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Record-breaking precipitation events have been frequent in Japan in recent years. To investigate the statistical characteristics of the frequency of record-breaking events, observations can be compared with the values derived from sampling theory with a stationary state. This study counted the number of record-breaking daily and 3-day total precipitation events at 58 rain-gauge stations in Japan between 1901 and 2018. The average number of record-breaking events over the 118-year period was 5.9 for daily total precipitation, which is larger than the theoretical value of 5.4 derived using the assumption that the climate system over the same period was stationary. Sampling theory was used to incorporate the influence of the long-term temperature trend from the Clausius&ndash, Clapeyron relation associated with the saturation vapor pressure. In theory, the long-term temperature trend gives a similar number of observed record-breaking events when the long-term temperature trend is approximately 0.5 Kelvin/100 years.

Understanding of Li mass transfer behavior in a tritium breeding blanket is an important issue from viewpoints of establishment of tritium cycle and tritium safety. In this work, weight reduction property of Li2TiO3 with excess Li pebbles, which were fabricated by National Institutes for Quantum and Radiological Science and Technology, was investigated and the amount of Li mass loss and the rate of Li mass loss in water vapor atmosphere at elevated temperatures were evaluated. The Li mass loss proceeding at 900 °C with a relatively high rate was limited. The Li mass loss of Pebble210 (Li/Ti = 2.10) was 1.2 wt% and that of Pebbe211 (Li/Ti = 2.11) was 1.4 wt%, eventually. The rate of the Li mass loss increased with increasing temperature and it seemed to increase proportionally to a square root of water vapor pressure. An empirical formula for the Li mass loss was proposed as a function of temperature, heating time and water vapor pressure in a purge gas.

New tritium breeding materials that maintain large tritium breeding ratio for thermonuclear fusion reactors should be developed. In this study, we investigate the lithium-vaporization behavior from the sintered bodies of Li8ZrO6 and Li5AlO4 having high lithium atom densities. From the viewpoint of lithium density, we investigate the possibility of using the sintered compacts of Li8ZrO6 and Li5AlO4 as a tritium breeder. Lithium vaporization rates from the sintered bodies of Li8ZrO6 and Li5AlO4 are high. However, for both materials, the lithium vaporization rate gradually decreases with the annealing time by “self-stabilization” in which the surfaces of each sintered body are covered by the stable layer of the second phase. Considering the temperature dependency of equivalent vapor pressure and the volume fraction of tritium breeding material loaded at high-temperature region, it is suggested that the sintered compacts of Li8ZrO6 and Li5AlO4 have high potentials for the tritium breeder.

The lithium isotope effect in ionic superconductors is numerically investigated. Using first-principles and kinetic Monte–Carlo simulations, the diffusion coefficients of 6Li and 7Li ions are calculated. Two important effects that cause the difference in the mobilities of lithium isotopes are also shown: the quantum effect, which decreases the activation barrier energy for lithium ion in a certain structure and increases the ratio of the diffusion coefficient of Li isotopes, as well as the correlation effect between 6Li and 7Li ions and vacancies. These results will assist in finding materials that exhibit large lithium isotope effect. The preferred chemical composition of lithium isotopes required to enhance the lithium isotope effect and the application of these isotopes as a separation membrane for the lithium ionic superconductors are discussed.

In a solid breeding blanket, ceramic breeder pebbles are in contact with reduced activation ferritic martensitic (RAFM) steel at high temperatures for years and accordingly form a corrosion layer on the blanket structural steel. Present study focuses on corrosion characteristics of EUROFER97 RAFM steel by an advanced breeder material of Li2TiO3 with excess Li (initial ratio of Li/Ti = 2.2) at 623, 823, and 1073 K under sweep gas (He + 0.1% H2) flow. Formation of a thick oxide double layer was found on the surface of the EUROFER plates heated at 823 and 1073 K, while the corrosion layer formed at 673 K was

Solid tritium breeding materials are expected to be used in high-temperature conditions for a long time in a fusion DEMO reactor. Thus, it is important to understand how bred tritium releases from the long-term heated material under the environment as close to a DEMO condition as possible to establish a tritium fuel cycle and keep it safe. In this work, the tritium release behavior from the irradiated Li2TiO3 pebbles that was preheated for 720 h at most was observed by heating at 1000 °C under 1000 Pa H2/Ar gas flow. The release peaks of HTO and HT were observed around 300 °C due to the desorption of the chemisorbed water. Also, the broad HTO peak was observed in a higher temperature region despite purging H2/Ar gas. This result suggests that this tritium was released without exchanging with H2 but with combining with oxygen in the pebbles. Moreover, the released tritium amount decreased as the pre-heating time. Finally, the amount of tritium that could not be released by the heating experiment was quantified by dissolving samples with an acid solution. Besides, the total tritium release ratio was discussed.

