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Trial examination of direct pebble fabrication for advanced tritium breeders by the emulsion method
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ARTICLE IN PRESS Fusion Engineering and Design xxx (2014) xxx–xxx
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Trial examination of direct pebble fabrication for advanced tritium breeders by the emulsion method Tsuyoshi Hoshino ∗ Breeding Functional Materials Development Group, Fusion Research and Development Directorate, Japan Atomic Energy Agency, 2-166 Obuchi, Omotedate, Rokkasho-mura, Kamikita-gun, Aomori 039-3212, Japan
h i g h l i g h t s • • • •
The integration of raw material preparation and granulation is proposed as a new direct pebble fabrication process. The emulsion method granulates gel spheres of Li2 CO3 and TiO2 or SiO2 . The gel spheres are calcined and sintered in air. The crush load of the sintered Li2 TiO3 or Li4 SiO4 pebbles obtained is 37.2 or 59.3 N, respectively.
a r t i c l e
i n f o
Article history: Received 26 August 2013 Received in revised form 20 December 2013 Accepted 20 December 2013 Available online xxx Keywords: Tritium breeder Lithium titanate Lithium silicate Pebble fabrication Emulsion method
a b s t r a c t Demonstration power plant reactors require advanced tritium breeders with high thermal stability. For the mass production of advanced tritium breeder pebbles, pebble fabrication by the emulsion method is a promising technique. To develop the most efficient pebble fabrication method, a new direct pebble fabrication process utilizing the emulsion method was implemented. A prior pebble fabrication process consisted of the preparation of raw materials followed by granulation. The new process integrates the preparation and granulation of raw materials. The slurry for the emulsion granulation of Li2 TiO3 or Li4 SiO4 as a tritium breeder consists of mixtures of Li2 CO3 and TiO2 or SiO2 at specific ratios. Subsequently, gel spheres of tritium breeders are fabricated by controlling the relative flow speeds of slurry and oil. The average diameter and crush load of the obtained sintered Li2 TiO3 or Li4 SiO4 pebbles were 1.0 or 1.5 mm and 37.2 or 59.3 N, respectively. The trial fabrication results suggest that the new process has the potential to increase the fabrication efficiency of advanced tritium breeder pebbles. © 2014 Elsevier B.V. All rights reserved.
1. Introduction Demonstration power plant (DEMO) reactors require advanced tritium breeders with high thermal stability. The development of an advanced tritium breeder was undertaken from 2007 to 2016 by a joint Japan–EU team in a DEMO R&D operation under the authority of the International Fusion Energy Research Centre (IFERC) as part of Broader Approach (BA) activities. Lithium-containing ternary oxides (Li2 TiO3 , Li4 SiO4 , Li2 ZrO3 , and LiAlO2 ) were proposed as breeder blanket materials [1]. Among them, lithium titanate (Li2 TiO3 ) is a prominent candidate material in Japan because of its chemical stability, good tritium release, and low-activation characteristics [2–4]. Lithium silicate (Li4 SiO4 ) is a candidate material in EU because of its high lithium density [5–8]. Li2 TiO3 with excess Li (Li2+x TiO3+y ) was developed as an advanced tritium breeder [9,10]. Recently, the development of
the emulsion method as a fabrication technique for Li2 TiO3 and Li2+x TiO3+y pebbles was undertaken [11]. Employing this promising method for mass pebble production, the pebble diameter was constrained within the target ranges. To minimize pebble fabrication costs, the trial examination of a new direct pebble fabrication process based on the emulsion method was performed. In a previous attempt at pebble fabrication, the process consisted of the preparation of raw materials followed by granulation [11]. In this study, the integration of preparation and granulation of raw materials is proposed as a new direct pebble fabrication process. A technique to fabricate Li2 TiO3 and Li4 SiO4 pebbles by the new process is developed, which is essentially an emulsion method. 2. Experimental 2.1. Principles of the emulsion method
∗ Tel.: +81 175 71 6703; fax: +81 175 71 6502. E-mail addresses: [email protected], [email protected]
The emulsion method can easily produce large volumes of uniform submicron particles [12]. However, micron-sized Li2 TiO3 or
0920-3796/$ – see front matter © 2014 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.fusengdes.2013.12.052
Please cite this article in press as: T. Hoshino, Trial examination of direct pebble fabrication for advanced tritium breeders by the emulsion method, Fusion Eng. Des. (2014), http://dx.doi.org/10.1016/j.fusengdes.2013.12.052
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Fig. 1. Pebble fabrication by the emulsion method.
