Regarding issues for sustainable use of nuclear energy based on the treatments of the Fukushima Daiichi Nuclear Power Plant accident and the final disposal of nuclear waste, some questions are taken up and examined on new regulatory standards, facility location / operation, information disclosure, etc. In addition, as a condition for flat investigation, examination and discussion to proceed regardless of individual opinions of approval or disapproval of implementation, all issues and matters can be discussed by the separation into "past and confirmed events" and "undecided future events". It will propose a "logical" examination method that includes various perspectives such as science, society, and beliefs.

In the Green Growth Strategy presented by the Japanese government in 2020, nuclear power stations are regarded as existing, well-established low carbon power sources and their continuous use is required to achieve the national goal of net zero greenhouse gas emissions by 2050. However, considering the damage caused by the Great East Japan Earthquake and resulting tsunami, the risk from potential accidents must be further mitigated. Prevention of a hydrogen explosion during a severe accident is one of the key issues to improve the safety of nuclear power stations. In this study, the behavior of a packed bed reactor of copper oxide pellets, used as part of a hydrogen treatment system, was examined. Reaction heat from the oxidation of hydrogen into water vapor accompanying complex reactions on the copper oxide surface increases the temperature of the packed bed and consequently the reaction rate. This positive feedback should be controlled to prevent thermal runaway by stabilizing the packed bed at the designed operating temperature of the hydrogen treatment system. The conditions leading to this low temperature positive feedback were experimentally confirmed with a bench-scale packed bed reactor and complementary numerical calculations. At temperatures 233~267 °C, temperature increase is governed by not only temperature-dependent reaction rate but also by competitive adsorption behavior between hydrogen and water vapor. At higher temperatures than 267 °C, hydrogen concentration governs the positive feedback effect, which implies necessity for appropriate design to prevent thermal runaway of the packed bed.

In Japan there are many essential industries like Iron product and Cement which cannot exist without fossil fuel like coal. They are hard walls for Carbon Neutrality. So I tried to find the best way to decrease CO₂ emission in Iron product process within now-available technology: Reformed Blast Furnace, Nuclear power, and Recycle, with keeping low product cost as now. The best way I found could decrease CO₂ emission half as now, but another half remain. There is another way using Hydrogen as Iron-Reduction materials. But Hydrogen cost is too much high to product Iron.

I have imaged the future Iron product process when coal-resource will be lost. Carbon is necessary materials for multiple purposes. So then Biomass Carbon product will be increased much more. Then we can use only Biomass Carbon as Iron-Reduction materials. High temperature Nuclear Reactor will be able to be Biomass Energy useful. That is Carbon Solution Reaction. (C+CO₂= 2CO: CO₂ issued from Blast Furnace) In 2050s Biomass Carbon cost will be still too high to replace coal. So I propose Preservation of Biomass Carbon Business is begun to realize Carbon Neutrality. Biomass Carbon is not burn out, but is preserved. Preservation of Biomass Carbon has so high value for Environment Protection, and is bought out by Government expenses, not by tax income. This is MMT Green deal policy.

A gas-liquid mixing nozzle and a multi-layer metal fiber filter are used, and a silver zeolite filter is installed for the purpose of removing organic iodine. Based on this technology, we have developed a demonstration machine for a large-capacity air purification system that purifies a large amount of contaminated air. A gas-liquid mixing nozzle driven by air blown from a blower sucks and accelerates water to form a high-speed two-phase flow. With this acceleration and centrifugal force field of water, almost all of the fine particles in the bubbles can be transferred to the liquid phase water and dissolved. We have developed a demonstration machine of an air purification system that can remove fine particles and viruses in the air of 100 m3/h with a single nozzle. Next, we also developed a large-capacity air purification system that can purify 2400 m3 of air per hour with 24 nozzles. The FCVS system, which is high-performance and passively activated, is thought to help eliminate obvious infringement of personality rights, avoid litigation outages, and promote public acceptance for nuclear power.

For the further advancement of a filter vent, the influence of silver zeolites on the hydrogen recombining reaction has been studied. It is confirmed that the AgX is active and plays an auxiliary role of hydrogen recombiner in the hydrogen catalyst reaction. On the other hand, it has been confirmed that AgX can also remove radioactive iodine in the atmosphere containing hydrogen gas. For AgR, it is proved that it is a kind of special silver zeolite which does not almost have hydrogen catalyst reaction. Owing to these characteristics, AgX and AgR are expected to be utilized under the severe conditions in a containment vessel. In this paper, the development status of these silver zeolites will be introduced, and some possible applications will be proposed.

In the filter vent, a technology to remove various radioactive substances by combining scrubber and metal fiber is used, but there was no example in the world until the iodine filter of silver zeolite was installed in Japan. This silver zeolite filter is required to function under high temperature, high humidity and high pressure in an accident. In addition, it is necessary to examine the influence of moisture adsorption, hydrogen and inhibitors. The methyl iodide adsorption performance of AgX and AgR was evaluated under the following conditions: 100% water vapor, temperature 105 to 160℃, pressure 1.2 to 6.0 bar, and gas velocity 0.2 to 0.5 m/s. Furthermore, the effect of inhibitors (CO, SO₂, HCl) on the adsorption performance of methyl iodide of AgX was also evaluated.

