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

Improvement
Improvement ofof Hydrogen
Hydrogen Isotope
Isotope Release
Release on
on Lithium
Lithium Orthosilicate
Orthosilicate Ceramic
Ceramic
PebblePebble by
by Catalytic
Catalytic Metals
MetalsabaaaChengjianRENa, Xiaoling GAO a, Xiaojun CHEN a,
Chengjian XIAOXIAO a,, Chunmei
Chunmei KANG
KANG b,, Xingbi
XingbiREN,
Xiaoling
GAO,
Xiaojun
CHEN
,
a
c, *
Heyi
WANG
a, Xiaolin WANG c, *Heyi WANG , Xiaolin WANG
aaInstitute of Nuclear Physics and Chemistry, CAEP, Box 919-214, Mianyang, Sichuan 621900, P. R. China

Institute of Nuclear Physics and Chemistry, CAEP, Box 919-214, Mianyang, Sichuan 621900, P. R. ChinabbScience and Technology Information Center, CAEP, Box 919-803, Mianyang, Sichuan 621900, P. R. China

Science and Technology Information Center, CAEP, Box 919-803, Mianyang, Sichuan 621900, P. R. ChinaccChina Academy of Engineering Physics, Box 919-214, Mianyang, Sichuan 621900, P. R. China
China Academy of Engineering Physics, Box 919-214, Mianyang, Sichuan 621900, P. R. China(Received: 9 May 2012 / Accepted: 26 October 2012)
Lithium Orthosilicate (Li4SiO4) ceramic pebble is considered as a candidate tritium breeding material of Chinese helium cooled
Lithium Orthosilicate (Li4SiO4) ceramic pebble is considered as a candidate tritium breeding material of Chinese helium cooledsolid breeder test blanket module㸦CH HCSB TBM㸧for the International Thermonuclear Experimental Reactor (ITER). In this paper,
solid breeder test blanket module㸦CH HCSB TBM㸧for the International Thermonuclear Experimental Reactor (ITER). In this paper,
Li4SiO4 ceramic pebbles deposited with catalytic metals, including Pt, Pd, Ru and Ir, were prepared by wet impregnation method. The
Li4SiO4 ceramic pebbles deposited with catalytic metals, including Pt, Pd, Ru and Ir, were prepared by wet impregnation method. The
metal particles on Li4SiO4 pebble exhibit a good promotion of hydrogen isotope exchange reactions in H2-D2O gas system, withmetal particles on Li4SiO4 pebble exhibit a good promotion of hydrogen isotope exchange reactions in H2-D2O gas system, withconversion equilibrium temperature reduction of 200í300 qC. The out-of-pile tritium release experiments were performed using 1.0
conversion equilibrium temperature reduction of 200í300 qC. The out-of-pile tritium release experiments were performed using 1.0
wt% Pt/Li4SiO4 and Li4SiO4 pebbles irradiated in a thermal neutron reactor. The results showed that Pt was effective to increase the
wt% Pt/Li4SiO4 and Li4SiO4 pebbles irradiated in a thermal neutron reactor. The results showed that Pt was effective to increase thetritium release rate at lower temperatures, and the ratio of tritium molecule (HT) to tritiated water (HTO) of 1.0 wt% Pt/Li4SiO4 wastritium release rate at lower temperatures, and the ratio of tritium molecule (HT) to tritiated water (HTO) of 1.0 wt% Pt/Li4SiO4 wasmuch more than that of Li4SiO4, which released mainly with HTO. Thus, catalytic metals deposited on Li4SiO4 pebble may help tomuch more than that of Li4SiO4, which released mainly with HTO. Thus, catalytic metals deposited on Li4SiO4 pebble may help toaccelerate the recovery of bred tritium particularly in low temperature region, and increase the tritium molecule form released from theaccelerate the recovery of bred tritium particularly in low temperature region, and increase the tritium molecule form released from thetritium breeding materials.
tritium breeding materials.

