mass loss of li2tio3 pebbles and li4sio4 pebbles
TRANSCRIPT
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Fusion Engineering and Design 88 (2013) 2202– 2205
Contents lists available at ScienceDirect
Fusion Engineering and Design
jo ur n al hom epa ge: www.elsev ier .com/ locate / fusengdes
ass loss of Li2TiO3 pebbles and Li4SiO4 pebbles
ideaki Kashimuraa,∗, Masabumi Nishikawaa, Kazunari Katayamaa,hohei Matsudaa, Motoki Shimozoria, Satoshi Fukadaa, Tsuyoshi Hoshinob
Interdisciplinary Graduate School of Engineering Science, Kyushu University, 6-10-1, Hakozaki, Higashi-ku, Fukuoka 812-8581, JapanBlanket Irradiation and Analysis Group, Fusion Research and Development Directorate, Japan Atomic Energy Agency, 2-166,aza-Obuchi-Aza-Omotedate, Rokkasho-mura, Kamikita-gun, Aomori 039-3212, Japan
r t i c l e i n f o
rticle history:eceived 9 September 2012eceived in revised form 9 May 2013ccepted 27 May 2013vailable online 5 July 2013
a b s t r a c t
It has been known that water vapor is released from ceramic breeder materials into the purge gasdue to desorption of adsorbed water under dry atmosphere and due to the water formation reactionunder hydrogen atmosphere. However, an effect of water vapor in the purge gas to Li mass loss has notbeen understood. In this study, mass loss of Li2TiO3 (NFI) and Li4SiO4 (FzK) under hydrogen atmosphere(1000 Pa H2/Ar), and mass loss of Li2TiO3 (NFI) and Li2TiO3 with additional Li which is in a developmentalstage (JAEA) under water vapor atmosphere (50 Pa H O/Ar) were compared, respectively. It was found
eywords:eramic breeder materiali2TiO3
i4SiO4
i mass loss
2
that under hydrogen atmosphere Li mass loss of Li4SiO4 and Li2TiO3 is same degree although the amountof water vapor released from Li4SiO4 is larger than that from Li2TiO3. It was clarified with regard to Li2TiO3
that Li mass loss in water vapor atmosphere is larger than that in hydrogen atmosphere. Mass loss ofLi2TiO3 with additional Li (JAEA) was larger than that of Li2TiO3 (NFI). It was observed by X-ray analysis
n the
ritiumurface waterthat Li deposits formed o
. Introduction
The present authors have made out the tritium release model toepresent the release behavior of bred tritium from ceramic breederaterials (Li2TiO3, Li4SiO4, Li2ZrO3, LiAlO2, and Li2O) [1,2]. Tri-
ium release curves estimated by the tritium release model gaveood agreement with experimental curves for the ceramic breederaterials under various purge gas conditions [3]. Fig. 1 shows the
ritium release model constructed by the blanket group of Kyushuniversity. This model takes into account tritium diffusion in areeder grain, tritium transfer to surface water at interfacial layer,nd surface reactions on grain surface as adsorption/desorption ofhysisorbed and chemisorbed water, isotopic exchange reactionith hydrogen in purge gas (isotope exchange reaction 1), isotopic
xchange reaction with water vapor in purge gas (isotope exchangeeaction 2), and water formation reaction of hydrogen in purge gasith oxygen in the ceramic breeder material.
The tritium release behavior from the ceramic breeder mate-ials packed in the blanket module under ITER-like operationalondition is estimated based on the tritium release model using
arameters obtained in our studies [2]. It is assumed in this estima-ion that purge gas is He mixed with 100 Pa H2 and that physisorbedater is removed completely before operation. The operational∗ Corresponding author. Tel.: +81 92 583 7607.E-mail addresses: [email protected],
[email protected] (H. Kashimura).
920-3796/$ – see front matter © 2013 Elsevier B.V. All rights reserved.ttp://dx.doi.org/10.1016/j.fusengdes.2013.05.098
inner wall of the quartz tube contain Li2SiO3.© 2013 Elsevier B.V. All rights reserved.
condition of ITER is repetition of a burning time of 400 s withdwell time of 1400 s. This model is one of the ITER test blan-ket module suggested by JAEA (Japan Atomic Energy Agency) [4].Fig. 2 shows the tritium release behavior from Li4SiO4 (FzK: For-shungszentrum Kahlsruhe) under the operational condition of ITERthat was numerically calculated based on Kyushu University’s tri-tium release model. It was estimated that the partial pressure ofwater vapor in gas phase was 100 Pa at the maximum and it iskept for about 25 h (50 shots). This water vapor not only affectsthe chemical form of the released tritium but also promotes theLi mass transfer from ceramic breeder materials due to chemi-cal reaction. A certain amount of Li is evaporated when ceramicbreeder materials are placed at high temperature conditions. Ifnon-negligible Li transfer is caused, it would possibly lead to seri-ous issues such as stuffing and erosion of pipes, and compositionchanges of ceramic breeder materials. However, Li mass transferfrom Li2TiO3 pebbles and Li4SiO4 pebbles has not been understoodenough although weight change and vaporization characteristic ofthe powder of crushed Li2TiO3 pellet has been investigated partly[5]. In this study, we investigated the changes in the Li mass lossof Li2TiO3 (NFI: Nuclear Fuel Industry), Li2TiO3 with additional Li(JAEA), and Li4SiO4 (FzK) at elevated temperatures in hydrogen orwater vapor atmosphere, and compared them.
