- Email: [email protected]
Experimental study of tritium recovery from liquid lithium by yttrium
Fusion Engineering and Design 81 (2006) 567–571
Experimental study of tritium recovery from liquid lithium by yttrium Mika Kinoshita b , Satoshi Fukada a,∗ , Naoya Yamashita b , Takeo Muroga c , Masabumi Nishikawa b a
c
Department of Applied Quantum Physics and Nuclear Engineering, Kyushu University, Hakozaki, Higashi-ku, Fukuoka 812-8581, Japan b Department of Energy Engineering Science, Kyushu University, Fukuoka 812-8581, Japan Fusion Engineering Research Center, National Institute of Fusion Sciences, Toki 509-5292, Japan Received 31 January 2005; received in revised form 20 April 2005; accepted 26 April 2005 Available online 18 January 2006
Abstract The recovery of hydrogen in liquid Li by Y was investigated in the range 573–773 K. To recover tritium down to 1 wppm from Li, it is necessary to absorb tritium in Li into the Y hydride around at 523 K, if Y is in a hydride phase. However, it was found that limiting the use of the Y bed until its ␣ phase relieves the temperature restriction. The hydrogen recovery rate was determined comparatively among the static Li–H2 , Y–H2 and Li–Y–H2 systems. Although the hydrogen absorbing rate of Li–Y–H2 was comparable to that of Y–H2 at 673 K, it decreased at temperatures lower than 623 K due to reaction resistance at the Y surface. Relation between the surface effect and temperature was discussed. © 2005 Elsevier B.V. All rights reserved. Keywords: Lithium; Tritium; Yttrium; Recovery; IFMIF
1. Introduction The International Fusion Materials Irradiation Facility (IFMIF) is now under design work and fundamental technological researches are being carried out intensively under the IEA collaboration work. In the IFMIF, liquid Li is used as a flowing target to ∗ Corresponding author. Tel.: +81 92 642 4140; fax: +81 92 642 3800. E-mail address: [email protected] (S. Fukada).
0920-3796/$ – see front matter © 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.fusengdes.2005.04.003
generate high-energy neutron for the material irradiation. Around seven gram of tritium per year as a by-product is generated in the Li loop [1]. Tritium is present in Li also with N and O impurities as well as other hydrogen isotopes of H and D. Impurities such as N, O and C should be removed from the Li loop system continuously in order to avoid material erosion. Although O and C can be removed by cold traps down to around 10 ppm, N and hydrogen isotopes cannot be removed sufficiently only by the cold trap because of their higher solubilities in Li. Especially, since tritium
568
M. Kinoshita et al. / Fusion Engineering and Design 81 (2006) 567–571
Fig. 1. Tritium recovery condition from Li by Y.
is a potentially hazardous radioisotope because of high exchange rates with other hydrogen isotopes, tritium removal becomes a serious issue. A Y bed is one of the most promising ways to recover tritium from the Li flow. Previously, hydrogen absorption by Y was experimentally investigated by an ORNL group in the US [2], and the possibility of tritium recovery from a fusion reactor blanket was investigated [3]. However, its recovery rate was not so high even at 773 K. In the present study, therefore, hydrogen recovery was intensively investigated in order to apply it to the IFMIF Li flow system. The recovery of hydrogen from the Li–H2 , Y–H2 and Li–Y–H2 systems were comparatively investigated experimentally. The dependence of recovery rate and absorption capacity on temperature was analyzed.
getter. We needed to operate a Y hot getter trap around at 573 K to remove tritium in Li down to 1 wppm, if Y is in the hydride phase. Then the recovery operation is carried out under equilibrium condition. The tritium concentration in the Y hot trap is assumed to be uniform throughout the bed. However, the tritium concentration varies from the hydride phase at the inlet to the ␣ phase at the outlet under dynamic operation. This situation was familiar to chemical engineering operation such as dynamic gas absorption process in the Y bed [6–8]. Consequently, this temperature condition can be lightened if the Y bed is operated under the ␣ phase region, for example YT0.006 . This does not mean that the hydrogen capacity of the whole Y bed decreases heavily. The region of the ␣ phase is limited in a narrow mass-transfer zone near the bed outlet. The rest of the bed is still in the hydride phase. The equilibrium pressure of a broken line in Fig. 1 was calculated by the following equation based on experimental results by Begun et al. [9]: C 23 200 −6 (1) √ = 2.92 × 10 exp p Rg T In order to achieve the T/Y atom ratio of C = 0.006, we need to desorb the Y bed at 1023 K under the vacuum condition of 1 ×10−3 Pa before the absorption operation. This does not seem to be hard for the operation of the Y bed. Then, the Y trap has a structure of particle packed bed operated at a dynamic flow-through condition. It can recover hydrogen down to 1 wppm even at 773 K unless the breakthrough occurs at its outlet. In the present study, these conditions were considered to be a target temperature in order to prove whether or not the Y trap can work as a hot trap of IFMIF.