Keywords: Lithium Orthosilicate (Li4SiO4); Hydrogen Isotope Exchange Reaction; Catalytic Metal; Tritium
Keywords: Lithium Orthosilicate (Li4SiO4); Hydrogen Isotope Exchange Reaction; Catalytic Metal; Tritium

rate, it is difficult to reflect tritium diffusion in the bulk ofrate, it is difficult to reflect tritium diffusion in the bulk ofgrain. Then, platinum and palladium were tried to deposit
grain. Then, platinum and palladium were tried to depositon lithium-containing ceramics, and exhibited aon lithium-containing ceramics, and exhibited a
promotion of hydrogen isotope exchange reactions at low
promotion of hydrogen isotope exchange reactions at low
temperatures [6-9]. Considering the practical application
temperatures [6-9]. Considering the practical applicationof neutron activity materials in a fusion reactor, manyof neutron activity materials in a fusion reactor, many
problems need systematic study, such as comparison ofproblems need systematic study, such as comparison ofdifferent metals, the optimization of catalytic metal
different metals, the optimization of catalytic metal
content and catalyst poisoning.
content and catalyst poisoning.
Now, Li4SiO4 ceramic pebble is considered as aNow, Li4SiO4 ceramic pebble is considered as a
candidate tritium breeder of Chinese helium cooled solid
candidate tritium breeder of Chinese helium cooled solid
breeder test blanket module for the international
breeder test blanket module for the international
thermonuclear experimental reactor㸦ITER㸧[4]. In orderthermonuclear experimental reactor㸦ITER㸧[4]. In order
to investigate the energetic tritium moving mechanism in
to investigate the energetic tritium moving mechanism inthe crystal grain of Li4SiO4 ceramic pebble, study thethe crystal grain of Li4SiO4 ceramic pebble, study theisotope exchange reactions on the gas/solid interface of
isotope exchange reactions on the gas/solid interface ofthe pebble, and search some way to enhance the tritium
the pebble, and search some way to enhance the tritium
release at low temperaure, it is necessary to investigate
release at low temperaure, it is necessary to investigate
the behavior of hydrogen isotope exchange influenced by
the behavior of hydrogen isotope exchange influenced bycatalytic active metal. In this work, Li4SiO4 ceramic
catalytic active metal. In this work, Li4SiO4 ceramic
pebbles deposited with four kinds of catalytic metals, Pt,
pebbles deposited with four kinds of catalytic metals, Pt,
Pd, Ru and Ir, were prepared. The effects of different Pt
Pd, Ru and Ir, were prepared. The effects of different Ptcontent and different metal role on the hydrogen isotope
content and different metal role on the hydrogen isotope
exchange reactions were examined in H2/D2O gas system.
exchange reactions were examined in H2/D2O gas system.
The tritium release behavior of the neutron-irradiated 1.0
The tritium release behavior of the neutron-irradiated 1.0
wt% Pt/Li4SiO4 and Li4SiO4 was compared through the
wt% Pt/Li4SiO4 and Li4SiO4 was compared through theout-of-pile tritium release experiments.
out-of-pile tritium release experiments.

