4
4
Southwestern Institute of Physics (SWIP),
Chengdu, Sichuan, China
CBBI-16, Portland, 8-10, September

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•
•
•
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Background
Fabrication Process and Results of Li
4
SiO
4 pebbles
Deuterium Retention and Desorption Behavior of Li
4
SiO
4
R&D Plans on Breeder Materials at SWIP
Summary
CBBI-16, Portland, 8-10, September

CN Helium Cooled Ceramic Breeder (HCCB) TBM designs based on the SB/He/FM concept.
Component
Structure
Coolant
Purge gas
Neutron multiplier
Breeder Li
Material
RAFM
He
He+0.1%H
2
Be
4
SiO
4
, Li
2
TiO
3
Explosive view of CN HCCB TBM Sub-module design
1-ton Ingot of CLF-1 Be pebbles by REP method
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 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 6 Li 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.
CBBI-16, Portland, 8-10, September

Melting pot
Raw materials: Li
2
CO
3
(Purity:99.99%)
SiO
Li/Si Molar ratio: 4
2
(Purity:99.99 )
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.
Heating and insulation
Gas jet sprayer
Bottom feeder
Schematic drawing of fabrication setup
Heat treatment condition: 1000℃, 2h
Production: 100Kg/year pebbles with 1.0 mm diameter
CBBI-16, Portland, 8-10, September
Fabrication facility


 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
CBBI-16, Portland, 8-10, September


Heat treatment atmosphere: Vacuum, air temperature: 1000 ℃ time: 2h
5000
3000
4000
3000
Li
2
CO
3
Li
2
SiO
3
Li
4
SiO
4
2500
2000
1500
Li
2
SiO
3
Li
4
SiO
4
2000
1000
500
1000
0
15 20 25 30 35 40 45 50 55 60 65 70
0
15 20 25 30 35 40 45 50 55 60 65 70
2 
XRD pattern of pebbles annealed at vacuum
2 
XRD pattern of pebbles annealed at air
Li
4
TG curve of Li
4
SiO
4
SiO
4 at CO
2 atmosphere as the major phase,
The diffraction peaks of Li
2
CO
3
, Li
2
SiO
3
,Li are observed. Carbon dioxide are easily
4
SiO
4 absorbed by Li
4
SiO
4
Li SiO
3 as a second phase
500℃ < Temp.< 720℃ absorption obviously;
720℃ < Temp.< 900℃ CO
2 desorption
CBBI-16, Portland, 8-10, September



TG
Measurement of Density and porosity by Hgporosimetry and He-pycnometry.
Specific surface area measurement by a multipoint BET method.
Mass change:-41.67%
716.7℃
DSC
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.
Density (% TD)
Open porosity (%)
Closed porosity(%)
Specific surface area (m 2 /g)
Total pore volume for pores (cc/g)
Initial state After Heat treatment
~ 93.5
~ 94
~ 5.7
~ 5.2
~ 0.8
~ 0.75
2.796
1.095
3.403e-03 2.012e-03
CBBI-16, Portland, 8-10, September


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.
0.6

Elements analysis by ICP-OES
0.5
0.4
0.3
0.2
Initial state
After annealing
0.1
0.0
0 10 20 30
Days
40 50
Weight increase of initial state pebbles and after annealing pebbles.
The amount of impurities are 0.116186%
Li/Si molar ratio ≠ 4
CBBI-16, Portland, 8-10, September


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
Initial state After Heat treatment pebble
Max. load (N) 12 16
Min. load (N)
Average load (N)
4.3
6.5
5.2
7.0
CBBI-16, Portland, 8-10, September

 The elucidation of tritium recovery from Li
4
SiO
4 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.
 D
2 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 D
2 materials.
desorption behavior in solid breeding
CBBI-16, Portland, 8-10, September

2
+
Sintering
Temperature: 1173 K
Heating time: 3 h
Heating treatment
Heating temperature: 1000 K
Heating time: 10 min
XPS X-ray source: K α of Al
D
2
+ Imp.
Ion energy: 3.0 keV D
2
+
Ion fluence : (0.4, 0.6, 0.8, 1.0) × 10 22 D + m -2
Ion flux: 2.0
× 10 18 D + m -2 s -1
Implantation temperature: R.T.
XPS
TDS
Heating rate: 5 K min -1
Heating region: R.T. - 1000 K
CBBI-16, Portland, 8-10, September
13


