Kuniaki WATANABE, Kenji ICHIMURA, Masao MATSUYAMA
Tritium Research Center, Toyama University,Gofuku 3190, Toyama 930, JAPAN
(Received December 25, 1985)

Abstract
In D-T fusion experiments, secondary multipliers will be widely used as detectors for plasma diagnostics and mass spectrometers for fuel analysis and vacuum measurement. However, as significant impairment of the multiplier performance is predicted owing to the β-rays from tritium adsorbed on the detector surface (contamination), in-situ decontamination technique are, therefore, required. On reviewing the contamination effect on the performance of the secondary electron multipliers and decontamination techniques, it is indicated that the adsorption of tritiated water vapor is more serious than tritium gas. In principle, the tritium contamination could be removed by vacuum heating but it is a time consuming technique. Since photon irradiation is more effective in the decontamination than vacuum heating, it is proposed as an in-situ decontamination method. It is pointed out, however, that more extensive studies are required to understand the decontamination and/or signal discrimination techniques.

Kenji ICHIMURA, Naoya INOUE^*, Kuniaki WATANABE, Ikuya MATSUURA
Tritium Research Center, Toyama University,Faculty of Science, Toyama UniversityGofuku 3190, Toyama 930, JAPAN
^*Present Address: Aloka Co. Ltd.,Mure 6-22-11, Mitaka, Tokyo 181
(Received December 25, 1985)

Abstract
The recovery of tritium from tritiated water is important for the safe handling of a large amount of tritium required in thermonuclear fusion devices and heavy water moderated fission reactors. Among a variety of techniques, photocatalytic decomposition of water is attractive because tritium in tritiated water is enriched here by use of the solar energy. From this viewpoint, the kinetics and separation factors for hydrogen evolution from H₂O-HTO and H₂O-D₂O systems over Pt/TiO₂ catalyst were investigated.
  The separation factors defined with the initial reaction rate were α_Ro (H₂O-D₂O)=5.1±0.05 and β_Ro (H₂O-HTO)=15.4±0.2. They were independent of the mixing ratio of the isotope waters but gradually decreased to steady values when a closed experimental system was used. The separation factors defined with the steady state were αe(H₂O-HDO)=3.6±0.05, αe(D₂O-HDO)=3.0±0.05, and βe(H₂O-HTO)=6.2±0.05. In addition, hydrogen evolution was found to be considerably enhanced by the synergistic effect of β-rays and photons.
  The separation factors, α_Ro and β_Ro, agreed with those predicted by theoretical calculation for catalytic model in electrolysis indicating that the rate determining step is the association reaction of hydrogen atoms absorbed on Pt surface. The separation factors, αe and βe, agreed with those for the gas-liquid equilibration reaction indicating that the equilibration reaction plays a role.

Kan ASHIDA, Kuniaki WATANABE^*
Radio-isotope Lab., Toyama University
^*Tritium Research Center, Toyama University
Gofuku 3190, Toyama 930, JAPAN
(Received December 25, 1985)

Abstract

To evaluate the recycling and inventory of tritium in the first wall for thermonuclear fusion devices, detailed investigation is required regarding the trapping and release of tritium in first wall materials. Among a variety of materials, graphite is the primary candidate for the first wall. In this respect, the thermal desorption spectra of hydrogen isotopes trapped in graphite was measurement and analyzed. The thermal desorption spectra consisting of three peaks (Ⅰ,Ⅱ, and Ⅲ) were deconvoluted into individual components with stepwise detrapping method. It is shown that the desorption of hydrogen isotopes forming the Ⅱ obeyed the second order kinetics with respect to the amount of trapped isotope atoms, indicating that the rate determining step for desorption is the recombination reaction of the trapped isotope atoms. The kinetic parameters were determined as

k_Ⅱ(H₂)=(7.5x10^-4)exp (-59x10³/RT)

k_Ⅱ(D₂)=(2.4x10^-4)exp (-59x10³/RT)

where the frequency factor and activation energy are in [molec・sec] and [cal/mol] unit, respectively. The activation energy for desorption of T₂ was the same as that for the other two isotopes. The frequency factor for T₂, however, considerably deviated from those for the other two. This is considered due to the present of impurity gases in the tritium gas used in the present study.

WATANABE, Kan ASHIDA^*
Tritium Research Center, Toyama University
^*Radio-isotope Labs., Toyama University
Gofuku 3190, Toyama 930, JAPAN
(Received December 25, 1985)

Abstract
Kinetics and mechanisms were studied for the thermal release of hydrogen isotopes implanted into pyrolytic graphite. The kinetic measurements were carried out with mass analyzed thermal desorption spectroscopy. The desorption spectra consisted of three peaks, Ⅰ, Ⅱ, and Ⅲ. The peak Ⅰ obeyed the second order kinetics regarding the amount of trapped hydrogen isotope atoms. The recombination factors averaged over the sub-surface layer were determined as

k_r(H₂)=(13.0x10^-19)exp(-44.0x10³/RT) [cm⁴/sec・molec]

k_r(D₂)=(7.18x10^-19)exp(-44.0x10³/RT)

k_r(T₂)=(5.26x10^-19)exp(-44.0x10³/RT)

The pseudo surface recombination factors were also determined as

k_s K² (H₂)=(4.68x10^-19)exp(-44.0x10³/RT) [cm²/sec・molec]

k_s K² (D₂)=(2.58x10^-19)exp(-44.0x10³/RT)

k_s K² (T₂)=(1.89x10^-19)exp(-44.0x10³/RT)

 

　It was concluded that the rate determining step for desorption forming the peak Ⅰ was the surface recombination reaction of hydrogen isotope atoms trapped on the normal graphite lattice of the basal plane.

