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Development of methods for reprocessing and reuse of tritium breeder materials in broader approach activities
Journal of Nuclear Materials 442 (2013) S425–S428
Contents lists available at SciVerse ScienceDirect
Journal of Nuclear Materials journal homepage: www.elsevier.com/locate/jnucmat
Development of methods for reprocessing and reuse of tritium breeder materials in broader approach activities 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
a r t i c l e
i n f o
Article history: Available online 28 March 2013
a b s t r a c t The amount of 6Li in a tritium breeder decreases as a result of it being burned during the operation of a fusion reactor; however, the used tritium breeder in the replaced blanket includes a large amount of unburned 6Li. In this study, appropriate conditions and a method for mass reprocessing and reusing were evaluated. In the case of a hydrogen peroxide (H2O2) solvent, most of the Li2TiO3 was soluble at room temperature, and the solubility of Li was 96.2%. Lithium was dissolved as lithium hydroxide (LiOHH2O) in an H2O2 solvent. Then a preliminary test of the preparation of raw material for Li2TiO3 pebble fabrication was carried out by using the LiOHH2O dissolution liquid. The dissolution liquid was heated and exposed to water vapor in another method. The recovery rate of LiOHH2O was about 100%. Ó 2013 Elsevier B.V. All rights reserved.
1. Introduction Demonstration power reactors (DEMOs) require 6Li-enriched tritium breeders that have high tritium breeding ratios in the blanket design in European Union (EU) countries and Japan [1]. Both EU countries and Japan have been working to develop fabrication and reprocessing technologies for Li2TiO3 and Li4SiO4 pebbles [2,3]. A tritium breeder with high 6Li enrichment is essential for the realization of a DEMO. The amount of 6Li in a breeder decreases as a result of it being burned during the operation of a reactor; however, the used breeder in the replaced blanket includes a large amount of unburned 6Li. The development of methods to reprocess and reuse this spent tritium breeder, including unburned 6Li, is important from the viewpoint of the effective utilization of 6Li, which is a finite resource. Work on the development of appropriate methods is underway in the DEMO R&D building of the International Fusion Energy Research Centre project as a part of the Broader Approach activities. In a previous study, experiments were conducted using approximately 1.00 g of Li2TiO3 [1]. However, in that study, the mass treatment of the tritium breeder proved difficult to control. In this study, a system to dissolve the ceramics and to recover Li elements such as LiOHH2O was investigated to assess the dissolution and raw material adjustment of Li2TiO3. Our proposed reprocessing and reuse process for tritium breeders consisted of two steps, as shown in Fig. 1. Step 1 was the ⇑ Tel.: +81 175 71 6703; fax: +81 175 71 6502. E-mail address: [email protected] 0022-3115/$ - see front matter Ó 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.jnucmat.2013.03.009
dissolution of used Li2TiO3 pebbles. Step 2 was the preparation of the raw Li2TiO3 material. After the completion of these two steps, Li2TiO3 pebbles fabricated from reused Li were installed in the blanket region. The optimization of the dissolution conditions for Step 1 and the preliminary tests required for Step 2 were also performed in this study. Initially, the dissolution characteristic of Li2 TiO3 was investigated.
2. Experimental 2.1. Dissolution characteristic The effect of the solvent used on the dissolution of Li2TiO3 powder was evaluated as follows. We used 5.00 g of Li2TiO3 powder with a purity of 99.9% as a starting powder, and the solubility of Li was evaluated by measuring the Li content in a solution by inductively coupled plasma atomic emission spectrometry. Hydrochloric acid (HCl) at 0.50–1.00 mol/l and sulfuric acid (H2SO4) at 0.25–0.50 mol/l were selected as solvents.
2.2. Li material refining The raw material for the fabrication of Li2TiO3 pebbles was prepared by using LiOHH2O dissolution liquid, because lithium was dissolved as LiOHH2O in H2O2. We dissolved 5.00 g of LiOHH2O in H2O2 at 5.00 mol/l, concentrated the dissolution liquid at 323 K, and dried it in a vacuum using an aspirator.
S426
T. Hoshino / Journal of Nuclear Materials 442 (2013) S425–S428 Table 1 Experimental results of dissolution of Li2TiO3.
DEMO
Li ceramics
Dissolution condition Solvent
(a) In HCl and H2SO4 Li2TiO3 HCl
Content (mol/l)
Temp.
