This paper describes the experimental setup for waste heat recovery system and power generation using thermo-electric devises (TEDs) for a water -cooled diesel engine with carbon neutral fuel such as biodiesel fuel. This paper reports the system integration of heat exchanger of engine systems, power conditioning using MPPT control and DC-DC converter by power conversion circuit through battery charging operation. As a result, a value of an open circuit voltage for evaluating at maximum output of TEDs should be modified from that at non-generation condition to that at power generation condition due to the reduction of the difference of temperature between surfaces of TEDs at power generation because of occurrence of Peltier effect as output current from TEDs increases. Furthermore, the circuit performance was evaluated, then it was shown that the power utilization efficiency is around 98 %, and the power conversion efficiency is around 91 %, then these values are almost the same as those previously evaluated by simulated power source.

This paper describes the production of biodiesel fuel (BDF) from oil in oily wastewater exhausted from cafeteria that is used by 120~150 people per day. Here, solvent extraction was applied to extract and purify oil from oily wastewater, and this paper also focuses degradation of recovered oil, then acid value of oil exhausted on the day was enough low so that alkyl catalysts methods can be applied, however, that of oil older than 180 days after exhausted was over 200 mgKOH/g then single-step acid catalyst method leads to acquire BDF. It also clarifies energy profit ratio of two above method can achieve almost equivalent to that of BDF production using waster-cooking oil, and acid value of recovered oil keeps almost constant after solvent extraction different from oil in oily wastewater left untreated, therefore, storing oil after solvent extraction is effective way in terms of increasing an amount of acquired BDF from the exhausted oil, refraining from producing BDF production in small lots and recovering a certain amount of oil from many cafeterias etc.

Biomass fuel is one of renewable energies and is expected toward a target of net GHG zero emissions in 2050 that Japanese government announced October 2020. Using biomass pellets in pulverized coal fired power plants is recently increasing to reduce CO2 emissions. On the other hands, various types of biomass pellets have been used at many power plants because of requirement by many power suppliers. Recently, not only conifer, but also broad-leaved tree and herbaceous plant have been used for biomass pellets. However, the burning behavior is different for each type of biomass. This study conducted experiments of thermal weight analysis. From the results obtained, the emission characteristics a little bit depend on the biomass types. Some types of the biomass showed two stage’s emission during the volatile matter release. The model of the volatile matter emission was determined.

The heater method is a clamp-on type flow measurement method that can be applied to metal pipes in high-temperature environments and is useful for determining the adequate flow rate in existing pipes for the stable operation of thermal power plants. Specifically, a ring-shaped heater is attached to the outer of an existing pipe, and the outer surface temperature of the pipe near the heater is measured to calculate the fluid flow rate in the pipe. Theoretically, the flow rate can be calculated by measuring the outer surface temperatures at three or more points at different locations in the flow direction. However, more practically, it is necessary to measure the temperature at three or more points where the temperature rise due to the heater heating can be detected with high accuracy. This study clarified the appropriate distance between the ring heater and the temperature measurement positions.

Bubble Void fraction α measurement is crucial for gas-liquid two-phase flow; however, it is difficult to monitor in bubbly flow. There is a lack of measurement equipment, and the accuracy of existing measurement methods is low. Among numerous current methods, the electrical impedance tomography (EIT) method stands out with the characteristic of low cost and high efficiency. It enables imaging of the bubble void fraction due to the different conductivities of gas bubbles and liquid. To generate a high-quality image of bubble void fraction, the EIT Method combined with machine learning (ML) is applied to increase the accuracy of output results. Moreover, with the advantage of reversibility and bijective mapping, the ML invertible neural networks (INN) model reconstructs the input from the output. It also can make output have a unique corresponding input and vice versa. The experiments were set up in a vertical pipe with an inner diameter D of 25 mm connected to a horizontal pipe by a 90-plastic elbow. In this study, the flow patterns were focused on the unstable α upstream. The flows with liquid and gas superficial velocities v were set at 0.2, 0.4, and 0.6 m/s, while v is 0, 0.11, 0.32, and 0.53m/s. As a result, the spatial-temporal void fraction image α is generated and successfully observed distinctly in the upstream. Conclusively, the completed experiment data demonstrates the characteristic of α with a relatively satisfactory accuracy in real-time measurement.

The purposes of this study are to develop a swirl flow separator by only gravitational falling to remove fine seaweeds from wastewater drained from each process of seaweed production and to clarify the design guideline. In this study, the characteristics of the swirl flow separator on flow rate fraction of the wastewater containing seaweeds have been experimentally investigated. The test liquid was quasi-seeweed wastewater including fine seaweeds made of commercial dried seaweed sheets and tap water. The swirl flow generator was composed of a vertical inner circular pipe of 67 mm i.d. The separation section was made of a cylindrical stainless steel mesh having 76 mm i.d. as same as outer diameter of the swirl flow generator and 120 mm in length. In the experiment, the range of total flow rate was from 64.5 l/min to 147.2 l/min, it corresponded to the range of the mean velocity of 3.95 m/s to 14.0 m/s at the slit section of the inner pipe. Furthermore, in order to solve a problem of unsteady separation phenomenon under transient state, numerical simulation of liquid flow at the inside and outside of the cylindrical mesh has been conducted by COMSOL Multiphysics software. The details of the experimental and analytical results are presented and discussed in this paper.

