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 pipe. In this paper, we focus on the attack angle and solidity that greatly affect the performance of wind turbines, and show the results of investigating their performance characteristics and internal flow by numerical analysis.

The objective of this study is to selectively obtain an arbitrary hydrocarbon component as base material of fuel from a triglyceride using a cross-metathesis reaction with olefins. In this paper, the effects of degree of unsaturation in triglyceride and the position of carbon double bonds in octane on produced hydrocarbon component were experimentally investigated. As a result, it was found that the lighter hydrocarbon component is generated by using the triglyceride having the high degree of unsaturation like linseed oil, and the narrow-cut hydrocarbon component is obtained by a change reactant from 1-octane to 2-octane.

This paper describes the fundamental study about utilization of co-glycerol derived from biodiesel fuel (BDF) production especially exhausted from small BDF plant which has no facility to dispose them by themselves. The method to add value to this co-glycerol is refining and production of pyrolysis oil under low temperature around 450 °C, using small solar thermal collector (STC) with type of parabola trough as its heat source. As a result, the temperature inside STC was increased from atmospheric temperature to 450 °C in ca 30 minutes even though the amount of co-glycerol was changed to 6 ~ 20 g due to line symmetry derived from trough shape STC, then, the products were acquired in the form of oil, glyceride-rich layer, gasification gas and char almost the same way as those of using electric furnace as heat source. And it is shown that oil contains hydrocarbon such as n-pentane, n-hexane, n-heptane, etc., in addition to BDF, excess methanol of BDF production, mono-glycerides derived from tri-glyceride of resource of BDF used.

Output power characteristics of a spark ignition engine fueled with the methane fermentation gas, which is methane and CO₂ mixture, were experimentally studied. Ammonia, byproduct of the methane fermentation, was decomposed into hydrogen and nitrogen through the electrolysis processing proposed in this study. Then hydrogen addition to the fermentation gas is supposedly improves the engine performance including the output power and thermal efficiency. To ensure this improvement with the hydrogen addition, the engine performance experiment was conducted with the ethane, CO₂ and hydrogen gas mixture from the pure-gas cylinders. The hydrogen addition improves the engine output power and thermal efficiency especially in the lean mixture (high excess air ratio) condition.

Predicting the time evolutions of electrode microstructures of solid oxide fuel cells (SOFCs) is a challenging task as the underlying mechanisms are not fully understood and the available experimental data are scarce. The present study proposes a machine learning method for predicting microstructural changes in the SOFC electrodes. A conditional generative adversarial network with an unsupervised image-to-image translation (UNIT) architecture is incorporated to predict the reduction process of NiO-based SOFC anode. UNIT successfully predicts the microstructural change during reduction for the new microstructures and can predict temperature dependence despite the limited number of training data.

In recent years, renewable energy-based power generation methods such as solar power generation have been attracting attention as an alternative to fossil fuel-based power generation methods such as thermal power generation to prevent global warming. In order to decarbonize the heat sector in addition to the power sector, the conversion of electricity derived from renewable energy sources into gaseous fuels such as hydrogen and methane is being considered. In this study, a solid oxide electrolytic cell was employed as a means of converting electricity into gaseous fuels. In addition, considering the simultaneous co-electrolysis and methanation inside the SOEC cell, a model that takes into account the temperature field inside the cell was developed and analyzed numerically. The reaction rates of the shift and methanation reactions were measured, and the obtained results were incorporated into the analysis to make the model more realistic. The results showed the potential to produce high-purity methane through a simpler system with lower facility costs.

ZnO/CuO nanowire (NW) catalysts for steam methanol reforming are prepared and evaluated for hydrogen supply to fuel cells. The NW catalysts are expected to be more durable than conventional nanoparticle catalysts due to their fine structure that prevents agglomeration. The NW catalysts are hydrothermally synthesized on a glass plate and coated with CuO by pyrolysis of an aqueous copper nitrate solution. The reforming tests of a packed bed NW catalysts reformer exhibit the effects of the fuel space velocity and the pulverization of the NW lump on the conversion and mass transport of the fed fuel gas.

