Developing a better ceramic breeder (Li-containing oxide) is a key challenge for realizing fuel-self-sufficient fusion reactors. Ceramic breeder pebbles of hyper-stoichiometric lithium metatitanate, ...Li2+x TiO3+y (Li/Ti > 2), have been developed for a demonstration fusion reactor as high Li density enhances fuel tritium production. Previous studies have reported that Li loss by vaporization at high temperatures was largely enhanced by the increase in Li/Ti ratio and environmental moisture concentration. Minimizing the Li loss is a key issue for sufficient tritium breeding and reduced corrosion of structural steel. However, a suitable environmental parameter for hyper-stoichiometric Li2+x TiO3+y pebbles has not yet been determined because of the unavailability of thermodynamic data. Herein, a solid/gas equilibria for Li2.12(2)TiO3+y was investigated by measuring vapor pressures using atmosphere controllable Knudsen cell high temperature mass spectrometry. The enhanced thermodynamic activities of Li and Li2O in Li2.12(2)TiO3+y in comparison with those in stoichiometric Li2TiO3 were obtained as functions of temperature and oxygen concentration. The equilibrium constants were used to achieve the optimum moisture concentration that can suppress the vapor reactions in a cylindrical breeding zone with inhomogeneous temperature distribution.
Chemical compatibility between ceramic breeder (Li4SiO4 + 20 mol% addition of Li2TiO3) and EUROFER97 steel was examined in this study. These materials were contacted and heated at 623, 823 and 1073 K ...under He + 0.1 vol.% H2 atmosphere for up to 12 weeks. Limited influence was found in the breeder specimens, although losses of the constituent elements appeared near the surface of the breeder pellets heated at 1073 K. For the EUROFER specimens with formation of a corrosion layer, element diffusivity was estimated based on diffusion kinetics. In the temperature range, effective diffusion coefficients of oxygen into EUROFER steel were in the range from 3.5 × 10−14 to 2.5 × 10−12 cm2/s and found to be faster than that of Li. The coefficients yielded an activation energy of 0.93 eV for oxygen diffusion into EUROFER steel and predicted the possible thickness of the corrosion layer after operational periods.
A large amount of Li‐containing ceramic breeder pebbles is packed in the solid breeding blanket of a nuclear fusion reactor. Several pebble fabrication technologies have been proposed in previous ...studies, including wet process, emulsion method, extrusion spheronization, additive manufacturing, and melt process. However, a simple, energy‐effective, and scalable fabrication technology remains to be developed for the automated mass production and reprocessing of used radioactive pebbles post‐operation. Selective laser melting potentially enables the quick and automated fabrication of breeder pebbles. Herein, we employ a high‐power density pulse laser to produce ceramic breeder pebbles. A pulsed YAG laser was irradiated over a lithium metatitanate (Li2TiO3) powder bed in air, and the corresponding temperature was monitored using fiber‐type infrared pyrometers. Spherical Li2TiO3 pebbles were successfully fabricated in a single step with an average diameter of 0.78 ± 0.13 μm and the sintering density of 87.4% ± 5.6% (input power: 7.9 J/pulse). The irradiated Li2TiO3 powder melted and turned spherical under surface tension and rapidly solidified, resulting in uniaxial fine grains and a decrease in the degree of long‐range cation ordering.
One‐step fabrication of Li2TiO3 pebble using pulsed YAG laser
Abstract
A large amount of Li‐containing ceramic breeder pebbles is packed in the solid breeding blanket of a nuclear fusion reactor. Several pebble fabrication technologies have been proposed in ...previous studies, including wet process, emulsion method, extrusion spheronization, additive manufacturing, and melt process. However, a simple, energy‐effective, and scalable fabrication technology remains to be developed for the automated mass production and reprocessing of used radioactive pebbles post‐operation. Selective laser melting potentially enables the quick and automated fabrication of breeder pebbles. Herein, we employ a high‐power density pulse laser to produce ceramic breeder pebbles. A pulsed YAG laser was irradiated over a lithium metatitanate (Li
2
TiO
3
) powder bed in air, and the corresponding temperature was monitored using fiber‐type infrared pyrometers. Spherical Li
2
TiO
3
pebbles were successfully fabricated in a single step with an average diameter of 0.78 ± 0.13 μm and the sintering density of 87.4% ± 5.6% (input power: 7.9 J/pulse). The irradiated Li
2
TiO
3
powder melted and turned spherical under surface tension and rapidly solidified, resulting in uniaxial fine grains and a decrease in the degree of long‐range cation ordering.
Lithium metal and lithium oxides are components of lithium–oxygen (Li–O2) batteries. To accurately identify Li compounds and understand the degradation mechanism, fundamental knowledge of the ...electron structures of constituent elements is vital. However, experimentally derived occupied states of Li have been missing due to the intrinsic difficulties in their detection. Herein, using soft X-ray emission spectroscopy, ultrahigh-energy-resolution spectra of Li–K were collected for three critical Li compounds: Li, Li2O2, and Li2O. Large chemical shifts to lower energies and peak broadening were observed in compound-specific Li–K and O–K spectra. Theoretical calculations confirm that these changes derive from the characteristic electronic configurations of 1s and 2p states with core-level shifts in Li+. The large chemical shift (∼4.6 eV) between the Li and Li2O peaks was utilized to visualize the chemical state mapping of the Li metal/oxide phase, facilitating the identification of chemical phases in Li compounds.
