For reducing environmental impact and keeping the reliable operation of solid-fueled boilers such as pulverized coal firing ones, the prediction method of the emission and operation reliability is important. Due to the recent growth of computer performance, numerical simulation is effective for understanding the complex phenomena inside the boiler furnace. We developed the simultaneous evaluation method of the emission and operation reliability such as metal temperature, wall corrosion, and slagging characteristics by numerical simulation. This paper presents the validation results of our simulation method from the lab-scale furnace to the actual boilers. The developed method well captured the emission and metal temperature characteristics of the actual boilers.
It is important to reveal the characteristics of flow structure and heat transfer of a turbulent flow in an H-shaped channel―two counterflow channels connected at the middle by a connection channel, since such flows can be seen in various engineering products and infrastructures. In this study, in order to investigate the effect of connection length of mixing region in the H-shaped channel on heat transfer processes, numerical simulations of two-dimensional incompressible turbulent heat transfer in H-shaped channel with various connection lengths are carried out. As a result, mainstreams change direction by 180 degrees in the mixing region whose length is 40 times as large as half-width of the inflow channels at Re 167400 and the temperature in the middle of the mixing region is found to be close to that of the channel walls.
When temperature and pressure of the liquid and gas are raised to the critical point, they start behaving as a supercritical fluid. The supercritical fluid has the characteristics of both the liquid and the gas. These characteristics have a wide range of application to engineering process namely, the energy devices, the semiconductor washing and so on. For device development, it is necessary to have a good understanding of this phenomenon. But it is difficult to simulate flow of supercritical fluid numerically by conventional methods, due to sudden change of the physical properties depending on pressure and temperature condition. In this paper, natural convections inside a cubical cavity and Rayleigh Benard convection calculated by using numerical simulation technique of the supercritical fluid developed by Yamamoto. The effect of the density difference induced by the phase change to the flow is investigated.
Water spray is used for cooling intake air of gas turbine in thermal power plant. Although the amount of residual droplets needs to be known to optimize the spray amount to improve the cooling efficiency, Phase Doppler Anemometry (PDA) is difficult to use in thermal power plants because it requires precision equipment. In this study, we developed a method for determining the residual droplet flow rate using the laser transmittance for the cooling water spray which can be used in thermal power plants. The optical path length dependence, spatial distribution, flow conditions, etc. of the laser were verified at the experimental level. The utility of the same apparatus was evaluated by using it in a real thermal power plant.
The present study investigates experimentally characteristics of dissolution of carbon dioxide (CO2) micro-bubbles into liquids. As the liquids, artificial seawater and tap water were used to know the effects of salinity on the dissolution. The Sauter mean diameter of the bubbles, concentration of dissolved CO2 in liquid, volumetric mass transfer coefficient, void fraction, were measured. In addition, the interfacial area concentration was determined from experimental values of the Sauter mean diameter and the void fraction. The volumetric mass transfer coefficient is larger for seawater than tap water because the interfacial area concentration is much larger for seawater than tap water.
In the recent years, the strong oxidation power of ozone and radicals has been expected to be useful to water treatment. The purpose of the present study is to improve a micro-bubble generator with gas-liquid interface discharge for the application of water treatment. In the experiment, the decolorization test was conducted using indigo carmine solution as a sample in order to clearly the effect of supplied air volume and applied voltage on the oxidative decomposition. The results show that the decolorization of solution by the gas-liquid interface discharge in micro bubble was succeeded in about 1 hour. In addition, the oxidative decomposition processing speed became faster with increasing of supplied oxygen volume and number of discharges.
Droplet spray flow with phase change appears during operation in various energy devices. Little has been reported on gas-liquid two-phase spray flow with condensation. Therefore, it is desired to grasp the flow characteristics of splay flow with condensation. The purpose of this study is to elucidate the flow behavior of gas-liquid two-phase spray flow with condensation. In this study, flow velocity of the spray flow and the droplet diameter were measured in the system. For flow velocity measurement, we applied PTV measurement. Droplet diameter was also measured with image processing. As a result, the water droplets decelerate in the downstream direction of the spray flow. Also, the distribution of water droplet diameter does not change. According to comparison with numerical analysis, the droplet flow velocity distribution did not agree, but the tendency to slow down the droplet agreed. In the future, it is necessary to measure the droplet flow velocity using the laser doppler velocimeter.