Understanding of Li evaporation properties is important because Li mass transfer decreases tritium breeding ratio and influences tritium behavior possibly. In QST, the pebbles of Li2TiO3 with excess Li were fabricated by the optimized sintering condition recently and it was confirmed that the pebbles have a good tritium release property. In this work, the weight reduction of the pebbles at elevated temperatures was investigated considering the releases of water vapor and CO2 from the pebbles. Furthermore the mechanism of Li mass loss from Li2TiO3 with excess Li pebbles was discussed by comparing the difference between the pebbles formed by the optimal fabrication method, Pebble210 and ones formed by the previous fabrication method, Pebble211. The release behaviors of water vapor from Pebble210 and Pebble211 were almost same except a small peak at 350 °C. A large amount of CO2 was released from Pebble211 at over 700 °C which is close to the melting point of Li2CO3. On the other hand, the release of CO2 from Pebble210 was not observed. The weight reduction excluding the contribution of water vapor for Pebble210 was smaller than that for Pebble211. The difference of weight reduction between Pebble210 and Pebble211 are caused by the presence of Li2CO3.

Changes in mechanical property and microstructure of sintered pebbles of lithium metatitanate (Li2TiO3) and Li excessive lithium metatitanate (Li2+xTiO3, x > 0) as tritium breeder pebbles for thermal fusion reactors, which were caused by thermal annealing, were investigated. The compressive strength was measured by using a universal tester. The Li2TiO3 pebble was stable during the thermal annealing at 900 °C, and its compressive strength was not decreased. In contrast, the microstructure and Li/Ti ratio of the Li2+xTiO3 pebble were markedly changed during the thermal annealing; the grain growth was severe and the excessive Li was disappeared in a 1000 h annealing. As a result, its compressive strength was significantly changed; it was drastically decreased by a 100 h annealing but it was once increased again in the additional annealing by a change in fracture mode.

Lithium vaporization properties of sintered compacts of single-phase Li2TiO3, Li8ZrO6, β-Li5AlO4, and two-phase β-Li5AlO4-Li8ZrO6 and β-Li5AlO4-Li2TiO3 are investigated. Li vaporization rates from the sintered pellets are measured by gravimetric methods, and crystalline phase changes are analyzed by X-ray diffraction. Li2TiO3 is stable during thermal annealing at 900 °C. In contrast, Li is evaporated from the other materials, and β-Li5AlO4 and Li8ZrO6 are, respectively, decomposed to LiAlO2 and a mixture of Li6Zr2O7 and Li2ZrO3. Considering the high Li density, which is estimated from the Li vaporization rate and initial Li density in the pebble, and appearance stability, the sintered compacts of single-phase β-Li5AlO4 and the two-phase materials β-Li5AlO4-Li2TiO3 and β-Li5AlO4-Li8ZrO6 have the potential to be applied to new advanced tritium breeders with high Li density.

Several key components, such as superconducting coils, remote handling equipment, heating systems, have been designed and manufactured by JADA (Japan Domestic Agency). These activities have been carried out in accordance with the agreed schedule; in collaboration with the ITER organization and other domestic agencies. As a significant technical program using ITER, to design and to manufacture the TBS (Test blanket system), some R&D and design activities have also been conducted in Japan. Under the IFERC (the International Fusion Energy Research Center) projects of BA (Broader Approach) activities, design and R&D activities on fusion DEMO reactor have been carried out. For the DEMO R&D activity, five basic R&D subjects for a DEMO blanket system have been selected, and been studies under close collaborations between EU and JA: structure materials (RAFM steels and SiC/SiC composites), functional materials (tritium breeders and neutron multipliers), and tritium technology. From 2007, the above project...

