J. Plasma Fusion Res. SERIES, Vol. 10 (2013)

Mass loss of Li2TiO3 pebbles in atmosphere containing hydrogen
Hideaki Kashimuraa,* , Masabumi Nishikawaa, Kazunari Katayamaa,Shohei Matsudaa, Satoshi Fukadaa, Tsuyoshi HoshinobaInterdisciplinary Graduate School of Engineering Science, Kyushu University, 6-10-1, Hakozaki, Higashi-ku, Fukuoka
812-8581, JapanbBlanket Irradiation and Analysis Group, Fusion Research and Development Directorate, Japan Atomic Energy Agency,
2-166, Oaza-Obuchi-Aza-Omotedate, Rokkasho-mura, Kamikita-gun, Aomori 039-3212, Japan.
(Received: 8 May 2012 / Accepted: 24 September 2012)

It has been found that water vapor is released from the ceramic b reeder materials into the purge gas due todesorption of adsorbed water and the water formation reaction, and affects the tritiu m release behavior. Additionally,
the release of water vapor possibly promotes the mass loss of Li fro m the ceramic breeder materials. In this study,
we investigated the changes in the mass of Li2 TiO3 (NFI, CEA) and Li2 TiO3 with additional Li (JA EA) at elevatedtemperatures. In hydrogen atmosphere (10,000 pp m H2 /Ar), the Li mass loss is close to be related to the amount ofadsorbed water and amount of water formation in each Li2 TiO3 , and the Li mass loss of Li2 TiO3 (CEA) is about
three times larger than that of the other Li2 TiO3 pebbles. It is considered that the chemical fo rm of released Li
different whether there is the adsorbed water and the water vapor by the water format ion reaction in the gas phaseor not.
Keywords: ceramic breeders, Li mass loss, surface water, water formation reaction, hydrogen atmosphere1. Introduction

The tritiu m release behavior fro m the ceramic b reeder
materials packed in the b lanket module under ITER-like
operational condition is estimated based on the tritium
release model using parameters obtained in our studies[2]. It is assumed in this estimation that purge gas is He
gas mixed with 100Pa H2 and that physisorbed water isremoved completely before operation. The operational
condition of ITER is repetition of a burning t ime o f 400
seconds with dwell t ime of 1400 seconds. This model
simp lifies the condition of the ITER test blanket modulesuggested by Japan Atomic Energy Agency (Fig. 2). Fig.
3 shows the tritiu m release behavior fro m Li2 TiO3 (NFI)
under the operational condition of ITER. It was estimatedthat the partial pressure of water vapor in gas phase wasabout 20Pa and it is kept for about 100hour. This watervapor affects the chemical form of the released trit iu m.
The reaction of released water vapor with the ceramic
breeder materials may pro mote the Li mass transfer.
When the ceramic breeder materials are p laced at h igh
temperature conditions, a certain amount of Li mayevaporate. If non-neglig ible Li transfer is caused, itwould possibly lead to serious issues such as stuffing anderosion of pipes, and drop o f TBR. However, the Li masstransfer in a packed bed of the ceramic breeder materials
has not been sufficiently understood to date. In thepresent study, we investigated the changes in the Li massloss of Li2 TiO3 (NFI, CEA), and Li2 TiO3 with additional
Li (JAEA ) at elevated temperatures in hydrogen
atmosphere, and compared them.

The present authors have developed an estimation modelto represent the tritiu m release behavior fro m ceramic
breeder materials, wh ich is valid for out-of-pile andin-pile conditions [1, 2]. Tritiu m release curves estimatedby the tritiu m release model gave good agreements withexperimental curves fro m the ceramic breeder materials
under various purge gas conditions [3]. Fig. 1 shows thetritiu m release model constructed by the present authors.
In the model, the trit iu m d iffusion in a breeder g rain,
tritiu m transfer to surface water at interfacial layer, andsurface reactions on grain surface as adsorption /desorption of physisorbed and chemisorbed water,
isotope exchange reaction with hydrogen in purge gas(isotope exchange reaction 1), isotope exchange reaction
with water vapor in purge gas (isotope exchange reaction2), and water formation react ion of hydrogen in purge gas
with oxygen in the material are taken into account.