3. Experimental 2. Reconsideration of tritium recovery condition by yttrium for IFMIF The chain and solid lines in Fig. 1 show the dissociation pressures of the Li hydride [4] and the Y hydride [5]. Although the dissociation pressure of the static Li–H2 system is low under the IFMIF operation temperature, Y is one of the few metallic getters that can remove hydrogen isotopes from Li. Therefore, Y was considered the most powerful candidate for tritium
Fig. 2 shows a schematic diagram of the experimental apparatus. In the present study, Li was always handled in an argon-atmosphere glove box that can be evacuated. Before any absorption experiment run, a Mo crucible was heated up to 1073 K in order to desorb gaseous pre-adsorbed impurities. Then 0.100 g Li was put on a Y plate with 0.25 mm in thickness and 1.33 cm2 in surface area in the Mo crucible. The Y plate was immersed in Li in the Mo crucible in a
M. Kinoshita et al. / Fusion Engineering and Design 81 (2006) 567–571
569
Fig. 2. A schematic diagram of the experimental apparatus.
quartz-glass tube in the Ar glove box that is shown by a broken line in the figure. The whole system was evacuated by a turbo-molecular pump before gas introduction. The system was heated up to 873 K for activation under Ar atmosphere and was cooled down to a specified hydrogen absorption condition. Ar and H2 gases of research-grade were further purified by SAES getter 707 and MS 3A traps, respectively. After Ar gas flowed through the Mo crucible for sufficient time, an Ar–H2 gas mixture with a constant flow rate regulated by mass-flow meters was introduced into the quartzglass tube. The inlet H2 concentration in Ar stream was 100 ppm. The H2 concentration of the effluent gas was detected by gas chromatography. After each absorption experiment, the Mo crucible, Li and Y plate were exchanged with new ones. The flow rates varied from 10 to 100 cm3 (NTP)/min. The recovery of H2 from Li by the Y plate was experimentally investigated under the conditions of 573–773 K.
Li promptly. At 673 K as seen in the latter figure, an induction time was observed in the initial H2 absorption behavior. The induction time is defined as time until the Y bed shows sufficient hydrogen absorption. This might be because the Y surface was not under an active condition initially but, after the contact with Li,
4. Experimental results and discussion Typical examples of variations of the effluent H2 concentration with time are shown in Figs. 3 and 4. At 773 K of the former figure, Y recovered H2 from
Fig. 3. Results of hydrogen absorption experiment at 773 K.
570
M. Kinoshita et al. / Fusion Engineering and Design 81 (2006) 567–571
Fig. 5. Comparison of hydrogen absorption rate between Li–Y–H2 and Y–H2 systems in 573–773 K. Fig. 4. Results of hydrogen absorption experiment at 673 K.
the Y surface was activated by the Li contact or the initial H2 absorption. After the initial induction time, H2 was recovered promptly in a similar way to the higher temperature. Thus, H2 was dissolved in Li smoothly and also in Y immersed in Li at 673 and 773 K. In other words, hydrogen atoms in Li could be recovered by Y under the temperatures higher than 673 K. Thus, Li was in the ␣ phase, and Y was in the  phase. However, similar H2 recovery was not achieved under the conditions of 573 and 623 K because of its very slow absorption rate. Here, we discuss the hydrogen absorption rate. The overall H2 absorption rate defined by jH2 is calculated from the following overall H2 mass balance equation: pV dyH2 = W(yH2 ,in − yH2 ) − jH2 Rg T dt
The effect of the induction time observed at 673 K on the hydrogen capacity was small. The steady-state H2 recovery rate at 673 K was comparatively fast. Fig. 6 shows a SEM photo of the interface between Li and a Y plate after 50 days contact with liquid Li.