Recently, the use of boiling cooling has been considered for emergency cooling in nuclear power plants and for cooling of large power devices. We fabricated electrodeposited porous plates with micro-scale honeycomb porous structure and improved the critical heat flux by using them. The structures of the porous plates were modified significantly by changing the electrodeposition conditions. The experimental results showed that the difference in the porous structure greatly affected to the critical heat flux. As for the relationship between the existence ratio of macro-channels and the critical heat flux, the critical heat flux was higher when there were few macro-channels than when the percentage of macro-channels were very high. It is thought that this tendency was obtained due to the role of porous part in retaining the liquid in boiling. In addition, the critical heat flux improved as the Wickability was increased. Therefore, the wicking performance of the porous plates is considered to have greatly improved the critical heat flux.

Critical heat flux (CHF) for downward flow is greatly affected by stagnation and counter-current of bubbles. In this series of studies, CHF experiments of downward flow using water as the working fluid have been conducted. The results showed that CHF characteristics changed before and after the inner diameter equivalent to the Taylor wavelength. In order to determine the Taylor wavelength as the representative length of downward flow CHF, it is necessary to gather CHF data with different physical properties. In this study, CHF experiments were conducted with R134a as the working fluid using upward flow and downward flow with inner diameters of 4, 6, and 8 mm. The obtained CHF was classified according to CHF locations and the corresponding flow patterns. CHF for water and R134a were evaluated using the dominant force regime map in coordination with Bond number, Weber number, and Froude number.

High-temperature heat pumps represent a pivotal technology in the pursuit of decarbonizing industrial process heating with the utmost efficiency. Steam serves as the energy carrier for many industrial systems, making steam supply heat pumps a promising approach for efficient decarbonization. In this paper, a thermodynamic and economic model of a heat pump system is developed based on the test results with a heat pump supplying steam up to 175°C. The model is used to analyze the change in COP (coefficient of performance) and LCOH (levelized cost of heat) when changing to new refrigerants.

The heat charger (HC) is the heat charging device of a mobile thermal energy storage system using zeolite which can expand utilization of unused heat. The direct heat exchange type is commonly employed as heat charging devices due to large heat transfer area. Since blower power injecting hot air into packed bed, which is one of dominant factor in operating costs, needs to be reduced, an indirect heat exchange type HC was investigated to reduce blower power. While the indirect heat exchange type can reduce operating costs, the increase in equipment costs due to the increase in the number of heat exchangers is a concern. The impact of the change in cost structure on the system was evaluated by calculating the operating and facility costs for each heat storage type. It was found that the introduction of the indirect heat exchanger type can reduce annual costs, including equipment and operating costs, under all conditions studied.

In recent years, the use of renewable energy has been expanding in the power industry. For the further development of renewable energy, it is essential to establish energy storage technologies that can fill the gap between electricity supply and demand. then, we have focused on the thermal energy storage technology with rock bed and are developing to improving heat storage and emission characteristics using a mock-up test facility equipped with a thermal storage vessel filled with rocks. In this paper, we obtained data on heat storage and emission characteristics when an electric heater was inserted into the thermal storage vessel for thermally charge the rocks through radiation. and we compared it with the case where high-temperature air heated by an electric heater is circulated inside the thermal storage vessel. We evaluated the effectiveness of radiant heat storage.

Thermal Energy Storage (TES) is one of the technologies for storing energy, and there are some methods for TES. Our TES system under developing utilized sensible heat of a substance. Natural rock was typically used as an energy storage material, and a packed rock bed which many rocks were filled into a storage vessel stores energy. The thermal-hydraulic characteristic of the rock bed was confirmed by the experiments with our mock-up facility, and the calculation models were developed, including CFD (Computational Fluid Dynamics). As the next step, the TES which was directly inserted the radiant heaters was developed. The TES could be heated by also the radiant heater efficiency. The experiments were conducted, and the calculation model of CFD was modified. Heat transfer mechanism from the heater to the rocks was mainly radiation, so the radiative heat transfer calculation code was added into the CFD model for the TES. The evaluation was carried out for the experimental result, and the model traced the measurement.

Regarding the urgent need for decarbonization and energy conservation, it is important to use enormous unused heat effectively. The amine-CO₂ cycle is a power generation system using the amine solution as the working fluid, which enables efficient heat recovery even at < 200 °C temperatures by not only condensation but also CO₂ absorption of the amine solution. The most important component for improving cycle efficiency is the absorbing condenser where condensation of water vapor and CO₂ absorption simultaneously occur, but few previous studies have been reported. In this study, we developed the pseudo two-dimensional steady state numerical simulation model for prediction of absorbing-condensation behavior based on two experimental data: basic properties of amine solution via wetted-wall column tests and absorbing-condensation behavior via visualization experiment. The simulation model employs the heat and mass transfer between three phases consisting of one gas phase and two liquid phases based on the two-phase binary condensation in horizonal tube reported by Oyama et al. (2000). Our model accurately simulated the amounts of CO₂ absorption and condensation in the visualization test section without applying a correction coefficient which was needed in two phases model, meaning that it captured actual physical phenomena.