•An ultra-compact neutron source based on a fusion device for diverse applications.•Multistage feedthrough technique used to reduce system size and increase neutrons.•Feedback control algorithm ...developed and adapted to increase the system stability.•Feasibility study of neutron radiography using the system, results are promising.•Higher neutron yield, more applications expected, upon the prospective developments.
Our group is developing an ultra-compact neutron source based on inertial electrostatic confinement (IEC) fusion device for various applications at Kyoto University. This IEC device is configured from a titanium anode and a molybdenum cathode with diameters of 17 and 6 cm, respectively. A high-intensity neutron source operated in a stable pulse shape is mandatory to increase the system’s reliability. Applying a higher voltage is a straightforward way to increase the neutron yield from the system. However, a contradiction between the increase of the applied voltage and the reduction of the system size limits such a proposal. A three-stage feedthrough system is employed in the developed compact IEC to address this contradiction. A feedback control system was developed and applied to the input and output parameters, such as the applied voltage and the neutron yield, to increase its stability in long-term operation. Characterization of the developed system was performed by scanning the neutron yield as a function of applied voltage and cathode current. To date, a maximum neutron yield of 9.2 × 107n·s–1 at 6.4 kW (80 kV and 80 mA) has been obtained. A study of the feasibility of using the IEC system for neutron radiography was performed. Preliminary analysis of the resulting images showed there was good contrast between the sample and the background. The results suggest that optimization of the experimental parameters is needed to perform higher accuracy neutron radiography.
•Effect of water vapor on chemical compatibility between EUROFER and ceramic breeder was investigated.•H2O addition enhanced formation of corrosion layer on EUROFER plate and decomposition in ceramic ...breeder.•The double corrosion layer on EUROFER surface showed parabolic growth at all heating temperature.•A possible thickness of the corrosion layer after a 2-year use was predicted based on a diffusion-controlled model.
Effect of moisture in sweep gas on chemical compatibility between ceramic breeder (Li4SiO4 with 20 mol% of Li2TiO3) and EUROFER97 was examined in this study. These materials were contacted and heated at 623, 823, and 1073K for up to 12 weeks where the H2O concentrations of the outlet gas were 0.13-0.24 vol.%. In the two-phase breeder specimen, Li4SiO4 was preferably decomposed into Li2SiO3 with a possible formation of Li2O or LiOH depending on environmental condition. Formation of corrosion layers on the EUROFER specimen was enhanced in the wet condition, especially at the elevated temperatures of 823 and 1073K. Though these results showed parabolic growth rates, an extrapolation from data of the elevated temperatures to 623K was not feasible in the wet atmosphere, which could derive from the difference of the chemical form in the breeder specimen. Effective diffusion coefficient of oxygen into EUROFER at 623K was given to be 4.5×10−14cm2/s and a possible thickness of the corrosion layer after a 2-year use was predicted.
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•Beryllide block will be used as neutron multiplier in solid breeding blankets.•Be12Ti and Be12V showed anisotropic thermal expansion along the c axis direction.•αa/αc of Be12Ti and ...Be12V were 0.71 and 0.79 at 873 K.•The direction of anisotropy in Be12Ti was inconsistent with the prediction.•The beryllides showed good thermal compatibility with other blanket materials.
Be12Ti and Be12V are promising candidates for neutron multipliers in solid breeding blankets, which is used in a bulk form to achieve the fuel tritium self-sufficiency. Previously, significant anisotropic thermal expansions were predicted for Be12Ti and Be12V along different crystallographic axes using density functional theory (DFT) calculations. Nevertheless, empirical confirmation through experimental data on thermal expansion anisotropy remains lacking. In this study, the thermal expansion behaviors of these materials were experimentally investigated by using high-temperature X-ray diffraction. Diffraction data were collected temperatures up to 873 K under vacuum condition, and structural refinement was carried out by Le Bail analysis using a partial structure. The results demonstrate that these materials exhibit moderate anisotropic expansion along the c-axis direction, contrary to previous prediction for Be12Ti. The average thermal expansion coefficients were compared with those of ceramic breeder pebble beds and structural steel material to discuss thermo-mechanical compatibility in a breeding blanket.
•Fe-5Ti alloys (d = 100–125 µm) after nitrogen trapping in lithium were investigated.•Nitrogen is trapped on the surfaces of Fe-5Ti immediately in the immersion tests.•Nitrogen diffusion in Fe-5Ti is ...much faster than in titanium.
Liquid lithium, a candidate material for the target of International Fusion Material Irradiation Facility (IFMIF), easily contains nitrogen. Nitrogen in liquid lithium should be removed as it accelerates corrosion of tubing materials. Hot trapping by iron-titanium alloys is expected to be a practical method. In order to understand the characteristics of nitrogen trapping with iron-titanium alloys in liquid lithium, nitrogen distribution was observed by Soft X-ray Emission Spectroscopy (SXES). Samples of Fe-5Ti alloys were immersed for 9–256 h in liquid lithium which contains 1000 w-ppm of nitrogen at 823 K and studied by X-ray Powder diffraction and SXES. The results show that nitrogen is trapped mainly in the grain boundaries and on the surfaces of the Fe-5Ti alloys and diffuses in Fe-5Ti much faster than in pure titanium. In addition, it is assumed that the amount of nitrogen trapping by the surface of Fe-5Ti alloys does not depend on the immersion time.
The fabricated 1.55µm high power superluminescent light emitting diodes (SLEDs) with 115mW maximum output power and 3dB bandwidth of 50nm, using active multi-mode interferometer (MMI), showed high ...coupling efficiency of 66% into single-mode fiber, which resulted in maximum fiber-coupled power of 77mW.
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