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Understanding the permeation behavior of tritium from a pebble bed breeding blanket is essential for establishing a self-sufficient fuel cycle in a nuclear fusion reactor. It is known that double corrosion layers forms on reduced activation ferritic-martensitic (RAFM) steel surface by gas release from a ceramic breeder material, however, its effect on hydrogen permeation behavior has not been elucidated. Herein, in-situ measurement of hydrogen permeation through an F82H RAFM wall of a ceramic breeder pebble bed was performed under H₂-added sweep gas conditions. The corrosion layer formed on the F82H sample had a dense microstructure, which reduced hydrogen permeation flux at least by one order of magnitude. The permeation reduction factors were 20–50 at the water-coolant temperature of a blanket. A self-repairing ability is expected for the surface oxide layer as the corrosion occurs spontaneously inside a breeding blanket.

A discharge-type fusion neutron source generates neutrons by fusion reactions of hydrogen isotope atoms. In order to operate the fusion device based on the deuterium–tritium (D–T) fusion reaction, the tritium inventory is required to be decreased. In the present work, a self-sufficient system was installed into the fusion device for reducing the amount of hydrogen isotope fuel gas. The fuel gas was supplied and recovered with an intermetallic compound ZrCo in a sealed chamber in this system. A deuterium–deuterium operation was maintained for more than 60 min with stable discharge voltages, and the temperature of the ZrCo bed was changed to improve the neutron production rate. Factors that influenced the pressure inside the chamber were determined and optimized. Gas analysis using a quadrupole mass spectrometer indicates a dilution of the deuterium fuel was caused by hydrogen isotope exchange between the supplied deuterium gas and the absorbed protium on the chamber and electrodes surface. This system's hydrogen isotope control method and the amount of fuel were proposed for a D–T operation.

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...

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 elect...

The use of an electronic descriptor is a high-throughput approach for predicting the chemical reactivities of various materials that has the potential to significantly facilitate the material design of Be intermetallic neutron multipliers for nuclear fusion applications. However, electronic descriptors for Be intermetallics with the desired properties, including radiation tolerance and reduced hydrogen retention, have been poorly understood. Herein, we perform first-principles calculations on 42 existing binary Be intermetallics to find an effective electronic descriptor. We demonstrate that the occupied Be p band center relative to the Fermi level is a bulk descriptor, correlating with the Be vacancy formation energy; a positive and linear correlation with a coefficient of determination R² = 0.85 was observed for Be₁₂X (X: transition metal). The upward shift in energy of the occupied Be p states with early or middle transition metals can reduce hydrogen solution energy, which could be attributed to the less filled anti-bonding state of interstitial hydrogen atom. It is confirmed that the bulk descriptor is an experimentally measurable scale, having the strong linearity (R² = 0.97) with the calculated; therefore, it can accelerate the material development of beryllium intermetallic neutron multipliers., 軽元素材料の特性を予測する電子的記述子を発見 --情報駆動型の材料開発に道筋--. 京都大学プレスリリース. 2022-10-21.

Since the low-carbon technology fusion energy is scheduled to be commercialized beyond 2050, the late-mover needs to flexibly and strategically operate for sustainable cash flow responding to the future market mechanism. Carbon sequestration of the fusion–biomass hybrid system by using low-temperature heat is proposed under the two preconditions: the establishment of the deregulated electricity market, and the emission trading market. When the price is above the breakeven price, the hybrid system generates electricity; otherwise, charcoal production is performed. Charcoal production is a stable solid form of carbon capture, and can possibly be traded on the emission credit market to secure profit. The experimental result shows that it is possible to produce charcoal at low temperature of 280 °C, indicating that any type of blanket design is applicable in the hybrid system concept. The carbon sequestration cost is 39 $/tCO2 at the default parameter of net electric output of 4000 $/kWe for the fusion power plant, and 60% of charcoal yield from experimental result. Comparison between the hybrid system and the fusion power plant proves that the fusion–biomass hybrid system prevents further loss, by setting two-track income structures in the various market mechanisms.