Li4 SiO4 tritium breeders should be fabricated using pebbles of 1 mm in diameter [13]. To determine whether the emulsion method is suitable for fabricating large volumes of tritium breeder pebbles, a granulator was used in pebble fabrication trials (Fig. 1). This granulator consisted of two syringes arranged in a T-shaped flow path. One syringe was filled with oil and the other with a tritium breeder slurry. The two flow lines from the syringes were connected in a Tshaped flow path. This arrangement allowed cutting the slurry flow with oil from the oil-filled syringe. The size of the tritium breeder gel particles was controlled by the flow speeds of oil and slurry. The gel particles were placed in an oil-filled container. The pebble formation process is shown in Fig. 2. Li2 TiO3 or Li4 SiO4 powder is synthesized by a solid-state reaction after mixing Li2 CO3 and TiO2 , or SiO2 , powders having a molar ratio of Li/Ti = 2.0, or Li/Si = 4.0. Subsequently, the emulsion method is used for the pebble fabrication of tritium breeders. 2.2. New direct pebble fabrication The new direct pebble fabrication process utilizing the emulsion method is shown in Fig. 3. Li2 CO3 and TiO2 , or SiO2 , powders with a molar ratio of Li/Ti = 2.0, or Li/Si = 4.0, are mixed. Subsequently, a binder is added to the mixture to form the slurry. The emulsion method turns the slurry into gel spheres; thereafter, the spheres are calcined and sintered in air. The diameter and sphericity were measured by optical microscopy. The density of the sintered pebbles was obtained by the mercury intrusion technique. The grain size was analyzed by scanning electron microscopy (SEM). The density of the sintered pebbles was obtained by the mercury intrusion technique. The actual Li/Ti, or Li/Si, mole ratio (2.11) was analyzed by inductively
Step 1: Preparation of the raw material powder
Li2CO3
TiO2 or SiO2
Precursors mixed in a molar ratio of Li/Ti = 2.0 or Li/Si = 4.0
Calcination Sintering
Li2TiO3 or Li4SiO4 powder
Step 2: Granulation
Slurry (Li2TiO3 or Li4SiO4 with binder) Emulsion method Gel spheres Calcination and Sintering
Sintered pebbles Fig. 2. Pebble formation by the emulsion method.
coupled plasma–atomic emission spectroscopy (ICP–AES). The crush load was measured using a universal testing machine. The crystal structure was analyzed by powder X-ray diffraction (XRD).
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Li2CO3
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Table 1 Characteristics of the sintered Li2 TiO3 pebbles produced by the new direct pebble fabrication process.
TiO2 or SiO2
Diameter (mm) Sphericity Density (% T.D.) Grain size (m) Ratio of Li/Ti Crush road (N)
Precursors mixed in a molar ratio of Li/Ti = 2.0 or Li/Si = 4.0
Slurry Emulsion method
Crystal structure
1.05 1.02 85.8 <5 1.99 35.0–40.0 Average: 37.2 Single-phase Li2 TiO3
Gel spheres the sintered Li2 TiO3 pebbles is in very good agreement with the JC-PDF-Card of Li2 TiO3 [14]. Table 1 summarizes the characteristics of the sintered Li2 TiO3 pebbles produced by the emulsion method. The XRD and ICP results suggest that the Li2 TiO3 pebbles are stoichiometric.
Calcination and Sintering
Sintered pebbles Fig. 3. New direct pebble fabrication process.
3.2. Li4 SiO4 pebbles The emulsion method was used to produce Li2 CO3 and SiO2 gel spheres. The spheres were subsequently calcined at 973 K for 5 h in air and sintered at 1273 K or 1323 K for 2 h in air to calculate the optimal sintering temperature.
Fig. 4. Sintered Li2 TiO3 pebbles.