0.5
R.T. 353 K R.T. 353 K
7.20 43.8 15.4 52.0
R.T. 353 K R.T. 353 K
14.9 42.7 15.6 48.0
R.T.
96.2
1.0
Used Li2TiO3 pebble
H2SO4
0.25 0.5
Blanket
Step1) Dissolution of used Li2TiO3
Li solubility (%)
(b) In H2O2 at room temperature Li2TiO3 H2O2 5
Step2) Preparation of Li2TiO3 raw material
Li2TiO3 pebbles Fig. 1. Reprocessing and reuse of Li2TiO3.
After 150 h in vacuum
Fig. 2. Dissolution of Li2TiO3.
Fig. 3. Concentration and vacuum-drying test.
3. Results and discussion 3.1. Dissolution characteristic Fig. 2 shows the dissolution status of Li2TiO3 in HCl at 353 K and H2SO4 at 353 K. Other tritium breeders such as Li2O or Li4SiO4 are
easily dissolved in acid solvent [2]; however, the Li2TiO3 proved to be almost insoluble, and many white precipitates (presumably titanium dioxide (TiO2) and Li2TiO3) were observed. The results shown in Table 1a indicate that the maximum solubility of Li was 52.0%.
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T. Hoshino / Journal of Nuclear Materials 442 (2013) S425–S428
Concentration condition Dissolving LiOH•H2O 5.00g in H2O2
10
Concentration at 323K
8.48g
8.48g
7.5
Weight (g
5.04g 5
(
2.5 Vacuum-drying
0
0
30
60
90
120
150
Water
Time h Fig. 4. Weight change of LiOHH2O in vacuum-drying test.
In order to increase the solubility of Li, hydrogen peroxide (H2O2) at 5.00 mol/l was selected as the solvent. The dissolving reaction of Li2TiO3 is shown in the following equation:
Li2 TiO3 þ 2H2 O2 ! 2LiOHhsolublei þ H2 TiO3 hsolublei þ O2
After 60 h
ð1Þ
In this case, most of the Li2TiO3 was soluble at room temperature (Fig. 2b). The results summarized in Table 1b indicate that the solubility of Li was 96.2% in H2O2. In this dissolution test, H2O2 was the most suitable solvent for Li2TiO3 dissolution, in which lithium was dissolved as LiOHH2O. 3.2. Li material refining
Fig. 5. Heating and water–vapor exposure test.
Heating condition Dissolving in H2O2
LiOH•H2O 5.00g
10
LiOH
Heating at 573K
2.91g
Water-vapor exposure
7.5
Weight (g
(
Photographs of the concentration and vacuum-drying test are shown in Fig. 3. The color of the LiOHH2O did not change, indicating that the chemical formula of the vacuum-drying sample was LiOHH2O. The weight of the LiOHH2O sample was then measured using a balance scale. We dissolved 5.00 g of LiOHH2O in H2O2 and concentrated it at 323 K. The weight of the pre-measurement sample, including a small amount of solution, was found to be 8.48 g. The result for the change in weight of LiOHH2O in a vacuum is shown in Fig. 4. Initially, the mass of the sample was found to decrease with time in a vacuum, but was later found to recover to almost the initial 5.04 g. The chemical formula was identified as LiOHH2O by X-ray diffraction measurement. Material refining of LiOHH2O was directly performed from dissolution liquid. Because the concentration time is longer for a large quantity of dissolution liquid, we developed a new material refining method. We dissolved 5.00 g of LiOHH2O in H2O2 at 5.00 mol/l, heated the dissolution liquid at 573 K, and then exposed it to water vapor using an aspirator. Photographs of the heating and water–vapor exposure test are shown in Fig. 5. The color of LiOHH2O did not change, as was the case in the vacuum-drying method, indicating that the chemical formula of the heating and water–vapor exposure sample was LiOHH2O. The weight of the LiOHH2O sample was then measured using a balance scale. We dissolved 5.00 g of LiOHH2O in H2O2 and dried it at 573 K in order to evaporate the water content in the sample. The chemical formula of this sample seemed to change to LiOH from LiOHH2O. The weight of the pre-measurement sample was 2.91 g. The result of the change in weight of this sample upon exposure to water vapor is shown in Fig. 6. The mass of the sample was found to have increased with time during exposure to water vapor because LiOH reacts readily with water (H2O). The LiOHH2O mass of the sample recovered almost to the initial 5.00 g.