1. Introduction
1. Introduction

Lithium-containing ceramics㸪such as Li2O, LiAlO2,
Lithium-containing ceramics㸪such as Li2O, LiAlO2,
Li2ZrO3, Li2TiO3 and Li4SiO4㸪are considered as tritium
Li2ZrO3, Li2TiO3 and Li4SiO4㸪are considered as tritium
breeding materials for securing an adequate tritium
breeding materials for securing an adequate tritium
supply to sustain the D-T fusion reaction in a fusion
supply to sustain the D-T fusion reaction
in a fusion
reactor [1-4]. Tritium is produced via 66Li(n,D)T in thereactor [1-4]. Tritium is produced via Li(n,D)T in thelithium ceramic pebbles, and extracted by a helium sweep
lithium ceramic pebbles, and extracted by a helium sweepgas with a fraction of hydrogen or deuterium from thegas with a fraction of hydrogen or deuterium from thesurface of the pebbles. Considering the reduction for thesurface of the pebbles. Considering the reduction for the
residence time of tritium in the breeder blankets, the bred
residence time of tritium in the breeder blankets, the bred
tritium must be carried out with a fast recovery rate overtritium must be carried out with a fast recovery rate overa broad range of temperatures, so some means shall bea broad range of temperatures, so some means shall be
developed to accelerate the tritium release rate.
developed to accelerate the tritium release rate.
The mass transfer mechanism of tritium released from
The mass transfer mechanism of tritium released fromlithium-containing ceramics is complicated, but it islithium-containing ceramics is complicated, but it isdeveloped and assumed commonly that tritium is bred indeveloped and assumed commonly that tritium is bred ingrain interior, diffuses to the surface layer, and thengrain interior, diffuses to the surface layer, and thentransfer to the surface water layer which consists oftransfer to the surface water layer which consists ofphysical, chemical and structural adsorbed water. Finally,physical, chemical and structural adsorbed water. Finally,
tritium at the surface water discharges to the purge gas
tritium at the surface water discharges to the purge gas
through such surface reactions as desorption, isotope
through such surface reactions as desorption, isotope
exchange reactions between hydrogen and water vapor in
exchange reactions between hydrogen and water vapor inpurge gas [5]. However, the isotope exchange reactions atpurge gas [5]. However, the isotope exchange reactions at
the interface between solid surface and sweep gas are
the interface between solid surface and sweep gas arevery slow at low temperature, only fast at relatively
very slow at low temperature, only fast at relatively
elevated temperatures (>700 qC) [6, 7]. When isotope
elevated temperatures (>700 qC) [6, 7]. When isotope
exchange reactions contribute strongly to tritium releaseexchange reactions contribute strongly to tritium releaseauthor’s e-mail: xiaocj@hotmail.com
author’s e-mail: xiaocj@hotmail.com

1©2013 by The Japan Society of Plasma
Science and Nuclear Fusion Research

C. Xiao et al., Improvement of Hydrogen Isotope Release on Lithium Orthosilicate Ceramic Pebble by Catalytic Metals

2. Experimental

the experiments were conducted under steady state
conditions at ambient atmosphere pressure. The
experimental conditions and the expeimental flow chart
for hydrogen isotope exchange reactions are shown in
Table1 and Fig.1 respectively.

2.1 Preparation of Sample
Li4SiO4 ceramic pebbles were fabricated byfreeze-sintering process[10]. The preparation processincluded mixing Li4SiO4 powder, polyvinylalcohol
solution and antifoam agent, dropping the preparedmixture into liquid nitrogen through a nozzle to generate
spheres, freeze-drying the spheres in a freeze dry system,
and calcinating the spheres programedly to get ceramic
pebbles.
Li4SiO4 ceramic pebbles (av. 0.9 mm in diameter)
were selected to be deposited with noble metals by wet
impregnation method. The pebbles were dried in a
vacuum drier at 150qC for 3h. Then the metal-containing
solution, H2PtCl6, H2IrCl6, PdCl2 and RuCl3, was drippedon the pebbles respectively, and was adsorbed swiftly by
the pebbles. When the pebbles were saturated with thesolution, they were dried for 1-2 h by infrared ray. After
repeating the above steps until the pebbles had adsorbed apredetermined content, they were transferred to deoxidize
in a 5 vol% H2/N2 mixture gas at 400-450 oC for 3h.
Finally Li4SiO4 ceramic pebbles with catalyst wereobtained.