Scattered Intensity
Sintered Li2TiO3 Pebbles ●
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2θ / ° Fig. 5. XRD pattern of sintered Li2 TiO3 pebbles.
3. Results and discussion 3.1. Li2 TiO3 pebbles Gel spheres of Li2 CO3 and TiO2 are granulated by the emulsion method. Thereafter, the gel spheres are calcined at 973 K for 5 h in air to remove the binder and sintered at 1373 K for 2 h in air. Fig. 4 shows the sintered Li2 TiO3 pebbles. The pebbles have a diameter of 1.05 mm and a sphericity of 1.02. The density of the pebbles analyzed by the mercury intrusion technique is 85.8% T.D. The grain size is less than 5 m, measured by SEM. The molar ratio (Li/Ti) of the sintered pebbles evaluated by ICP–AES is 1.99. The crush load of 20 Li2 TiO3 pebbles was measured, and the average value is 37.2 N. The crystal structure of the sintered Li2 TiO3 pebbles was examined by XRD. The results are shown in Fig. 5. The XRD pattern of
Fig. 6. SEM images of sintered Li4 SiO4 pebbles.
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Table 2 Characteristics of the sintered Li4 SiO4 pebbles at 1273 K produced by the new direct pebble fabrication process. Diameter (mm) Sphericity Density (% T.D.) Grain size (m) Ratio of Li/Si Crush load (N) Crystal structure
1.50 1.07 66.1 <5 3.65 45.3–69.5 Average: 59.3 Mixture of Li4 SiO4 and Li2 SiO3
Fig. 7. Sintered Li4 SiO4 pebbles at 1273 K.
4. Conclusion
Sintered Li4SiO4 Pebbles ●
Scattered Intensity
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2θ / ° Fig. 8. XRD patterns of the sintered Li4 SiO4 pebbles at 1273 K.
The temperature was adjusted to optimize the grain size of the sintered Li4 SiO4 pebbles. The results of this procedure are shown in Fig. 6. The grain size of the sintered Li4 SiO4 pebbles increased with increasing sintering temperature. The grain size is <5 m at 1273 K and >10 m at 1323 K, as measured by SEM. Considering the tritium release characteristics of the blanket, the desired grain size after sintering is <5 m. Therefore, the optimal sintering temperature of Li4 SiO4 gel spheres is 1273 K. The sintered Li4 SiO4 pebbles at 1273 K are white (Fig. 7). The diameter of the pebbles is 1.50 mm, and their sphericity is 1.07. The density of the pebbles is 66.1% T.D., as analyzed by the mercury intrusion technique. The grain size is <5 m, as measured by SEM. The crystal structure of the sintered Li4 SiO4 pebbles was analyzed by powder XRD. The XRD pattern of the sintered Li4 SiO4 pebbles (Fig. 8) is almost the same as that of Li4 SiO4 in the JCPDF-Card [15]. Small additional intensities indicated the presence of Li2 SiO3 as listed in the JC-PDF-Card [16]. The XRD pattern shows that sintered Li4 SiO4 is a mixture of Li4 SiO4 and Li2 SiO3 . The molar ratio (Li/Si) of the sintered pebbles evaluated by ICP–AES is 3.65. The molar ratio of sintered pebbles is smaller than the original mixing ratios of Li2 CO3 and SiO2 . It appears that Li is lost during the new process. This decrease in the molar ratio is considered an aftereffect of Li vaporization during sintering. The crush load of 20 sintered Li4 SiO4 pebbles was measured. The maximum value was 69.5 N and the minimum was 45.3 N. The average crush load was 59.3 N. In the EU, the pebble fabrication of Li4 SiO4 with Li2 TiO3 was conducted to increase the crush load of Li4 SiO4 pebbles [8]. Clearly, this study contributes to these efforts. Table 2 summarizes the characteristics of the sintered Li4 SiO4 pebbles produced by the emulsion method. The optimum diameter and density after sintering are 1 mm and >85% T.D., respectively. Thus, the next step is to optimize grinding conditions.