5.17g
5 2.5
2.91g
00
10
20
30
40
50
60
Time h Fig. 6. Weight change of LiOHH2O in heating and water–vapor exposure test.
LiOHH2O is the raw material for the synthesis of Li2TiO3 powder [4]. The heating method is faster than the concentration method at 323 K. Therefore, heating and water–vapor exposure is a candidate method for raw material adjustment, from the mass material refining perspective.
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T. Hoshino / Journal of Nuclear Materials 442 (2013) S425–S428
4. Conclusions The development of methods to reprocess and reuse this spent breeder, including unburned 6Li, is important from the viewpoint of the effective utilization of 6Li, which is a finite resource. In this study, appropriate methods for the dissolution of and raw material adjustment for Li2TiO3 were evaluated. The effect of the solvent used on the dissolution of Li2TiO3 powder was evaluated. In the case of the H2O2 solvent, most of the Li2TiO3 was soluble at room temperature. This result indicates that the solubility of Li was 96.2% in the case of an H2O2 solvent. Raw material for Li2TiO3 pebble fabrication was prepared using the LiOHH2O dissolution liquid. LiOHH2O was dissolved in H2O2 and the dissolution liquid was concentrated and dried in a vacuum, or heated and exposed to water vapor. The weight of the pre-mea-
surement sample recovered to the initial weight of LiOHH2O. Because the heating method was faster than the concentration method, the heating and water–vapor exposure method is the candidate method for raw material adjustment. The overall results suggest that this study on the reprocessing and reuse of Li2TiO3 will prove useful in realizing an ecologically clean and low-cost recycling technology for a tritium breeder. References [1] T. Hoshino, T. Terai, J. Nucl. Mater. 417 (2011) 696–699. [2] T. Hoshino, K. Tsuchiya, K. Hayashi, M. Nakamura, H. Terunuma, K. Tatenuma, J. Nucl. Mater. 386–388 (2009) 1107–1110. [3] R. Knitter, B. Lobbecke, J. Nucl. Mater. 361 (2007) 104–111. [4] T. Hoshino, K. Kato, Y. Natori, F. Oikawa, N. Nakano, M. Nakamura, K. Sasaki, A. Suzuki, T. Terai, K. Tatenuma, J. Nucl. Mater. 417 (2011) 684–687.
Contents lists available at SciVerse ScienceDirect
Journal of Nuclear Materials journal homepage: www.elsevier.com/locate/jnucmat
Development of methods for reprocessing and reuse of tritium breeder materials in broader approach activities 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
a r t i c l e
i n f o
Article history: Available online 28 March 2013
a b s t r a c t The amount of 6Li in a tritium breeder decreases as a result of it being burned during the operation of a fusion reactor; however, the used tritium breeder in the replaced blanket includes a large amount of unburned 6Li. In this study, appropriate conditions and a method for mass reprocessing and reusing were evaluated. In the case of a hydrogen peroxide (H2O2) solvent, most of the Li2TiO3 was soluble at room temperature, and the solubility of Li was 96.2%. Lithium was dissolved as lithium hydroxide (LiOHH2O) in an H2O2 solvent. Then a preliminary test of the preparation of raw material for Li2TiO3 pebble fabrication was carried out by using the LiOHH2O dissolution liquid. The dissolution liquid was heated and exposed to water vapor in another method. The recovery rate of LiOHH2O was about 100%. Ó 2013 Elsevier B.V. All rights reserved.
1. Introduction Demonstration power reactors (DEMOs) require 6Li-enriched tritium breeders that have high tritium breeding ratios in the blanket design in European Union (EU) countries and Japan [1]. Both EU countries and Japan have been working to develop fabrication and reprocessing technologies for Li2TiO3 and Li4SiO4 pebbles [2,3]. A tritium breeder with high 6Li enrichment is essential for the realization of a DEMO. The amount of 6Li in a breeder decreases as a result of it being burned during the operation of a reactor; however, the used breeder in the replaced blanket includes a large amount of unburned 6Li. The development of methods to reprocess and reuse this spent tritium breeder, including unburned 6Li, is important from the viewpoint of the effective utilization of 6Li, which is a finite resource. Work on the development of appropriate methods is underway in the DEMO R&D building of the International Fusion Energy Research Centre project as a part of the Broader Approach activities. In a previous study, experiments were conducted using approximately 1.00 g of Li2TiO3 [1]. However, in that study, the mass treatment of the tritium breeder proved difficult to control. In this study, a system to dissolve the ceramics and to recover Li elements such as LiOHH2O was investigated to assess the dissolution and raw material adjustment of Li2TiO3. Our proposed reprocessing and reuse process for tritium breeders consisted of two steps, as shown in Fig. 1. Step 1 was the ⇑ Tel.: +81 175 71 6703; fax: +81 175 71 6502. E-mail address: [email protected] 0022-3115/$ - see front matter Ó 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.jnucmat.2013.03.009
dissolution of used Li2TiO3 pebbles. Step 2 was the preparation of the raw Li2TiO3 material. After the completion of these two steps, Li2TiO3 pebbles fabricated from reused Li were installed in the blanket region. The optimization of the dissolution conditions for Step 1 and the preliminary tests required for Step 2 were also performed in this study. Initially, the dissolution characteristic of Li2 TiO3 was investigated.
