No abstract available

[en] Active cooling components have to be employed in the divertor of a fusion reactor to handle the large power flow from the core plasma. The extremely large thermal stress and electromagnetic forces acting on these components may cause cracking of cooling pipe. Since the inner wall and the vacuum vessel are significantly damaged by this loss of coolant accident, LOCA, the control scheme have to be considered. The process of in-vessel LOCA was investigated, and then several control schemes such as the use of expansion volume, the use of shielding shutter and the use of heat sink were suggested. In addition, the pressure rise of the vacuum chamber due to water leak was calculated for the scheme to uses of the expansion volume and roughing pump systems by using the parameters of ITER/CDA. The pressure rise in the vacuum chamber can be controlled within designed pressure of chamber, e.g., 2 atm, when the pinhole diameter is less than 1 mm. When the expansion volume is assumed to be the same size as the chamber, the time period until the pressure increases up to 2 atm becomes 3 hr when the pinhole diameter is 10 mm. The pressure can be decreased to 0.2 atm by using a roughing pump system. (author)

[en] The hydrogen absorption and desorption properties of oxidized Ti-6Al-4V alloy were evaluated under a condition of a fusion reactor operation. When the hydrogen pressure and absorption temperature were kept 10 Pa and 673 K for 1 hr, respectively, the absorption amount of hydrogen decreased with increase of the surface oxidation of Ti-6Al-4V alloy. Also the peak temperature of hydrogen desorption shifted to higher temperature, as the increase of surface oxidation. In the alloy oxidized at 873 K, the absorption amount of hydrogen was 1/50 times smaller than that without oxidation, and the desorption temperature was approximately 200 K higher. When the oxide layer is thicker than 10 nm, the absorption amount of hydrogen can be sufficiently low if the hydrogen absorption temperature is kept below 773 K. (author)

[en] Hydrogen retention properties of Li, B, graphite, B₄C, SiC and W are described. The amount of hydrogen for Li, B, B₄C or SiC is comparable with that of graphite. To reduce the hydrogen retention, Li or B is baked at a temperature that is less than that required to reduce the retention of hydrogen in graphite (∼800degC). It is also presumed that the required temperature for reducing the hydrogen retention in W is much lower than that of graphite. Helium ion impact desorption for retained hydrogen in Li, graphite, B₄C, SiC or W is also presented. The reduction amount is as high as approximately 50% for every material, under the condition with 5 keV helium ion energy. (author)

[en] Excitaion temperature of helium atom in the vicinity of substrate in an ECR helium plasma was measured based on multi-thermal equilibrium (MTE). In the case of no substrate in the plasma, clear atomic line spectra of excited helium were not observed. The intensities of line spectra increased with the negative voltage biased at the substrate and the discharge pressure. The intensities were also strong at the position close to the substrate. From the Boltzmann plot, an excitation temperature of approximately 4000 K for helium atom was obtained. This temperature was a little higher in the case of lower pressure and farther from the substrate. (author)

[en] Hydrogen retention properties of Li were investigated using a dc glow discharge apparatus with a heater for Li evaporation. Hydrogen retention of Li after the evaporation was measured based upon a residual gas analysis, In addition, the recovery effects for hydrogen trapping of Li due to baking and He discharge cleaning were examined. The hydrogen gas pressure largely decreased in the initial discharge stage and then the decreasing ratio became small with the discharge time. The initial decrease is due to the trapping of H⁺ and the hydrogen concentration becomes approximately unity in atomic ratio, H/Li, in the ion implantation depth. The slow trapping is presumed to be the diffusion of H into the bulk of Li film. When the Li evaporation amount was small, both the decrease of hydrogen pressure and the desorption of H₂O were observed. Since the oxide, Li₂O, is partly formed, it is regarded that the reaction, Li₂O+2H₂→H₂O+2LiH, took place. After the hydrogen discharge for the Li film, the baking with 100 degC or He discharge cleaning was conducted, and followed by again the hydrogen discharge was made. Compared with the case of He discharge cleaning, the hydrogen trapping was largely recovered in the case of such the baking. (author)

[en] Coatings of TiC and TiC-TiN were prepared by a reactive RF sputtering on Mo and 304SS substrates. Depth profiling measurements of these coatings were carried out using AES and XPS with Ar ion sputter-etching. These coatings were heated under high vacuum at different temperatures by electron beams. When the TiC coating on the MO substrate was heated at 1100⁰C for 10 min, Mo diffused through the TiC layer and segregated at the surface. With TiC-TiN double layer coatings, diffusion of Mo atoms was not observed with this same heat treatment or even after 10 min at 1200⁰C. In the case of the 304SS substrates, a remarkable increase of nitrogen concentration and a decrease of carbon concentration in the TiC layer was observed after a heat treatment of the film for 30 min at 1000⁰C. Microhardnesses of these films were also measured as a function of heating temperature. (orig.)

[en] Short communication

[en] In nuclear fusion reactors, the high heat flux device consisting of the joined materials with forced cooling are installed in divertors, and heat and particles are controlled while the heat flux of several tens MW/m² is removed. As for high heat flux equipment, at the time of disruption, when excessive thermal load and electromagnetic force act, it is expected that cooling pipes break down, and loss of coolant accident (LOCA) occurs. LOCA can be classified into in-vessel LOCA and ex-vessel LOCA. LOCA is important for the evaluation of the safety, maintenance, repair and plasma discharge scenario. In the ITER/EDA, the evaluation of LOCA has begun. In this research, the breakdown and damage due to in-vessel LOCA and ex-vessel LOCA were examined, and the countermeasures to LOCA were investigated. The scenario of LOCA is explained. As the countermeasures, the detection of coolant leakage, the immediate stop of plasma discharge, the operation of the backup cooling system, and the stop of cooling water supply are necessary. As the active method for minimizing the effect of LOCA, an additional vacuum vessel for lowering pressure is installed under the divertor, and the divertor part, in which water leak occurred, is isolated by inserting a shutter from the main plasma discharge part. The most serious end of LOCA is the breakdown of the vessel by pressure rise, and the method of lowering pressure by expansion volume is important. (K.I.)

[en] Department of electron energy on electron stimulated desorption (ESD) yield of deuterium was investigated for various plasma facing materials. Signal intensities of D₂ and HD were detected at higher electron energy than 400 eV and 200 eV, respectively. A maximum of ESD yield was observed at around 800 eV. The maximum yields of HD and D₂ were approximately 0.03 HD/electron and 0.02 D₂/electron for a ferritic steel (F82H). Desorption of atomic hydrogen due to ESD was also detected. The dependence of electron energy on the ESD yield was almost the same in all material. (author)