To minimize the pebble fabrication costs of advanced tritium breeders, a trial examination of a new process by the emulsion method was conducted. Previous attempts to fabricate Li2 TiO3 pebbles in Japan consisted of the preparation of raw materials followed by granulation. In this study, the integration of the preparation and granulation of raw material was proposed as a new direct pebble fabrication process. First, for granulation, employing the emulsion method, starting powders of Li2 CO3 and TiO2 , or SiO2 , with a molar ratio of Li/Ti = 2.0 or Li/Si = 4.0, were mixed. In addition, a binder was added to the mixture of starting powders to form the slurry. The gel spheres were granulated using the slurry of starting powders with the binder. Thereafter, they were calcined and sintered in air. The diameter, sphericity, density, grain size, molar ratio (Li/Ti), crystal structure, and crush load of Li2 TiO3 pebbles are 1.05 mm, 1.02, 85.8% T.D., <5 m, 1.99, single phase, and 35–40 N, respectively. These values are the optimum conditions for Li2 TiO3 pebbles. The diameter of the Li4 SiO4 pebbles is >1.0 mm, and the density is <85% T.D. Thus, the survey of granulation conditions for the direct pebble fabrication process utilizing the emulsion method will be continued as the optimum diameter and density after sintering are 1 mm and >85% T.D., respectively. On the other hand, the Li4 SiO4 pebbles obtained by this process are effective in increasing the crush load. Therefore, further studies will contribute to the pebble fabrication of Li4 SiO4 . Furthermore, the results show that pebble fabrication utilizing the proposed process is a promising technique for the mass production of advanced tritium breeder pebbles. The next step is to fabricate advanced tritium breeders such as Li2 TiO3 with excess Li (Li2+x TiO3+y ). Acknowledgments This report has been prepared within the framework of the agreement between the Government of Japan and the European Atomic Energy Community for The Joint Implementation of The Broader Approach Activities in the Field of Fusion Energy Research. The author would like to thank all the contributors to the IFERC projects in Japan and also all the members of the IFERC Project Team. References [1] L. Giancarli, V. Chuyanov, M. Abdou, M. Akiba, B.G. Hong, R. Lässer, et al., J. Nucl. Mater. 367–370 (2007) 1271–1280. [2] N. Roux, J. Avon, A. Floreancig, J. Mougin, B. Rasneur, S. Ravel, J. Nucl. Mater. 233–237 (1996) 1431–1435. [3] N. Roux, S. Tanaka, C. Johnson, R. Verrall, Fusion Eng. Des. 41 (1998) 31–38. [4] J.P. Kopasz, J.M. Miller, C.E. Johnson, J. Nucl. Mater. 212–215 (1994) 927–931. [5] R. Knitter, B. Löbbecke, J. Nucl. Mater. 361 (2007) 104–111. [6] R. Knitter, Proc. CBBI-15, JAEA, 2010, pp. 82–100. [7] M.H.H. Kolb, R. Knitter, U. Kaufmann, D. Mundt, Fusion Eng. Des. 86 (2011) 2148–2151. [8] R. Knitter, M.H.H. Kolb, U. Kaufmann, A.A. Goraieb, J. Nucl. Mater. 442 (2013) S433–S436.
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[9] T. Hoshino, M. Yasumoto, K. Tsuchiya, K. Hayashi, H. Nishimura, A. Suzuki, et al., Fusion Eng. Des. 82 (2007) 2269–2273. [10] T. Hoshino, K. Kato, Y. Natori, M. Nakamura, K. Sasaki, K. Hayashi, et al., Fusion Eng. Des. 84 (2009) 956–959. [11] T. Hoshino, M. Nakamichi, Fusion Eng. Des. 87 (2012) 486–492. [12] X. Du, J. He, J. Colloid Interface Sci. 345 (2010) 269–277.
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[13] T. Hirose, Y. Seki, H. Tanigawa, H. Tanigawa, D. Tsuru, M. Enoeda, et al., Fusion Eng. Des. 85 (2010) 1426–1429. [14] PDF#33-0831, PDF-Card, Material Data Inc. [15] PDF#37-1472, PDF-Card, Material Data Inc. [16] PDF#29-1828, PDF-Card, Material Data Inc.