2. Experimental 2.1. Dissolution characteristic The effect of the solvent used on the dissolution of Li2TiO3 powder was evaluated as follows. We used 5.00 g of Li2TiO3 powder with a purity of 99.9% as a starting powder, and the solubility of Li was evaluated by measuring the Li content in a solution by inductively coupled plasma atomic emission spectrometry. Hydrochloric acid (HCl) at 0.50–1.00 mol/l and sulfuric acid (H2SO4) at 0.25–0.50 mol/l were selected as solvents.
2.2. Li material refining The raw material for the fabrication of Li2TiO3 pebbles was prepared by using LiOHH2O dissolution liquid, because lithium was dissolved as LiOHH2O in H2O2. We dissolved 5.00 g of LiOHH2O in H2O2 at 5.00 mol/l, concentrated the dissolution liquid at 323 K, and dried it in a vacuum using an aspirator.
S426
T. Hoshino / Journal of Nuclear Materials 442 (2013) S425–S428 Table 1 Experimental results of dissolution of Li2TiO3.
DEMO
Li ceramics
Dissolution condition Solvent
(a) In HCl and H2SO4 Li2TiO3 HCl
Content (mol/l)
Temp.
0.5
R.T. 353 K R.T. 353 K
7.20 43.8 15.4 52.0
R.T. 353 K R.T. 353 K
14.9 42.7 15.6 48.0
R.T.
96.2
1.0
Used Li2TiO3 pebble
H2SO4
0.25 0.5
Blanket
Step1) Dissolution of used Li2TiO3
Li solubility (%)
(b) In H2O2 at room temperature Li2TiO3 H2O2 5
Step2) Preparation of Li2TiO3 raw material
Li2TiO3 pebbles Fig. 1. Reprocessing and reuse of Li2TiO3.
After 150 h in vacuum
Fig. 2. Dissolution of Li2TiO3.
Fig. 3. Concentration and vacuum-drying test.
3. Results and discussion 3.1. Dissolution characteristic Fig. 2 shows the dissolution status of Li2TiO3 in HCl at 353 K and H2SO4 at 353 K. Other tritium breeders such as Li2O or Li4SiO4 are
easily dissolved in acid solvent [2]; however, the Li2TiO3 proved to be almost insoluble, and many white precipitates (presumably titanium dioxide (TiO2) and Li2TiO3) were observed. The results shown in Table 1a indicate that the maximum solubility of Li was 52.0%.
S427
T. Hoshino / Journal of Nuclear Materials 442 (2013) S425–S428
Concentration condition Dissolving LiOH•H2O 5.00g in H2O2
10
Concentration at 323K
8.48g
8.48g
7.5
Weight (g
5.04g 5
(
2.5 Vacuum-drying
0
0
30
60
90
120
150
Water
Time h Fig. 4. Weight change of LiOHH2O in vacuum-drying test.
In order to increase the solubility of Li, hydrogen peroxide (H2O2) at 5.00 mol/l was selected as the solvent. The dissolving reaction of Li2TiO3 is shown in the following equation:
Li2 TiO3 þ 2H2 O2 ! 2LiOHhsolublei þ H2 TiO3 hsolublei þ O2
After 60 h
ð1Þ
In this case, most of the Li2TiO3 was soluble at room temperature (Fig. 2b). The results summarized in Table 1b indicate that the solubility of Li was 96.2% in H2O2. In this dissolution test, H2O2 was the most suitable solvent for Li2TiO3 dissolution, in which lithium was dissolved as LiOHH2O. 3.2. Li material refining
Fig. 5. Heating and water–vapor exposure test.