This paper aims to make an investigation on economic analysis of fusion-biomass hybrid system for clean fuel production. A blanket concept with lithium lead (LiPb) and silicon carbide (SiC) technology such as dual coolant lithium lead (DCLL) is capable of delivering over 600 °C of high temperature heat for endothermic gasification reaction. This technical extension enables to produce syngasane gas which converts into either artificial diesel by Fischer-Tropsch reaction or hydrogen by water-gas shift reaction. An experiment has been perform to learn the mass loss and endothermic heat of biomass in the high temperature condition. With the experimental result, levelized cost of fuel (LCOF) was calculated 0.46 $/liter (9.2 $/GJ) for diesel and 1.05 $/kg (8.7 $/GJ) for hydrogen. Also further economic analysis of internal rate of return and discounted payback period was demonstrated for the feasibility of the future deployment.

Tritium breeding ratio (TBR) is one of the most important parameters determining the tritium self-sufficiency of a deuterium-tritium fusion reactor. A neutronics experiment is planned to measure the spectral neutron fluences two-dimensionally (2D) using a discharge-type compact fusion neutron source and a neutron imaging plate (NIP), respectively. We report a calibration method for the NIP and optimization of the discharge condition to enhance the neutron production rate. A linear relationship between the neutron fluence in the NIP and photostimulated luminescence (PSL) per area was obtained in the range of the neutron fluence from 103 to 107 n/cm2. A neutron production rate higher than 107 n/s was successfully achieved by the optimized discharge condition. It is shown that a quantitative 2D measurement by the NIP is feasible using the linear relationship and a correlation coefficient on the energy spectrum.

Monoclinic lithium metatitanate, β-Li2TiO3, is a member of the Li2MO3 (M = Ti, Mn, Sn, Ru, and/or Ir) series and an important cation conductor for various energy applications such as Li-ion batteri...

Be-rich intermetallics (beryllides) have gathered wide attentions to be adopted for high temperature environments, such as an advanced neutron multiplier in fusion reactors. This study reveals the ...

We report a neutronics study of a blanket mock-up using a discharge-type compact fusion neutron source. Deuterium–deuterium fusion neutrons were irradiated to the mock-ups composed of tritium breeder and neutron reflector/moderator. The tritium production rate (TPR) per source neutron was measured by a single-crystal diamond detector with a 6Li-enriched lithium fluoride film convertor after the calibration process. Despite the low neutron yield, energetic alpha and triton particles via 6Li(n, t)α neutron capture as well as 12C via elastic scattering were successfully detected by the SDD with high signal to noise ratios. The TPRs were experimentally evaluated with errors of 8.4%–8.5% at the 1σ level at the positions with high thermal neutron fluxes where the errors were dominantly introduced by uncertainties in the monitoring of the neutron production rate. The calculated to experimental (C/E) values of TPR were evaluated to be 0.91–1.27 (FENDL-2.1) and 0.94–1.28 (FENDL-3.1). As the neutron source can generate 14 MeV neutrons using a mixed gas of deuterium and tritium, this approach provides more opportunities for blanket neutronics experiments.

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.

Chemical compatibility between ceramic breeder (Li 4 SiO 4 + 20 mol% addition of Li 2 TiO 3 ) 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.% H 2 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 cm 2 /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.

Wet-chemical fabrication processes are highly adaptable to a wide range of raw materials and are therefore well suited for evaluating new material compositions. Here the established emulsion method was modified to fabricate novel two-phase Li 4 SiO 4 pebbles of 1 mm diameter with additions of Li 2 TiO 3 , LiAlO 2 or Li x La y TiO 3 . As the lithium density of the latter two compounds is relatively low, only moderate contents were added. The Li 2 TiO 3 additions, however, cover the full compositional range. The fabrication process was characterized with regard to its constancy and aptness for the anticipated pebble compositions by optical pebble size measurements. Also the phase content and the elemental composition of the fabricated pebbles were analyzed by XRD and ICP-OES combined with XRF, respectively. This work shows that the emulsion method is an appropriate method to produce pebbles with the anticipated Li 2 TiO 3 and LiAlO 2 concentrations in a Li 4 SiO 4 matrix. However, Li 4 SiO 4 and Li x La y TiO 3 react with each other to a number of different phases. To evaluate the activation properties of the pebbles, FISPACT calculations with a DEMO relevant neutron source are applied as well. The addition of aluminum seems to be unfavorable for a fusion application, but moderate concentrations of lanthanum can be tolerated.