Recently, the development of a small and high efficient heat exchanger, which is utilized in a fuel battery and a heat pump system for Carbon dioxide refrigerant and so on, is strongly required. In the previous study, a prototype of stacked high-pressure resistance microchannel heat exchanger manufactured with diffusing bond technique has been proposed. It has been confirmed that it achieves miniaturization to one hundredth and a heat transfer rate equal to or higher than that of existing heat exchangers. In the present study, the objective is to reveal flow and heat transfer properties of this microchannel heat exchanger when water and vapor are employed as low and high-temperature fluids, respectively. However, what makes these heat exchangers high efficient than previous heat exchangers is not clear. Hence, illuminate that by simulating the microchannels of the heat exchanger. The shape of microchannel is rectangular, and hydraulic diameters is 500 μm. From experimental results, it was shown that the flow performance of boiling and condensation in a microchannel. Furthermore, it is found that the condensation heat transfer is changed by the location of the microchannel.
Understanding of an onset of boiling plays an important role in the design of boiling equipment. The onset of boiling condition in downward flow is complex due to stagnant and/or reverse bubble caused by buoyancy force on thermalnonequilibrium flow field. The purpose of this study is to clarify the characteristics of onset of boiling under downward flow. We conducted heat transfer experiments with different heating length under both upward flow and downward flow. The onset of boiling condition is estimated by using the pressure drop of test section. In the case of long heating length, low heat flux condition, the thermal equilibrium quality on onset of boiling condition had almost constant value regardless of mass flux. In the case of shot heating length, high heat flux condition, the thermal equilibrium quality on onset of boiling condition was drastically decreased with an increase of mass flux. These characteristics were classified into two groups; the thermal dominant condition and the thermal-fluid dominant condition. The modified Bowring’s correlation and modified Levy’s correlation were in good agreement with the experimental results for each condition.
Centrifuges are one of the most commonly applied devices for solid-liquid separation in the factory. The problems needed to be solved in separation process are the most efficient ratio between separation and the energy utilization efficiency. In general, the separation ratio is very low when the speed of centrifugation is limited. The power required by the centrifuge is not consumed efficiently which leads to high operational cost. A device which able to be attached in the rotating centrifuge to measure the solid phase distribution in the separation process is proposed to give a compromise solution. This wireless device is developed by simulating the particle field in the measurement domain based on electrical resistivity resistance technique. The model consists of two adjacent pole to pole array electrodes in a cubical apparatus. The simulation results show the effect of the particle presence based on its electrical properties to the particle thickness distribution. The comparison to the experimental data gives a good tendency to develop the whole systems.
Toward the improvement of electric vehicle (EV) performance, the design of the motor shape appropriate to heat removal is important. A typical EV motor is composed of a pair of coaxial cylinders with a fixed outer cylinder (stator) and a rotating inner cylinder (rotor). The gap region between the rotating coaxial cylinders is very narrow compared to the diameter, and it is thought that heat is easily accumulated. Moreover, since heat removal is promoted by convection, there is a deep relationship between flow and heat transfer in the gap region. Therefore, to clarify the influence of the time change of rotor rotation speed on the flow inside the gap region of the rotating coaxial cylinders simulating the EV motor, we have conducted visualization experiment of flow at gap region. Experiments were conducted to increase the rotation speed from the stop state linearly and to decrease the rotation speed linearly from the initial rotation speed to the stop state. Regarding the flow in the gap region, it was found that the critical Reynolds number for transition from couette flow to Taylor vortex flow increases as the rotation speed increase. In addition, it was found that the critical Reynolds number in the case of linearly increasing the rotation speed is larger than the critical Reynolds number in steady state rotation. Moreover, it was found that the flow when the rotor was stopped was more turbulent when higher decrease rate of rotation speed.
Regarding the storage of fuel debris accompanying the decommissioning of the Fukushima Daiichi Nuclear Power Plant, management of hydrogen gas generated by radiolysis of water is indispensable. For this reason, it is important to maintain the concentration of hydrogen in sealed vessels below the explosion limit in order to improve the safety of long-term waste storage containers. Then, it was considered that the generated hydrogen is combined with oxygen by the passive autocatalytic recombiner (PAR) and return to water. Basic experiments were performed to investigate the reduction performance of hydrogen concentration of a sealed container with PAR and Preliminary numerical simulations were carried out to predict hydrogen behavior in the container. The present study shows the results of the basic experiments and preliminary numerical simulations.
