30aB04
Li17Pb83中に生成したトリチウムのホットアトム反応によるLiTの形成
Formation of lithium-tritiate by hot atom reactions of tritium produced in Li17Pb83
1

奥野健二、1小林真、2山西敏行、1大矢恭久
Kenji Okuno, Makoto Kobayashi, 2Toshiyuki Yamanishi and 1Yasuhisa Oya
1

静大理放射研、2原子力機構
1
Shizuoka Univ. 2JAEA
literature values. The deuterium solubility wasalso determined as S = 6.56 x 10-7 exp(-0.11[eV] / kT) [at. fr, Pa0.5], from the results for
deuterium gas exposure experiments. An
additional tritium release stage was observed
around600K,forthethermal
neutron-irradiated alloy while no deuterium
release was found in the same temperature
region for the thermally doped alloy. The
amount of additional tritium release was about
5% of total tritium. From the kinetic analyses
for the additional release peak, the activationenergy of tritium release at 600 K wasdetermined to be about 1.4 eV, which is almost
consistent with the decomposition energy ofLiH, showing that LiT could be formed in theLi17Pb83 eutectic alloy by hot atom reactions oftritium produced by the nuclear reactions. It is,therefore, important to consider the possibilityof the formation of LiT to estimate tritium
inventories in Li17Pb83 blanket systems.
Especially, in the liquid state of Li17b83 under
the operation temperature, LiT would be themajor source of tritium retention in Li-Pbsystem and the tritium inventory would beunderestimated with regardless of the formationof LiT.
-1 -1

A blanket concept using lithium–lead(Li17Pb83) eutectic alloy is considered as one ofthe promising liquid state blanket systems forfusion reactors. The tritium inventory inLi17Pb83 eutectic alloy has been estimated to benegligibly small due to its low tritium solubility,
which was determined by thermal doping
methods. However, there could be a possibilityof LiT formation in the neutron-irradiated
Li17Pb83 alloy by a hot atom reaction of tritium,
resulting in enhancement of its tritium
inventory. There have been few reports about
the formation of LiT in neutron-irradiated
Li17Pb83 alloys. In the present study, thermal
neutron irradiation for the Li17Pb83 eutectic
alloy was carried out in the KUR reactor atKyoto University with the thermal neutron
fluence of 3.1 × 1015 n cm-2, and JRR-3 at
JAEA with the thermal neutron fluence of 3.3 ×
1016 n cm-2 at ambient temperature to produce
hot tritium into the alloy. The deuterium gas
exposure was also performed to introduce
deuterium under thermal-equilibrium. The
release behaviors of both hydrogen isotopes
were evaluated by Thermal Desorption
Spectroscopy (TDS) under the heating rate of 5
K/min. Comparing both the TDS results, thepossibility of hot atom reactions of tritium
produced in the Li17Pb83 eutectic alloy wasinvestigated.
Figure shows the TDS spectra of hydrogenisotopes for Li17Pb83 exposed to D2 gas orirradiated with thermal neutron. It wasobserved that a major release stage of hydrogenisotopes was appeared in the temperature
region just a little higher than the melting point(508 K) of the Li17Pb83 alloy. Major hydrogenisotope release was found to be governed bydiffusion process in the liquid phase of Li17Pb83.
The tritium and deuterium diffusion
coefficients agreed with each other and the1D2 exposure

10

Neutron irradiation (JRR-3)
Neutron irradiation (KUR)141

H isotope release rate / 10 s g

101010-110-2400500

600700Temperature/ KFig. TDS spectra of hydrogen isotopes released fromLi17Pb83 exposed to D2 gas or irradiated withthermal neutron