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[en] The existing state of hydrogen isotopes in lithium oxide (Li2O) was studied using Fourier transform infrared absorption spectroscopy (FT-IR). Infrared spectra in Li2O single crystals which were treated by thermal absorption and consequent quenching were observed from room temperature to 773 K. Multiple peaks were observed in the O-D stretching vibration region and these peaks had different dependence on temperature. These peaks were attributed to the stretching vibrations of O-D presenting as LiOD or Li2O-D+ in bulk Li2O with or without defects. Above 623 K, most of the deuterium ions in Li2O exist as Li2O-D+ and the infrared absorption peak for them was observed around 2520 cm-1. The absorbance decrease of this peak during the isothermal annealing was well analysed by a diffusion model. Diffusion behaviour of hydrogen isotopes in Li2O was discussed from the in-situ observation of O-D
[en] The interaction of hydrogen isotopes with defects in Li2O was studied by ab-initio quantum chemical calculations. Three kinds of F-centers and the lithium vacancy were considered. The relaxation of ions around the vacancy and the stable position of a proton were calculated when the vacancy was produced in the Li2O crystal. From the obtained energies and the electronic charge density maps for each configuration, the effects of the vacancies on the proton were discussed
[en] In order to clarify the existing states and the diffusion process of hydrogen isotopes in Li2O, the quantum chemical analysis has been conducted especially emphasising interaction with charged defects such as F-centers. Using two calculation codes based on different theories, treatment of charged defects was discussed. From the comparison with FT-IR or diffusion model studies, the interaction of hydrogen isotopes with defects was explained taking electron transfer between them into consideration
[en] The electronic states of Li2O were observed using ultraviolet photoelectron spectroscopy (UPS) and X-ray photoelectron spectroscopy (XPS). By exposing to the different pressures of H2O vapor, the peak attributed to the surface hydroxyl groups was observed. After exposing to the enough pressure to compose LiOH, an obvious change has not been observed in UPS spectra by the precision of the present study although the change was observed in XPS. The density of states (DOS) of Li2O was calculated using CASTEP code, and the obtained spectra were discussed using the results of the calculation
[en] The existing state of hydrogen isotopes in lithium oxide was studied using the Fourier transform infrared absorption spectroscopy. Infrared spectra in Li2O single crystals irradiated by 1 MeV deuteron were recorded. Multiple peaks were observed in the O-D stretching vibration region under or after the irradiation. These peaks were attributed to the stretching vibrations of O-D present as Li2O-D+ in bulk Li2O with defects. When the irradiated sample was annealed, a large peak attributed to the LiOD phase was observed. The present study shows that most of the implanted deuteron exists without O-D bonding in the bulk Li2O crystal
[en] The adsorption behavior of H2O on Li2O was studied by X-ray photo electron spectroscopy (XPS) and ultraviolet photo electron spectroscopy (UPS). XPS and UPS spectra of Li2O single crystals which were exposed to different pressure of H2O vapor were observed. In O(1s) region, two peaks were observed and they were assigned to O(1s) in precipitated LiOH on the surface and O(1s) in Li2O. After H2O exposure, a peak broadening and an appearance of a new peak were observed at the higher binding energy region than O(1s) in Li2O. They were attributed to surface -OH and H2O molecule adsorbed on the surface. The adsorption behavior of H2O was discussed from the observation of electronic structure in Li2O surface
[en] Highlights: • Structural responses on WCCB TBM under In-Box LOCA were evaluated. • Improvement of the TBM design was carried out based on the FEM analysis results. • Structural integrity of the TBM designs was evaluated according to ASME BPVC section III NB. • Filled region of the modified TBM design increased by up to 20% compared to the original model. • TBR of the modified TBM design increased by up to 12% compared to the original model. - Abstract: The Water Cooled Ceramic Breeder Test Blanket module (TBM) has been developed for a demonstration of the major functions under the fusion reactor environment in ITER. Testing of the TBM shall neither hinder the ITER operation, nor threaten safety of operation even at water ingress into a box structure of the TBM (In-Box Loss of Coolant Accident, In-Box LOCA). In present study, the structural responses on the TBM under In-Box LOCA were evaluated by using Finite Element Method. Based on the analysis results, the TBM design was modified. The filled region and Tritium Breeding Ratio of the modified TBM design adding the fillet with 35 mm of radius increased by up to 20%, 12%, respectively, compared to the original TBM model without fillet.
[en] Oxygen-related defect complexes are important intrinsic defects in AlN ceramics, and their dynamic behavior has a close relationship with physical properties at high temperature. Gamma-ray irradiation has a major effect on the electronic excitation of intrinsic defects. Hence, thermoluminescence measurements after irradiation by gamma-ray can show the dynamic behavior of intrinsic defects or oxygen-related defect complexes in AlN ceramics. By choosing different kinds of AlN ceramics, the basic types of oxygen-related defect complexes (VAl-ON-3N and VAl-2ON-2N) are reflected by studying the spectra of luminescence measurements in the present research. The results of a quantum chemistry simulation indicates that the stability of the VAl-2ON-2N defect system is higher than that of the VAl-ON-3N defect system, and the difference in total energy for two kinds of defects is 0.56 eV
[en] Highlights: • Shutdown dose rate was analyzed to consider a maintenance progress for DEMO by using MCNP-5 and DCHAIN-SP2001. • The dose rate of pipe cutting and re-welding points in the maintenance ports was as low as 0.01 Gy/h for blanket segment and 0.1 Gy/h for divertor cassette. • In terms of spatial dose rate, the maintenance scheme for ITER, such as pipe cutting and re-welding, is applicable also to DEMO. - Abstract: The shutdown dose rate at Japan’s demonstration nuclear fusion (DEMO) plant was analyzed using MCNP-5 and DCHAIN-SP2001 to assess its significance in the development of a maintenance program. It was assumed that the blanket segments were integrated with a shielding plug (SP) and replaced through vertical upper ports, whereas divertor cassettes, also integrated with the SP, were replaced through bottom ports. To minimize the dose rate, remote handling equipment should approach from behind the SP and be fixed with an attachment to it. The estimated dose rates during manifold cutting and rewelding in the maintenance ports were as low as 0.01 Gy/h for the blanket segment and 0.1 Gy/h for the divertor cassette. When the outboard blanket segments and divertor cassettes were removed along with the SP, a spatial dose rate of 100 Gy/h was found at the maintenance ports. The spatial dose rate of the in-vacuum vessel at ITER during maintenance using remote handling equipment is limited to 250 Gy/h. The study confirmed that a maintenance scheme involving pipe cutting or rewelding would be applicable to ITER at the estimated spatial dose rates.
[en] For application to bore welding of hydraulic connection in the ITER blanket module, laser welding presents the following benefits: low weld heat input is preferred for re-welding of the irradiated material. Its contactless process can intrinsically avoid a failure mode of the tool sticking on the weld. The exact requirements for pipe alignment were assessed in comparison with the assembly tolerance. The groove geometry was modified to expand the allowable initial gap. The groove was machined to be partially thick to obviate the filler wire. First, plates with partially thick grooves were welded to elucidate the preferred groove geometry and welding conditions. With the modified groove, the plates were welded for the initial gap of 1.0 mm. Then the groove geometry and welding conditions were adjusted based on results of pipe welding tests. By application of the additional 0.5-mm-thick and 2.5-mm-wide metal in the groove, pipes with an initial gap of 0.7 mm were welded successfully.