Using the air purification technology developed in the Filtered Containment Venting System (FCVS), we have been studying the further upgrading of the air purification system in nuclear energy field. The use of silver zeolite technology in place of activated carbon and metal fibers in place of HEPA filters is expected to make the system non-flammable and eliminate the effects of fire and concerns about hydrogen gas in the event of an accident. Furthermore, by combining the scrubber technology developed by FCVS, a safer air purification system can be proposed.

Air purification systems using Filtered Containment Venting System(FCVS) technology is expected to be used in a variety of nuclear applications. Conventional air purification systems using activated carbon requires ancillary equipment such as drying equipment, but it can be expected that the equipments can be significantly reduced by using silver zeolite, metal fiber filter and scrubber, and it seems possible to realize mobility. If mobile is realized, it can be expected that it can be used for various facilities such as emergency response stations, SGTS use, air purification system for Fukushima decommissioning, and reprocessing facility. We report on the feasibility of mobileization using these technologies. Advancement radioactive material removal system by silver zeolite" was adopted in the 2020 fiscal year as a project "nuclear-power-industry base strengthening enterprise" of the Ministry of Economy, Trade and Industry. We propose developed FCVS, air purification system, and rare gas adsorption system to in and outside the country.

In nuclear power plants, measures against radioactive noble gases are required. Until now, special activated carbon that easily adsorbs noble gases has been used in some nuclear facilities. However, activated carbon has a small adsorption capacity and is greatly affected by other gases and environmental humidity. Therefore, to develop a new adsorbent with high adsorption performance is necessary. At emergency response stations, it is necessary to take measures using air cylinders. It was confirmed that the newly developed silver zeolite XeA has more than 10 times the adsorption efficiency of activated carbon for noble gas adsorption. In this paper, we will report on the basic noble gas adsorption performance of XeA and compare the adsorption performance between XeA and activated carbon.

Since it is difficult to remove radioactive noble gas, the development of high performance adsorbent has been desired from the viewpoint of exposure prevention. We were able to develop a new adsorbent, XeA that has more than 10 times the performance of existing products. By utilizing this adsorbent in nuclear power plants, it is possible to contribute to improve noble gas equipment, non-combustibility and reduction of radiation exposure.

In the ULOHS tests performed in the experimental fast reactor U.S. EBR-II, the thermal stratification in the cold pool (CP) has influence on the whole plant behavior during the events because the secondary sodium pump tripped without scram nor tripping the primary pumps. In order to create the one-dimensional model for the CP of the plant dynamics analysis code, the multi-dimensional thermal hydraulics analyses using computational fluid dynamics (CFD) code were conducted to investigate the thermal hydraulics phenomena in the CP. It was found by comparison with the experimental data that the modeling of the detail sodium flow at the outlet of the intermediate heat exchanger, the leakage flow from the inner components to the cold pool, and the heat radiation from the CP to the atmosphere was important to the evaluation of the thermal stratification.

In the safety study of sodium cooled fast reactor, it is important to appropriately evaluate the event progression of Core Disruptive Accident (CDA). In previous studies, the reliability and validity of the evaluation method of the early stage of CDA, which is named Initiating Phase (IP), was significantly enhanced by applying Phenomena Identification and Ranking Table (PIRT) approach to the Unprotected Loss of Flow (ULOF). In this study, PIRT approach was applied to Unprotected Transient over Power (UTOP), which was one of the most important and typical events in CDA as well as ULOF, and physical phenomena relating to UTOP were ranked in order of the degree of importance. As a result, 8 key phenomena were identified. Compared UTOP with ULOF, both rankings were almost same, however it was clarified in this study that the ranking of the physical phenomena related to the coolant in UTOP was lower than that in ULOF, since in UTOP primary flow remains constant and coolant behavior doesn’t cause large reactivity changes.

If a pressurized water/water-vapor leaks from a heat transfer tube in a steam generator (SG) in a sodium-cooled fast reactor (SFR), sodium-water reaction forms high-velocity, high-temperature, and corrosive jet. It would damage the other tubes and might propagate the tube failure in the SG. Thus, it is important to evaluate the effect of the tube failure propagation for safety assessment of SFR. The computational code LEAP-III can evaluate water leak rate during the tube failure propagation with short calculation time, since it consists of empirical formulae and one-dimensional equations of conservation. One of the empirical models, temperature distribution evaluation model, evaluates the temperature distribution in SG as circular arc isolines determined by experiments and preliminary analyses instead of complicated real distribution. In order to improve this model to get more realistic temperature distribution, we have developed the Lagrangian particle method based on engineering approaches. In this study, we have focused on evaluating gas flow in a tube bundle system, and constructed new models for the gas-particles behavior around a tube to evaluate void fraction distribution near the tube. Through the test analysis simulating one target tube system, we confirmed the capability of the models and next topic to improve the models.