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Contents lists available at ScienceDirect
Fusion Engineering and Design journal homepage: www.elsevier.com/locate/fusengdes
Trial examination of direct pebble fabrication for advanced tritium breeders by the emulsion method Tsuyoshi Hoshino ∗ Breeding Functional Materials Development Group, Fusion Research and Development Directorate, Japan Atomic Energy Agency, 2-166 Obuchi, Omotedate, Rokkasho-mura, Kamikita-gun, Aomori 039-3212, Japan
h i g h l i g h t s • • • •
The integration of raw material preparation and granulation is proposed as a new direct pebble fabrication process. The emulsion method granulates gel spheres of Li2 CO3 and TiO2 or SiO2 . The gel spheres are calcined and sintered in air. The crush load of the sintered Li2 TiO3 or Li4 SiO4 pebbles obtained is 37.2 or 59.3 N, respectively.
a r t i c l e
i n f o
Article history: Received 26 August 2013 Received in revised form 20 December 2013 Accepted 20 December 2013 Available online xxx Keywords: Tritium breeder Lithium titanate Lithium silicate Pebble fabrication Emulsion method
a b s t r a c t Demonstration power plant reactors require advanced tritium breeders with high thermal stability. For the mass production of advanced tritium breeder pebbles, pebble fabrication by the emulsion method is a promising technique. To develop the most efficient pebble fabrication method, a new direct pebble fabrication process utilizing the emulsion method was implemented. A prior pebble fabrication process consisted of the preparation of raw materials followed by granulation. The new process integrates the preparation and granulation of raw materials. The slurry for the emulsion granulation of Li2 TiO3 or Li4 SiO4 as a tritium breeder consists of mixtures of Li2 CO3 and TiO2 or SiO2 at specific ratios. Subsequently, gel spheres of tritium breeders are fabricated by controlling the relative flow speeds of slurry and oil. The average diameter and crush load of the obtained sintered Li2 TiO3 or Li4 SiO4 pebbles were 1.0 or 1.5 mm and 37.2 or 59.3 N, respectively. The trial fabrication results suggest that the new process has the potential to increase the fabrication efficiency of advanced tritium breeder pebbles. © 2014 Elsevier B.V. All rights reserved.
1. Introduction Demonstration power plant (DEMO) reactors require advanced tritium breeders with high thermal stability. The development of an advanced tritium breeder was undertaken from 2007 to 2016 by a joint Japan–EU team in a DEMO R&D operation under the authority of the International Fusion Energy Research Centre (IFERC) as part of Broader Approach (BA) activities. Lithium-containing ternary oxides (Li2 TiO3 , Li4 SiO4 , Li2 ZrO3 , and LiAlO2 ) were proposed as breeder blanket materials [1]. Among them, lithium titanate (Li2 TiO3 ) is a prominent candidate material in Japan because of its chemical stability, good tritium release, and low-activation characteristics [2–4]. Lithium silicate (Li4 SiO4 ) is a candidate material in EU because of its high lithium density [5–8]. Li2 TiO3 with excess Li (Li2+x TiO3+y ) was developed as an advanced tritium breeder [9,10]. Recently, the development of
the emulsion method as a fabrication technique for Li2 TiO3 and Li2+x TiO3+y pebbles was undertaken [11]. Employing this promising method for mass pebble production, the pebble diameter was constrained within the target ranges. To minimize pebble fabrication costs, the trial examination of a new direct pebble fabrication process based on the emulsion method was performed. In a previous attempt at pebble fabrication, the process consisted of the preparation of raw materials followed by granulation [11]. In this study, the integration of preparation and granulation of raw materials is proposed as a new direct pebble fabrication process. A technique to fabricate Li2 TiO3 and Li4 SiO4 pebbles by the new process is developed, which is essentially an emulsion method. 2. Experimental 2.1. Principles of the emulsion method
∗ Tel.: +81 175 71 6703; fax: +81 175 71 6502. E-mail addresses: [email protected], [email protected]
The emulsion method can easily produce large volumes of uniform submicron particles [12]. However, micron-sized Li2 TiO3 or
0920-3796/$ – see front matter © 2014 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.fusengdes.2013.12.052
Please cite this article in press as: T. Hoshino, Trial examination of direct pebble fabrication for advanced tritium breeders by the emulsion method, Fusion Eng. Des. (2014), http://dx.doi.org/10.1016/j.fusengdes.2013.12.052
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Fig. 1. Pebble fabrication by the emulsion method.