Wind tunnel experiments were carried out to develop a vibrational power generator using a magnetostrictive material from the flow-induced transverse vibration of a cantilevered prism having a rectangular cross-section. We focus on the low-speed galloping vibration for a rectangular prism with side ratio of D/H = 0.2 (where D is the depth of the prism in the flow direction and H is the height of the prism), the low-speed and high-speed galloping vibrations for a rectangular prism with D/H = 0.4, and the high-speed galloping vibration for a rectangular prism with D/H = 1.0. The effect of the turbulence flows on the vibration characteristics and the power of the flow-induced vibrational generator was investigated. The turbulent flow was generated by double active turbulence grids, which can maintain a uniform turbulence intensity regardless of changing wind speed. The reduced velocity of vibration onset has little effect on the turbulence intensity. The response amplitude decreases in the regions of the low-speed galloping, the vortex-induced vibration, and the high-speed galloping with increasing turbulence intensity. For the high turbulence flow, the prism with D/H = 0.4 is suitable for the wind receiver of the vibrational power generation as compared to the other prisms because it has the largest power output.

To improve a vibrational power generator using a magnetostrictive material, i.e., Iron-gallium alloy, and flow-induced vibration of a cantilevered cylinder, a rigid fin plate was attached behind a cantilevered circular cylinder. Effects of the length of fin plates on the performance of the response amplitude, the power of the flow-induced vibrational power generator, and the vortex shedding frequency were investigated through wind tunnel experiments. Flow visualizations around a circular cylinder were also conducted by a smoke-wire method using a high-speed camera. The test model had a span length L of 300 mm, and a diameter D of 40 mm. The length of the fin plate was changed from 20 to 60 mm. The onset velocity of vibration increases with increasing the length of the fin plate. The circular cylinder with l_f/D = 0.5 has the maximum amplitude at Vr ≈ 9.5. From the smoke wire visualization, it is related to the inner circulatory flow which is generated on the fin plate behind the circular cylinder. The circular cylinder with l_f/D = 1 is suitable for the wind receiver to the vibrational power generation compared to the other cylinder because it oscillates at the widest range of wind speeds compared to the other models.

We proposed a prediction method for aerodynamic noise which is no dependence on the specific parameters of the impeller and discussed the performance of its broadband noise generated from a stall-controlled wind turbine. From the comparison on the two types of the wind turbines, it indicates the narrowband noise of the wind turbines is generated by the Karman vortices shed from the blade elements at the blade tips. Moreover, we indicated that these vortices are hard to form at the wind speed at the start of stall-control, whereas the wind speed at the end of the stall-control increases the broadband noise due to the high relative velocity of the separated flow.

In recent years, growing concern over global warming caused by the use of fossil fuels has led to a demand for clean power generation that can be used semi-permanently and is environmentally friendly. Wind power generation is expected as the development of new energy sources accelerates. Propeller wind turbines are widespread for large wind turbines. On the other hand, a wide variety of small wind turbines exist. Among them, the authors consider that 1kW wind power generation is important for the spread of small wind turbines, and are focusing on contra-rotating propeller wind turbines, which are expected to achieve high output. In this research, we aim to increase the output of a small wind turbine by installing a wind collecting device suitable for a contra-rotating propeller. However, since the aerodynamic characteristics of the contra-rotating propeller installed inside the hollow body have not been clarified. Therefore, we investigate the performance characteristics of the contra-rotating propeller wind turbine by numerical flow analysis using a model with the contra-rotating propeller installed inside the wind collecting device and pipe. In this paper, we focus on the design tip speed ratio, and show the results of investigating their performance characteristics and internal flow by numerical analysis.

A Magnus wind turbine uses a rotating cylinder as a substitution for airfoil-shaped blades of a common wind turbine. Magnus force shows extraordinary results in producing lift force, and this lift is sufficient to generate electricity by rotating the wind turbine to which the cylinders are attached. In a previous study, it was concluded that the performance of the Magnus wind turbine can be enhanced by fins attached to the surface of the cylinder. However, the effect of fin cross-sectional shape on lift force has not yet been clarified. Wind tunnel experiments were conducted using two types of fin shapes in the present study. It was confirmed that the strength of vortices generated by the interaction between the fin and the freestrem is affected by the fin shape, and therefore, the lift generation depends on the fin shape.

We conducted wind tunnel experiments and computational fluid dynamics (CFD) analyses to investigate the characteristics of power output, wake, and wind load of a V-type vertical axis wind turbine (V-VAWT). The experimental results showed that the highest power coefficient was obtained at a coning angle of 50° and a tip speed ratio of 3.7. Measurements of the wake velocity were conducted in a circuit-type wind tunnel with both open and closed test section conditions. The results indicated that the tendencies for a greater velocity deficit and higher turbulence intensity were more pronounced on the retreating side of the wind turbine and at the blade bottom height. Furthermore, the closed test section condition generally resulted in a greater velocity deficit and higher turbulence intensity compared to the open test section condition. Moreover, the CFD results of the wake more closely matched those obtained under the closed test section condition than those under the open test section condition. Regarding the wind load on the V-VAWT, the range of variation in the horizontal component of the wind load observed in the wind tunnel experiments was significantly larger than that predicted by the CFD results.