In order to reduce the power generation of the CSP plants, an economical and technical solution in the heat storage is a key point. In the previous study, an TES (thermal energy storage) system which using air as HTF (heat transfer fluid) and stone as the storage material have been developed. This paper describes the CFD study on a TES system with stone using high-temperature air as HTF to be hybridized with CL-CSP (Cross Liner-CSP). The numerical simulation is performed using commercial CFD software ANSYS Fluent using a pilot-scale TES model. The influencing factors which affect the thermal stratification, such as the inlet temperature and mass flow rate, are taken into consideration. Furthermore, the thermocline thickness is discussed for the CFD simulation result to evaluate the performance of charging and discharging of TES tank.
Elemental analysis system was proposed to enhance the efficiency of fuel debris retrieval on the Fukushima Daiichi NPP. The elemental analysis system required high radiation. Designing an elemental analysis system requires a fundamental study in several aspects. It includes the effect of sound spatial distribution inside the container. In this paper, the sound spatial distribution along the length of the container was investigated chemically using Luminol. The reaction between the Luminol (C8H7N3O2) and hydrogen peroxide (H2O2) produced from the collapsing bubble under ultrasound sonication was used to visualize the position of intense sound pressure. The sound pressure was observed under various ultrasonic frequency and liquid height. The result showed the sound pressure plays a high role in the light emission. The broader sound spatial distribution was observed under high ultrasonic frequency. The variation of liquid height showed the sound reflection occurred in the presence of different phase inside the container.
In general, when cooling high temperature circular or rectangular channel by forced convection, there are several methods for enhancement of heat transfer such as attaching radial or spiral fins on the channel surface or inserting twisted tape in the channel. For example, there is method of attaching various fins on the heat transfer surface, method of processing the surface roughly, and so on. However, it has to take into consideration the deterioration of the structure strength by attaching the fins on the heat transfer surface with the design of the cooling channel. The best design exists to increase the heat transfer and to reduce the flow resistance of the channel. Then, the purpose of this study is to investigate the heat transfer characteristics not only by forced convection but also natural convection in the vertical rectangular channel inserting the copper thin wire with high porosity. Experiments were also carried out to investigate the heat transfer and fluid flow characteristics by natural convection when the porous material with high porosity is inserted into the channel. This paper described the heat transfer coefficient and the amount of the removed heat in the proposed channel.
A small cooling device with multi-nozzle impinging jets is proposed for cooling an on-vehicle inverter with the heat generation of ~ 500 W/cm2 . In order to minimize the cooling device, a double flow channel concept is introduced. In addition, to increase the critical heat flux, a heat transfer surface with uni-directional groove is utilized. 39 nozzles of 1.0 mm in diameter are set 2.0 mm above the heat transfer surface. The groove size is 1.0 mm x 1.0 mm. The experimental data shows that the critical heat flux of the cooling device exceeds 400 W/cm2 and achieved 745 W/cm2 at the maximum.
One of the main concerns regarding in-vessel retention (IVR) during a severe accident is guaranteeing sufficient cooling performance to avoid the melt-through of the pressure vessel. In such an event, the vessel is submerged in water, and boiling is occurred to remove the heat. However, the main problem is that there is a limit to the pool boiling heat transfer at the outer surface of the reactor vessel due to occurrence of critical heat flux (CHF) conditions. Therefore, CHF enhancement is important to increase safety margin of IVR. In previous studies, CHF was enhanced approximately twice compared to bare surface by attaching honeycomb porous plate (HPP) to the heated surface. In order to establish the IVR, the cooling technology should be considered in forced flow boiling with the downward heat transfer surface. Moreover, we proposed a two-layer structured HPP for further CHF enhancement. Therefore, in the present paper the effect of the single and two layers HPPs on the critical heat flux under flow boiling with the downward heat transfer surface was investigated experimentally. As a result, the coalescent vapor bubbles cover the heated surface for a long period depending on the flow pattern under the flow boiling condition, resulting in liquid drying inside a HPP and reduction of CHF. Even in this situation, a two-layer structured HPP can be applied to CHF enhancement in flow boiling with the downward heat transfer surface.