(2)
Here W is the Ar + H2 molar flow rate and yH2 is the H2 molar fraction in the effluent gas. The Y absorption rate determined from variations of the H2 concentration with time is shown in Fig. 5 comparatively between the Y–H2 and Li–Y–H2 systems. As seen in the figure, the absorption rate of Y was almost unchanged regardless of the two different conditions of Y immersed in Li and Y under the Ar–H2 gaseous atmosphere. Thus, it was found that high H2 absorption capacity could be expected also in Y immersed in Li at temperatures higher than 673 K.
Fig. 6. (a) SEM photo of Y plate immersed in Li at 400 ◦ C for 50 days; (b) SEM photo of Y plate before hydrogen absorption.
M. Kinoshita et al. / Fusion Engineering and Design 81 (2006) 567–571
571
Table 1 Hydrogen absorption amount for Y and Li–Y–H2 system
Acknowledgement
Temperature (K)
Y–Li–H2 (mol H/mol Y)
Y–H2 (mol H/mol Y)
773 673 573
1.64 2.05 0.02
1.87 1.75 0.91
This work has been performed under the NIFS LHD coordinated research (contract number NIFS05KOBF010).
References There was no change at the interface. Therefore, there was very small corrosion action on Y surface. Table 1 shows comparison of the H2 amounts absorbed in Y between the Y–H2 and Li–Y–H2 systems. The H2 absorption amounts at 673 and 773 K were almost equal to the original H2 capacity of Y that is expected from the equilibrium pressure–composition isotherm [9]. This means that Y holds its original H2 absorption capacity even under the condition of Li immersion. However, Y under the immersion condition did not show sufficient hydrogen capacity at 573 K. This is because a Y oxide that was inevitably formed on surfaces was not activated sufficiently. We need to develop a better activation technique for Y if operation at 573 K or below is necessary.
5. Conclusions The recovery of H2 from liquid Li was experimentally investigated from 573 to 773 K. Strict handling under Ar atmosphere enabled Y to recover H2 from Li at 673 K with a sufficient rate. The Y plate showed sufficient H2 absorption performance on rate and capacity even at 673 K.
[1] H. Nakamura, M. Ida, M. Sugimoto, T. Yutani, H. Takeuichi, Removal and control of tritium in lithium target for international fusion materials irradiation facility (IFMIF), Fusion Sci. Technol. 41 (2002) 845–849. [2] S.D. Clinton, J.S. Watson, Tritium removal from liquid metals by sorption on yttrium, in: Proceedings of the Seventh Symposium on Engineering Problems of Fusion Research, IEEE Publication No. 77CH1267-4-NPS, 1979. [3] H. Moriyama, S. Tanaka, D.-K. Sze, J. Reimann, A. Terlain, Tritium recovery from liquid metals, Fusion Eng. Des. 28 (1995) 226–239. [4] E. Veleckis, E.H. Van Deventler, M. Blander, The lithium–lithium hydride system, J. Phys. Chem. 78 (1974) 1933–1940. [5] L.N. Yannopoulos, R.K. Edwards, P.G. Warlbeck, The thermodynamics of the yttrium–hydrogen systems, J. Phys. Chem. 69 (1965) 2510–2515. [6] S. Fukada, S. Kitajima, N. Mitsuishi, Effects of mass transfer resistances on hydrogen absorption in yttrium bed, J. Nucl. Sci. Technol. 25 (1988) 895–897. [7] S. Fukada, N. Mitsuishi, S. Kitajima, T. Nakahara, Absorption and desorption characteristics of hydrogen from inert gas mixtures in yttrium particle bed, Mem. Fac. Eng. Kyushu Univ. 48 (1988) 281–294. [8] S. Fukada, M. Nishikawa, Recovery of tritium from liquid lithium blanket of lithium, Li–Pb eutectic alloy or molten salt, Ann. Rep. Hydrogen Isotope Res. Cent. Toyama Univ. 14 (1994) 1–21. [9] G.M. Begun, J.F. Land, J.T. Bell, High temperature equilibrium measurements of the yttrium–hydrogen isotope (H2 , D2 , T2 ) systems, J. Chem. Phys. 72 (1980) 2959–2966.