A decay heat removal system based on the natural circulation (NC-DHRS) is expected to be developed for the safety improvement of sodium-cooled fast reactors. Uncertainty evaluation of experimental data is a key issue to establish an experimental database regarding NC-DHRS. In this study, the uncertainty evaluation method has been developed for thermocouples in the test section of the sodium experimental facility PLANDTL-2, considering the effect of the heat loss in the test section and the uncertainty of reference thermocouples. Monte Carlo method has been used for the uncertainty evaluation of the temperature measurement data in the relative calibration and the steady state experiment. As a result, it was confirmed that the confidence intervals were asymmetric due to the heat loss in the relative calibration and the steady state heat removal experiment with DHX. Confidence intervals of thermocouples near the simulated core outlet were increased due to mixing the cold sodium from DHX and the hot sodium from the simulated core.

The seismic evaluation of the important component such as the reactor vessel is important for the seismic probabilistic risk assessment in a Sodium-Cooled Fast Reactor (SFR). The improvement of the evaluation method in the seismic probabilistic risk assessment for the fast reactor is investigated. In the improvement of the evaluation method, the evaluation method, which can evaluate the failure of the important components such as reactor vessels, is necessary. The correlation of the fatigue failure and the integrated vibration energy to the component was confirmed in the past study. Furthermore, the failure evaluation with the vibration energy was investigated. The probability of failure at components can be evaluated by comprehension of the vibration energy necessary for failure. Accordingly, the integrated vibration energy can apply to the failure probability curve. In this study, the failure probability evaluation method, which evaluates integrated vibration energy to the component during an earthquake, is developed. The simple examination specimens, whose main vibration mode is the bending vibration, were made. Furthermore, the vibration examination with the simple examination specimens was carried out by the sine wave. The integrated energy at the simple examination specimen was investigated in the vibration examination. As a result, the integrated energy to failure was approximately 4700 [J] on the examination condition.

Progress of severe accidents (SAs) has been previously evaluated by transferring analytical results between multiple analysis codes. In this study, a new analysis code, SPECTRA was developed for integrated analysis of in- and ex-vessel phenomena during SAs. SPECTRA consists of in- and ex-vessel modules which have a thermal hydraulics (TH) module as a base part. The in-vessel TH module computes complicated multi-dimensional behavior of liquid sodium and gas by using the multi-fluid model considering compressibility. Relocation of a molten core is computed by the dissipative particle dynamics method. A lumped mass model was employed for computation of ex-vessel multi-component gas flow including aerosols. The fully implicit scheme was applied to both the TH modules to enable computation with a large time step width. Analytical models for sodium fire, sodium-concrete interaction, and debris-concrete interaction were integrated into the ex-vessel module. The in- and ex-vessel modules were coupled by exchanging the amount of leaked sodium and debris at every time step. Basic capability of SPECTRA was demonstrated through analysis of a loss of reactor level event.

In the severe accident evaluation of sodium-cooled fast reactors (SFRs), a module to analyze core disruptive accidents (CDAs) from the initiating phase to the transition phase of various cores has been developed for the purpose of consistent evaluation of the entire accident process from the initial to the final state. In this paper, the physical phenomena in steady-state irradiation and CDA events of mixed oxide (MOX) fuel and metallic fuel of sodium-cooled fast reactors are summarized and the functions to be included in the analysis module are discussed. For both fuel compositions, the deformation of the core material due to the accumulated FP gas in the fuel caused by neutron irradiation and the post-failure migration were the main important issues. Eutectic and extrusion are also important issues as features of metallic fuels.

The SPECTRA code has been developed as an integrated simulation system for severe accident evaluation in a sodium cooled fast reactor. In this study, the sodium pool fire model of SPECTRA is accessed through the benchmark analysis of the F7-1 pool fire experiment. As well as the comparison with the experimental data, the SPECTRA result is also compared to the results of the MELCOR and SPHINCS codes. All the SPECTRA results well agree with the results of SPHINCS from which the pool fire model of SPECTRA is adapted. The comparisons with MELCOR and experiment show also reasonable agreements in the essential pool fire behavior. The principal difference is the combustion rare after sodium supply stopping especially in the comparison with the experiment. This affects smaller temperature decreasing of the pool, catch-pan, and gas in SPECTRA. Such differences should be investigated more in the future works.

In sodium-cooled fast reactors (SFRs), it has been pointed out that molten fuel may be discharged from the core during a severe accident (SA) accompanied by core damage, and may solidify into debris particles with diameters ranging from several millimeters to several hundred micrometers due to interaction with the sodium coolant and accumulate at the bottom of the reactor vessel. Therefore, it is necessary to understand the behavior of such debris particles appropriately to evaluate the SA event progression. To meet these requirements, a molten fuel behavior analysis code using dissipative particle dynamics (DPD), a kind of particle method, has been developed as a part of the SPECTRA code, tool for consistent analysis of in-vessel and ex-vessel events in sodium fast reactor accidents. In this study, it was found that the new analyses code can reproduce sedimentation behavior of particles by adding a new stress term in the shear direction.

