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CBBI-16, Portland, 8-10, September
Fabrication and performance of Li4SiO4 pebbles by
the melt spraying method
Yongjin Feng
Southwestern Institute of Physics (SWIP), Chengdu, Sichuan, China
CBBI-16, Portland, 8-10, September
• Background
• Fabrication Process and Results of Li4SiO4 pebbles
• Deuterium Retention and Desorption Behavior of
Li4SiO4
• R&D Plans on Breeder Materials at SWIP
• Summary
Outlines
CBBI-16, Portland, 8-10, September
CN Helium Cooled Ceramic Breeder (HCCB) TBM designs based on the SB/He/FM concept.
1. Background
Explosive view of CN HCCB TBM Sub-module design
Be pebbles by REP method1-ton Ingot of CLF-1
Component Material
Structure RAFM
Coolant He
Purge gas He+0.1%H2
Neutron multiplier
Be
Breeder Li4SiO4 , Li2TiO3
CBBI-16, Portland, 8-10, September
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;
CBBI-16, Portland, 8-10, September
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.
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.
CBBI-16, Portland, 8-10, September
Schematic drawing of fabrication setup
Heating and insulation
Melting pot
Bottom feeder
Gas jet sprayer
2. Fabrication process and Results
Fabrication facility
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.
Heat treatment condition: 1000 , 2h℃
Production: 100Kg/year pebbles with 1.0 mm diameter
CBBI-16, Portland, 8-10, September
Optical micrographs and SEM
Most of the pebbles are well spherically shaped, smooth surface.
Shape and surface structure
Optical micrographs and SEM of the pebbles with 1mm diameter SEM of pebble’s surface
Broad size distribution.
CBBI-16, Portland, 8-10, September
Phase analysisHeat treatment atmosphere: Vacuum, air temperature: 1000℃ time: 2h
XRD pattern of pebbles annealed at air
The diffraction peaks of Li2CO3, Li2SiO3,Li4SiO4 are observed. Carbon dioxide are easily absorbed by Li4SiO4
15 20 25 30 35 40 45 50 55 60 65 700
500
1000
1500
2000
2500
3000
Inte
rnsi
ty (C
ounts
)
2
Li4SiO
4
Li2SiO
3
XRD pattern of pebbles annealed at vacuum
Li4SiO4 as the major phase,
Li2SiO3 as a second phase
15 20 25 30 35 40 45 50 55 60 65 700
1000
2000
3000
4000
5000
Inte
rnsi
ty (C
ounts
)
2
Li4SiO
4
Li2SiO
3
Li2CO
3
TG curve of Li4SiO4 at CO2 atmosphere
Temp. <500 absorb rate very slow;℃ 500 < Temp.< 720 absorption obviously;℃ ℃720 < Temp.< 900 CO℃ ℃ 2desorption
CBBI-16, Portland, 8-10, September
Thermal analysis
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.
Thermoanalysis of mixed raw materials
DSC
TG
Mass change:-41.67%
716.7℃
Physical properties
Measurement of Density and porosity by Hg-porosimetry and He-pycnometry.Specific surface area measurement by a multipoint BET method.
Initial state After Heat treatment
Density (% TD) ~ 93.5 ~ 94
Open porosity (%) ~ 5.7 ~ 5.2
Closed porosity(%)
~ 0.8 ~ 0.75
Specific surface area (m2/g)
2.796 1.095
Total pore volume for pores (cc/g)
3.403e-03 2.012e-03
CBBI-16, Portland, 8-10, September
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.
Weight increase of initial state pebblesand after annealing pebbles.
0 10 20 30 40 500.0
0.1
0.2
0.3
0.4
0.5
0.6
We
igh
t in
cre
ase
(w
t%)
Days
Initial state After annealing
Chemical Composition of pebbles
The amount of impurities are 0.116186%
Li/Si molar ratio ≠ 4
Elements analysis by ICP-OES
CBBI-16, Portland, 8-10, September
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.