Measuring methods of spatial neutron distribution have been required for the evaluation of TBR inside the blanket. In this paper, neutron transport inside a blanket mock-up, mainly assembled by beryllium neutron multiplying layers and lithium breeding layers, was simulated for measurements of the neutron energy spectrum and the spatial distribution with activation analyses using activation foils and an imaging plate. Transport of deuterium-tritium (DT) fusion reaction neutrons were simulated by MCNP6 and activation calculations were performed by DCHAIN. These results of neutron transport indicate that activation foils were reacted to neutrons with specific energies; dysprosium for thermal, manganese with cadmium for epi-thermal and niobium or cobalt for fast neutrons. The results of activation calculations indicate each activity of activation foils inside the blanket, which proposes the exposure conditions for measurements using imaging plate.

Reduced activation ferritic/martensitic steel F82H samples with tritium permeation barriers were annealed in contact with ceramic breeder pebbles at 550 °C and 700 °C for up to 32 days under purge gas. Cr2O3-formed F82H rapidly reacted to form three layers at 550 °C, and pure Fe projections grew with annealing time. Diffusion kinetics of O and Li were well fitted with Fick’s first law of diffusion. Er2O3 coatings did not react with the pebbles, but deteriorated by oxygen diffusion through the coatings. The impurity concentrations in the system and the coating thickness affect the coating compatibility in solid breeder blanket environments.

We evaluated the two dimensional (2D) distribution of the divertor heat flux in LHD. The Infrared (IR) thermography was performed to measure the surface temperature at a divertor plate. The 3D heat conduction equation was solved using the finite element method (FEM) by taking into account the practical divertor geometry including the heat sink behind the graphite tile and the cooling system. The FEM analysis successfully reconstructs heat load distribution from the measured temperature pattern. Significant difference was found between the temperature and the heat load patterns. The FEM analysis shows that the highest heat deposition is observed at the strike line with 5–10 MWm−2 of ∼ 10 mm width in NBI heated discharge. In addition to the strike line there is also found the lower heat deposition region of ∼ 1 MW m−2 with wide channel width ∼ 30 mm. The detailed heat transport analysis inside the divertor components shows that the heat transport process is different between the strike line and the other region due to the heat channel width and to the divertor component structure. The comparison between the heat flux obtained by the thermography and that by the Langmuir probes shows reasonable agreement, except that the peak value of the heat load is higher in the IR thermography than in the Langmuir probe. By relaxing the assumption that electron temperature, Te, equal to be ion temperature, Ti, in the sheath model for the Langmuir probe analysis, the agreement becomes better for the case with Ti > Te.

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.

An inertial electrostatic confinement (IEC) fusion device accelerates ions, such as deuterium (D) or tritium (T), to produce nuclear fusion and generate neutrons. The IEC’s straightforward configuration consists of a concentric spherical transparent cathode at a negative bias in a grounded spherical anode center. The effects of cathode properties on the neutron production rate (NPR) remains, to date, inadequately studied. This study aims to determine the impact of cathode material on NPR by investigating fusion reactions on the cathode surface. Two buckyball-shaped cathodes made of stainless steel (SS) and titanium (Ti), both of 5 cm diameter, fabricated using selective laser melting and a 3D printer, are used for this investigation. A SS spherical chamber of 25 cm inner diameter is used as an anode in this experiment. A performance evaluation of surface fusion reaction in the IEC using SS and Ti grids is conducted by scanning the NPR as a function of the applied voltage and grid currents at different gas pressures. So far, IEC with Ti and SS cathodes achieves NPRs of 2.32 and 1.41×107 n/s, respectively, at 5.6 kW (70 kV, 80 mA). The normalized NPR (NPR/I-cathode) from IEC using SS and Ti cathode are compared. The results demonstrate that fusion reactions occur on the cathode surface, while the fusion reaction ratio increases with the applied voltage. The measured NPR/I-cathode for IEC with Ti cathode is more elevated than the SS cathode with 1.36 to 1.64 times for 20 to 70 kV range. Moreover, fusion on the cathode surface enhances the total NPR from the IEC with Ti cathode significantly compared to IEC with SS cathode under the same conditions. The Ti’s considerable ability to accumulate D ions and molecules compared with that of SS explains the difference of measured NPR results.