2. Experimental
Li2TiO3 pebbles from NFI, Li2TiO3 with additional Li pebbles,2.06 in Li/Ti ratio, from JAEA, and Li4SiO4 pebbles from FzK were
H. Kashimura et al. / Fusion Engineering and Design 88 (2013) 2202– 2205 2203
Fig. 1. The tritium release model from ceramic breeder materials.
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Fig. 2. Simulation of tritium release behavior from Li4SiO4.
sed. Li2TiO3 (NFI) is the first candidate material in JAEA, andi2TiO3 with additional Li is in developing stage in JAEA as andvanced tritium breeder material for DEMO blanket. Li4SiO4 (FzK)s now the first candidate in Europa. The sample pebbles of 0.5 g
ere packed in a quartz tube, 4 mm in inner diameter, and 36 mmong for Li2TiO3 (NFI) and 29 mm for Li2TiO3 with additional LiJAEA), and 28 mm for Li4SiO4 (FzK) in bed length. Fig. 3 shows aEM (Scanning Electron Microscope) picture inside a Li4SiO4 (FzK)
Fig. 3. The SEM picture of Li4SiO4 pebble (FzK).
Fig. 4. The schematic diagram of the experiment.
pebble. It was recognized from SEM observation that the graindiameter of Li2TiO3 is 5 �m for NFI, 30 �m for JAEA, and that ofLi4SiO4 is 1 �m for FzK. Each pebble diameter is 2 mm, 1 mm, and0.1 mm, respectively.
Fig. 4 shows the schematic diagram of the experimental appara-tus in this work. The detail around the sample bed and experimentalprocedures were reported in the previous paper [6]. After thedesorption of physisorbed water from the sample pebbles by intro-duction of Ar gas at room temperature, the gas was changed to theone containing hydrogen, or water vapor, and the sample bed washeated to 900 ◦C with a ramp rate of 5 ◦C/min, and the tempera-ture was held. 1000 Pa H2/Ar gas was used for Li4SiO4 (FzK), and50 Pa H2O/Ar gas was used for Li2TiO3 (NFI, JAEA). 50 Pa H2O/Argas was generated from 50 PaH2/Ar gas by using CuO bed heatedat 350 ◦C. The water vapor concentration in the outlet gas of thesample bed was measured with a hygrometer (MAH-50, SHIMAZUCo.). The weight changes of sample pebbles were measured beforeand after the experiment. It is considered that the weight loss ofsample pebbles is caused by desorption of adsorbed water vapor,release of Li-containing species, and disassociation of oxygen withwater formation reaction. In this study, the rest weight subtractedby total weight of released water vapor and oxygen from the weightloss of sample pebbles is calls as Li mass loss.
3. Results and discussion
Fig. 5 shows the concentration of water vapor at outlet of thesample bed of Li2TiO3 (JAEA) [6]. It is observed that when dry
0 1 2 3 4 5 60
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Fig. 5. Example of the water release curve from Li2TiO3 (JAEA).
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0 10 20 30 40 50
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Purge gas: 1,000PaH2/Ar gas
flo w r ate 400cc /min
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weight of sample Li ma ss los sLi
2TiO
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weight of sample Li ma ss los s
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0 10 20 30 40 50 60 70 800.93
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Li2TiO
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Li2TiO
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flow ra te 400cc /mi n
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(JAEA).Fig. 9 shows a result of XRD (X-ray diffraction) for the white
turbidity part of the quartz used for Li2TiO3 (JAEA) after 75 h experi-ment under water vapor atmosphere at 900 ◦C. The diffraction peak
ig. 6. Result of the experiment to the weight changes of sample and mass loss ofi in hydrogen atmosphere.
2 gas is introduced, physisorbed water can be released at roomemperature and chemisorbed water is almost removed by ele-ating the temperature to about 500 ◦C. On the other hand, when000 Pa H2/N2 gas was introduced to sample bed, the same ten-ency with dry gas conditions was observed till below 500 ◦C,ut some release peaks were observed at higher temperatures.his water vapor was released due to water formation reactionetween H2 and oxygen in the sample. There are two peaks inhe release of chemisorbed water and in the release of generatedater, respectively. It is supposed that there are two kinds of ener-
ies required for water desorption and water formation reaction,espectively. The estimated formula of amount of chemisorbedater and amount of water formation reaction about Li2TiO3 (NFI,
AEA) has been reported by the present authors in [4,6]. Bred tritiumhich diffuses in the bulk of grain reacts with this surface water
nd released as HTO from the surface of the grain at the initial stagef operating a fusion reactor.