Li4 SiO4 tritium breeders should be fabricated using pebbles of 1 mm in diameter [13]. To determine whether the emulsion method is suitable for fabricating large volumes of tritium breeder pebbles, a granulator was used in pebble fabrication trials (Fig. 1). This granulator consisted of two syringes arranged in a T-shaped flow path. One syringe was filled with oil and the other with a tritium breeder slurry. The two flow lines from the syringes were connected in a Tshaped flow path. This arrangement allowed cutting the slurry flow with oil from the oil-filled syringe. The size of the tritium breeder gel particles was controlled by the flow speeds of oil and slurry. The gel particles were placed in an oil-filled container. The pebble formation process is shown in Fig. 2. Li2 TiO3 or Li4 SiO4 powder is synthesized by a solid-state reaction after mixing Li2 CO3 and TiO2 , or SiO2 , powders having a molar ratio of Li/Ti = 2.0, or Li/Si = 4.0. Subsequently, the emulsion method is used for the pebble fabrication of tritium breeders. 2.2. New direct pebble fabrication The new direct pebble fabrication process utilizing the emulsion method is shown in Fig. 3. Li2 CO3 and TiO2 , or SiO2 , powders with a molar ratio of Li/Ti = 2.0, or Li/Si = 4.0, are mixed. Subsequently, a binder is added to the mixture to form the slurry. The emulsion method turns the slurry into gel spheres; thereafter, the spheres are calcined and sintered in air. The diameter and sphericity were measured by optical microscopy. The density of the sintered pebbles was obtained by the mercury intrusion technique. The grain size was analyzed by scanning electron microscopy (SEM). The density of the sintered pebbles was obtained by the mercury intrusion technique. The actual Li/Ti, or Li/Si, mole ratio (2.11) was analyzed by inductively
Step 1: Preparation of the raw material powder
Li2CO3
TiO2 or SiO2
Precursors mixed in a molar ratio of Li/Ti = 2.0 or Li/Si = 4.0
Calcination Sintering
Li2TiO3 or Li4SiO4 powder
Step 2: Granulation
Slurry (Li2TiO3 or Li4SiO4 with binder) Emulsion method Gel spheres Calcination and Sintering
Sintered pebbles Fig. 2. Pebble formation by the emulsion method.
coupled plasma–atomic emission spectroscopy (ICP–AES). The crush load was measured using a universal testing machine. The crystal structure was analyzed by powder X-ray diffraction (XRD).
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Li2CO3
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Table 1 Characteristics of the sintered Li2 TiO3 pebbles produced by the new direct pebble fabrication process.
TiO2 or SiO2
Diameter (mm) Sphericity Density (% T.D.) Grain size (m) Ratio of Li/Ti Crush road (N)
Precursors mixed in a molar ratio of Li/Ti = 2.0 or Li/Si = 4.0
Slurry Emulsion method
Crystal structure
1.05 1.02 85.8 <5 1.99 35.0–40.0 Average: 37.2 Single-phase Li2 TiO3
Gel spheres the sintered Li2 TiO3 pebbles is in very good agreement with the JC-PDF-Card of Li2 TiO3 [14]. Table 1 summarizes the characteristics of the sintered Li2 TiO3 pebbles produced by the emulsion method. The XRD and ICP results suggest that the Li2 TiO3 pebbles are stoichiometric.
Calcination and Sintering
Sintered pebbles Fig. 3. New direct pebble fabrication process.
3.2. Li4 SiO4 pebbles The emulsion method was used to produce Li2 CO3 and SiO2 gel spheres. The spheres were subsequently calcined at 973 K for 5 h in air and sintered at 1273 K or 1323 K for 2 h in air to calculate the optimal sintering temperature.
Fig. 4. Sintered Li2 TiO3 pebbles.
Scattered Intensity
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2θ / ° Fig. 5. XRD pattern of sintered Li2 TiO3 pebbles.