Experimental study of tritium recovery from liquid lithium by yttrium Mika Kinoshita b , Satoshi Fukada a,∗ , Naoya Yamashita b , Takeo Muroga c , Masabumi Nishikawa b a
c
Department of Applied Quantum Physics and Nuclear Engineering, Kyushu University, Hakozaki, Higashi-ku, Fukuoka 812-8581, Japan b Department of Energy Engineering Science, Kyushu University, Fukuoka 812-8581, Japan Fusion Engineering Research Center, National Institute of Fusion Sciences, Toki 509-5292, Japan Received 31 January 2005; received in revised form 20 April 2005; accepted 26 April 2005 Available online 18 January 2006
Abstract The recovery of hydrogen in liquid Li by Y was investigated in the range 573–773 K. To recover tritium down to 1 wppm from Li, it is necessary to absorb tritium in Li into the Y hydride around at 523 K, if Y is in a hydride phase. However, it was found that limiting the use of the Y bed until its ␣ phase relieves the temperature restriction. The hydrogen recovery rate was determined comparatively among the static Li–H2 , Y–H2 and Li–Y–H2 systems. Although the hydrogen absorbing rate of Li–Y–H2 was comparable to that of Y–H2 at 673 K, it decreased at temperatures lower than 623 K due to reaction resistance at the Y surface. Relation between the surface effect and temperature was discussed. © 2005 Elsevier B.V. All rights reserved. Keywords: Lithium; Tritium; Yttrium; Recovery; IFMIF
1. Introduction The International Fusion Materials Irradiation Facility (IFMIF) is now under design work and fundamental technological researches are being carried out intensively under the IEA collaboration work. In the IFMIF, liquid Li is used as a flowing target to ∗ Corresponding author. Tel.: +81 92 642 4140; fax: +81 92 642 3800. E-mail address: [email protected] (S. Fukada).
0920-3796/$ – see front matter © 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.fusengdes.2005.04.003
generate high-energy neutron for the material irradiation. Around seven gram of tritium per year as a by-product is generated in the Li loop [1]. Tritium is present in Li also with N and O impurities as well as other hydrogen isotopes of H and D. Impurities such as N, O and C should be removed from the Li loop system continuously in order to avoid material erosion. Although O and C can be removed by cold traps down to around 10 ppm, N and hydrogen isotopes cannot be removed sufficiently only by the cold trap because of their higher solubilities in Li. Especially, since tritium
568
M. Kinoshita et al. / Fusion Engineering and Design 81 (2006) 567–571
Fig. 1. Tritium recovery condition from Li by Y.
is a potentially hazardous radioisotope because of high exchange rates with other hydrogen isotopes, tritium removal becomes a serious issue. A Y bed is one of the most promising ways to recover tritium from the Li flow. Previously, hydrogen absorption by Y was experimentally investigated by an ORNL group in the US [2], and the possibility of tritium recovery from a fusion reactor blanket was investigated [3]. However, its recovery rate was not so high even at 773 K. In the present study, therefore, hydrogen recovery was intensively investigated in order to apply it to the IFMIF Li flow system. The recovery of hydrogen from the Li–H2 , Y–H2 and Li–Y–H2 systems were comparatively investigated experimentally. The dependence of recovery rate and absorption capacity on temperature was analyzed.
getter. We needed to operate a Y hot getter trap around at 573 K to remove tritium in Li down to 1 wppm, if Y is in the hydride phase. Then the recovery operation is carried out under equilibrium condition. The tritium concentration in the Y hot trap is assumed to be uniform throughout the bed. However, the tritium concentration varies from the hydride phase at the inlet to the ␣ phase at the outlet under dynamic operation. This situation was familiar to chemical engineering operation such as dynamic gas absorption process in the Y bed [6–8]. Consequently, this temperature condition can be lightened if the Y bed is operated under the ␣ phase region, for example YT0.006 . This does not mean that the hydrogen capacity of the whole Y bed decreases heavily. The region of the ␣ phase is limited in a narrow mass-transfer zone near the bed outlet. The rest of the bed is still in the hydride phase. The equilibrium pressure of a broken line in Fig. 1 was calculated by the following equation based on experimental results by Begun et al. [9]: C 23 200 −6 (1) √ = 2.92 × 10 exp p Rg T In order to achieve the T/Y atom ratio of C = 0.006, we need to desorb the Y bed at 1023 K under the vacuum condition of 1 ×10−3 Pa before the absorption operation. This does not seem to be hard for the operation of the Y bed. Then, the Y trap has a structure of particle packed bed operated at a dynamic flow-through condition. It can recover hydrogen down to 1 wppm even at 773 K unless the breakthrough occurs at its outlet. In the present study, these conditions were considered to be a target temperature in order to prove whether or not the Y trap can work as a hot trap of IFMIF.