Fig.1 Experimental flow chart for hydrogen isotope
exchange reactions
2.4 Tritium Thermal Desorption
Li4SiO4 and 1.0 wt% Pt/Li4SiO4 ceramic pebbles,
which had been dried at 150 oC for 2 h in vacuum, weresealed in quartz capsules with He gas less than 10 Pa.
Then the encapsulated samples were irradiated in areactor with a neutron flux of 7.1×1012 cm-2s-1 for 100min
at ambient temperature (29-36 oC). Tritium was producedby thermal neutron capture of lithium via the reaction of
6
Li(n, Į)T. After irradiation, the samples were placed atroom temperature for two years. The quartz capsules
were broken in a glove bag filled with He gas. Somepebbles about 0.01-0.02 g were transferred into a reactor
tube made of quartz for tritium thermal desorption, andthe others were removed into a small test tube which wasstored in a desiccator for stand-by.

2.2 Physical Characterization
Powder X-ray diffraction (XRD) patterns of 1.0 wt%
Pt/Li4SiO4 were determined on a DX-2600SSC
diffractometer (Cu KD radiation at 40 kV and 30 mA) at ascanning speed of 1.2o miní1 from 15 o to 95 o. Pt particle
size was analyzed by Philips- CM30 transmission
electron microscope at an acceleration voltage of 200 kV.
Pt particles more than 100 were chosen randomly to test
the metal particle size by Photoshop CS2 software.
Table1 Experimental conditions

2.3 Hydrogen Isotope Exchange Reactions
The samples were dried at 150 oC for 2h in a vacuum
drier, and then installed in a settled reactor (I = 8 mm)
made of stainless steel. A mixture gas of 1.08 % H2/He
and 1.12 vol% D2O/He was introduced into the reactor.
The concentration of D2O was controlled by D2/He gas
passing through a CuO bed of 350 oC. The deuterium
concentration of HD in the outlet stream was measured
by gas chromatogram (Agilent 6890N). 601 column wasused as the column material. The HD peak could beobtained depending on the thermal conductivity
coefficient when hydrogen was used as a carrier gas. All

Fig.2 Experimental flow chart for tritium release
Tritium release experiments were performed byapplying the out-of-pile temperature programmed
desorption technique. The flow chart of the experimental
system is shown in Fig.2.The reactor tube was heated in a
tube furnace at a heating rate of 5 oC min-1 from room
temperature to 800 oC, while a purge gas of He containing
1vol% H2 carried the released tritium (HT and HTO)
through the experimental system at a flow rate of 50 ml
22

C. Xiao et al., Improvement of Hydrogen Isotope Release on Lithium Orthosilicate Ceramic Pebble by Catalytic Metals

min-1. The first ionization chamber measured total tritium
released from the ceramic pebbles, the second ionizationchamber measured tritium released as HT. The amount oftritium in the bubblers, which were used to adsorb HTO(T2O) with glycol solution as adsorbent, was measured byliquid scintillation counting. Details of the experiments
were cited in the previous literature[11,12].

3.Results and Discussions
3.1 Preparation of Sample
As the data shown in Table 2, Li4SiO4 ceramic
pebble fabricated by freeze-sintering process has good
sphericity, high density and material phase purity .

Fig.5 TEM micrograph of 1.0 wt% Pt/Li4SiO4 pebble

Table 2 Characteristics of Li4SiO4 ceramic pebble
Distribution( %)

40
30
20
10
0

0

2

4

6
8 10 12
Particle size( nm)14

16

Fig.6 Distribution of Pt particles on the surface of 1.0 wt%
Pt/Li4SiO4 pebble

impregnation method. When the catalytic metals were
deposited on Li4SiO4, the surface color changed fromwhite to greyδ0.1 wt% Ptε, brown (0.5 wt% Pt) or blackδ1.0 wt% Ptε as shown in Fig.3. It is determined by
X-ray diffraction that Pt particles on the pebble surface
belong to face centered cubic structure with the
crystalline planes of Pt (1 1 1) and Pt (2 0 0) in Fig.4.
TEM analysis in Fig.5 shows that the agglomeration of Pt
particles is obvious, but the maximal size of Pt particles isless than 20 nm as shown in Fig.6. The mean size of Pt
particles is 6.7 nm.