The designs of neutron spectrum-shaping assembly (NSSA) composed with various shielding materials with natural isotopic abundance were evaluated to construct the neutron field dominated with thermal neutron or epi-thermal neutron for the application of neutron filed in the torus hall of LHD toward the BNCT research. According to the neutron transport calculation by MCNP6, the fast neutron moderation efficiency was higher in polyethylene (PE) compared to lithium fluoride (LiF) and magnesium fluoride (MF), although LiF showed relatively large epi-thermal and thermal neutron absorption. This comparison showed that the thermal neutron field can be effectively achieved with using PE. For constructing the NSSA which can provide the neutron field dominated with epi-thermal neutron, several NSSA designs were evaluated with respect to fast neutron flux, epi-thermal neutron flux, and gamma-ray dose. The combination of MF, lead (Pb) and cadmium (Cd) can provide the good epi-thermal neutron field with the mitigations of fast neutron flux and gamma-ray dose, which is also suitable for BNCT research in the torus hall of LHD.

Multiple tritium breeder recycling is an attractive option to make a future fusion power reactor ecologically and economically sustainable. This research project aims at exploring the feasibility of multiple breeder ceramics recycling by remelting with regard to the activation behavior. The average activation level of multiple reused breeder pebbles is calculated for a DEMO reactor with HCPB (Helium Cooled Pebble Bed) blankets on the assumption that all spent pebbles are mixed and reprocessed by remelting. The calculation loop verifies the feasibility of a multiple reprocessing scheme with an acceptable waiting period of approximately 22 y for the remote handling dose rate level—even after 15 times recycling. This paper also describes the limitation of the current approach for the average activation property and provides some recommendations for future improvements.

Li vaporization property of two-phase materials of Li2TiO3 and Li2SiO3 in a working condition for the solid tritium breeder used in the demonstration power plant of fusion reactor was investigated, and the suppression mechanism of the vaporization was considered. The Li vaporization rate from the specimen pellet was measured by gravimetric method, and the change of Li concentration distribution in the pellet was analyzed by time-of-flight secondary ion mass spectrometer. Li was vaporized only from the Li2SiO3 at the vicinity of the surface of the pellet. The remarkable vaporization of Li arose only in an early short time. The inhibition of the vaporization from the Li2SiO3 was successful by adding the small amount of the stable secondary phase of Li2TiO3.

The vaporization property and the crystal structure of lithium metatitanate with excess Li, which has been developed as an advanced tritium breeder, were studied. After synthesizing the lithium metatitanate specimens with Li/Ti = 2.0–2.3 (at mixing of the starting materials), the vaporization properties were investigated by measuring the mass losses during heating at 1173 K. The Li excessive specimens indicated higher rates of mass loss than the stoichiometric one during heating as long as excessive lithium atom exists. The crystal structures of stoichiometric and nonstoichiometric lithium metatitanates were discussed with the result of neutron diffraction and the refined structural parameters by Rietveld analysis. The refinement ( R wp = 7.98, R p = 5.96 and R e = 2.58) suggested that lithium metatitanate with excess Li has β-Li 2 TiO 3 structure and excess Li atoms exist at unstable sites with the formation of reduced titanium or site vacancies.

Enthalpy of Li2TiO3, which was synthesized by a neutralizing method and its Li/Ti ratio was determined to be Li/Ti ratio (mol/mol) = 1.97, was measured by a drop calorimeter, and its heat capacity was derived as a function of temperature. XRD (X-ray diffraction) analysis of the sample before and after the enthalpy measurement indicated no phase change during the measurement and a single phase of Li2TiO3 was observed. The enthalpy data were expressed as H(T) − H(323.17) (J/g) = 2.2 × 10−5·T2 + 1.4·T + 2.7 × 104/T − 5.6 × 102 (373–1273 K), where T is temperature in K. The heat capacity was calculated as Cp (J/g K) = 2.2 × 2 × 10−5·T + 1.4–2.7 × 104/T2 by differentiating the equation by temperature. These equations have accuracy of 3%.

Effect of moisture in sweep gas on chemical compatibility between ceramic breeder (Li 4 SiO 4 with 20 mol% of Li 2 TiO 3 ) and EUROFER97 was examined in this study. These materials were contacted and heated at 623, 823, and 1073 K for up to 12 weeks where the H 2 O concentrations of the outlet gas were 0.13-0.24 vol.%. In the two-phase breeder specimen, Li 4 SiO 4 was preferably decomposed into Li 2 SiO 3 with a possible formation of Li 2 O 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 1073 K. Though these results showed parabolic growth rates, an extrapolation from data of the elevated temperatures to 623 K 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 623 K was given to be 4.5 × 10 −14 cm 2 /s and a possible thickness of the corrosion layer after a 2-year use was predicted.