The pebble properties of 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 are evaluated in this work as a function of the second phase concentration and the microstructure of the pebbles. The characterization focused on the mechanical strength, microstructure and open as well as closed porosity. Therefore crush load tests, SEM analyses as well as helium pycnometry and optical image analysis were performed, respectively. This work shows that generally additions of a second phase to Li 4 SiO 4 considerably improve the mechanical strength. It also shows that the fabrication processes have to be well-controlled to achieve high mechanical strengths. When Li 2 TiO 3 is added in different concentrations, the determinant for the crush load seems to be the open porosity of the pebbles. The strengthening effect of LiAlO 2 compared to Li 2 TiO 3 is similar, while additions of Li x La y TiO 3 increase the mechanical strength much more. Yet, Li 4 SiO 4 and Li x La y TiO 3 react with each other to a number of different phases upon sintering. In general the pebble properties of all samples are favorable for use within a fusion breeder blanket.

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.

This study aims to evaluate the change in flood inundation in the Chitose River basin (CRB), a tributary of the Ishikari River, considering the extreme rainfall impacts and topographic vulnerability. The changing impacts were assessed using a large-ensemble rainfall dataset with a high resolution of 5 km (d4PDF) as input data for the rainfall–runoff–inundation (RRI) model. Additionally, the prediction of time differences between the peak discharge in the Chitose River and peak water levels at the confluence point intersecting the Ishikari River were improved compared to the previous study. Results indicate that due to climatic changes, extreme river floods are expected to increase by 21–24% in the Ishikari River basin (IRB), while flood inundation is expected to be severe and higher in the CRB, with increases of 24.5, 46.5, and 13.8% for the inundation area, inundation volume, and peak inundation depth, respectively. Flood inundation is likely to occur in the CRB downstream area with a frequency of 90–100%. Additionally, the inundation duration is expected to increase by 5–10 h here. Moreover, the short time difference (0–10 h) is predicted to increase significantly in the CRB. This study provides useful information for policymakers to mitigate flood damage in vulnerable areas.

Lithium titanate with excess lithium (Li 2+x TiO 3+y ) is one of the most promising candidates among advanced tritium breeders for demonstration power plant reactors because of its good tritium release characteristics. However, the tritium breeding ratio (TBR) of Li 2+x TiO 3+y is smaller than that of e.g., Li 2 O or Li 8 TiO 6 because of its lower Li density. Therefore, new Li-containing ceramic composites with both high stability and high Li density have been developed. Thus, this study focused on the development of a solid solution with a new characteristic. The solid-solution pebbles of Li 2+x TiO 3+y with Li 2 ZrO 3 (Li 2+x (Ti,Zr)O 3+y ), designated as LTZO, were fabricated by an emulsion method. The X-ray diffraction patterns of sintered LTZO pebbles are approximately the same as those of Li 2+x TiO 3+y pebbles, and no peaks attributable to Li 2 ZrO 3 are observed. These results demonstrate that LTZO pebbles are not a two-phase material but rather a solid solution. Furthermore, LTZO pebbles were easily sintered under air. Thus, the LTZO solid solution is a candidate breeder material for super advanced (SA) tritium breeders.

Li8ZrO6 contains a large amount of Li and has a significant potential as a tritium breeder. However, few syntheses of fine-grain, high-purity Li8ZrO6 powder have been reported. In this study, a high-purity powder of Li8ZrO6 was synthesized by solid state reaction under hydrogen atmosphere combined with an effective lithium source and a suitable initial Li:Zr molar ratio. Mixed powders of Li2CO3 and ZrO2 were fired at around 630 °C in H2 for several hours and several firing cycles. The low firing temperature inhibited the vaporization of Li during the heating, so that excessive amounts of Li were not needed for the synthesis, and the Li:Zr ratio in the starting material was 10:1 (mol:mol). In this synthesis, Li2O was generated via the decomposition of Li2CO3 during firing in H2, and reacted with ZrO2 to form Li6Zr2O7, which reacted with itself to form Li8ZrO6.

The development of a water cooled ceramic breeder (WCCB) test blanket module (TBM) is being performed as one of the most important steps toward DEMO blanket in Japan. For the TBM testing and development of DEMO blanket, R&D has been performed on the module fabrication technology, breeder and multiplier pebble fabrication technology, tritium production rate evaluation, as well as structural and safety design activities. The fabrication of full-scale first wall, side walls, breeder pebble bed box and back wall was completed, and assembly of TBM with box structure was successfully achieved. Development of advanced breeder and multiplier pebbles for higher chemical stability was continued for future DEMO blanket application. From the view point of TBM test result evaluation and DEMO blanket performance design, the development of the blanket tritium transport simulation technology, investigation of the TBM neutron measurement technology and the evaluation of the tritium production and recovery test using D-T neutron in the fusion neutron source (FNS) facility has been performed. This paper provides an overview of the recent achievements of the development of the WCCB Blanket in Japan.