3. Experimental 2. Reconsideration of tritium recovery condition by yttrium for IFMIF The chain and solid lines in Fig. 1 show the dissociation pressures of the Li hydride [4] and the Y hydride [5]. Although the dissociation pressure of the static Li–H2 system is low under the IFMIF operation temperature, Y is one of the few metallic getters that can remove hydrogen isotopes from Li. Therefore, Y was considered the most powerful candidate for tritium
Fig. 2 shows a schematic diagram of the experimental apparatus. In the present study, Li was always handled in an argon-atmosphere glove box that can be evacuated. Before any absorption experiment run, a Mo crucible was heated up to 1073 K in order to desorb gaseous pre-adsorbed impurities. Then 0.100 g Li was put on a Y plate with 0.25 mm in thickness and 1.33 cm2 in surface area in the Mo crucible. The Y plate was immersed in Li in the Mo crucible in a
M. Kinoshita et al. / Fusion Engineering and Design 81 (2006) 567–571
569
Fig. 2. A schematic diagram of the experimental apparatus.
quartz-glass tube in the Ar glove box that is shown by a broken line in the figure. The whole system was evacuated by a turbo-molecular pump before gas introduction. The system was heated up to 873 K for activation under Ar atmosphere and was cooled down to a specified hydrogen absorption condition. Ar and H2 gases of research-grade were further purified by SAES getter 707 and MS 3A traps, respectively. After Ar gas flowed through the Mo crucible for sufficient time, an Ar–H2 gas mixture with a constant flow rate regulated by mass-flow meters was introduced into the quartzglass tube. The inlet H2 concentration in Ar stream was 100 ppm. The H2 concentration of the effluent gas was detected by gas chromatography. After each absorption experiment, the Mo crucible, Li and Y plate were exchanged with new ones. The flow rates varied from 10 to 100 cm3 (NTP)/min. The recovery of H2 from Li by the Y plate was experimentally investigated under the conditions of 573–773 K.
Li promptly. At 673 K as seen in the latter figure, an induction time was observed in the initial H2 absorption behavior. The induction time is defined as time until the Y bed shows sufficient hydrogen absorption. This might be because the Y surface was not under an active condition initially but, after the contact with Li,
4. Experimental results and discussion Typical examples of variations of the effluent H2 concentration with time are shown in Figs. 3 and 4. At 773 K of the former figure, Y recovered H2 from
Fig. 3. Results of hydrogen absorption experiment at 773 K.
570
M. Kinoshita et al. / Fusion Engineering and Design 81 (2006) 567–571
Fig. 5. Comparison of hydrogen absorption rate between Li–Y–H2 and Y–H2 systems in 573–773 K. Fig. 4. Results of hydrogen absorption experiment at 673 K.
the Y surface was activated by the Li contact or the initial H2 absorption. After the initial induction time, H2 was recovered promptly in a similar way to the higher temperature. Thus, H2 was dissolved in Li smoothly and also in Y immersed in Li at 673 and 773 K. In other words, hydrogen atoms in Li could be recovered by Y under the temperatures higher than 673 K. Thus, Li was in the ␣ phase, and Y was in the  phase. However, similar H2 recovery was not achieved under the conditions of 573 and 623 K because of its very slow absorption rate. Here, we discuss the hydrogen absorption rate. The overall H2 absorption rate defined by jH2 is calculated from the following overall H2 mass balance equation: pV dyH2 = W(yH2 ,in − yH2 ) − jH2 Rg T dt
The effect of the induction time observed at 673 K on the hydrogen capacity was small. The steady-state H2 recovery rate at 673 K was comparatively fast. Fig. 6 shows a SEM photo of the interface between Li and a Y plate after 50 days contact with liquid Li.