Crystal grain growth and crystallization of lithium metatitanate with excess Li (Li 2+x TiO 3+y ), which is expected as an advanced ceramic breeder for a future DEMO fusion reactor, were studied in this paper. By the observation of sintered pellets using scanning electron microscope, it was shown that the Li 2.1 TiO 3+y specimens, which have small grains (1–2 μm) and narrow size distribution, can be obtained by sintering in the temperature range from 1000 to 1100 °C. The observation also showed the rapid grain growth in the Li 2.1 TiO 3 specimens sintered above 1150 °C. The changes in the crystal structure and the phase transformation with the increase of sintering temperature were also investigated by means of powder X-ray diffraction. Finally, the relationship between the grain growth and the phase state at high temperature was discussed.

A non-stoichiometric solid state compounds of lithium titanate of the Li 2 SnO 3 -type structure with the space group C 2/ c (No. 15), Z = 8 (denoted as Li 2 TiO 3 ss) were successfully synthesized using the powders of LiOH·H 2 O and H 2 TiO 3 as the starting materials. The crystal structure of the compounds was analyzed by X-ray diffractometry using Cu Kα radiation. The Li/Ti ratio in the compounds was analyzed by an inductively coupled plasma–optical emission spectroscopy. The microstructure was analyzed by scanning electron microscopy. Thermal diffusivity was measured by the laser flash method. The influences of the Li/Ti ratio on microstructure, Li density, and thermal diffusivity were investigated. Li density of the compounds increased due to the synergy effect of the good sintering behavior and the Li-rich composition. The increase in the Li/Ti ratios of the compounds encouraged the sintering and increased the thermal diffusivity.

The demand is growing that a robot manipulates a deformable object. Scenarios for both of a grasping point and transfer of grasped point are required, in order to manipulate a deformable object by a robot. Therefore, it is important for a robot to recognize its form by using image information. In this paper, three-dimensional points groups of a string are obtained by a camera that has distance measure equipment. A shape model called “point chain model” is obtained from points group based on proposed algorithm. In this algorithm, first, points which are estimated to be outside of target object are removed from obtained points groups. Secondly, points groups obtained from various viewpoints are combined to reconstruct three-dimensional shape of a string. Thirdly, central axes of a string are abstracted from combined points groups. Finally, central axes are chained to construct the point chain model. Effectiveness of proposed algorithm is confirmed by experiment.

High-temperature and high-density plasmas are achieved by means of real-time control, fast diagnostic, and high-power heating systems. Those systems are precisely controlled via highly integrated electronic components, but can be seriously affected by radiation damage. Therefore, the effects of irradiation on currently used electronic components should be investigated for the control and measurement of Large Helical Device (LHD) deuterium plasmas. For the precise estimation of the radiation field in the LHD torus hall, the MCNP6 code is used with the cross-section library ENDF B-VI. The geometry is modeled on the computer-aided design. The dose on silicon, which is a major ingredient of electronic components, over nine years of LHD deuterium operation shows that the gamma-ray contribution is dominant. Neutron irradiation tests were performed in the OKTAVIAN at Osaka University and the Fast Neutron Laboratory at Tohoku University. Gamma-ray irradiation tests were performed at the Nagoya University Cobalt-60 irradiation facility. We found that there are ethernet connection failures of programmable logic controller (PLC) modules due to neutron irradiation with a neutron flux of 3 × 106 cm−2 s−1. This neutron flux is equivalent to that expected at basement level in the LHD torus hall without a neutron shield. Most modules of the PLC are broken around a gamma-ray dose of 100 Gy. This is comparable with the dose in the LHD torus hall over nine years. If we consider the dose only, these components may survive more than nine years. For the safety of the LHD operation, the electronic components in the torus hall have been rearranged.

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.

Low thermal resistance of high power superluminescent diodes (SLEDs) by using active multi-mode interferometer (active-MMI) is presented in this paper. The active layer temperature evaluation demonstrates that the power saturation mechanism in active-MMI SLED is heat for the first time. Low thermal resistance of 4.83 K/W in active-MMI SLEDs leads to a high power of 115 mW. Moreover, the effect of the active area size on the output power is demonstrated both experimentally and theoretically. Good agreement between the theoretical and experimental results indicates that active-MMI configuration is a new design in support of efficient heat dissipation and thermal resistance reduction for SLEDs.