3. Results and discussion 3.1. Li2 TiO3 pebbles Gel spheres of Li2 CO3 and TiO2 are granulated by the emulsion method. Thereafter, the gel spheres are calcined at 973 K for 5 h in air to remove the binder and sintered at 1373 K for 2 h in air. Fig. 4 shows the sintered Li2 TiO3 pebbles. The pebbles have a diameter of 1.05 mm and a sphericity of 1.02. The density of the pebbles analyzed by the mercury intrusion technique is 85.8% T.D. The grain size is less than 5 m, measured by SEM. The molar ratio (Li/Ti) of the sintered pebbles evaluated by ICP–AES is 1.99. The crush load of 20 Li2 TiO3 pebbles was measured, and the average value is 37.2 N. The crystal structure of the sintered Li2 TiO3 pebbles was examined by XRD. The results are shown in Fig. 5. The XRD pattern of
Fig. 6. SEM images of sintered Li4 SiO4 pebbles.
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Table 2 Characteristics of the sintered Li4 SiO4 pebbles at 1273 K produced by the new direct pebble fabrication process. Diameter (mm) Sphericity Density (% T.D.) Grain size (m) Ratio of Li/Si Crush load (N) Crystal structure
1.50 1.07 66.1 <5 3.65 45.3–69.5 Average: 59.3 Mixture of Li4 SiO4 and Li2 SiO3
Fig. 7. Sintered Li4 SiO4 pebbles at 1273 K.
4. Conclusion
Sintered Li4SiO4 Pebbles ●
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2θ / ° Fig. 8. XRD patterns of the sintered Li4 SiO4 pebbles at 1273 K.
The temperature was adjusted to optimize the grain size of the sintered Li4 SiO4 pebbles. The results of this procedure are shown in Fig. 6. The grain size of the sintered Li4 SiO4 pebbles increased with increasing sintering temperature. The grain size is <5 m at 1273 K and >10 m at 1323 K, as measured by SEM. Considering the tritium release characteristics of the blanket, the desired grain size after sintering is <5 m. Therefore, the optimal sintering temperature of Li4 SiO4 gel spheres is 1273 K. The sintered Li4 SiO4 pebbles at 1273 K are white (Fig. 7). The diameter of the pebbles is 1.50 mm, and their sphericity is 1.07. The density of the pebbles is 66.1% T.D., as analyzed by the mercury intrusion technique. The grain size is <5 m, as measured by SEM. The crystal structure of the sintered Li4 SiO4 pebbles was analyzed by powder XRD. The XRD pattern of the sintered Li4 SiO4 pebbles (Fig. 8) is almost the same as that of Li4 SiO4 in the JCPDF-Card [15]. Small additional intensities indicated the presence of Li2 SiO3 as listed in the JC-PDF-Card [16]. The XRD pattern shows that sintered Li4 SiO4 is a mixture of Li4 SiO4 and Li2 SiO3 . The molar ratio (Li/Si) of the sintered pebbles evaluated by ICP–AES is 3.65. The molar ratio of sintered pebbles is smaller than the original mixing ratios of Li2 CO3 and SiO2 . It appears that Li is lost during the new process. This decrease in the molar ratio is considered an aftereffect of Li vaporization during sintering. The crush load of 20 sintered Li4 SiO4 pebbles was measured. The maximum value was 69.5 N and the minimum was 45.3 N. The average crush load was 59.3 N. In the EU, the pebble fabrication of Li4 SiO4 with Li2 TiO3 was conducted to increase the crush load of Li4 SiO4 pebbles [8]. Clearly, this study contributes to these efforts. Table 2 summarizes the characteristics of the sintered Li4 SiO4 pebbles produced by the emulsion method. The optimum diameter and density after sintering are 1 mm and >85% T.D., respectively. Thus, the next step is to optimize grinding conditions.