(2)
Here W is the Ar + H2 molar flow rate and yH2 is the H2 molar fraction in the effluent gas. The Y absorption rate determined from variations of the H2 concentration with time is shown in Fig. 5 comparatively between the Y–H2 and Li–Y–H2 systems. As seen in the figure, the absorption rate of Y was almost unchanged regardless of the two different conditions of Y immersed in Li and Y under the Ar–H2 gaseous atmosphere. Thus, it was found that high H2 absorption capacity could be expected also in Y immersed in Li at temperatures higher than 673 K.
Fig. 6. (a) SEM photo of Y plate immersed in Li at 400 ◦ C for 50 days; (b) SEM photo of Y plate before hydrogen absorption.
M. Kinoshita et al. / Fusion Engineering and Design 81 (2006) 567–571
571
Table 1 Hydrogen absorption amount for Y and Li–Y–H2 system
Acknowledgement
Temperature (K)
Y–Li–H2 (mol H/mol Y)
Y–H2 (mol H/mol Y)
773 673 573
1.64 2.05 0.02
1.87 1.75 0.91
This work has been performed under the NIFS LHD coordinated research (contract number NIFS05KOBF010).
References There was no change at the interface. Therefore, there was very small corrosion action on Y surface. Table 1 shows comparison of the H2 amounts absorbed in Y between the Y–H2 and Li–Y–H2 systems. The H2 absorption amounts at 673 and 773 K were almost equal to the original H2 capacity of Y that is expected from the equilibrium pressure–composition isotherm [9]. This means that Y holds its original H2 absorption capacity even under the condition of Li immersion. However, Y under the immersion condition did not show sufficient hydrogen capacity at 573 K. This is because a Y oxide that was inevitably formed on surfaces was not activated sufficiently. We need to develop a better activation technique for Y if operation at 573 K or below is necessary.
5. Conclusions The recovery of H2 from liquid Li was experimentally investigated from 573 to 773 K. Strict handling under Ar atmosphere enabled Y to recover H2 from Li at 673 K with a sufficient rate. The Y plate showed sufficient H2 absorption performance on rate and capacity even at 673 K.
[1] H. Nakamura, M. Ida, M. Sugimoto, T. Yutani, H. Takeuichi, Removal and control of tritium in lithium target for international fusion materials irradiation facility (IFMIF), Fusion Sci. Technol. 41 (2002) 845–849. [2] S.D. Clinton, J.S. Watson, Tritium removal from liquid metals by sorption on yttrium, in: Proceedings of the Seventh Symposium on Engineering Problems of Fusion Research, IEEE Publication No. 77CH1267-4-NPS, 1979. [3] H. Moriyama, S. Tanaka, D.-K. Sze, J. Reimann, A. Terlain, Tritium recovery from liquid metals, Fusion Eng. Des. 28 (1995) 226–239. [4] E. Veleckis, E.H. Van Deventler, M. Blander, The lithium–lithium hydride system, J. Phys. Chem. 78 (1974) 1933–1940. [5] L.N. Yannopoulos, R.K. Edwards, P.G. Warlbeck, The thermodynamics of the yttrium–hydrogen systems, J. Phys. Chem. 69 (1965) 2510–2515. [6] S. Fukada, S. Kitajima, N. Mitsuishi, Effects of mass transfer resistances on hydrogen absorption in yttrium bed, J. Nucl. Sci. Technol. 25 (1988) 895–897. [7] S. Fukada, N. Mitsuishi, S. Kitajima, T. Nakahara, Absorption and desorption characteristics of hydrogen from inert gas mixtures in yttrium particle bed, Mem. Fac. Eng. Kyushu Univ. 48 (1988) 281–294. [8] S. Fukada, M. Nishikawa, Recovery of tritium from liquid lithium blanket of lithium, Li–Pb eutectic alloy or molten salt, Ann. Rep. Hydrogen Isotope Res. Cent. Toyama Univ. 14 (1994) 1–21. [9] G.M. Begun, J.F. Land, J.T. Bell, High temperature equilibrium measurements of the yttrium–hydrogen isotope (H2 , D2 , T2 ) systems, J. Chem. Phys. 72 (1980) 2959–2966.