A Very High Temperature Reactor (VHTR) is one of the next generation nuclear reactor systems. From a view point of safety characteristics, a passive cooling system should be designed as the best way of a reactor vessel cooling system (VCS) in the VHTR. Therefore, the gas cooling system with natural circulation is considered as a candidate for the VCS of the VHTR. Japan Atomic Energy Agency (JAEA) is advancing the technology development of the VHTR and is now pursuing design and development of commercial systems such as the 300MWe gas turbine high temperature reactor GTHTR300C (Gas Turbine High Temperature Reactor 300 for Cogeneration). In the VCS of the GTHTR300C, many rectangular flow channels are formed around the reactor pressure vessel (RPV), and a cooling panel utilizing natural convection of air has been proposed. In order to apply the proposed panel to the VCS of the GTHTR300C, it is necessary to clarify the heat transfer and flow characteristics of the proposed channel in the cooling panel. Thus, we carried out an experiment to investigate heat transfer and fluid flow characteristics by natural convection in a vertical rectangular channel heated on one side. Experiments were also carried out to investigate the heat transfer and fluid flow characteristics by natural convection when a porous material with high porosity is inserted into the channel. In this paper, we discuss the heat transfer and fluid flow characteristics of the proposed channel. From the results obtained in the experiment, it was found that the amount of removed heat decreased with increasing of temperature of gas when a copper wire was inserted into the channel with high porosity.
Bubble size is an important fundamental parameter in subcooled flow boiling. In this study, bubble behavior in subcooled flow boiling was visualized to confirm that mean bubble size is considerably different between different nucleation sites. Empirical correlations were developed using the present experimental data for the distribution of mean bubble size and the distribution of the size of bubbles produced in each site. Observation of the nucleation sites using a microscope revealed that tower-shaped structure is present at the nucleation sites where small bubbles are produced whilst no such structure was found at the sites where large bubbles are produced. This result suggest that bubble size is dependent significantly on the nucleation site geometry.
Clamp-on ultrasonic flowmeters are useful devices to measure flow rates in existing pipes. Many investigations have been carried out to measure steam flow rates using the ultrasonic flowmeters. However, the steam wetness increases with heat losses and the presence of liquid film and droplets may alter the propagation paths of the ultrasonic signals. Furthermore, signal-to-noise ratio decreases because the large acoustic impedance difference between the pipe material and fluid, strong signal attenuation in the fluid, and high temperature. Therefore, applicable conditions of the flowmeters are limited in the steam flow. In this study, the effects of liquid film and droplets on the characteristics of ultrasonic signal propagations in two-phase flows were investigated in adiabatic liquid-air two-phase and steam flows. Two ultrasonic transducers were used to measure the ultrasonic time-of-flight. Standard deviation was proposed to calculate the transit-time difference between upward and downward ultrasonic propagation. It is shown that the standard deviations of the target signals are more apparent than the averaged signals. Movement of liquid film inside the pipe wall is critical issues for increasing the noises. The standard deviation can be used to evaluating the setting suitability of the sensors.
We propose a PIV method which uses digital single-lens reflex (SLR) camera and diode laser which illuminates several pulses for obtaining several pairs of images from single image. This method can improve the resolution of the visualized images and it aim at the application to high-speed airflow measurement and acceleration measurement. Each pairs of trajectory of each particle are recognized in visualized image and the distance between each center of weight of each pulse are evaluated to generate velocity vectors. In this paper, in order to measure the velocity of the swirling flow in the system of transferring the semiconductor wafer, we developed a trajectory detection algorithm based on the relative shape of the trajectory. The system is the non-contact convey method which uses the balance of negative pressure by the velocity in the chamber and positive pressure by blowing out the air. Flow rate of the air is set to 5.0 L/min and the total time of a pair of pulse is 5ms. Visualized area was illuminated by DPSS laser (1000mW) and visualized images are taken by digital SLR camera (6000 × 4000 pixels). About 40% of the trajectories were detected by combining several results which were obtained from one visualization image. The mismatched vector generated in the detection process was removed manually. It is necessary to improve the recognition of trajectories by improving the algorithm of image processing and visualization method.
In this study, we propose a temperature measurement method that uses ultra-fine fluorescent wires. This is possible because its structure is simple, and any material can be used for the wire. Hence, ultra-fine wires whose Reynolds number is less than 1.0 can be selected. This means that turbulent flow is not generated downstream of the wire and that its wake is negligibly small. Fluorescent paint (containing Rhodamine B) was coated on the surface of the wires. The test volume was illuminated by using UV lights. The paint emits a very tiny orange-colored fluorescent light whose intensity changes with the temperature of the atmosphere. A very high sensitivity color camera (ISO 25600, 14 bit, 6,000×4,000 pixels) was used to record the visualized image.
