Current Status of Lithium Ceramic Pebble Manufacturing in Korea Yi-Hyun Park 1, In-Keun Yu 1, Mu-Young Ahn 1, Seungyon Cho 1, Duck Young Ku 1, and Sang-Jin Lee 2 1 National Fusion Research Institute, Daejeon, Korea 2 Mokpo National University, Jeonnam, Korea

CBBI-16, Sep. 8-10, 2011, Red Lion on the River, Portland, OR, USA Contents 1 Ⅰ Ⅱ Ⅲ Ⅳ Background R&D Status-1 : Synthesis of Li 4 SiO 4 Powder R&D Status-2 : Fabrication of Li 4 SiO 4 Pebble  Compression Molding Method  Slurry Droplet Drying Method  Slurry Droplet Wetting Method Summary and Future Works

CBBI-16, Sep. 8-10, 2011, Red Lion on the River, Portland, OR, USA Background 2 Korea Helium Cooled Solid Breeder TBM (KO HCSB TBM) Reduced Activation Ferritic/Martensitic steel as structural material Li 4 SiO 4 (LS) or Li 2 TiO 3 (LT) pebble as breeder Be pebble as multiplier Graphite pebble as reflector SiC coating is necessary to avoid air/water contact, to enhance pebble strength, and to handle easily. ParameterValues FW heat flux Average 0.3 MW/m 2 Peak 0.5 MW/m 2 Neutron wall load0.78 MW/m 2 Thermal Power1.01 MW Tritium Breeding Ratio 1.1 Structural materialRAFM (< 550 o C) Breeder Li 4 SiO 4 pebble bed Li 2 TiO 3 pebble bed (optional) < 920 o C Multiplier Be pebble bed < 650 o C ReflectorGraphite pebble bed Size1208x710x600 (mm) Coolant 8 MPa He kg/s FW ( 300 o C / 390 o C ) Breeding Zone(390 o C/500 o C ) PurgeHe with 0.1 % H 2

CBBI-16, Sep. 8-10, 2011, Red Lion on the River, Portland, OR, USA Required Properties for Li-ceramic 3 MaterialPropertyRequirementRemarks Powder Particle Size< 0.5 μmsuccess (LS) Crystalline Phase> 98.5 %success (LS) Impurities Co : < 1 ppm Al : < 35 ppm from activation/waste Pebble Particle Size< 10 μmneed to control Diameter1.0 mmneed to control Porosity< 20 %need to control Sphericity< Crush Load> 15 N- Quality Controllability, Mass Production, High-yield, Good Reproducibility, Reprocessing (Recycling)

CBBI-16, Sep. 8-10, 2011, Red Lion on the River, Portland, OR, USA Contents 4 Ⅰ Ⅱ Ⅲ Ⅳ Background R&D Status-1 : Synthesis of Li 4 SiO 4 Powder R&D Status-2 : Fabrication of Li 4 SiO 4 Pebble  Compression Molding Method  Slurry Droplet Drying Method  Slurry Droplet Wetting Method Summary and Future Works

CBBI-16, Sep. 8-10, 2011, Red Lion on the River, Portland, OR, USA Synthesis Process of Li 4 SiO 4 powder 5  Synthesis Process for Li 4 SiO 4 powder by PVA Solution Route Lithium Nitrate (LiNO 3 ) Silica sol (SiO 2 ) D.I. water PVA 5 wt.% PVA solution D.I. water Mixing (entrapment) Drying (Li 4 SiO 4 ceramic precursor) Calcination & Crystallization

CBBI-16, Sep. 8-10, 2011, Red Lion on the River, Portland, OR, USA Thermal Analysis of Li 4 SiO 4 Precursor 6  Thermo Gravimetry (TG) / Differential Thermal Analyzer (DTA) The calcination process was finished below about 800 o C. Crystallization Process : >800 o C

CBBI-16, Sep. 8-10, 2011, Red Lion on the River, Portland, OR, USA Synthesized Li 4 SiO 4 Powders 7  Effects of Crystallization Temperature 800 o C 1000 o C 900 o C Primary Particle Size : about 200 nm

CBBI-16, Sep. 8-10, 2011, Red Lion on the River, Portland, OR, USA Synthesized Li 4 SiO 4 Powders 8 Low Mw High Mw Low Mw High Mw  Effects of PVA Type  Effects of PVA Content 5 wt.% 10 wt.% 5 wt.% 10 wt.%

CBBI-16, Sep. 8-10, 2011, Red Lion on the River, Portland, OR, USA Contents 9 Ⅰ Ⅱ Ⅲ Ⅳ Background R&D Status-1 : Synthesis of Li 4 SiO 4 Powder R&D Status-2 : Fabrication of Li 4 SiO 4 Pebble  Compression Molding Method  Slurry Droplet Drying Method  Slurry Droplet Wetting Method Summary and Future Works

CBBI-16, Sep. 8-10, 2011, Red Lion on the River, Portland, OR, USA Fabrication of Pebble : Compression Molding Method 10 PVA solutionLi 4 SiO 4 powder Mixing Pressing using Compression Mold Sintering Granulation  Fabrication Process of Compression Molding Method Li 4 SiO 4 Granules Compression Mold for Pebble Dia. : about 0.3mm PVA cont.: 5~10wt.% Punch Spherical Green Body