The capability of stable cooling and avoiding re-criticality on the debris bed are the main issues for achieving In-Vessel Retention (IVR). In the actual situation, the debris bed is composed of mixed-density debris particles. Hence, when these mixed-density debris particles were launched to re-distribute, the debris bed would possibly form a density-stratified distribution. For the proper evaluation of this scenario, the multi-physics model of CFD-DEM-Monte-Carlo based neutronics is established to investigate the coolability and re-criticality on the heterogeneous density-stratified debris bed with considering the particle relocation. The CFD-DEM model has been verified by utilizing water injection experiments on the mixed-density particle bed in the first portion of this research. In the second portion, the coupled system of the CFD-DEM-Monte-Carlo based neutronics model is applied to reactor cases. Afterward, the debris particles' movement, debris particles' and coolant's temperature, and the k-eff eigenvalue are successfully tracked. Ultimately, the relocation and stratification effects on debris bed's coolability and re-criticality had been quantitatively confirmed.

The reactor vessel cooling system is a static cooling system that removes decay heat from the core by convection and radiation heat transfer without using dynamic components and is one of the safety systems that constitute the inherent safety features of High Temperature Gas Reacter. However, the natural convection of the gas may cause hot spots on important structures such as the pressure vessel during the cooling using this system. For this reason, a three-dimensional numerical model simulating the High Temperature Test Reacter 1/6 scale model was developed and numerically analyzed. It was found that it is better to use the surface-to-surface model for the radiation model and the k-ε model for the turbulence model. We also examined the effect of adding components to the model. It was found that there was no need to model the cooling pipe.

A depressurization accident is one of the postulated accident events in the Very High Temperature Reactor (VHTR). It is an accident unique to the VHTR, in which a large amount of air entering the reactor core oxidizes graphite, which can cause the generation of combustible gas and the release of fission products due to damage to the core geometry. When the main piping is connected horizontally, air immediately enters the lower part of the break due to the counter current flow, and a stable density stratification layer is formed. The infiltrated air promotes gas mixing by local natural convection and counter current flow in addition to molecular diffusion. The experimental apparatus consists of a coaxial double cylindrical vessel and a coaxial horizontal double circular tube. The horizontal double circular tube is closed by a ball valve. The experimental procedure is as follows. First, the inside of the experimental apparatus is evacuated and filled with helium gas. The inner cylinder is the heated with a heater and the outer cylinder is cooled with water to ensure that the gas and wall temperatures have reached a steady state. Then, the valve is opened to reproduce the decompression accident. The experimental results show the following. After the air enters the apparatus, a stable density stratification of air and helium is formed and the air ingress rate decreases. Afterwards, the buoyancy of the air in the inner cylindrical vessel increases due to the heating of the air by the heater, and the stable density stratification is eliminated. Finally, a natural circulation flow is generated, which circles around the machine.

A very high-temperature reactor (VHTR) is one of the next generation nuclear reactor systems. A gas cooling system with natural circulation is considered as a candidate for the pressure vessel cooling system (VCS) of the VHTR. The Japan Atomic Energy Agency is pursuing the design and development of commercial systems such as the 300 MWe gas turbine high-temperature reactor 300 for cogeneration (GTHTR300C). These is a need for a passive method in which the cooling system operates even when all power is lost in the accident of a nuclear power plant. The gas cooling system with natural circulation is considered as a candidate for the VCS of the VHTR. In the VCS of the GTHTR300C, many rectangular flow channels are formed around the reactor pressure vessel. A cooling panel utilizing natural convection of air has been proposed. However, the amount of removed heat is inferior to that of cooling by forced convection. Hence, we propose a method of inserting a porous material into the heating surface to promote heat transfer. In this study, we use an experimental apparatus that simulated the cooling panel of VCS. The experimental apparatus is a U-shaped flow channel, and the heating surface side is a vertical rectangular flow channel. Fine copper wire (diameter: 1.5 mm) was used as a porous material. A porosity of the channel is changing from 0.996 to 0.999. We investigated the amount of removed heat by intermittently inserting metal wires into the one side heated vertical rectangular channel to reduce the pressure drop.

In the recent years, the strong oxidation power of ozone and radicals generated by advanced oxidation method has been expected to be useful to water treatment. In this study, energy conservation advanced oxidation process by fusion of microbubbles and plasma, which can be driven by a household bath pump, was proposed and evaluated for usefulness and practical feasibility. In the experiment, the decolorization test was conducted using indigo carmine solution as a sample in order to clearly the effect of supplied gas types, ozone and radicals on the oxidative decomposition. In addition, the dissolved concentration measurements for H₂O₂ and O₃, and the spectroscopic measurement were conducted. The results show that O radical and ozone generated by the gas-liquid interface discharge in bubble were the dominant influences for decolorization test.