The purpose of this study is to develop a wire mesh sensor for measurement of void fraction distribution in refrigerant-air two phase flow in order to clarify experimentally void fraction distribution. In the case of a refrigeran (HFE-71IPA), the liquid has a highly insulation with the quite low surface tension against air of 0.014 N/m and the low viscosity of 0.68 mPa∙s. In the experiment, the test channel was a vertical circular pipe of 9 mm i.d. The volumetric flux of the gas was 0.5 m/s, and that of the liquid was 0.2 m/s. The high voltage wire mesh sensor method applicable to the highly insulated liquid has been developed and used to measure the cross sectional void fraction distribution. In addition, void fraction data obtained in the past and literatures were compared with the present data.
This paper presents the development of Ultrasonic Velocity Profiler (UVP) method to obtain a two dimensional (2D) velocity distribution of the bubble and liquid phase in counter-current bubbly flow simultaneously. The multiple transducers and phase separation algorithm have been applied to the UVP system to achieve the target. In order to confirm the ability of Developed-UVP, the experiment was conducted on a bubble column flow loop apparatus which simulated the counter-current bubbly flow. The velocity distribution of both phases could be obtained reasonably and the information of both phases was classified obviously by using the Developed-UVP.
In core disruptive accidents of sodium cooled fast reactors, molten core materials are probably discharged from an original core region through control rod guide tubes and penetrate into sodium in a lower part of reactor vessel. In this study, to obtain fundamental knowledge with respect to penetration behavior of molten core materials into sodium, molten stainless steel which is one of components of molten core materials was poured into sodium pool in the state of liquid column and its penetration behavior into sodium was observed using X-ray system. The results showed that molten stainless steel poured into about 570 K sodium pool was fragmented at a depth of a few tens of millimeters with generation of sodium vapor. This suggests that sodium was locally vaporized due to contact of molten stainless steel, and rapid sodium vapor expansion broke liquid column of stainless steel. Fragmentation of stainless steel led increase of contact area between sodium and stainless steel, and it made molten stainless steel cooled during penetration into sodium within a depth of several hundred millimeters.
Decay heat removal system using a dipped-type direct heat exchanger (DHX) is recognized as a promising system from the viewpoint of the safety enhancement of sodium cooled fast reactors including severe accident situations. In this study, a steady state sodium experiment was carried out using PLANDTL-2 facility to grasp the core cooling behavior only relying on the natural circulation inside the vessel using dipped-type DHX and to provide validation data for evaluation method based on numerical approaches. As the result, temperature distributions in the core were quantitatively grasped under a situation where cold coolant from DHX penetrated the core. Furthermore, it was observed that temperature distribution at the middle height of core became flat due to the flow redistribution among heating channels resulting from the buoyancy balance between channels.
This reactor that was proposed since 2018 has Block Metal-Fuel (U-Pu-10%Zr) as Fuel-Core which involves no metallic structure. This paper proposes more improved this reactor with two types, the first type for Plutonium-breeding reactor, the second type for power plant. There is improving point, that is cooling temp. Change to inlet 480℃, outlet 720℃ to put down void swelling, and get enough cooling effect. Because Block Metal-Fuel of the first type(U-7.5%Pu-10%Zr) can endure 900℃. Because the self weight pressure load only exist. The first type has high density of heavy-metal (9000kg/m3)so that this reactor has high Plutonium-breeding capacity. The second type is simple fast reactor like as Toshiba 4S small reactor, but has Block Metal-Fuel as Fuel Core, and has high density of heavy-metal (8200kg/m3) is improved to have more power 250MWe and be able to produce Plutonium.
