles has been developed. Li4SiO4pebbles produced by spray of liquid droplets have almost spherical shape, a smooth surface and high density, but the produced pebbles exhibit a broad size distribution that limits the yield. • The mechanical stability of different batches are scattered. This would endanger the safety of TBM, and also does not satisfy the requirements of TBM. • A series of tests with pebbles of different composition treated in an optimized heat treatment conditions will be performed in our following work. • Optimized process is undergoing at SWIP. • It was confirmed that the new chemical states of lithium, oxygen and silicon on • the surface of D2+-irradiated Li4SiO4 was formed due to typical irradiation • defects induced by D2+-irradiation. • Thermo-mechanical behavior, long-term stability, the behavior under neutron • irradiation and the tritium release properties will be performed.

  20. Thank You !

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