In order to improve the load following performance of ultra-super critical sliding pressure once-through boilers, evaporator tubes are required to operate under conditions different from those in the past. However, the conditions for occurrence of density wave oscillation in the multiple parallel tube structure used in the boiler was not clear. Therefore, verification tests were conducted in a condition equivalent to that of an actual boiler, and an evaluation method of flow stability was developed. The test was conducted using water as the working fluid in 4 parallel tubes with an inner diameter of 10 mm and a heating length of 7.4 m. The calculation results by developed evaluation method were in good agreement with the test results.

This study investigated experimentally the effect of the fuel rod fixing protrusions on the grid spacer on the pressure loss and the liquid film thickness around the rod in air-water two-phase flow in simulated BWR fuel rod bundle channel. From the investigation, the following findings were obtained; (a) there was almost no change in pressure loss with or without the protrusions, (b) the liquid film around the rod downstream of the spacer becomes thicker when there is the protrusion. As a result, the effect of the protrusions on the gas-liquid two-phase flow is found to be favorable at the power output, where the pressure drop was small and the liquid film thickness was large.

Steam is widely utilized for thermal energy supply in the industrial fields. It is vital to be aware of the flow rate of the steam at demand end from the viewpoint of energy management. The practical steam piping of the factories often have a wet steam flow resulting from heat loss, heat supply, work, and so forth. It is well known that the measurement error of the steam flow rate is caused by the steam wetness. However, the method for estimating the measurement error has not been established yet since it is hard to evaluate the effects of the steam wetness quantitatively in plants and factories. A clamp-on type ultrasonic steam flow meter is useful for the factory since it is not necessary to pipe processing. We have conducted the wet steam flow test with this clamp-on type ultrasonic flow meter and found some characteristics. In this paper, we conducted the steam flow test with the same flow meter to the piping having different diameter from our previous measurement. Based on the measurements, we considered the correction method for measurement using the clamp-on ultrasonic flow meter in a wet steam flow by correcting the density in the flow rate calculation.

Currently, the MH21-S R&D Consortium (MH21-S) supported by the Ministry of Economy, Trade and Industry (METI) are developing the commercial production process of methane gas from methane hydrate. In order to develop the gas production, an objective identification of the flow regime of gas-liquid two-phase flow under high pressure conditions is required. Therefore, in the present research, the identification of the flow regime has been conducted by classifying the image using clustering algorithms, namely the principal component analysis (PCA) and k-means method. Specifically, the sequence image of the upward gas-liquid two-phase flow under high pressure taken with a high-speed camera is merged into a single image by the time strip method, and these single images were then processed with PCA and classified by the k-means method. As a result, bubbly flow and slug flow is classified with high recall value. Thus, this study has shown that the identification of the flow regime can be performed by classifying the single images of upward gas-liquid two-phase flow, merged by the time strip method, with PCA and k-means method.

The purpose of this study is to develop a small wire mesh sensor for measurement of void fraction distribution in refrigerant-air two phase flow in order to clarify experimentally the two phase flow parameters. In this study, since we suppose HFE-71IPA for the liquid phase as one of the actual refrigerant, which can flow the small electric current under high voltage, the small wire mesh sensor for the high voltage has been developed. In this report, as a purpose of verification of flow regime difference for the small wire mesh sensor, instantanious and time averaged void fraction distribution in water-air two phase flow in vertical small diameter pipe was experimentally measured and analyzed for bubble and slug flows. In the experiment, the test channel was a vertical circular glass pipe of 9 mm i.d. The each volumetric flux were 0.2-2.0 m/s for the gas phase and 0.1 m/s for the liquid phase in bubble flow, and 0.5-1.0 for the gas phase and 0.2-0.5 m/s for the liquid phase in slug flow. In this report, the obtained void fraction distribution data were compared between different flow regimes, and with the past data and literatures.

In this study, pressure drop experiments for single-phase flow were carried out using rectangular microchannels with high aspect ratio. The results showed although the friction factor of the test section with De>0.3 mm could be estimated well by the correlations developed for the microchannels with a larger equivalent diameter that De>0.5 mm, the experimental friction factor of the test sections with De<0.3mm was much higher than that of the test section with a larger equivalent diameter that De>0.3 mm, and the conventional correlations for the friction factor was not applicable to the channel whose De<0.3mm. To interpret the experimental results, we focused on the effect of channel roughness. In the laminar flow region, by incorporating the roughness viscosity in addition to the conventional viscosity of the liquid, we found the pressure drop could be evaluated from the theoretical equation for infinite plate laminar flow. While in the turbulent region, the traditional correlation that considering the roughness effect (Colebrook–White equation), after being coupled with the factor that considering the aspect ratio in the rectangular channel, was found still insufficient to predict the data accurately.