In order to expand the practical application range of the proton exchange membrane water electrolyzers (PEMWE), it is necessary to reduce the mass transport loss due to oxygen at the anode. Oxygen transport near the catalyst layer (CL) is thought to have two transport mechanisms, gaseous oxygen and dissolved oxygen. However, as far as we know, there are no reports of experimental investigation of the presence of dissolved oxygen in PEMWE. In this study, the behavior of bubbles floating near CL was observed with a high-speed camera, and the bubble diameter was measured. Even after the bubbles left the CL surface, the bubble diameter continued to increase, confirming the presence of dissolved oxygen and the formation of an oxygen supersaturated region.

To install huge renewable energy such as solar, wind power, energy storage and transportation system should be installed since renewable energy has vulnerability with time fluctuation. In such systems, toluene-methylcyclohexane (MCH) conversion system are considered as a good candidate of it. Toluene would be hydrogenated into MCH then hydrogen would be transported and stalled as MCH. They are paid highly attention since they can be handled liquid at ambient temperature and pressure. But a problem to cause reduction of total efficiency is the transported water from anode side at cathode. In the toluene-MCH conversion cell, toluene is hydrogenated at cathode side and water electrolysis is performed at anode to produce proton.

Hydrogen marketplace is expected to grow exponentially, hydrogen is getting attention as a clean energy source that does not emit CO₂. We are studying the hydrogen production method by reaction of water and aluminum powder. In this study, it was necessary to increase the rate of hydrogen production. Therefore, we investigated the time variation of the hydrogen production rate, which has not been done before. Al powder was stirred in water and hydrogen was extracted. Three types of powder were used in this experiment: Al powder, Al-5wt%Sn alloy powder, and mixture Al and Sn powder. The objective of this experiment is to determine the optimum conditions for increasing the hydrogen production rate. Hydrogen flow rates were found to temporarily exceed 0.1 ml/s. The powder that produced the most hydrogen was an Al-5wt%Sn alloy powder. By measuring the flow rate of hydrogen, it is possible to predict the mechanism of the reaction of Al powder and water.

The introduction of Power-to-Gas systems that actively use renewable energy to produce hydrogen is expected to expand. To achieve this, there is an urgent need to reduce the unit cost of hydrogen production. It is necessary to operate the system under the optimal operation strategy while forecasting the ever-changing spot price and solar power generation. Currently, the method of sequentially deriving and controlling operational measures is computationally burdensome. In this paper, we report the effectiveness of a simple control rule derived by analyzing the annual optimal operation strategy with the technique of decision tree derived for the purpose of cost minimization.

For cold startup of a polymer electrolyte fuel cell (PEFC), rapid output increase after the temperature rise is a critical issue. This study investigated experimentally the effective cell structure for this issue. In the experiment, we used an adiabatic cell to simulate the temperature rise of the stack by using separators with a small heat capacity and insulation material around it. The sub-zero startup with the cell with 1.0 mm wide channel and rib was successful from –10 ℃, but the shutdown occurred immediately due to flooding after the load increase. In the power increase with 0.3 mm wide channel and rib, it was shown that the cell voltage with 0.3mm wide channel and rib becomes more stable after the load increase than with the 1.0 mm wide channel and rib. This indicates that the narrow rib and channel is effective to improve the rapid power increase after the cold startup. This is considered because the liquid water is less likely to accumulate at the interface between MPL and CL in the cell with 0.3 mm wide channel and rib.

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 transport loss, heat flow loss, which are irreversible losses when current, mass transport and heat flow occur in cell. Loss analysis found that current loss, in particular activation overvoltage, is the largest of the components, and current loss determines the efficiency of the fuel cell. An enlarged electrode area embedded in the cell was proposed to reduce the current loss. Since there is a trade-off relationship between the three losses, we calculated the electrode area so that the total loss is minimized. We also examined the effect of expanding the electrode area on the output density.