Savonius wind turbines have attracted attention to generate electric power in urban areas subject to high turbulence. To further improve the performance, we designed a spherical Savonius turbine expecting robustness to the change in wind direction and speed. The inflow angle was varied between 0 and 180 degrees. In addition, the performance was compared between the inflow with low turbulence intensity (1%) and high turbulence intensity (18%) using an open-jet wind tunnel. The rotational speed measured by a tachometer shows that the idling tip speed ratio increases in the high turbulence. Furthermore, the spherical Savonius turbine showed a better performance than the conventional Savonius turbine when the inflow angle is high. Further, the spherical Savonius turbine exhibited a much improved performance in turbulence, indicating it is more suitable in the urban environment than the conventional Savonius turbine.

We developed a machine learning model that utilizes data from a demonstration test conducted in the Obama hot spring, Unzen City, as its training dataset. This model was designed to predict the output power of an air-cooled regenerative Organic Rankin Cycle (ORC) based on the ambient temperature and hot water temperature, while considering the mass flow rate, turbine outlet pressure, and outlet temperature. Our results indicate that the machine learning model can predict the actual output power of the ORC by effected the influence of the mass flow rate of the working fluid. Additionally, the model demonstrated the potential to predict the ORC output using actual ambient temperature data obtained at the Obama hot spring.

In a liberalized electricity market, the long-term profit of power generation companies is affected by the short-term price fluctuations in the wholesale market. While Japanese government has implemented the feed-in premium (FIP) system to the wholesale market to encourage low-carbon power sources, the effect of policies targeting wholesale market on the long-term plan for power plant construction is unclear. This study developed an agent-based simulation (ABS) that models daily auctions in a wholesale market and power plant construction every five years in an integrated manner, and investigated the impact of the FIP on the long-term power supply mix. While most ABS studies dealing with power supply system focus on daily market transactions, this study focuses on the interaction between short-term market transactions and long-term power plant construction. The simulation results showed that the FIP system could encourage the diffusion of renewable power sources while the share of renewable power sources did not exceed these of fossil fuel power sources. The agents with renewable power sources appeared to narrow their investment in new power plants so that fossil fuel power sources remain in the market. Such a strategy keeps the selling price in wholesale market relatively high and increase the profit of renewable power agents.

One solution to solve a global warming and a fossil fuel depletion is to install the power generation system using renewable energy more. However, Japan does not high potential to install the power generation system using renewable energy compared to the other countries, while more energy can be obtained by installing it overseas, where the potential is higher. In this study, we propose a new smart network model consisting of large-scale photovoltaic (PV) installed in Kolkata, India, which obtains superior solar radiation compared to Japan. The electricity generated from PV is used to produce H₂ via water electrolyzer. The produced H₂ is then converted into liquefied H₂, methylcyclohexane (MCH), liquefied CH₄, and liquefied NH₃. After that, they are transported to Japan. We propose that these H₂ carriers are utilized as a fuel for proton exchange membrane fuel cells (PEFC) system, NH₃ gas turbines and LNG gas turbines for power generation in Japan. We evaluate the energy efficiency and the amount of CO₂ emission control for the whole process. As to the energy efficiency, it is revealed that the power generation by LNG gas turbines after liquefied CH₄ transportation is the optimum. Regarding CO₂ emission reduction, it is clear that the power generation by PEFC system after liquefied CH₄ transportation is the optimum.

Currently, most underground heat exchangers are installed by burying pipes vertically in the ground and allowing water or air to flow through them for heat exchange. However, in Japan, the strata are fragile to collapse, making construction costs high and making it difficult to spread. Therefore, by using the Horizontal Directional Drilling (HDD) method, which buries pipes horizontally in the ground, construction costs can be kept low. In addition, Japan has many geological formations rich in groundwater, and it is known that high performance can be expected from groundwater over a long period of time (several weeks) if the pipes are buried in a permeable layer rich in groundwater. Therefore, we conducted an experiment using two underground heat exchangers buried orthogonally to each other using the HDD method to evaluate the heat transfer performance. The experimental results showed that groundwater flow did not clearly improve the performance, but it was clear from the experiment that groundwater flow near the surface at a depth of 3 m could be affected by the temperature of the groundwater when it rains. Although the heat transfer rate decreased due to the influence of groundwater near the surface, an increase in heat transfer rate can be expected with deeper groundwater.

Since the power output of variable renewable energies (VREs) depends on weather conditions, it is difficult to supply electricity according to demand. The introduction of a large amount of VREs will result in excess power plant capacity to meet electricity demand, increasing costs associated with power generation and power plant capacity, etc. Therefore, it is important to reduce wasted electricity. One effective way to use surplus electricity is to utilize it for automobile traffic. In this study, we analyzed the optimal power supply configuration and cost reduction effects by utilizing surplus power from the massive introduction of VREs for electric vehicles (EVs) and hydrogen production power for fuel cell vehicles (FCVs). Adding the demand for hydrogen from FCVs as well as EVs demand can reduce the overall cost of the system by effectively utilizing the surplus electricity from the increased share of VREs after 50%. Optimizing EVs recharging and hydrogen filling leads to reductions in power plant capacity and storage battery installation, effective use of the facilities in each region, and contributing to the reduction of excess electricity.