In the development of compact heat exchangers with additive manufacturing, thermal-hydraulic characteristics in a rectangular channel of which equivalent diameter is 4mm were evaluated experimentally. The test section having double-tube-like structure was manufactured by using powder bed fusion type metal 3D printer. For reducing the amount of heat release from inside of test section to outside, experiments were carried out with a configuration which cooling water flows in the outer flow path of test section. The results show that the correlation of heat transfer performance with steam quality depends on the flow rate.

If the water piping system under high temperature and pressure is damaged and water is ejected into the atmosphere, jet with depressurization boiling (Flashing) may occur. Therefore, it is necessary to evaluate the range of the impact on surrounding equipment and people, but the existing standards do not specify the spreading angle of the flashing jet. In order to evaluate the spreading angle of the flashing jet in the case of pipe failure, the solution method and characteristics of a flow analysis code were investigated to develop a method for evaluating the flashing jet behavior. As a result, CRUNCH CFD was selected with the necessary simulation model to analyze the flashing jet. A simulation test of the flashing jet was performed to confirm the validity of the simulation method. The shock wave behavior, and pressure and temperature distribution near the nozzle of the flashing jet were reproduced, and the validity of the simulation method for the flashing jet using CRUNCH CFD was confirmed.

One strategy for dealing with severe accidents is in-vessel retention (IVR) of corium debris. In-vessel retention consists of external cooling of the reactor vessel in order to remove decay heat from the molten core by lower head of the vessel. In this system, it is important to establish techniques to 1) cool the high-temperature reactor vessel in order to change the boiling regime from film boiling to nucleate boiling as soon as possible, because the heat transfer coefficient for film boiling is very low, and 2) enhance the critical heat flux (CHF), because heat removal is limited by the occurrence of the CHF condition at the outer surface of the reactor vessel. Furthermore, approaches for increasing the IVR capability must be simple and installable at low cost. Regarding 2) CHF enhancement, we have demonstrated CHF enhancement of a large heated surface by a honeycomb porous plate (HPP) in saturated pool boiling of distilled water.

In the present paper, we focus on the mechanism of quenching behavior of a heated surface with a honeycomb porous plate.

When the flow rate of liquid film flow becomes smaller than a certain critical value, a part of the wall surface begins to dry. The critical flow rate is an important issue related to drainage in fuel cells and other engineering devices. In this study, the critical flow rate of the liquid film flowing through rectangular groove was studied theoretically and experimentally. The surface profile of the liquid film in the channel cross section was obtained theoretically from a simple model using the balance between viscous and gravitational forces. Considering the work of wetting behavior and the surface energy change of the liquid film when a part of the wall surface is dried, the critical flow rate at which dryout occurs was obtained from the condition that the total energy change becomes zero. The experimental results conducted with the liquid film flow flowing down the rectangular groove channel with width of 1.5 to 9 mm showed good agreement with the theoretical model proposed in this study.

Generating electricity by renewable energy is one of the key contributor to reduce greenhouse gas (GHG) emissions. In this paper, specific attention is paid to current status and prospects of offshore wind around the world and especially in Japan. At first the huge potential of offshore wind is introduced and the advantage of offshore wind farm compared to onshore are discussed. Next, the reasons of success of European coast are introduced and the recent domestic trend, i.e. the policy of government to the goal of carbon neutral and increasing investment of private companies, are pointed out. Finally, the technologies of bottom fixed and floating foundations for supporting wind turbine are reviewed. The technology of bottom fixed foundations is almost established. On the other hand, floating foundations are in development competition around the world.

Savonius wind turbine is a vertical axis wind turbine driven by drag force and has been spread gradually in urban areas. In the present study, we quantify the performance of a Savonius wind turbine in a flow with high isotropic turbulence over 20% produced in a far field of an open-jet type wind tunnel. The performance of the Savonius wind turbine estimated from measured rotational speed using a tachometer shows that the idling tip speed ratio increases in the high turbulent flow in comparison with the case in the flow inside potential core. The result implies that Savonius turbine has a function to capture the turbulence as an additional source of power.

In floating offshore wind turbine-generator systems, wind and wave variations cause platform pitching motion and increase fatigue loads. A feedforward control based on the preview of the inflow wind speed to the wind turbine is combined with a gain-scheduling feedback control of the generator speed to stabilize platform motion and reduce dynamic load variations at high wind speeds. In this feedforward control, the blade pitch is manipulated in response to the previewed wind speed so that the generator speed is maintained at the rated value. An aero-elastic-hydro-control coupled simulation using the developed feedback-feedforward controller is performed for a 5-MW floating offshore wind turbine-generator system. The simulation results under turbulent wind fields and irregular wave height variations reveal that the stabilization of the platform motion and the reduction in the dynamic load variations at the tower base and blade root as well as the low-speed shaft are achieved by using the spatial mean wind speed as the previewed wind speed. Moreover, the impact of the previewing error of the inflow wind speed with high-frequency turbulence on the control performances is clarified.