We have performed the tritium release experiment on the fusion reactor blanket at JAEA/FNS since 2009, and then clarified the ratio of tritium release and the recovered tritium chemical form. In order to acquire the detailed tritium recovery performances, we have started a new blanket tritium recovery experiment with ionization chamber (IC) at JAEA/FNS. For the appropriate tritium measurement with IC, we improved the experimental container and carried out with an intense DT neutron source at JAEA/FNS. From our new experiment, the tritium recovery radioactivity from the LSC measurement corresponds with the calculation within 6%. However, it was pointed out that further improvement in the quantitative tritium measurement by IC method was needed.

Li2TiO3 with excess Li (Li2+xTiO3+y) has been developed as an advanced tritium breeder. With respect to the tritium release characteristics of the blanket, the optimum grain size after sintering was less than 5 μm. Therefore, an emulsion method was developed to fabricate pebbles with this target grain size. The predominant factor affecting grain growth was assumed to be the presence of binder in the gel particles; this remaining binder was hypothesized to react with the excess Li, thereby generating Li2CO3, which promotes grain growth. To inhibit the generation of Li2CO3, calcined Li2+xTiO3+y pebbles were sintered under vacuum and subsequently under a 1% H2–He atmosphere. The average grain size of the sintered Li2+xTiO3+y pebbles was less than 5 μm. Furthermore, the tritium release properties of Li2+xTiO3+y pebbles were evaluated, and deuterium–tritium (DT) neutron irradiation experiments were performed at the Fusion Neutronics Source facility in the Japan Atomic Energy Agency. To remove the tritium produced by neutron irradiation, 1% H2–He purge gas was passed through the Li2+xTiO3+y pebbles. The Li2+xTiO3+y pebbles exhibited good tritium release properties, similar to those of Li2TiO3 pebbles. In particular, the released amount of tritiated hydrogen gas for easier tritium handling was greater than the released amount of tritiated water.

The accurate measurement of behavior of bred tritium released from a tritium breeder is indispensable to understand the behavior for a design of a tritium extraction system. The tritium collection method combined a CuO bed and water bubbles was not suitable to measure transient behavior of tritium released from Li2TiO3 during neutron irradiation because tritium released behavior was changed to be delayed due to adsorption of oxidized tritium on the CuO. Hence, the tritium collection method with hydrophobic catalyst instead of the CuO was demonstrated and succeeded the accurate release measurement of tritium from Li2TiO3. With the method, we assessed the behavior of tritium release under the various conditions since tritium should be released from Li2TiO3 as the form of HT as much as possible from the view point of the fuel cycle. Our results indicated; promotion of isotopic exchange reaction on the surface of Li2TiO3 by addition of hydrogen in sweep gas is mandatory in order to release tritium smoothly from Li2TiO3 irradiated with neutrons; the favorable sweep gas to release as the form of HT was hydrogen added inert gas; and the temperature of Li2TiO3 was the dominant parameter to control the chemical form of tritium released from the Li2TiO3.

The increasing demand for sustainable energy results in the development of new technologies of energy generation. The key objective of hydrogen economy is the introduction of hydrogen as main energy carrier, along with electricity, on a global scale. The key goal is the development of hydrogen-related technologies needed for hydrogen generation, hydrogen storage, hydrogen transportation and hydrogen distribution as well as hydrogen safety systems. It is commonly believed that hydrogen is environmentally clean since its combustion results in the formation of water. However, the technology currently employed for the generation of hydrogen from natural gas, does in fact lead to the emission of greenhouse gases and climate change. Therefore, the key issues in the introduction of hydrogen economy involve the development of environmentally clean hydrogen production technology as well as storage and transport. The clean options available for hydrogen generation using nuclear energy; such as advanced nuclear fission and, ultimately, nuclear fusion, are discussed. The latter, which is environmentally clean, is expected to be the primary approach in the production of hydrogen fuel at the global scale. The present work considers the effect of hydrogen on properties of TiO2 and its solid solutions in the contexts of photocatalytic energy conversion and the effect of tritium on advanced tritium breeders.