Small-scale hydropower is one of the important alternative energy, and is expected because of its large amount of energy and high capacity factor. However, small hydropower generation over 10kW have problems that there is a limit to the installation place and the environmental load is relatively large. Therefore, we focused on pico hydropower less than 1 kW, which can be applied to agricultural pipelines and has a low environmental load. Since pico hydropower has the problem of low efficiency, we adopt contra-rotating rotors that can be expected to achieve high performance. It is necessary to develop small hydroturbines that can keep high performance over a wide flow rate range.

In previous research, we have designed turbines with diameters of 49 mm and 76 mm, and these turbines have specifications that are suitable for the medium-head environments in which they are expected to be used, such as agricultural canals and river fish farms. Therefore, in this study, with the aim of expanding the application field of small hydroturbines and understanding the application range of the counter-rotating mechanism, we designed new turbines with diameters of 76 mm and 121 mm (D76 low head model，D121model) , and evaluated their performance characteristics and internal flow by numerical analysis. In addition, for the D76 low head model, we manufactured a turbine and a demonstration test apparatus, and conducted a power generation experiment under a test environment simulating a field environment to evaluate the power generation performance of small hydroturbines at each flow point.

In order to develop an in-line small hydroturbine that can generate 300W at a small flow rate of 3l/s, we adopted a contra-rotating rotors to achieve both miniaturization and high efficiency of our hydroturbine in this study. A centrifugal rotor that can be applied to small flow rates and high heads is used for a front rotor, and a hybrid rotor that combines a mixed flow rotor and an axial flow rotor is used for the rear rotors with the propose of recovering the same head as the front rotor. The performance of the front rotor was greatly improved by providing a pre-swirl by a volute, and the target performance was achieved. In this study, an experimental apparatus was constructed to understand the performance of the actual model, and a numerical flow analysis was conducted focusing on the exit angle and tip clearance of the front rotor to increase the swirl flow into the rear rotor.

Thermal fatigue cracking can initiate at tee pipes where high and low-temperature fluids flow in. In this study, the heat transfer process from the fluid to a branch pipe was investigated under flow patterns where the main pipe flow impinges on the branch pipe wall and penetrates into the branch pipe. The test section consisted of a horizontal main pipe with an inner diameter of 150 mm and a vertical branch pipe with an inner diameter of 50 mm. The fluid temperature difference at the inlets was about 30°C. The ratio of momentum in the inlets for the main and branch pipes was changed. Temperature distribution along the branch pipe was measured with three measurement blocks. Each block had two sheathed thermocouples installed. This allowed simultaneous measurement of the fluid temperature at 1 mm from the wall and the temperature at the pipe inner surface. The temperatures at the fluid and pipe inner surface fluctuated, because the hot flow in the main pipe penetrated into the branch pipe. The heat transfer coefficient on the pipe inner surface was obtained using the power spectrum method. When a 45-degree elbow was installed at the upstream part of the branch pipe, the heat transfer coefficient increased, reaching up to 1.9 times the value compared to the case without the elbow.

Thermal fatigue is caused by the mixing of hot and cold fluids in pipe geometries such as T-junction piping. In previous studies, it was found that flow from the main fluid intermittently penetrate into the branch pipe depending on the momentum ratio between main and branch flows. In this study, numerical simulation was conducted to investigate the effect of the confluence geometry on the penetration flow in the branch pipe. The computation domain was 100 mm of the main pipe radius and 50 mm of the branch pipe without pipe walls. The turbulence model used the Large Eddy Simulation (Dynamic Smagorinsky). The results showed that the confluence geometry influenced the penetration flow pattern in the branch pipe.

The mass transfer coefficient, which is related to the flow characteristics within pipe elements, is one of the important parameters to predict the pipe-wall thinning due to flow-accelerated corrosion. In this study, we evaluate the measurement uncertainty of the calcium sulfate dissolution method, which is a method for measuring mass transfer coefficients, to clarify the mass transfer characteristics of pipe elements such as elbows and T-shaped pipes. The relationship between the flow and mass transfer characteristics is also considered based on the results of mass transfer experiments on various piping elements.

Flow-accelerated corrosion (FAC) is a pipe wall thinning phenomenon caused by a combination of thermal-hydraulic, water chemistry, and material factors. The current management of the pipe wall thinning of Japanese nuclear power plants is based on the thinning rate and residual lifetime evaluated using the measured pipe wall thickness. While current management has the advantage of directly identifying the residual wall thickness of pipes and the timing of replacement and repair, there are issues with management for piping sections and systems where the actual residual lifetime cannot be accurately identified because it has not been measured or because it is difficult to measure. To rationalize the current management, we have been developing FALSET, a pipe wall thinning prediction software, to improve its prediction accuracy and to study its specific applications in wall thinning management. However, the actual plant includes watersteam two-phase flow systems in its thinning management targets. In this study, we updated the two-phase flow FAC prediction model by applying the concept of the water single-phase flow FAC prediction model, and confirmed the prediction performance by comparing the predicted and measured wall thinning rates for an experimental system with a low chromium content.