Lithium-air battery attracts great attention because of its high energy density. However, due to the low solubility and diffusivity of oxygen in the electrolyte, oxygen transport to the reaction site of the positive electrode is limited. The aim of this study is to reduce the oxygen transport resistance and increase the power output by using thin solid electrolyte membranes (ionomer). It is thought that ionomers can form a thin solid electrolyte film, which is difficult with liquid electrolytes, and can reduce oxygen transport resistance. The ionomer produced by coating the cathode with lithiated Nafion solution and drying. In this study, the effect of ionomer coating was investigated by conducting discharge experiments using cathodes with and without ionomer coating, respectively. Experimental results showed that performance was improved by using ionomer. Additionally, it was also suggested that the water content of the ionomer can affect the discharge performance.

When a lithium-air battery is discharged, lithium ions normally react with oxygen at the positive electrode, but when the positive electrode potential drops significantly, water in the electrolyte reacts with lithium ions to generate hydrogen. In this study, we proposed a new system for high-density energy storage and hydrogen supply using lithium by utilizing the structure of lithium-air batteries and this working principle, and conducted basic experiments. As a result, it was confirmed that a large overvoltage is involved for the hydrogen production reaction compared to the theoretical potential. In addition, the formation behavior of hydrogen bubbles was observed, and it was confirmed that the almost spherical bubbles were generated in this experimental system. In the future, we will investigate the detailed causes of the overvoltage and hydrogen production behavior in the hydrogen production reaction and propose methods to reduce the overvoltage in order to improve the efficiency of hydrogen production.

In response to the issue of climate change, Japan announced that it will take on the challenge of achieving carbon neutrality in 2050 and a 46% reduction in greenhouse gas emissions in 2030, while continuing efforts for a further 50% reduction target in 2030. In addition, Japan's Sixth Strategic Energy Plan, announced in October 2021, indicated that the path of the energy policy to realize this goal was based on the idea of using all available technologies and the S + 3E (Safety + stable supply, economy, environment) perspective. This report provides an overview of our company's efforts to achieve decarbonization and net-zero carbon, mainly in the field of thermal power generation, and introduces the status of the development and practical application.

The expansion of the hydrogen utilization is one of key technology for the decarbonization society, and both sides of hydrogen supply and utilization are necessary. For the large-scale utilization of hydrogen, it is expected that the hydrogen is utilized in existing boilers widely distributed in the world. Hydrogen ultilization with exisiting faciliies can makes much economical change from fossil fuels to hydrogen.

Hydrogen has a lower calorific value per unit volume than conventional gas fuel, so the supply equipment and combustion equipment for hydrogen must be larger. However, as higher fuel gas supply pressure can leads to smalller fuel volume, equipment can be downsized and much economical design can be realized, too.

In this study, the high pressure hydrogen combustion technology developed and verified in the preceding research was applied to burners used for various boiler combustion systems, and the performance was verified by carrying out the actual test, and the technology to improve the applicability to the existing boiler was developed.

The unit commitment of the thermal power units is calculated when fuel ammonia is introduced to the coal-fired power units; the capacity of power units in the discussed area consists of average capacity of existing power units in Japan. The fuel ammonia is supposed to introduce to the flexible coal-fired power units which cover the load frequency control,

LFC, of the power system. It is found that the introduction of the fuel ammonia to the coal-fired power units, that are operated as LFC, is responsible for the increase of utilization factor of the units. The ammonia supply rate enlarged in the case that the fuel ammonia price is set relatively higher than that of gray ammonia, due to the increased utilization factor of the coal-fired power units.