Comparision of before implanation and after implanation
0.4*10
Before implantation
22
D
+ m
-2
0.8*10
22
D
+ m
-2
0.6*10
22
D
+ m
-2
1.0*10
22
D
+ m
-2
Before implanation
0.4*10
22
D
+ m
-2
0.6*10
22
D
+ m
-2
0.8*10
22
D
+ m
-2
1.0*10
22
D
+ m
-2
0.4*10
22
Before implanation
D
+ m
-2
0.6*10
22
D
+ m
-2
0.8*10
22
D
+ m
-2
1.0*10
22
D
+ m
-2
64 62 60 58 56 54
Binding Energy (eV)
52 50 48 112 110 108 106 104
Binding Energy (eV)
102
Li-1s XPS spectra
Atom Li: 55.6 eV
Li-O- : 53.3 eV
Si-2p XPS spectra
Si-O- : 107.1 eV
Si-O-D : 105.2 eV
CBBI-16, Portland, 8-10, September
538 536 534 532
Binding Energy (eV)
530 528
O-1s XPS spectra
O-Si : 536.1eV
D-O-D : 533.8eV
O-D : 531.3eV


Comparision of before implanation and after implanation
Before Dimplan
After TDS
After Dimplan
Before Dimplan
After TDS
After Dimplan
Before Dimplan
After TDS
After Dimplan
64 62 60 58 56 54 52
Binding Energy (eV)
50 48 46
112 110
Li-1s XPS spectra
108 106 104
Binding Energy (eV)
Si-2p XPS spectra
102 100
542 540 538 536 534
Binding Energy (eV)
532
O-1s XPS spectra
530 528
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 Li
4
SiO
4 will be recovered after TDS.
CBBI-16, Portland, 8-10, September

0.8
0.8
0.6
0.4
0.2
1.0*10
22
D
+ m
-2
0.8*10
22
D
+ m
-2
0.6*10
22
D
+ m
-2
0.4*10
22
D
+ m
-2
0.6
0.4
0.2
14.0
12.0
10.0
8.0
6.0
4.0
2.0
0.0
0.4
Peak 1
Peak 2
Peak 3
Total
0.6
0.8
fluence / 10
22
D m
-2
1.0
D
2 retention of Li
4
SiO
4 at different fluence
0.0
300 400 500 600
Temperature (K)
700 800
0.0
TDS spectra of D
2 for Li
4
SiO
4 at different fluence
300 400 500 600 700 800
Temperture / K
Peak analysis for TDS spectrum at the fluence 1.0
× 10 22 D m -2
The D
2
TDS spectrum of Li
4
SiO
4 can be divided into 3 peaks. The first is due to the material surface adsorption, the second could be from the defects caused by D
2
+ 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
 D
2 desorption rate and the total D
2 retention increase with the increasing of implantation fluence.

All of D + are trapped by oxygen vacancy to form –OD bond.
CBBI-16, Portland, 8-10, September

 For Fabrication:
•
LiOH and SiO
2 will be used as raw materials, and compared with the current raw materials, the heat treatment will be optimized;
•
The reprocessing of Li
4
SiO
4 pebbles will be considered by remelting;
•
Li
2
TiO
3 pebbles shall be produced using Extrusion-spheronizationsintering 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 Li
4
SiO
4 will be considered to carry out in this year;
(Temp. : < 353 K, T. N. flux: 5.5
×
10 12 cm 2 s -1 , T. N. fluence: 3.3
×
10 15 cm 2 )
•
Effect of implantation temperature on retention behavior of deuterium in
Li
4
SiO
4 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

 A melt-spraying fabrication process for Li
4
SiO
4 pebbles has been developed.
Li
4
SiO
4 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 D
2
+ -irradiated Li
4
SiO
4 was formed due to typical irradiation defects induced by D
2
+ -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

CBBI-16, Portland, 8-10, September