Assuming damage to the piping system due to deterioration or damage at a power plant site, the fluid held inside the system will be dispersed into the surrounding area, which may affect the function of peripheral equipment and work safety at the site. In particular, if the piping is held under high pressure, the high-speed impact of the leaked fluid may increase operational risks due to external injuries. In this study, among the indicators that contribute to the importance of maintenance, we focused on human external wounds, which can be a risk to work safety, and conducted experiments to measure the impinging pressure of jets under various flow conditions. The obtained experimental data were assigned to the AIS (Abbreviated Injury Scale) model to evaluate the probability of a serious injury level when a jet impinged a human body. The results suggest that low-temperature water with high fluid density, in particular, has a relatively higher risk of serious injury due to external wounds than high-temperature steam or flashing.

In order to evaluate Flow Accelerated Corrosion (FAC) in local depressions, the correlation between wall thinning rate in the depressions and the geometry and flow conditions was evaluated by CFD analysis and wall thinning evaluation method. The results of the evaluation showed that the flow structure at the depression changed with an increase in the aspect ratio of the depression. As a result of evaluating the geometry factor, which is the relative flow factor of the FAC, the geometry factor at the bottom of the depression exceeded 1.0 under conditions where the aspect ratio was small, however, a decreasing trend was observed when the aspect ratio was above 1.0. From the evaluation, it can be considered that when wall thinning occurs in a local depression, it is necessary to evaluate the rate of wall thinning in accordance with the progress of wall thinning.

Unnecessary plant shutdowns are avoided using the cumulative absolute velocity (CAV) on the nuclear power plant’s free-field seismic instrumentation to determine operating basis earthquake in the US; however, the relationship between the CAV and damage mechanism has not yet been clarified. In a previous study, authors found that the CAV of the piping vibration response can relate to the vibration stress, using the velocity rule from the ASME standard for the Operation and Maintenance (OM) of Nuclear Power Plants. Using the velocity rule, a new evaluation method of cumulative fatigue damage can be derived as proportional to CAV of the vibration response to the 2.4th power. In this study, the Z-bend pipeline is considered to confirm the applicability of the new method based on the velocity rule to more general pipelines. The vibration response of the Z-bend pipeline to seismic waves was calculated, and the cumulative fatigue damage was evaluated using both the new method and direct calculations. The results were in good agreement.

Next generation innovative reactors have a new value of their flexibility with variable renewable energy. A sodium-cooled fast reactor (SFR) can make flexibility by coupling a thermal energy storage (TES) system with molten salt. New challenging items for the SFR coupled with TES are to develop safety design approach and a heat exchanger between sodium and molten salt. On that account, a three-year project has been performed to develop 1) a safety design approach and risk assessment methodology of the SFR with TES, 2) a performance evaluation technology of a heat exchanger between sodium and molten salt as well as heat transfer improvement measures, and 3) an evaluation technology of chemical reaction characteristic between sodium and molten salt as well as safety improvement measures. This paper describes the effect of sodium-molten salt heat transfer tube failure in addition to the project overview and progress.

Next generation innovative reactors have a new value of their flexibility with variable renewable energy. A sodium-cooled fast reactor (SFR) can make flexibility by coupling a thermal energy storage (TES) system with molten salt. New challenging items for the SFR coupled with TES are to develop safety design approach and a heat exchanger between sodium and molten salt. The heat exchanger types suitable for the SFR coupled with TES are selected. Simple evaluation of heat transfer performance using heat transfer coefficient formula is performed. And Computational Fluid Dynamics (CFD) thermal analyses by STAR-CCM+ Code with partial model of selected heat exchanger are performed to develop evaluation technology. This paper describes the study of the performance evaluation technology of a heat exchanger between sodium and molten salt and the confirmation of heat transfer improvement measures effects up to FY2023.

In a sodium-cooled fast reactor (SFR) coupled to thermal energy storage system, the reaction between nitrate molten salt as thermal storage material and sodium as coolant of SFR may occur under the postulated acccidental condition such as the failure of heat transfer tube of sodium–molten salt heat exchanger. Thus, reaction behavior of sodium-nitrate molten salt is one of the important phenomena in terms of safety assessment of the cited system. For the first step to clarify reaction behavior of sodium-nitrate molten salt, the thermal analyses using individual nitrate molten salt reagents were performed to obtain the fundamental information as reference data for sodium-nitrate molten salt reaction experiment. It was confirmed that thermal physical properties such as melting point and enthalpy for NaNO₃, KNO₃ and solar salt (NaNO₃-KNO₃) are comparable to the thermochemical data base. Besides, the preliminaly tests for Na-NaNO₃ and Na-KNO₃ reactions were carried out. It was found that Na-NaNO₃ and Na-KNO₃ reactions may occur after sodium melting below the melting point of NaNO₃ and KNO₃, respectively.

The design optimization process for plant structure is being developed as development of design support tool for sodium-cooled fast reactor. The process which is possible to optimize various design parameters with consideration of actual design was developed and implemented to the system. To confirm the applicability of implemented process, the process was applied to the optimization problem of minimizing failure provability based on thermal transient and seismic loads which show conflicting requirements for the wall thickness. In its optimization problem, the optimization targets were the wall thickness of reactor vessel and plant parameter which effect to the thermal transient load against the wall. Through the process application to the optimization problem, it was confirmed the applicability of implemented process to multivariable optimization problem.