Fig. 6 shows the comparison of the weight change and Li massoss of Li4SiO4 (FzK) and Li2TiO3 (NFI). The result for Li2TiO3NFI), and Li2TiO3 (JAEA) under hydrogen atmosphere have beenescribed by the authors in [7]. It was observed that the weight lossf Li4SiO4 was mainly caused by release of adsorbed water and oxy-en which reaction leads to the water formation reaction, and themount of the Li mass loss was small. It was also turned out that thei mass loss of Li4SiO4 was smaller than that of Li2TiO3 although themounts of released adsorbed water and oxygen are larger than thatf Li2TiO3. The small variation was arisen in the data of weight lossf Li4SiO4 was caused because the amount of released physisorbedater changed in each experiment. Although it has been known
hat Li4SiO4 pebble melts easily by the reaction with water, thei mass loss was relatively small in this experimental condition. Its considered that the time when the sample bed was exposed to
ater vapor in purge gas is short, and the reaction rate of Li4SiO4ith water vapor may be smaller than that of Li2TiO3. In the near
uture Li mass loss of Li4SiO4 in water vapor atmosphere will benvestigated. It will be also necessary to do experiment of Li massoss of Li4SiO4 for a long exposing time under high temperatures.
Fig. 7 shows the weight changes of sample pebbles and the Liass loss at 900 ◦C under the water vapor condition (50 Pa H2O/Ar).
n the case of Li2TiO3 (NFI), the weight loss of sample pebbles isbout 1.0 wt%, the Li mass loss is about 0.7 wt% at 27 h. The Li massoss seems to be progressing slowly. On the other hand, for Li2TiO3JAEA), the weight loss of sample pebbles is over 5.0 wt%, Li mass
oss is about 4.0 wt% at 75 h, and the Li mass loss still continuesbviously. In this experiment, a huge mass loss in Li2TiO3 (JAEA)as observed compared with Li2TiO3 (NFI). It is considered by theresent authors that the amount of released water is different byFig. 7. Result of the experiment to the weight changes of sample pebbles and massloss of Li in water vapor atmosphere.
manufacturing method for sample pebbles. The behavior of Li massloss may also vary by the manufacturing process. There is a possi-bility that Li addition enhances the reactivity of the pebbles withwater vapor. Further investigation is necessary to clarify the causeof Li mass loss. For Li2TiO3 (NFI), the weight loss of sample peb-bles and the mass loss of Li are almost the same between hydrogenatmosphere and water vapor atmosphere in this work. Li2TiO3 (NFI)pebbles are made of Li2O and TiO2 (Li/Ti = 1.0) in sintering pro-cess [8], and if the sample pebbles are under saturated condition,the amount of Li mass loss may not so huge even in water vaporatmosphere.
Fig. 8 shows the picture of the quartz tube after 75 h experi-ment (Li2TiO3 (JAEA)) in water vapor atmosphere. White turbidityis formed on the inner wall of the quartz tube. It is speculated that Lireacted with the water vapor on the surface of the breeder materialand is vaporized as LiOH, and then deposited. For Li2TiO3 (NFI), thewhite turbidity formed only around the wall of the sample bed, butfor Li2TiO3 (JAEA), the one is formed on the wall around the samplebed and the wide region of downstream. In the previous study [7],it has been observed that the Li compounds also stain on the wallof the quartz tube after 53 h experiment in hydrogen atmospherefor Li2TiO3 (JAEA), but it was not as much as this. In this picture, wecan also visually clarify that the Li mass loss is promoted in watervapor atmosphere compared with hydrogen atmosphere in Li2TiO3
Fig. 8. Picture of the quarts tube after experiment under water vapor atmosphere.
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Fig. 9. Result of XRD analysis for the quartz wall of sample bed.
or Li2SiO3 was observed. This indicates that some amounts of Lieposited on the wall of the quartz tube reacted with SiO2 chemi-ally. In this work, it is not clear quantitatively where the Li releasedorm the sample bed goes to. In a blanket module of a fusion reac-or, if a large amount of Li adheres to the inner wall and transferso the downstream as shown in Fig. 8, it will cause serious issuesuch as reduction of available Li for the reaction with neutron andormation of clog in piping system.
. Conclusions
In water vapor atmosphere, the amount of Li mass loss is largerhan that in hydrogen atmosphere for Li2TiO3. For Li2TiO3 (NFI),
[
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the Li mass loss is about 0.5 wt%, and about 0.7 wt% in water vaporatmosphere after 27 h. For Li2TiO3 (JAEA), the Li mass loss is about1.0 wt% in hydrogen atmosphere after 50 h, and about 4.0 wt% inwater vapor atmosphere after 75 h.
The Li mass loss was relatively small although Li4SiO4 is knownas a ceramic breeder material which melts easily by the reactionwith water. The weight loss Li4SiO4 was mainly caused by releaseof adsorbed water and oxygen which reacts due to water formationreaction.
It is observed that the surface of the quartz tube after experimentunder hydrogen or water vapor atmosphere is stained by Li due tothe release from sample pebbles. It was found by X-ray analysisthat Li deposits formed on the inner wall of the quartz tube containLi2SiO3.
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