Heating condition Dissolving in H2O2
LiOH•H2O 5.00g
10
LiOH
Heating at 573K
2.91g
Water-vapor exposure
7.5
Weight (g
(
Photographs of the concentration and vacuum-drying test are shown in Fig. 3. The color of the LiOHH2O did not change, indicating that the chemical formula of the vacuum-drying sample was LiOHH2O. The weight of the LiOHH2O sample was then measured using a balance scale. We dissolved 5.00 g of LiOHH2O in H2O2 and concentrated it at 323 K. The weight of the pre-measurement sample, including a small amount of solution, was found to be 8.48 g. The result for the change in weight of LiOHH2O in a vacuum is shown in Fig. 4. Initially, the mass of the sample was found to decrease with time in a vacuum, but was later found to recover to almost the initial 5.04 g. The chemical formula was identified as LiOHH2O by X-ray diffraction measurement. Material refining of LiOHH2O was directly performed from dissolution liquid. Because the concentration time is longer for a large quantity of dissolution liquid, we developed a new material refining method. We dissolved 5.00 g of LiOHH2O in H2O2 at 5.00 mol/l, heated the dissolution liquid at 573 K, and then exposed it to water vapor using an aspirator. Photographs of the heating and water–vapor exposure test are shown in Fig. 5. The color of LiOHH2O did not change, as was the case in the vacuum-drying method, indicating that the chemical formula of the heating and water–vapor exposure sample was LiOHH2O. The weight of the LiOHH2O sample was then measured using a balance scale. We dissolved 5.00 g of LiOHH2O in H2O2 and dried it at 573 K in order to evaporate the water content in the sample. The chemical formula of this sample seemed to change to LiOH from LiOHH2O. The weight of the pre-measurement sample was 2.91 g. The result of the change in weight of this sample upon exposure to water vapor is shown in Fig. 6. The mass of the sample was found to have increased with time during exposure to water vapor because LiOH reacts readily with water (H2O). The LiOHH2O mass of the sample recovered almost to the initial 5.00 g.
5.17g
5 2.5
2.91g
00
10
20
30
40
50
60
Time h Fig. 6. Weight change of LiOHH2O in heating and water–vapor exposure test.
LiOHH2O is the raw material for the synthesis of Li2TiO3 powder [4]. The heating method is faster than the concentration method at 323 K. Therefore, heating and water–vapor exposure is a candidate method for raw material adjustment, from the mass material refining perspective.
S428
T. Hoshino / Journal of Nuclear Materials 442 (2013) S425–S428
4. Conclusions The development of methods to reprocess and reuse this spent breeder, including unburned 6Li, is important from the viewpoint of the effective utilization of 6Li, which is a finite resource. In this study, appropriate methods for the dissolution of and raw material adjustment for Li2TiO3 were evaluated. The effect of the solvent used on the dissolution of Li2TiO3 powder was evaluated. In the case of the H2O2 solvent, most of the Li2TiO3 was soluble at room temperature. This result indicates that the solubility of Li was 96.2% in the case of an H2O2 solvent. Raw material for Li2TiO3 pebble fabrication was prepared using the LiOHH2O dissolution liquid. LiOHH2O was dissolved in H2O2 and the dissolution liquid was concentrated and dried in a vacuum, or heated and exposed to water vapor. The weight of the pre-mea-
surement sample recovered to the initial weight of LiOHH2O. Because the heating method was faster than the concentration method, the heating and water–vapor exposure method is the candidate method for raw material adjustment. The overall results suggest that this study on the reprocessing and reuse of Li2TiO3 will prove useful in realizing an ecologically clean and low-cost recycling technology for a tritium breeder. References [1] T. Hoshino, T. Terai, J. Nucl. Mater. 417 (2011) 696–699. [2] T. Hoshino, K. Tsuchiya, K. Hayashi, M. Nakamura, H. Terunuma, K. Tatenuma, J. Nucl. Mater. 386–388 (2009) 1107–1110. [3] R. Knitter, B. Lobbecke, J. Nucl. Mater. 361 (2007) 104–111. [4] T. Hoshino, K. Kato, Y. Natori, F. Oikawa, N. Nakano, M. Nakamura, K. Sasaki, A. Suzuki, T. Terai, K. Tatenuma, J. Nucl. Mater. 417 (2011) 684–687.