Hitoshi MIYAKE, Masao MATSUYAMA, Kuniaki WATANABE
Tritium Research Center, Toyama University, Gofuku 3190, Toyama 930, JAPAN
(Received December 25, 1985)

Abstract
　Permeation and solution of tritium through/in organic polymers are important problems for applying these materials to tritium handling systems. In this connection, the solution and diffusion of tritium in several polymers were studied by means of time-lag method and considerable abnormal behavior for tritium permeation though polycarbonate film was observed. The causes of this abnormality were investigated by measuring diffusivity and solubility of tritium under various experimental conditions. It was observed that the solubility and diffusivity and hence permeability of tritium was significantly affected by the presence of residual solvent originating from the manufacturing processes. In addition, the residual solvent enhanced the solution of isobutene contained in counting gas when the permeation was measured by β-ray counting method using G-M counter. Both the residual solvent and dissolved isobutene disturbed the diffusion of tritium. The latter, however, significantly impaired the diffusion of tritium. When the residual solvent was removed from the film in vacuum and the permeation was measured by quadrupole mass spectrometer, the abnormality disappeared and normal isotope effect was observed. The extent of isotope effect, however, differed from that of the classical rate law prediction.

Masao MATSUYAMA, Kenji ICHIMURA, Kuniaki WATANABE, Kazuma KATO^*,Hiroshi MAEKAWA^*, Hiroo SATO^*

Tritium Research Center, Toyama University,Gofuku 3190, Toyama 930, JAPAN
^*Research and Development Laboratory, Aloka Co. Ltd.,Mure 6-22-1, Mitaka, Tokyo 181, JAPAN
(Received December 25, 1985)

Abstract
The adsorption of tritium on material surface causes significant contamination of tritium handling systems, β-ray counting devices and parts contained in them. Therefore, it is necessary to establish effective decontamination techniques or develop materials free from contamination. From this viewpoint, the decontamination of a gold-plated ionization chamber was studied in which tritiated water was adsorbed by photon irradiation in order to establish an in-situ decontamination technique.
  It was observed that photon irradiation enhanced the desorption of tritiated water. The extent of the enhancement was larger in deuterium lamp illumination than halogen lamp illumination. The photon irradiation in various atmospheres such as room air, argon and moistened argon gave no appreciable differentce in the decontamination effect, indicating that the enhanced desorption of tritiated water was not due to the interaction between adsorbed tritiated water and ions produced in the phase but caused by photodesorption of tritiated water. It was concluded that the irradiation of photons in the ultraviolet region was applicable as the in-situ decontamination technique to devices such as ionization chamber where materials with low thermal stability are used.

Isao KANESAKA, Kiyoyasu KAWAI, Kenji ICHIMURA^*, Kuniaki WATANABE^*

Faculty of Science, Toyama University
^*Tritium Research Center, Toyama University
Gofuku 3190, Toyama 930, JAPAN
(Received December 25, 1985)

Abstract

The absorption coefficient, ε, of HDO was reported for two bands and compared with those of T₂O and D₂O (Ichimura et al., Nuclear Instr. Methods Phys. Res., A241, (1985), 614). It is noted that ε of some bands is important for determination from view point that ε depends on temperature. The additional values of ε are tabulated for T₂O. The useful bands for determination of T₂O, D₂O and HDO are discussed on the basis of assignments.

Takeyoshi ASANO, Reiko KIRITANI, Tetsuro KAWANISHI^*

Radiation Center of Osaka Prefecture,Shinke-cho, Sakai, Osaka, JAPAN
^*Kinki University, Department of Agriculture,Kowakae, Higashiosaka, Osaka, JAPAN
Gofuku 3190, Toyama 930, JAPAN
(Received December 25, 1985)

Abstract

The radioactivity of spot doubly labeled ³H- and ¹⁴C- compound on a thin layer chromatograph plate was measured with a radiochromatogram spark chamber. The results were compared with those obtained from a radio thin layer chromatograph and an autoradiograph. For the radiochromatogram spark chamber, the lower limits on detectable intensity of ³H- and ¹⁴C-radioactivities were 1000 dpm and 100 dpm, respectively. Accordingly, it was found that more than 10⁵ dpm of radioactivity was required for the detection of the doubly labeled compound，which has a ¹⁴C/³H radioactivity ratio of 1/490 on this instrument. Further, it was revealed that the amount of radioactiveity of tritium and carbon-14 could be estimated from the brightness of spark images.