Initial state After Heat treatment
Max. load (N) 12 16
Min. load (N) 4.3 5.2
Average load (N) 6.5 7.0
After heat treatment , the crush load increased. The value is scattered. The mechanical stability must be improved.
pebble
press
CBBI-16, Portland, 8-10, September
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.
CBBI-16, Portland, 8-10, September 13
Experimental procedures of D2+ implantation
TDSHeating rate: 5 K min-1
Heating region: R.T. - 1000 K
Heating treatment
Heating temperature: 1000 K
Heating time: 10 min
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.
XPS
D2+ Imp.
X-ray source: K α of Al
XPS
SinteringTemperature: 1173 K
Heating time: 3 h
CBBI-16, Portland, 8-10, September
64 62 60 58 56 54 52 50 48
Binding Energy (eV)
Before implantation
0.4*1022D+m-2
0.6*1022D+m-2
0.8*1022D+m-2
1.0*1022D+m-2
Atom Li: 55.6 eV
Li-O- : 53.3 eV
Li-1s XPS spectra
112 110 108 106 104 102 100
Binding Energy (eV)
Before implanation
0.4*1022D+m-2
0.6*1022D+m-2
0.8*1022D+m-2
1.0*1022D+m-2
Si-O- : 107.1 eV
Si-O-D : 105.2 eV
Si-2p XPS spectra
540 538 536 534 532 530 528
Binding Energy (eV)
Before implanation
0.4*1022D+m-2 0.6*1022D+m-2
0.8*1022D+m-2 1.0*1022D+m-2
O-Si: 536.1eV
D-O-D: 533.8eV
-O-D: 531.3eV
O-1s XPS spectra
XPS results
Comparision of before implanation and after implanation
CBBI-16, Portland, 8-10, September
64 62 60 58 56 54 52 50 48 46
Binding Energy (eV)
Before Dimplan After TDS
After Dimplan
542 540 538 536 534 532 530 528
Binding Energy (eV)
Before Dimplan After TDS
After Dimplan
112 110 108 106 104 102 100
Binding Energy (eV)
Before Dimplan After TDS
After Dimplan
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.
Li-1s XPS spectra Si-2p XPS spectra O-1s XPS spectra
Comparision of before implanation and after implanation
CBBI-16, Portland, 8-10, September
TDS spectra of D2 for Li4SiO4 at different fluence
TDS results
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.
Peak analysis for TDS spectrum atthe fluence 1.0×1022 D m-2
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.
0.4 0.6 0.8 1.00.0
2.0
4.0
6.0
8.0
10.0
12.0
14.0
D r
eten
tion
/ 10
19 D
m-2 Peak 1
Peak 2 Peak 3 Total
fluence / 1022 D m-2
D2 retention of Li4SiO4 at different fluence
Peak 1 (400 K) → Surface adsorption
Peak 2 (500 K) → Defect
Peak 3 (650 K) → -O-D- bond
300 400 500 600 700 8000.0
0.2
0.4
0.6
0.8
Desorp
tion r
ate
/ 10
18 m
-2s
-1
Temperture / K
300 400 500 600 700 8000.0
0.2
0.4
0.6
0.8
1.0*1022D+m-2
0.8*1022D+m-2
0.6*1022D+m-2
0.4*1022D+m-2
De
so
rpti
on
Ra
te (
1018
D2m
-2s
-1)
Temperature (K)
CBBI-16, Portland, 8-10, September
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) ).
CBBI-16, Portland, 8-10, September
Irradiation properties of pebbles:
• Tritium behavior in thermal neutron irradiated Li4SiO4 will be considered to
carry out in this year;
(Temp. : < 353 K, T. N. flux: 5.5×1012 cm2 s-1, T. N. fluence: 3.3×1015 cm2)
• 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 ) ℃
CBBI-16, Portland, 8-10, September
5. Summary A melt-spraying fabrication process for Li4SiO4 pebbles has been developed.
Li4SiO4 pebbles 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.
CBBI-16, Portland, 8-10, September