Fig.3 Appearance of 1.0 wt% Pt/Li4SiO4 pebble

3.2 Isotope Exchange Reactions on pebble
The mixture gas of H2, D2O and He was feeded into
the reaction bed, D2O was adsorbed on the grain surfaceof the sample, and then the isotope exchange reactions
took place over the grain surface between the adsorbed
D2O and H2 in the gas. The exchange reactions on thebasis of the simplified model were expressed as
D2O(s) + H2(g) я HD (g) + HDO(s)HDO(s) + H2(g) я HD (g) + H2O(s)Fig.4 XRD patterns of Li4SiO4 and 1.0 wt% Pt/Li4SiO4

0.1í1.0 wt% Pt/Li4SiO4 and 0.1 wt% M/Li4SiO4 (M=Pd, Ru, Ir) ceramic pebbles were obtained by the wet

was
3
3

(1)
(2)

The deuterium concentration in the outlet stream
measured with gas chromatogram, and the

C. Xiao et al., Improvement of Hydrogen Isotope Release on Lithium Orthosilicate Ceramic Pebble by Catalytic Metals

influence the enhancement of the isotope exchange
reactions. The conversion ratio of 0.1 wt% Pt/Li4SiO4reached equilibrium after 350 oC, and that of 0.5-1.0 wt%
Pt/Li4SiO4 reached around 300 oC. It indicates that more
content of Pt on the pebble surface would provide more
active adsorption localities, and the lower equilibrium
temperature for the isotope exchange reaction would beobtained. However, the efficiency of noble metals of thesurface should depend on the surface coverage for the
samples having different specific surface area. Y. Narisato
and K. Mochizuki reported that the better content rangeof Pd on lithium ceramic pebbles was 0.15-1.6 wt% or
0.02-0.2 wt% [5, 13].
Pd, Ru, and Ir were also deposited on Li4SiO4respectively, and exhibited to enhance the isotope
exchange reactions as shown in Fig.9. It is suggested thatmany catalytic metals could be used to promote hydrogenisotope exchange reactions on Li4SiO4 ceramic pebble.

conversion of D-atoms for the isotope exchange reaction
was defined as the formula (3) , where CD,out was theconcentration of HD in the outlet stream, and CD,in was
the concentration of D-atoms in the inlet stream.

RCDˈoutCDˈin(3)

Fig.7. Conversion ratio of hydrogen isotope exchange reactions

With respect to the virgin Li4SiO4, the rate of theisotope exchange reaction taking place on the surface wasquite slow, and the conversion ratio reached equilibrium
above 650 oC. However, the conversion ratio of 1.0 wt%
Pt/Li4SiO4 ceramic pebble increased rapidly between 200o
C and 300 oC, and reached equilibrium above 300 oC.
The experimental curves in Fig.7 indicate that theconversion equilibrium temperature decreased about 300o
C if 1.0 wt% Pt was deposited on the surface.
Catalytic metal deposited on Li4SiO4 ceramic pebbles
would provide active adsorption sites for H2 in the gas,and had a tendency to decompose H2(ads) into H(ads).
The H(ads) atom had higher reactivity and quicker
transfer capability, so the activation energy for theexchange reaction was reduced, and it’s easy to occur
hydrogen isotope exchange between the H(ads) atom andD2O molecule adsorbed on the surface of ceramic pebbles[6-9]. The hydrogen isotope exchange reaction process
may be expressed as follows.