A gaseous ammonia supply system was used in gas turbine combustors developed in the previous research and development. As the gaseous ammonia supply system requires a liquid ammonia vaporizer and a gas compressor, the initial costs of the system and electric consumption for powering the vaporizer and compressor are expensive and thus must be minimized. Therefore, the direct supply of liquid ammonia to the gas turbine combustor is considered more desirable. Although most studies show those phenomena mainly at stable injection periods, one of the most significant problem associated with the start of injection was because of the residual gas in the liquid supply line, which leads to a two-phase flow thereby encouraging a fluctuation in flow rate, and consequently the power output and rotating speed of the gas turbines. It can be inferred that the fluctuation of the flow rate arises from upstream pressure fluctuation before the pump. The amplitude of the fluctuation of pressure before the pump is not the same, assigned to the random phenomena before the pump, and it is the effect of the gas-liquid mixing phase..

Waste brine produced from the existing fleet of desalination facilities could remove and stabilize ~231 Mt-CO₂/y as Mg-carbonate. The source carbon dioxide can range in concentration from the ambient atmosphere to 100% CO₂, allowing for a range of applications, including as an alternative to underground storage for direct air capture and point source CO₂ capture systems. To achieve rapid CO₂ removal via mineralization into Mg-carbonate, it is necessary to establish a process for thermally decomposing hydrated Mg-chloride extracted from waste brine. When heated above 400–450 °C, hydrated Mg-chloride thermally decomposes into MgO. While this route is operated industrially using fossil fuel burners at >800 °C, we produced MgO from waste brine-derived Mg-chloride dihydrate in an electric, rotary kiln at temperatures <600 °C. In our process, thermal decomposition to MgO reached 96.7% when the kiln was operated at 600 °C. Subsequent gas-solid reaction of MgO with CO₂ in a 30 °C incubator found that MgO produced in the range of 534-571 °C yielded the fastest CO₂ mineralization. To further accelerate the CO₂ mineralization rate, the energy consumption of grinding the MgO to smaller particles sizes and increasing the concentration of CO₂ were evaluated; grinding was found to be substantially less energy intensive than increasing the CO₂ concentration. Optimizing CO₂ mineralization using desalination brine can be achieved by a combination of low-temperature thermal decomposition of hydrated Mg-chloride and fine grinding of the generated MgO; deliberate concentration of CO₂ is not recommended unless case-specific factors such as site footprint require additional mineralization acceleration.

In the aviation industry, measures to prevent global warming by reducing carbon dioxide emissions are becoming a problem against the background of aviation demand that is expected to expand in the future. The International Civil Aviation Organization (ICAO) has set long-term carbon dioxide emission reduction targets, and the total emissions will not increase after 2021. In order to achieve these targets, it is essential to promote the spread of bio jet fuel. Our company uses the gasification / Fischer-Tropsch (FT) synthesis as a bio jet fuel manufacturing technology. In the gasification process, the entrained flow gasifier has been developed that realized high temperature gasification, reduced tar generation, and stable gas composition generation. Good results were obtained in a pilot scale demonstration test.

In order to design a commercial plant, it is necessary to change the shape by scaling up and to accommodate a wide range of biomass feedstocks. Numerical analysis is one of the methods to evaluate these effects quickly and inexpensively. In the previous report, the "Biomass Gasification Performance Prediction Tool" that can predict gasification performance based on basic tests was constructed, and good results were obtained in the simulation of demonstration tests. However, previously reported tools only deal with wood chip calculations. Therefore, in this paper, model parameters of multiple biomass were determined on the basis of basic tests, and gasification performance of commercial machines was evaluated.

In Central Research Institute of Electric Power Industry (CRIEPI), we are developing the basic technology for a polygeneration system with CO₂ capture utilizing various fuels such as coal, waste plastic and biomass. The system is using an O₂/CO₂/H₂O blown gasifier for producing syngas. We investigated the effect of adding plastic to coal on gasification performance experimentally using 3t/d coal research gasifier. The gasifier is pressurized, two-stages composed of a combustor and a reductor, and entrained-bed type. In this study, we evaluated the gasification characteristics of a plastic fuel that fed into the combustor and the reductor respectively. It is clarified that plastic fuel fed into the combustor is more effective for higher carbon conversion than fed into the reductor in this polygeneration system.