Japan Atomic Energy Agency is developing an innovative design system named ARKADIA to achieve the design of an advanced nuclear reactor as a safe, economic, and sustainable carbon-free energy source. ARKADIA consists of three systems: the Enhanced and AI-aided optimization System (EAS), the Virtual plant Life System (VLS), and the Knowledge Management System (KMS). In the first phase of its development, ARKADIA-Design for design study and ARKADIA-Safety for safety assessment are being developed individually. In this paper, focusing on the ARKADIA-Design, achievements in the development of optimization processes in the fields of the core design, the plant structure design, and the maintenance schedule planning, as major function of ARKADIA-Design, and numerical analysis methods to be used for the detailed analysis to confirm the plant performance after optimization are introduced at this point in time.

Due to growing concerns over climate change as well as to recent cost declines, variable renewable energies (VRE) have rapidly been diffusing worldwide. Massive deployment of VRE, however, requires additional costs related to the intermittency of VRE, known as integration costs. These cost increases are related closely to the required power storage capacities. Electrification should be promoted in non-electric sectors, such as industries, which shares approx. 70% of enthalpy-basis energy consumption in Japan. Given that thermal energy is mostly used in the industry sector, energy policy makers should consider energy balance over society. One of green transformation policies is the energy storage. The research committee of energy storage technologies toward carbon neutrality developed four suggestions: 1) Development of energy storage best mix, 2) Transformation to green society, 3) utilization of heat storage technologies, and 4) Development of energy storage strategy beyond 2050. This paper describes suggestion 1) Development of energy storage best mix in response to large-scale deployments of variable renewable energy.

Due to growing concerns over climate change as well as to recent cost declines, variable renewable energies (VRE) have rapidly been diffusing worldwide. Massive deployment of VRE, however, requires additional costs related to the intermittency of VRE, known as integration costs. These cost increases are related closely to the required power storage capacities. Electrification should be promoted in non-electric sectors, such as industries, which shares approx. 70% of enthalpy-basis energy consumption in Japan. Given that thermal energy is mostly used in the industry sector, energy policy makers should consider energy balance over society. One of green transformation policies is the energy storage. The research committee of energy storage technologies toward carbon neutrality developed four suggestions: 1) Development of energy storage best mix, 2) Transformation to green society, 3) utilization of heat storage technologies, and 4) Development of energy storage strategy beyond 2050. This paper describes suggestion 2) Transformation to green society by zero-carbon energy, 3) further utilization of heat storage technologies in the industry and civil sectors, and 4) Development of energy storage strategy toward achievement of carbon negative emission beyond 2050.

As the importance of energy storage technology increases for the decarbonization of energy systems in the future, various types of energy storage technologies are supposed to be used depending on their characteristics. In this study, we analyzed the role of thermal storage technology in the energy storage mix using a mathematical optimization model based on linear programming. Compared to the assumed cost of lithium-ion batteries of 15,000 yen/kWh, if the cost of heat storage equipment exceeds 10,000 yen/kWh, it will hardly be installed. Conversely, as the cost becomes lower, the optimal amount of installation will increase rapidly. Also, if the cycle efficiency were to rise to 65% from the assumed value of 45%, the optimal amount of energy to be introduced would exceed 200GWh, indicating that improving cycle efficiency is also important for promoting the introduction of heat storage equipment. Thus, it is important to maintain a variety of technological options to deal with future uncertainties, and to proceed with technological development aimed at reducing the cost of promising technologies.

The big picture of the energy transition toward 2050 is achieving carbon neutrality, followed by green transformation. The role of energy storage systems is one of the means for these aims, not the ends. Many policy papers have already described that carbon neutrality would be achieved by both wheels of deep decarbonization of primary energy sources and electrification of utility, and to achieve that, enormous variable renewable energy should be introduced being supported by batteries and hydrogen produced by water electrolysis and its versatile usage. However, since the required amount of energy storage is too large and the remaining time to 2050 is too short, the energy storage system requires economically affordable and easily scalable technologies with a high technical readiness level. The importance of thermal energy storage systems is emerging from the background and situation.

Silver zeolites AgX and AgR with high adsorption performance for iodine in high temperature and high humidity vent gases have been developed. In actual operation, it is desirable that the adsorption performance is maintained even when the zeolite is stored for a long time before use or exposed to a high temperature and high humidity atmosphere at more than 100 °C for several days after use. For this reason, silver zeolites were stored under various severe conditions, and it was confirmed that the adsorption performance was maintained. The adsorption of iodine is chemisorption. To verify the reaction mechanism, the formation of methanol from methyl iodide was evaluated.

When a severe accident occurs at a nuclear power plant, various radioactive substances are generated such as inorganic iodine, organic iodine, noble gases, and particulate matter. As a measure to remove these substances, Filtered Containment Venting System (FCVS) has been installed. However, radioactive noble gases are difficult to remove because they have poor chemical reactivity and low solubility in water. RASA Industries, Ltd. has developed silver zeolite XeA as a noble gas adsorbent to replace conventional activated carbon. XeA has superior Xe retention performance compared to activated carbon used for noble gas adsorption, and it is possible that conventional hold-up systems can be made more compact by replacing activated carbon with XeA. Additionally, replacing flammable activated carbon with nonflammable silver zeolite can improve fire safety. This paper reports the results of XeA performance evaluation tests under various conditions.