Fig.8. Conversion ratio of isotope exchange reactions on
Pt/Li4SiO4 pebble

According to the thermodynamic functions,hydrogen isn’t adsorbed on catalytic active metal surface
in intact molecule, and it combines with metal atoms insingle atom [13, 14]. Water vapor molecule exists inintact molecule on Pt surface, but has a tendency to bedissociated to OH(ads) and H(ads) on Ir or Ru surface. So
there were different hydrogen isotope exchanging
processes on the surface of M/Li4SiO4 pebbles. It
indicates that if Pt or Pd with rational intermingles of Ru,
Ir or Fe, deposited on Li4SiO4 pebbles together, would
incease the catalytic activity. In that case, the amount of
the noble metal could be reduced in the tritium breeder
materials.

H2 (g) + 2M (s) я 2M-H (s)(5)
M-H(s) + D2O(ads) я M-H(D2O) я M-D(HDO) я
M-D(s) + HDO(ads)(6)
M-H(s) + M-D(s) я 2M(s) + HD(g)(7), where M(s) is the catalytic metal deposited on solid
surface.
To investigate the catalytic effect depended on
different metal content, the Li4SiO4 ceramic pebbles were
deposited with 0.1 wt%, 0.5 wt% and 1.0 wt% content of
Pt respectively. According to the experimental results
shown in Fig.8, the content of Pt on the surface could

3.3 Tritium Thermal Desorption
Fig.10 and 11 present the tritium release behavior ofneutron-irradiated Li4SiO4 and 1.0 wt% Pt/Li4SiO4pebbles under the 1.0 vol% H2/He purge gas flow. After
44

C. Xiao et al., Improvement of Hydrogen Isotope Release on Lithium Orthosilicate Ceramic Pebble by Catalytic Metals

Fig.9. Fig.9.
Conversion
Conversion
ratio ofratio
isotopeof isotope
exchangeexchange
reactions onreactions
on4SiO
M/Li
M/Li
4SiO4 pebble
4 pebbleFig.10 Tritium release of neutron-irradiated Li4SiO4 pebble

the specimens were swept by pure He gas to wipe off thetritium adsorbed physically on the pebble, the purge gas
was changed to 1.0 vol% H2/He, and then the reactor tube
was heated at a rate of 5 oC /min. The blue curve
represents the total tritium concentration denoted as
HT&HTO released from the pebbles, and the red curve
represents the molecular form of tritium denoted as HT.
Fig. 10 shows the tritium release curves of virgin
Li4SiO4. There are two large peaks of total tritium from
R.T to 800 oC. One peak, appeared at around 259 oC, andthe second one, relatively larger than the former,
appeared at 418 oC. It’s evidently that tritiated water,
denoted as HTO, is much more than HT in the annealingcourse, especially at low temperature less than 400 oC. As
shown in Table 3, the fraction of HTO was 96.2 % of thetotal tritium, but HT was 3.8 %. It indicated that tritium
was released mainly as the chemical form of tritiatedwater in the experimental conditions of this paper.
Fig.11 shows the tritium release curves of 1.0 wt%
Pt/Li4SiO4. There are two peaks for both the total tritium
and the tritium molecular form during the annealingcourse. With regard to the total tritium curve, the larger
peak was observed at 218 oC, and the smaller peak
appeared at 468 oC. It means that most of tritium wasreleased at lower temperature less than 400 oC. The
tritium release curve of HT had a similar shape as that of
the total tritium. Table 3 shows that the fraction of HTO
was 36.9 %, but HT was increased to 63.1%. The fractionof chemical forms was quite different from that of thevirgin Li4SiO4. It indicates that the tritium molecularform (HT) became the main component when noble
metal deposited on the surface of Li4SiO4.
To compare the tritium release amount of Li4SiO4
and 1.0 wt% Pt/Li4SiO4, 37.4% of the total amount oftritium was released at 350 °C for Li4SiO4, but 66.9% for
1.0 wt% Pt/Li4SiO4. The largest peak of total tritium was
at 418 °C for Li4SiO4, but 218 °C for 1.0 wt% Pt/Li4SiO4.
So the catalytic effect of Pt was evidently. Even at
temperature less than 200 °C, the tritium concentration in
the outlet stream of the reactor tube increased rapidly