In Central Research Institute of Electric Power Industry (CRIEPI), we are developing the basic technology for a polygeneration system utilizing various fuels for capturing CO₂. The system is an Integrated Gasification Combined Cycle (IGCC) that uses various fuels other than coal and can generate electricity with high efficiency even after capturing CO₂. In addition, since not only electric power but also valuables are produced, the supply and demand adjustability of electric power is improved and CO₂ capturing cost is reduced. In this development, the gasification reaction characteristics and the tar generation behavior in a gasifier of fuel fed into the reductor of the gasifier are examined using a solid fuel gasification experimental facility simulating reductor of gasifier. In this study, we evaluated the gasification characteristics of fuel that is a mixture of coal and plastics.

To use the biomass fuel in pulverized coal-fired boilers, it is necessary to reduce the particle size of biomass (< 2 mm). Steam explosion is known as a pretreatment method for rupture biomass fibers. Our group has been conducting research on this steam explosion technique, which is a crushing method applicable to various biomass. This time, the steam explosion test was conducted on cedar chips and rice husks using the demonstration equipment (amount of processing: 50 kg). In this session, we report the difference in crushability and yields depending on the type of biomass and treatment conditions. Using the result in the demonstration test, we will proceed more detailed system design for commercialization.

The grindability of biomass pellets is important to get high efficiency of combustion in a boiler. However, it can’t be evaluated easily. In this paper, various biomass pellets were characterized by SEM observation and chemical analysis to predict the grindability of biomass pellets. It was found that the relationship between cell wall size and grindability. Regression analysis with cell wall size data and chemical analysis results was performed, and grindability could be predicted more precisely.

For realizing Carbon Neutral by the year 2050 it is vital to utilize Variable Renewable Energy (VRE) at maximum extent on the electricity grid. Consequently, i) lowering the minimum output of fossil fuel power plant which have been performing the important role of securing the grid frequency stability and ii) storing surplus peak power at daytime and utilizing with time offset, are inevitably needed. In this article, two examples of the potential solutions Thermal Energy Storage (TES) are introduced. TES with pressurized hot water, which is intended for meeting the need i) above, is to store surplus boiler steam with mixing the turbine condensate at the hot water tank and then use as deaerator feedwater. TES with molten salt for ii), is to store surplus electricity as sensible heat of molten salt by means of electric heater at around 565 degC and then use as the heat source of steam generator for turbine-generator. For further development of TES, Phase Change Material (PCM) which is utilizing latent heat, is expected as one of the compact heat storage media.

Though the introduction of the renewable energy is promoted in our country, a part of photovoltaic power generation is refused to be connected to the electric power system, because the electric power supply quantity to the electric power system becomes excessive in the time when the power generation quantity is large in the sunny day. In our company, research of large-scale thermal storage system for steam power plant capable of storing energy of surplus electric power is being promoted under NEDO Project. This paper introduces the conceptual design results of a large-scale thermal storage system using metal PCM as a thermal storage material.

A water hydraulic motor was developed for driving a crawler of a decommissioning work robot under the radiation environment. A cam mechanism in which reciprocation of radially arranged four pistons is changed to rotary motion was adopted to reduce pulsation of rotation speed and torque of the motor. A cam profile was designed as the theoretical pulsation of the rotation speed and torque was zero. A relation between the load on the cam and the output torque was confirmed by the experiment. A slide plate system was adopted as a distribution valve that switches water flow to the cylinder. The distribution valve was driven by the Scotch yoke mechanism which synchronized with the output shaft of the motor. The developed motor has moved by the pressure of the 0.2 MPa under no-load condition. The experimental value of the rotation speed was obtained almost as the theoretical value, which indicates the internal leakage and drain flow rate were small enough.