This paper describes the performance of orthopter-type wind turbine with S-shaped blades using two-dimensional numerical simulation. Orthopter-type wind turbine is one of the variable-pitch vertical-axis wind turbine of which each blade rotates on their own axis meanwhile all of blades rotate on its main axis. This configuration ensures that the blades rotate around their own axis by 360° during each two-full revolution of the main rotor. In this paper, the effect of the number of S-shaped blades is researched. The number of blades N is varied to N = 2, 3, 4. The diameter of the wind turbine is 510 mm. The chord length c is 400 mm (N = 2, 3) and 290 mm (N = 4). The averaged power coefficient C_P with two S-shaped blades is larger than those with three and four S-shaped blades. The number of blades has effects on pressure distributions around the wind turbine. Thus, orthopter-type wind turbine with two S-shaped blades is suitable shape for the orthopter-type wind turbine.

Savonius wind turbine is categorized as a vertical axis wind turbine driven by drag force. This study aims to improve the performance of the turbine by means of jets provided around the surface of backets. For a small model of Savonius turbine made for wind tunnel experiments, whose diameter is 175 mm with the jet-control mechanism, we measured torque performance and flow structure modified by the jets. The torque and the power were estimated by measuring acceleration of angular velocity of the turbine using angular equation of motion. The result showed the power coefficient was improved from 0.17 to 0.41 in the maximum value and also from 1.0 to 1.3 in operatable range in tip-speed ratio. This was proved by flow visualization of the phase-averaged field using PIV, i.e., flow separation from the tip of the advancing bucket was enhanced by the jet at the turbine angle of around 75 deg. so that the buckets receive drag stronger than the case without jet supply.

The carbon tax is expected to have two types of effects: direct behavior change after introduction and indirect behavior change due to the introduction notice. This study uses a multiplayer game that simulates a competitive energy market to investigate the impact of carbon taxes on the conversion from fossil fuels to renewable energies. Comparing the experimental results under the condition without carbon tax and the condition with certain conditions, the behavior change of the participants was limited after taxation, and the behavior change due to the tax notice was not recognized. As a result of the questionnaires, it was found that even if the taxable amount and taxable time were announced at the start of the game, the participants' anxiety about the energy transition could not be resolved.

To reduce the amount of CO₂ emission, it is important to construct the supply chain of renewable H₂. This study aims to investigate the feasibility on the supply chain of H₂ converted by water electrolysis from electricity generated by large scale wind turbine which is assumed to be installed in Yokkaichi. The converted H₂ is assumed to be consumed in Yokkaichi as well as transported to Nagoya and Iiyama and consumed there. This study compares not only the energy efficiency but also the effect of reducing CO₂ emission among different H₂ carriers such as compressed H₂, liquefied H₂, compressed CH₄, liquefied CH₄, organic hydride and NH₃. In addition, this study investigates the effect of LNG cold heat as a sub-heat source to liquefy H₂ on the energy efficiency and CO₂ reduction. As a result, it is revealed that the best H₂ carrier is the liquefied H₂ using LNG cold heat for liquefying H₂ irrespective of wind turbine output and transportation distance.

This paper describes disaster prevention and energy in cities. There are many high-rise condominiums in Koto-Ku, Tokyo, where our campus is located. Therefore, it is necessary to secure the necessary energy for water supply, toilets, and elevators. Our research group created a concept, experimented with, and considered energy use in the event of a disaster in the city. We performed the following three experiments, there were discussed in this paper.1.Experiment to operate an elevator by supplying electricity from an electric vehicle to a high-rise house.2.Experiment to supply electricity from a battery ship to a university hospital.3.Experiment to watch over elderly persons using a net power meter. From these facts, it was found that all of 1, 2, and 3 are effective. In addition, 1 and 3 are promoting social implementation in collaboration with companies.

In order to prevent global warming, many technologies for CO₂ reduction have been developed. As a solution, photovoltaic (PV) & electric vehicle (EV) integrated system which can reduce CO₂ emissions with high economic efficiency has been proposed. In this paper, the authors have studied the effect of introducing the integrated system to a city bus line (between Gifu University Hospital and JR Gifu Station) based on the energy balances of the entire system including power consumption by air conditioning and traveling of the bus. As a result, CO₂ emissions can be reduced more than 90% and 80% of the whole energy consumption can be replaced by PV power.

A hybrid ocean thermal energy conversion (H-OTEC) system combines an ocean thermal energy conversion (OTEC) system, which generates electricity using the temperature difference between the surface and deep layers of the ocean, with a flash desalination system to produce freshwater from seawater. The H-OTEC generates steam by vacuuming the warm seawater and convey the steam to the power generation system as the heat source. The H-OTEC can prevent the performance degradation of the heat exchanger due to bio-fouling, improve the heat transfer coefficient by condensation heat transfer on the heat source side, and reduce the cost of the heat exchanger by using stainless steel or other low-grade materials instead of titanium.