Fig.11 Tritium release of neutron-irradiated 1.0 wt% Pt/Li4SiO4pebbleTable 3 Fraction of tritium released from samples

from 1.0 wt% Pt/Li4SiO4. It means that when catalytic
metal was deposited on the surface of Li4SiO4, thehydrogen isotope exchange reactions were enhanced
between H2 in the purge gas and tritium adsorbed on thesolid surface.
With regard to the tritium chemical form, 3.8 % of
the total tritium was released as HT from room
temperature to 800 °C for Li4SiO4, and a small peak ofHT appeared at 463 °C. However, the fraction of HT was
63.1 % for 1.0 wt% Pt/Li4SiO4 with only one large peakat 236°C. The HT curve strongly influenced the shape ofthe total tritium curve for 1.0 wt% Pt/Li4SiO4. It indicatedwhen 1.0 wt% Pt was deposited on Li4SiO4, the hydrogenisotope exchange reactions, expressed as (5)-(7),wereeasy to proceed at the temperatures less than 460 °C.
The isotope exchange reactions on 1.0 wt%

5C. Xiao et al., Improvement of Hydrogen Isotope Release on Lithium Orthosilicate Ceramic Pebble by Catalytic Metals

Acknowledgements

Pt/Li4SiO4 proceeded much faster than that on virgin
Li4SiO4 , and the chemical forms of the released tritiumchanged. It was attributed to the catalytic effect of noble
metal on the solid surface. Without the effect of catalyst,
the exchange reaction rates of (1) and (2) were far smaller
than the desorption rate or the rate of isotope exchange
reaction (8), then the conversion of tritium (HTO intoHT) was quite slow.

H2O(g) + HTO(s) я HTO(g) + H2O(s)This work is financially supported by theDevelopment Fund of China Academy of Engineering
Physics (2010B0301035) and the National Magnetic
Confinement Fusion Science Program (2010GB112004).

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㸦8㸧

With the help of catalyst, it’s easy to occur hydrogenisotopes exchanging between H(ads) atoms and T
adsorbed on the surface of ceramic pebbles at lower
temperature as the formula(6). As soon as T exchanged
with H(ads) and migrated to the active adsorption locality,
it would discharge quickly combined with anotherH(ads).
Considering the high neutron activity in practicalapplication, the content of noble metals should be
reduced on lithium ceramic pebble, and some new metal
with low neutron activity need to discover.

Conclusions

Wet impregnation method has been used to fabricate
Li4SiO4 ceramic pebbles deposited with catalytic active
metals including Pt, Pd, Ru and Ir.
Lithium orthosilicate pebble deposited with noble
metals exhibite a promotion of hydrogen isotope
exchange reactions in H2/D2O gas system. With respect tovirgin Li4SiO4, the rate of the isotope exchange reaction
taking place on the surface was quite slow, and theconversion ratio reached equilibrium after 650 oC.
However, the conversion ratio of M/Li4SiO4 wasincreased obviously from 200 oC and 300 oC. Morecontent of the catalytic metal provided more active
adsorption localities on the pebble, so the conversion
ratio of 0.1 wt% M/Li4SiO4 reached equilibrium after 350
oC, and that of 0.5-1 wt% M/Li4SiO4 reached equilibrium
after 300 oC.
Most tritium was released at lower temperaturesfrom neutron-irradiated 0.1 wt% Pt/Li4SiO4, and thechemical form of HT was increased remarkably
compared with that of Li4SiO4. The result indicates thatcatalytic metal deposited on Li4SiO4 ceramic pebble
could reduce activation energy, facilitate H-T(D) isotope
exchange reaction, and influence the tritium releasemechanism. Consequently, the deposition of catalytic
metal on Li4SiO4 is an effective way to promote thetritium release from the breeder materials, and is infavor of the design of tritium cycle system about
extracting, separating and purifying in a D-T fusion
reactor.

66