Tritium breeding ceramic materials are placed at high temperatures for a long period in a fusion DEMO reactor. Therefore, the understanding of Li mass loss phenomena and its influence on tritium behavior are important. In this study, the pebbles of Li2TiO3 with excess Li were heated at 900 °C for 30 days in a 1000 Pa H2/Ar flow and tritium sorption and recovery experiments were carried out. Li mass loss by the heating was evaluated to be 0.7 wt%. The value of Li mass loss was almost same as that for 3 days heating at the same condition. Tritium sorption capacity for the heated pebbles at 600 °C and 900 °C were almost same as that for the pebbles as received. Tritium sorbed in the pebbles could not be recovered effectively by the 1000 Pa H2/Ar purge at room temperature and 300 °C but it could be recovered at 600 °C and 900 °C. The influence of the long-time heating on the behavior of tritium sorbed in the pebbles was not large.

Solid tritium breeding materials are used in a high temperature condition for a long time in a fusion reactor blanket. It is expected that a certain amount of Li will be evaporated and the pebble structure will be changed. Understanding of Li mass transfer behavior in the blanket is an important issue from viewpoints of establishment of tritium cycle and tritium safety. In this work the pebbles of Li2TiO3 with excess Li were heated at 900 °C in 1000 Pa H2/Ar flow for a long time (72, 240, 720, 1200 h). The amount of Li mass loss under the hydrogen atmosphere was 0.665 wt% which was less than that under the water vapor atmosphere observed in the previous study. No significant Li mass loss was observed after 240 h. By heating for 240 h, the grain diameter increased from 1.8 to 3.1 μm and the specific surface area decreased from 0.72 to 0.20 m2/g. After 240 h, no significant grain growth and no significant decrease in the specific surface area were observed. From these results, it seems that there is a relation between Li mass loss and grain growth.

We investigate isotope effects of lithium-ion diffusion in Lithium-ion conductors using ab initio computational methods in light of recently proposed novel lithium isotope separation technology based on ionic conductors. Using ab initio molecular dynamics simulations, we compute the diffusion coefficients D6(7) of 6Li+ (7Li+) in tetragonal Li7La3Zr2O12 and Li10GeP2S12 as a slow Li+-ion conductor and a fast Li+-ion conductor, respectively. We note that careful uncertainty estimations in the molecular dynamics simulations would be necessary to extract many-body effects on the diffusion coefficient ratio D6/D7 beyond the canonical value given by the transition-state theory. Numerical results for Li10GeP2S12 indicate that the isotope effect depends on the migration path. Specifically, the faster diffusion path along the c−axis exhibits a stronger isotope effect that is also temperature dependent, whereas the diffusion on the ab−plane shows a relatively weaker and temperature-independent effect. We introduce the probability distribution of the ionic displacement to reveal distinct differences in the ion-diffusion mechanism.

Previous studies have shown that the acceleration of global warming will increase the intensity of rainfall induced by tropical cyclones (TCs) (hereinafter referred to as &ldquo, TC-induced rainfall&rdquo, ). TC-induced rainfall is affected by TC position and topography (slope shape and direction). Thus, TC-induced rainfall is expected to vary by sub-basin due to varying topographies. However, these relationships have not been explained, as historical TCs, which occurred several decades earlier, do not exhaustively encompass all TC positions that could potentially affect each basin. We used large ensemble regional climate model experiments with 5 km grid spacing, which enabled us to prepare a huge TC database for understanding the characteristics of TC-induced rainfall over sub-basins. We quantified the characteristics of TC-induced rainfall (rainfall volume, relationship between TC position and rainfall intensity, and contribution of TC intensity on rainfall) over four sub-basins in the Tokachi River basin, central Hokkaido, northern Japan. The results reveal differences in TC-induced rainfall characteristics between the sub-basins. In addition, the large ensemble data under a future climate scenario were used to evaluate future changes in the characteristics of TC-induced rainfall for each sub-basin.

The pebbles of Li2TiO3 with excess Li, which is in a developmental stage in JAEA (Japan Atomic Energy Agency) as an advanced tritium breeding material, were exposed to water vapor at elevated temperatures. In the temperature rising process from room temperature to 900 °C, pore distribution and BET surface area were largely changed. The surface area decreased gradually by a sintering effect when maintained at 900 °C for a long time. The release of water vapor was observed at about 450 °C by the decomposition of LiOH in addition to the release of adsorbed water at the beginning of heating. A large release peak of CO2 was observed at 700 °C. This is caused by the decomposition of Li2CO3. A remarkable melt layer was formed on the pebble surface over 700 °C by melting of Li2CO3. The change of pebble structure and the influences of LiOH and Li2CO3 have to be taken into account, when the release behavior of bred tritium from Li2TiO3 pebbles is discussed.