Fig. 1 The tritium release model from ceramic breeder materials
kashimura@aees.kyushu-u.ac.jp

18©2013 by The Japan Society of Plasma
Science and Nuclear Fusion Research

H. Kashimura et al., Mass Loss of Li2TiO3 Pebbles in Atmosphere Containing Hydrogen

Fig. 2Fig. 3Fig. 4

The ITER-TBM type model

The simulation result of tritium and water release
curve under the operational condition of ITER

The SEM picture of as-received Li2TiO 3 (NFI)

Fig. 5 The SEM picture of as-received Li2 TiO3 (CEA)
was held. The water vapor concentration at outlet wasmeasured by a hygro meter (MAH-50, SHIMAZU Co.).
The weight changes of sample pebbles were measured
before and after the experiment. It is considered that theweight loss of sample pebbles is caused by desorption ofadsorbed water vapor, disassociation of oxygen withwater formation reaction and release of Li-containing
species. In this study, weights of released water vapor andoxygen are subtracted fro m the weight loss of sample
pebbles and the rest is defined as Li mass loss.

2. Experimental
In this experiment, Li2 TiO3 pebbles produced by Nuclear
Fuel Industry (NFI), Co mmissariat à l'énerg ie atomique(CEA ), and Li2 TiO3 with addit ional Li, 2.06 in Li/Ti ratio,
produced by Japan Atomic Energy Agency (JAEA) wereused. The Li2 TiO3 with additional Li is in developmental
stage in JA EA as an advanced tritiu m breeder material for
DEMO blanket. The samp le pebbles of 0.5 g were packedin a quart z tube, 4 mm in inner d iameter, and 36 mm longfor Li2 TiO3 (NFI) and 29 mm for Li2 TiO3 (CEA ), and29mm for Li2 TiO3 with additional Li (JA EA) in bed
length. Fig. 4, 5 shows a SEM p icture of the inside of
Li2 TiO3 (NFI) and Li2 TiO3 (CEA ) pebble. It wasestimated fro m SEM observation that the grain diameterof Li2 TiO3 is 5μm for NFI, 1μm for CEA, and 30μm forJAEA. Each pebble diameter is 2mm, 1mm, and 1mm,respectively. The details of the experimental procedures
were reported in the prev ious paper [4]. After thedesorption of physisorbed water from the sample pebbles
by introduction of H2 /Ar (1000PaH2 /Ar) gas at room
temperature, the sample bed was heated to 900 °C, or
600 °C with a ramp rate of 5 °C/min, and the temperature

3. Result and Discussion
Fig. 6 shows the concentration of water vapor at outlet ofthe quartz tube when Li2 TiO3 (NFI) sample bed was heatedwith a ramping rate of 5 °C/ min to 900 °C. It is observedthat when H2 /Ar gas is introduced, physisorbed water canbe released at room temperature and chemisorbed wateris almost removed by elevating temperature to about
400 °C. At over 500 °C, the water vapor is released by thewater formation reaction between H2 and oxygen in thematerial. The weight of chemisorbed water and o xygen
are obtained to be 6.52×10-3 g  and 1.55×10-3 g  onaverage.

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H. Kashimura et al., Mass Loss of Li2TiO3 Pebbles in Atmosphere Containing Hydrogen

but we use Li2 TiO3 (CEA) which surface area is smaller
than that of Li2 TiO3 (NFI) in this experiment, the Li massloss of Li2 TiO3 (CEA) is promoted. Fig. 8 shows therelationship between the amount of released water and theLi mass loss. In this figure, the Li mass loss of Li2 TiO3(CEA) is three times larger than that of the others , and theamount of released water of Li2 TiO3 (CEA) is also about
three times larger. It is suggested that the Li mass loss is
closely associated with the amount of released water fromthe sample pebbles. The water formation reaction is
promoted at high temperatures in hydrogen atmosphere.
Therefore it is predicted that the amount of Li mass loss inhydrogen atmosphere is larger than that in dry gas
condition, but it is not carried out yet.
Fig. 6Fig. 7

Example of the water release curve from Li2TiO3 (NFI)

Result of the experiment to the weight changes ofsample and mass loss of Li at 900 °C

Fig. 8Fig. 7 shows the weight changes of sample pebbles andthe Li mass loss. In the case of Li2 TiO3 (NFI), the weightloss of sample pebbles is about 1.0 wt% and the Li massloss is about 0.7wt% after 50hours. The weight of sample
seems to be almost steady after 24hours. For the data ofLi2 TiO3 (CEA), a huge mass loss is observed after 8hours.
After 50hours, the weight loss of samp le pebbles is about
4.0 wt% and the Li mass loss is about 3.0 wt%. In thecase of Li2 TiO3 with additional Li, the weight loss ofsample pebbles is 2.0 wt%, and the Li mass loss is about
1.0 wt% after 50hours. It seems that the Li mass loss stillcontinues.
The Li mass loss per gram of Li2 TiO3 (CEA) is about
three times larger than those of Li2 TiO3 (NFI) and Li2 TiO3with additional Li. It is considered that the amount of Li
mass loss is related to the difference of surface area and theamount of released water. It is found by the present authorsthat the amount of chemisorbed water per surface area ofLi2 TiO3 (NFI) are about twice larger than that of Li2 TiO3(CEA) and, the amount of generated water per surface areaof Li2 TiO3 (CEA) and that of Li2 TiO3 (NFI) are almost
same. Therefore it is considered that the Li mass loss ofLi2 TiO3 (NFI) is promoted by the release of water vapor,