Increased ventilation is required in all buildings as a preventive countermeasure against novel coronavirus infection. However, increasing the ventilation volume may increase the energy consumption of the air conditioner and reduce the comfort of the occupants. Then, we decided to explore countermeasure to dissolve the tradeoff relation between mass ventilation and air conditioner energy consumption experimentally. Therefore, we performed long-term continuous measurements on the energy-saving effect of mass ventilation using a total heat exchanger and the reduction of the concentration of pollutants in the indoor air.

In the current study, the enhancement of evaporation rate for a thermally driven pumping system was investigated experimentally. Porous copper insert of variable density was applied into the evaporation chamber of the system as a method of evaporation enhancement. The investigation was carried out in a TDP system that was developed for waste heat utilization from microgrid system for rural area applications. The experiment results showed a variable level of evaporation rate and the thermal efficiency of the system. The observed general trend is that the heat transfer rate and the delivery flow rate of the system are improved significantly with the decrease of the porosity of the mesh while the thermal efficiency of the system shows an optimum level. The enhancement method resulted in 47 – 144 % increment of the heat transfer rate and 38 - 186% increment in the delivery flow rate of the system in comparison to the case where no porous mesh was used. Generally, the results seem to suggest that the enhancement method could be promising for the intended application.

In the previous report, a new seismic fatigue evaluation method was developed based on the vibration velocity of the piping system. In this study, if two parameters, that is, the maximum value of stress per unit displacement and the participation factor in each vibration mode appearing in the new method, are appropriately selected, the cumulative fatigue damage for seismic motion of general piping will be on the safety side. By this method, the relationship between the natural frequency of general piping and the maximum cumulative fatigue damage, which envelops the entire plant piping subject to a certain seismic motion, can be obtained, and an example is shown.

High efficiency coal fired power plants are expected to operate at a certain rate due to low generated electricity costs. In coal fired power plants, coal mills are important machinery that pulverize the coal and supplies the coal powder to the boiler. To protect the bearings from coal dust, seal air is added. The seal air is supplied from one seal air blower to each position of several coal mills at a target power station. An imbalance in its flowrate can lead to coal mill failures, thereby affecting the operation of coal fired power plants. In order to diagnose any problems with the operation of a coal mill immediately after maintenance, the heater method was used to measure the seal air at five locations from the outside of the supply pipes. The heater method is possible to measure the flow rate of compressed air and steam in the pipes from the outside of the pipes without any modification of the pipes, and has previously been applied to the measurement of cooling air flow in gas turbines. Due to the effects of the corona disaster and other work, the measurement schedule at the power station was restricted and the installation, measurement and removal of instruments at five locations was carried out in a period of five days. As a result, it was confirmed that the seal air flowrate at each of the coal mill locations was normal value and that there were no problems with operation.

Thermal fatigue cracking may initiate at a tee pipe where high and low temperature fluids flow in. The mixing flow causes temperature fluctuation at the pipe inner surface and may result in fatigue crack initiation. In this study, fluid temperature fluctuations in a branch pipe of mixing tee were investigated under flow patterns where the main pipe flow impinges on the branch pipe wall and penetrates into the branch pipe. The test section is 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. Fluid temperature difference in the inlets was about 30°C. The ratio of momentum in the inlets for main and branch pipes was changed. Temperature distribution along the branch pipe was measured with three measurement blocks. Two sheathed thermocouples were installed in the block. It was allowed to measure the fluid temperature at 1 mm from the wall and the temperature at the pipe inner surface simultaneously. The temperatures at the fluid and pipe inner surface fluctuated, because the hot flow in the main pipe penetrated into the branch pipe. The temperature fluctuation for small momentum ratio conditions increased with the momentum ratio and decreased in the direction of branch pipe axis. The temperature fluctuation for large momentum ratio conditions was saturated and became constant in the direction of branch pipe axis.