The basic thermodynamic characteristics of the H-OTEC have been clarified by parametric analysis, but the performance of the Evaporator-Condenser (Eva-Con), which condenses water vapor generated by flash evaporation and evaporates ammonia using the latent heat of condensation as a heat source, has not been experimentally clarified. In this study, the authors report the heat transfer performance test results of the Eva-Con.

Ocean thermal energy conversion (OTEC) is a system to convert the thermal energy stored as the vertical temperature gradient in the ocean into the electricity. On account of the low available temperature difference for heat engines, the heat exchangers are the key component in terms of the efficient energy conversion. However, the performance of heat exchanger is, in general, evaluated as the heat transfer performance and the pressure drop, and the relation of the performance and the effectiveness for achieving the net power has not been clarified yet. This research proposes the comprehensive heat exchanger performance index based on finite-time thermodynamics for designs and developments in plate heat exchangers. The proposed performance evaluation index is applied to existing plate heat exchangers, and the sensitivities of the index to the heat source temperature is confirmed.

A framework for automated SOFC microstructure reconstruction from large asymmetric-resolution FIB-SEM datasets is proposed. Machine learning techniques are used for super-resolving the in-depth direction, i.e. FIB slicing direction, and for automating the phase segmentation. Deep neural networks consisting of patch-VDSR residual network for the increasing slicing resolution of FIB-SEM data and patch-CNN in the encoder-decoder configuration for semantic segmentation are incorporated. The proposed algorithm can shorten the FIB-SEM measurement time or increase the size of microstructures maintaining high resolution.

In porous anodes of solid oxide fuel cells (SOFCs) fabricated by adding a pore former, correlation between bimodal pore structure and its permeability is investigated. The pore structures of the anodes were analyzed in 3D using the focused ion beam and scanning electron microscopy (FIB-SEM). The quantified microstructural parameters indicate that increasing the amount and size of the pore former increases the porosity and mean pore size, reducing the complexity of the pore structure. From the analysis of the pore-size distribution, the pore structure in the porous anodes consists of two types of structures; one is formed at sintering and reduction and has fine pores around 1 μm (Pore_REF), and the other is formed by the pore former and has relatively large pores around 2-5 μm (Pore_PF). Permeability of the porous anode is evaluated in experiment on the basis of the Darcy’s law. The results indicate that decreasing the complexity of the pore structure increases the permeability. From the correlation between the pore-size distribution and the permeability, it is found that the permeation flow rate is limited by the structure with Pore_REF when the main flow paths formed by Pore_PF are connected only by Pore_REF.

Energy losses inherit in PEFC structure was analyzed to find optimum cell structure. As for a representative cell, JARI cell was examined and analyzed with simple model. In the model, the losses are calculated with distinguishing current loss, mass flow loss, heat flow loss, which are irreversible losses when current, mass flow and heat flow occur in cell. The loss analysis found that the current loss is the largest among the three components, and that the current loss determines fuel cell efficiency. An enlarged electrode area embedded in the cell was proposed to reduce the current loss. This trial suggested that enlarged electrode area lowers both current and heat loss, but raises mass flow loss. Thus, energy analysis in this study suggests that trade-off issue exists between the three losses and optimum electrode is decided in this scenario.

In order to improve the performance of polymer electrolyte fuel cell (PEFC), management of liquid water generated by cell operation is an important issue. The water generated in the catalyst layer is transported to the channel through the microporous layer (MPL) and gas diffusion layer (GDL). It has been suggested that water condenses and accumulates at the interface between the MPL and the catalyst layer. Since the condensed water accumulated at the interface inhibits oxygen transport, clarification of the water distribution and its behavior is required to improve the cell performance. In this study, we developed a new device for visualizing the water that condenses at the interface, and observed the distribution of the condensed water. In order to observe the condensed water at the interface, a transparent water vapor permeable membrane that mimics the catalyst layer was used. Water vapor was condensed by imposing a temperature gradient inside the cell with cooling the anode-side separator. As a result of the experiment, condensed water generated at the interface was successfully visualized. In the future, condensed water will be observed under the same settings as the actual cell operating conditions. Improvement of the internal structure of the cell and adequate control of the temperature gradient will be effective solutions.

This study investigated the relationship between the cell performance and the proton transport resistance of ionomerfree graphene catalyst layer in polymer electrolyte fuel cell (PEFC). We used original catalyst layers: graphene nanoplatelets were used instead of ketjen black and ionomer as the transport material of electron and proton in the CL. I-V measurement and impedance measurement were conducted to investigate the cell performance and the proton transport resistance respectively before and after two types of conditionings, scanning voltage loading for 1000 cycles and constant voltage loading for 15h. From these results, it was shown that the proton resistance in the CL increases in proportion to the Pt loading of the CL and this leads to decline of the cell performance against increase in the Pt-loadings. In addition to this, the proton resistance can be decreased by the scanning voltage loading and the following constant voltage loading. This indicates the possibility that the cell performance of PEFC with graphene ionomer-free CL may be further improved by appropriate conditionings.