CBBI-16, Sep. 8-10, 2011, Red Lion on the River, Portland, OR, USA Strength Properties 11 No.Dia. (mm)Crush Load (N)Max. Contact Pressure (GPa) Equipment : Micro-force Material Tester Cross-head Speed : 0.5 mm/min Test Temperature : R.T. Pebble Upper anvil Lower anvil

CBBI-16, Sep. 8-10, 2011, Red Lion on the River, Portland, OR, USA Fabrication of Pebble : Slurry Droplet Drying Method 12  Fabrication Process of Droplet Drying Method by using Hydrophobic Cloth D.I. waterLi 4 SiO 4 powder Mixing (1:2 wt.%) Dropping on Hydrophobic Cloth Drying (24h) Rolling Sintering

CBBI-16, Sep. 8-10, 2011, Red Lion on the River, Portland, OR, USA Photographs of Green Bodies 13 slurry droplets as-dried green body rolled green body rolling (3h, 100 rpm) Average diameter of rolled green body was about 1 mm. It could be easily controlled by changing of rolling conditions.

CBBI-16, Sep. 8-10, 2011, Red Lion on the River, Portland, OR, USA Fabrication of Pebble : Slurry Droplet Wetting Method 14  Fabrication Process of Dropping Wetting Method by using Hydrogen Peroxide Solution PVA solution D.I. water Li 4 SiO 4 Powder PVA Mixing Dropping into 34%-H 2 O 2 solution Drying (R.T., 12h) Sintering Li 4 SiO 4 powder 10wt.% PVA solution slurry syringe needle H 2 O 2 solution gel-sphere

CBBI-16, Sep. 8-10, 2011, Red Lion on the River, Portland, OR, USA Photographs of Gel-spheres 15  Dropped and Floating Gel-spheres gel-sphere bubble after 30 seconds After about 30 seconds settling at the bottom, Li 4 SiO 4 gel-spheres came up to the surface of the H 2 O 2. Decomposition Reaction of H 2 O 2 : 2 H 2 O 2 (aq)  2 H 2 O (l) + O 2 (g) Flat surface was not observed at the gel-sphere.

CBBI-16, Sep. 8-10, 2011, Red Lion on the River, Portland, OR, USA Photographs of Green Body and Pebble 16  Spherical Green Bodies and Sintered Li 4 SiO 4 Pebbles sintering (1000 o C, 4h, in air) spherical green bodiessintered Li 4 SiO 4 pebbles average diameter : 2.5 mmaverage diameter : 1.5 mm

CBBI-16, Sep. 8-10, 2011, Red Lion on the River, Portland, OR, USA XRD Patterns of Powder and Sintered Pebble 17 2θ ( o ) Intensity (counts) pebble powder  Li 2 Si 2 O 5 and SiO 2 included in starting powder were reacted and removed by sintering process.

CBBI-16, Sep. 8-10, 2011, Red Lion on the River, Portland, OR, USA Crush Load and Microstructure 18 Displacement (mm) Compressive Load (N) 50μm 10μm Diameter : about 1.5 mm 0.5 mm/min Room Temp.  Crush Load : 15 N ~ 35 N  Particle Size < 10 μm

CBBI-16, Sep. 8-10, 2011, Red Lion on the River, Portland, OR, USA Contents 19 Ⅰ Ⅱ Ⅲ Ⅳ Background R&D Status-1 : Synthesis of Li 4 SiO 4 Powder R&D Status-2 : Fabrication of Li 4 SiO 4 Pebble  Compression Molding Method  Slurry Droplet Drying Method  Slurry Droplet Wetting Method Summary and Future Works

CBBI-16, Sep. 8-10, 2011, Red Lion on the River, Portland, OR, USA Summary and Future Works 20  Pure and stable Li 4 SiO 4 powder was successfully synthesized by polymer solution route employing PVA as an organic carrier.  Li 4 SiO 4 pebbles with relatively high sphericity, high strength and fine grain size could be successfully fabricated by a compression molding method, a slurry droplet drying method, and a slurry droplet wetting method.  It is expected that these methods are easily-controllable and high- yield process for solid breeder pebbles.  These methods should be constantly improved for high performance of Li-ceramic pebbles such as high-temperature properties, irradiation properties, and recycling process.

CBBI-16, Sep. 8-10, 2011, Red Lion on the River, Portland, OR, USA 21 Thank you for Your Attention !!!

CBBI-16, Sep. 8-10, 2011, Red Lion on the River, Portland, OR, USA 22 (a) Excess or not enough polymer results in large particle size distributions. (b) the optimal amount should give a more uniform distribution. O : cation ion ~ : polymer chain PVA type and mixing amount Two types of PVA  High degree of polymerized PVA :D.P. value = 1625 (monomers/polymer) molecular weight = 153,000  Low degree of polymerized PVA : D.P. value = 428(monomers/polymer) molecular weight = 40,000 PVA content The proportions of the PVA to cation sources in the solution were adjusted in such a way that there were 0.5~1 times more positively charged valences from the cations than from the potentially negatively charged –(OH) functional groups of the polymers. PVA amount of polymer controls the particle size distribution