"Advanced radioactive material removal system using silver zeolite" aimed at developing an advanced Filtered Containment Venting System or “FCVS” has been qualified for the Ministry of Economy, Trade and Industry's 2020-2023 "Nuclear Industry Infrastructure Strengthening Project". Based on the advanced FCVS technology, such as a high performance scrubbing nozzle and a multi-layer metal fiber filter, and a silver zeolite filter to remove organic iodine. To install an advanced FCVS in nuclear power plants, a test device simulating the FCVS using high-temperature steam was manufactured. The equipment is branched into two systems; the normal pressure system and the high-pressure system. We will give an overview of these devices. In addition, we report the results of the Methyl Iodide adsorption performance test.We get the result of decontamination factor (DF) >780 with normal pressure system and DF>800 withthe high-pressure system.

Differential pressure type water level gauges are generally used to measure a water level in a reactor pressure vessel (RPV), but they may not be able to measure a water level correctly in severe accident environments. Therefore, we are developing a Clamp-on Ultrasonic Water Level Measurement Method that can measure a water level in a RPV even under severe accident conditions. In this study, we measured water levels using Clamp-on Ultrasonic Water Level Measurement Method in the range of 0 to 28 cm water level using a small laboratory test apparatus. Ultrasonic transducers have a resonant frequency of 2 MHz. The test showed that the ultrasonic signal propagating through the vessel wall tended to attenuate as the water level in the vessel increased. The results were in good agreement with the ultrasonic wave propagation analysis by the finite element method (FEM) using a two-dimensional simplified model. Furthermore, an experimental equation was developed to obtain the water level from the ultrasonic received signals measured at the lowest and highest water levels, and compared to the actual water level, the deviation was less than ±1 cm.

To achieve decommissioning, drying of wet absorbent in containers for contaminated water treatment is considered to be effective in preventing dose leakage due to water leakage. Therefore, vacuum drying by heating from the side of the container is being considered, and it is very important to evaluate the feasibility and drying time in advance. However, absorbent is porous, and it is difficult to clarify the physical phenomenon because it is a very complex phase change that occurs in a system in which water and vapor exist between the absorbent particles and the inside of the pores. In this study, we designed and fabricated a vacuum drying apparatus for wet absorbent in a half-height container of actual diameter, in order to evaluate the drying method. The apparatus consists of a cylindrical container with a torus drainage tube at the bottom, an outer cylinder with a heater installed on its outer surface, a temperature controller, 39 thermocouples, a condenser, a condensate tank, a water level gauge, a vacuum pump, and a computer for data input. After each test, mass ratios of water content to absorbent were measured by sampling the absorbent to confirm that the lower part of the torus drain pipe was also dry. In addition, we tried to demonstrate the possibility of determining the end of drying by using the rate of change in the temperature of the outer wall of the container over time as a parameter.

To achieve decommissioning, drying of wet absorbent in absorption towers for contaminated water treatment is considered effective in preventing dose leakage due to water leakage. Vacuum drying by heating from the side of the absorption container is being considered for this purpose⁽¹⁾⁽²⁾. In this case, the effective thermal conductivity in the wet absorbent particle-filled layer is required for the design of the drying system. However, the moisture distribution within the layer is affected by temperature and its gradient, moisture content, and particle properties. In addition, moisture moves through the voids between particles, in the form of vapor and liquid water⁽¹⁾, making the prediction of the distribution complex. In general, during the drying process involving heating, heat is transferred within the layer as the moisture repeatedly evaporates and condenses between the particles, and the effective thermal conductivity is highly dependent on the liquid phase fraction. In the case of porous particles such as absorbent, the phenomenon is further complicated by the involvement of liquid between the particles and in the pores of the particles. In this study, the effects of water content, layer temperature, and pressure on the effective thermal conductivity of absorbent used in absorption towers (SARRY) were investigated by one-dimensional steady-state heat conduction experiments, using a cylindrical absorbent container that rotates to make moisture content uniform. The effective thermal conductivity differs from the original thermal conductivity and includes the heat transfer phenomena described above.

During severe accidents such as an anticipated transient without scram in sodium-cooled fast reactors, it is important to analyze multiphase multi-component flow behavior, when a part of disrupted core material is discharged outside the disrupted core region through control rod guide tubes (CRGTs). In particular, the fuel crust formation on a CRGT wall of the disrupted core side is an important phenomenon that affects the redistribution of disrupted fuel (the fuel discharged and the fuel remaining in the disrupted core region). Fast reactor safety analysis codes, SIMMER-III and SIMMER-IV, have been developed to evaluate the possibility of prompt criticality caused by the motion of molten core materials, and the material relocation of the disrupted core materials. This paper describes a developed model for phenomenological uncertainty of the fuel crust formation in core disruption phases in actual reactors. The model improves the applicability of the SIMMER code to the actual reactors.