To minimize the pebble fabrication costs of advanced tritium breeders, a trial examination of a new process by the emulsion method was conducted. Previous attempts to fabricate Li2 TiO3 pebbles in Japan consisted of the preparation of raw materials followed by granulation. In this study, the integration of the preparation and granulation of raw material was proposed as a new direct pebble fabrication process. First, for granulation, employing the emulsion method, starting powders of Li2 CO3 and TiO2 , or SiO2 , with a molar ratio of Li/Ti = 2.0 or Li/Si = 4.0, were mixed. In addition, a binder was added to the mixture of starting powders to form the slurry. The gel spheres were granulated using the slurry of starting powders with the binder. Thereafter, they were calcined and sintered in air. The diameter, sphericity, density, grain size, molar ratio (Li/Ti), crystal structure, and crush load of Li2 TiO3 pebbles are 1.05 mm, 1.02, 85.8% T.D., <5 m, 1.99, single phase, and 35–40 N, respectively. These values are the optimum conditions for Li2 TiO3 pebbles. The diameter of the Li4 SiO4 pebbles is >1.0 mm, and the density is <85% T.D. Thus, the survey of granulation conditions for the direct pebble fabrication process utilizing the emulsion method will be continued as the optimum diameter and density after sintering are 1 mm and >85% T.D., respectively. On the other hand, the Li4 SiO4 pebbles obtained by this process are effective in increasing the crush load. Therefore, further studies will contribute to the pebble fabrication of Li4 SiO4 . Furthermore, the results show that pebble fabrication utilizing the proposed process is a promising technique for the mass production of advanced tritium breeder pebbles. The next step is to fabricate advanced tritium breeders such as Li2 TiO3 with excess Li (Li2+x TiO3+y ). Acknowledgments This report has been prepared within the framework of the agreement between the Government of Japan and the European Atomic Energy Community for The Joint Implementation of The Broader Approach Activities in the Field of Fusion Energy Research. The author would like to thank all the contributors to the IFERC projects in Japan and also all the members of the IFERC Project Team. References [1] L. Giancarli, V. Chuyanov, M. Abdou, M. Akiba, B.G. Hong, R. Lässer, et al., J. Nucl. Mater. 367–370 (2007) 1271–1280. [2] N. Roux, J. Avon, A. Floreancig, J. Mougin, B. Rasneur, S. Ravel, J. Nucl. Mater. 233–237 (1996) 1431–1435. [3] N. Roux, S. Tanaka, C. Johnson, R. Verrall, Fusion Eng. Des. 41 (1998) 31–38. [4] J.P. Kopasz, J.M. Miller, C.E. Johnson, J. Nucl. Mater. 212–215 (1994) 927–931. [5] R. Knitter, B. Löbbecke, J. Nucl. Mater. 361 (2007) 104–111. [6] R. Knitter, Proc. CBBI-15, JAEA, 2010, pp. 82–100. [7] M.H.H. Kolb, R. Knitter, U. Kaufmann, D. Mundt, Fusion Eng. Des. 86 (2011) 2148–2151. [8] R. Knitter, M.H.H. Kolb, U. Kaufmann, A.A. Goraieb, J. Nucl. Mater. 442 (2013) S433–S436.
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[9] T. Hoshino, M. Yasumoto, K. Tsuchiya, K. Hayashi, H. Nishimura, A. Suzuki, et al., Fusion Eng. Des. 82 (2007) 2269–2273. [10] T. Hoshino, K. Kato, Y. Natori, M. Nakamura, K. Sasaki, K. Hayashi, et al., Fusion Eng. Des. 84 (2009) 956–959. [11] T. Hoshino, M. Nakamichi, Fusion Eng. Des. 87 (2012) 486–492. [12] X. Du, J. He, J. Colloid Interface Sci. 345 (2010) 269–277.
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[13] T. Hirose, Y. Seki, H. Tanigawa, H. Tanigawa, D. Tsuru, M. Enoeda, et al., Fusion Eng. Des. 85 (2010) 1426–1429. [14] PDF#33-0831, PDF-Card, Material Data Inc. [15] PDF#37-1472, PDF-Card, Material Data Inc. [16] PDF#29-1828, PDF-Card, Material Data Inc.
Please cite this article in press as: T. Hoshino, Trial examination of direct pebble fabrication for advanced tritium breeders by the emulsion method, Fusion Eng. Des. (2014), http://dx.doi.org/10.1016/j.fusengdes.2013.12.052