Fig. 9Comparison between the amount of released water andthe amount of the Li mass loss

Result of the experiment to the weight changes ofsample pebbles and mass loss of Li at 600 °C

Fig. 9 shows the weight changes of sample pebbles when
Li2 TiO3 with additional Li were heated to 600 °C. In thisfigure, the weight loss of the sample pebbles is 1.0 wt%,
and the Li mass loss is 0.5 wt% after 50hours. It is about
one-half of the Li mass loss at 900 °C. In the previous
studies, it has been found that the amount of generated
water by the water format ion reaction at 600 °C is smaller

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H. Kashimura et al., Mass Loss of Li2TiO3 Pebbles in Atmosphere Containing Hydrogenthan that at 900 °C for Li2 TiO3 [5,10]. Therefore it can besaid that the Li mass loss at 600 °C is s maller than that at900 °C because the release of Li by the reaction withgenerated water at 600 °C is smaller. The weight ofsample pebbles seems to be almost steady after 40 hours.
We are also considering that the amount of released
water is associated with the method of Li2 TiO3manufacturing. By the present authors, Li2 TiO3 (NFI) is
made by the wet process, and Li2 TiO3 (CEA) is made by
the extrusion-spheronization-sintering process. [6, 7] It isconsidered that the amount of released water is related towhether water is used or not in manufacturing process.

It is obtained that the Li mass loss of Li2 TiO3 withadditional Li (JAEA) at 600 °C is half t imes larger thanthat of Li2 TiO3 with additional Li at 900 °C. It is supposedthat the rate of water formation velocity is lo w at 600 °C,
and the amount of released water is less than that of900 °C.
In hydrogen atmosphere, the chemical form of released Liis different whether there is the adsorbed water and thewater vapor by the water formation reaction in the gas
phase or not. If there is the absorbed water and the watervapor by the water formation reaction in the gas phase, thechemical form of released Li is LiOH, and there is nowater vapor in the gas phase, Li could evaporate from thesurface of Li2 TiO3 .

References

Fig. 10[1] T. Kinjyo, et al., Fusion Eng. Des. 83, (2008) 580 587.
[2] T. Kinjyo, et al., J. Nucl. Mater. 367 - 370, (2007)
1361 - 1365.
[3] T. Kinjyo, et al., Fusion Eng. Des. 82, (2007) 15 - 24.
[4] M. Nishikawa et al., J. Nucl. Mater., 325, (2004) 87- 93.
[5] T. Hanada, et al., J. Nucl. Mater., 417, (2011) 735-738.
[6] K. Tsuchiya, et al., J. Nucl. Mater., 258-263, Part 2,(1998) 1985 - 1990.
[7] J. D. Lulewicz and N. Rou x, J. Nucl. Mater. 307-311,Part 1, (2002) 803-806.
[8] T. Hoshino, et al., Fusion Eng. Des. 81, (2006)
555-559.
[9] T. Kin jyo, et al., Fusion Eng. Des. 83, (2008)
580-587.
[10] K. Katayama, et al., Fusion Eng. Des. 87, (2012)927-931.

Picture of the quartz tube after the experimentFig. 10 shows the picture of quartz tubes when Li2 TiO3(NFI) was used for sample bed after experiment. In thispicture, the wall of the quartz tube after experiment isstained with the Li compounds. White turbidity is formed
around the sample bed and the downstream region wherethe temperature is lower than that at the sample bed. It is
speculated that Li reacts with the water vapor on thesurface of the breeder material and vaporized as LiOH, andthen deposits at lower temperature region. White turbidity
around the sample bed may be caused by just Li
evaporation. It has been observed by Hoshino et al. that Li
partial pressure is higher than LiOD partial pressure at hightemperature under D2 atmosphere [8]. When the sample
bed is held at high temperature for a long time andadsorbed water and the generated water by the water
formation reaction expended completely, and Li would
evaporate as Li atoms from the surface of the breeder
material slowly.

4. Conclusions
The Li mass loss of Li2 TiO3 in hydrogen atmosphere isclose to be related to the amount of adsorbed water andamount of water formation in each breeder material. The Limass loss of Li2 TiO3 (CEA) is about three times larger thanthat of Li2 TiO3 (NFI) or Li2 TiO3 with additional Li(JAEA).

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