In order to clarify the effect of flow on pipe wall thinning due to flow-accelerated corrosion at a T-shaped pipe junction, we measured the flow field using particle image velocimetry. In the experiment, a T-shaped pipe with a pipe diameter ratio of 1 between the branch pipe and the main pipe was used, and the effect of the flow ratio between the branch pipe and the main pipe was investigated. It was clarified that the inflow from the branch pipe was separated at the connection with the main pipe to form a recirculation region of the flow, and that the separation region of the flow increased as the flow rate from the branch pipe increased.

Flow Accelerated Corrosion (FAC) is one of the causes of pipe wall thinning in power plants. It is widely known that FAC is usually experienced between 90 ℃ and 230 ℃, and that the maximum FAC rate is shown at about 150 ℃. Low-temperature FAC (< 90 ℃) has been also reported, however, knowledge of the effects of material and environmental factors on FAC rate at low-temperature is very limited. In this study, effects dissolved oxygen (DO, up to 20 ppb) on FAC rate of carbon steels with different Cr content (up to 1 wt.%) at low temperature (30 ℃ and 50 ℃) were investigated. The results indicate that the amount of DO require to suppress FAC depends on the Cr content of the steel and the temperature.

Pipe wall thinning phenomena, as often seen in nuclear or thermal power plants, are serious problems especially for the operation and management of nuclear power plants. To operate nuclear power plants with safety for a long time, it is important to predict where the pipe wall thinning phenomena occur. Flow accelerated corrosion (FAC) is one of the pipe wall thinning phenomena. The pipe wall thinning area is large in case of FAC. FAC is a complex phenomena of the corrosion due to water chemistry and the acceleration of corrosion by hydrodynamics. The effect of the water chemistry is mainly represented by the solubility of iron and the effect of hydrodynamics is represented by the mass transfer coefficient. From some researches of FAC under water-steam two-phase flow, the relationship between liquid film and FAC mechanism was almost same as the relationship between that of FAC under water single-phase flow. From these results, FAC predict model under water-steam two-phase flow are constructed based on that of water single-phase flow in CRIEPI. The FAC predict model under water-steam two-phase flow are checked by FAC experimental results under the water-steam two-phase flow. When the thinning rate is low, the measure of change of wall thickness is difficult. The wall thickness is continuous measured by thin-film UT, and then the uncertainty is low, so that the change of the wall thickness is evaluated.

“On-Line Maintenance (OLM)” with effective utilization of IRIDM (Integrated Risk Informed Decision Making) can contribute both plant safety enhancement and plant operability improvement simultaneously in nuclear power plants (NPPs). At the stage of planning and implementing OLM in NPPs, all workers in NPP should recognize the risks, and establish risk management actions. These processes are very important to enhance plant safety. OLM can contribute leveling maintenance work load which used to be accumulated during outage. The more chances experienced workers have to lead maintenances, the more technical transfer from experienced worker to young worker will be made. As OLM has already had excellent results in the United States and Europe, we shall promote implementation of OLM in NPPs in Japan.

It is important to improve both plant safety and plant operability simultaneously in nuclear power plants (NPPs). “On-Line Maintenance (OLM)” is one of solutions for this issue. This paper proposes “Concept of risk management for On-Line Maintenance” based on IRIDM (Integrated Risk Informed Decision Making). In this proposal, implementation of OLMs should be decided by CDF (Core Damage Frequency) and CFF (Containment Failure Frequency) under system configuration for OLMs, and completion time of OLMs should be decided by increment of CDF and CFF.

The purpose of this document is to provide guidance how to establish risk mitigation and management actions for On Line Maintenance (OLM). Effective utilization of integrated risk-informed decision-making (IRIDM) is the key issue for this planning. These mitigation and management actions, which are utilization of portable equipment or preparation of emergency procedure, can restore and enhance plant safety during OLM. This guidance shows processes how to establish the actions and how to access these.