In order to explore the deep space, such as Mars, Jupiter, Saturn, etc in the future, a spacecraft that will be driven by nuclear power should be developed. At present, satellites or space probes have been using mainly electric source of chemical battery, fuel battery, solar battery, and RI battery. However, considering highly developed and extensive space exploration in the future, it is obvious that larger electric power is required over the long term space travel more than several years. Additionally, the solar battery used in space will be fundamentally impossible to use in planetary exploration father away form Mars because sunlight is attenuated. Therefore, lager electric power source must be installed in the space craft. In this study, we consider about co-generation system for heat and electricity using nuclear power. We think that the nuclear power is appropriate for using in deep space because of a long time operation without refueling and possibility in downsizing due to higher power density. We selected the SMR type fast reactor system of about 18 MWth compared with other type of reactors, such as PWR and high temperature gas reactor. With regard to a power generation system, we examined about efficiency of Stirling engine compared with a gas-turbine engine. Theoretical efficiency of Stirling engine is much higher than that of gas-turbine engine. Therefore, we selected Stirling engine and we have started the model test of a Stirling engine. Total power generation at International Space Station (ISS) that has been built since 1998 is about 110kWe. We estimated that about 5times as much electricity as that of ISS is enough to explore or develop the space. In that case, 2.5MWe will be generated by the system, number of crews will be about 5 and 2MW will be used to electric propulsion.
In a sodium-cooled fast reactor (SFR), it is important to control the amount of the non-condensable gas in the primary coolant system to prevent the occurrences of core power disturbance and/or the degradation of heat exchange efficiency in IHX. Therefore, a numerical simulation code named SYRENA has been developed in Japan Atomic Energy Agency to analyze the behavior of gas bubbles and/or dissolved gas in the primary coolant system. In the present study, the effect of the non-condensable gas entrainment at the free surface on the bubble and the dissolved gas behavior in the primary coolant system were investigated for a typical pool type reactor, and also effect of a dipped-plate (D/P) installed below the free surface in the reactor vessel to suppress the gas bubble entrainment into the primary coolant system was especially investigated. It was clarified that the D/P was influential to the non-condensable gas behavior and the molar flow rate of gas bubbles in the primary coolant system varies depending on the relationship between the gas entrainment rate at the free surface and the exchange flow rate through the D/P.
In case pressurized water or vapor leaks from a failed heat transfer tube in a steam generator of a sodium-cooled fast reactor, a high-velocity, high-temperature, and corrosive jet with sodium-water chemical reaction may cause tube failure propagation. In this study, a numerical analysis method to predict occurrence of tube failure propagation by overheating rupture was constructed to expand an application range of an existing computer code. This method consists of the elemental analysis models for a sodium-side temperature distribution formed by a reacting jet, water-side thermal hydraulics, heat transfer of a tube, and tube failure by internal pressure. Applicability of the method was investigated through a numerical analysis of an experiment on water vapor discharging in liquid sodium. In this experiment, one tube for water vapor discharging and the 91 target tubes were placed in a liquid sodium pool. The numerical analysis showed that temperature of the target tubes increased by the effect of the reacting jet. Some of the target tubes near the initial water leak resulted in overheating rupture as with the experimental result.
Sodium fire is one of key issues in sodium-cooled fast reactor (SFR) plant. JAEA has developed sodium fire analysis codes to evaluate the consequence of sodium fire events. This paper describes a PIRT (Phenomena Identification and Ranking Table) process for sodium fire events. Rnaking table for important phenomena and an assessment matrix are completed. The ranking table has been established through both element- and sequence-based phenomena analyses in addition to the engeneering judgement. The assessment matrix comfirms sufficiency of experimental data for validation of models corresponding to the identified important phenomena in the sodium fire analysis codes. As a part of comprehensive validation, an experimnetal analysis for a large scale sodium spray fire experiment Run-E1 is conducted by using a zone model sodium fire analysis code SPHINCS. The analytical result shows good agreement with the experimental result of gas pressure.
In Fukushima accident on 2011, after the loss of both the emergency core cooling system and IC core cooling, primary containment vessel (PCV) pressure increased. Water level measurement drifted because of water evaporation in the reference leg. Radiation level increased at a turbine building (T/B). There was a hydrogen explosion the after the suppression chamber (S/C) wet venting. By using the FCVS technology, the such the risk reduction during severe accidents in NPPs were attained. But owing to the global warming, the risk of natural hazards are increased, such as typhoon, hard rain, hot summer, severe snowfall, melt snow in north pole and south pole. It is very important to reduce CO2 emission by best mix of utilizing renewable energy and the safety enhanced nuclear power plants.
The new data from video investigation of the 1F Unit 2 pedestal debris performed by TEPCO was analysed. The debris features as derived from visual appearance on the video compared with the debris obtained after the CLADS-MADE-01 test. Some speculative conclusions concerning the properties and possible nature of the debris can be made.
At the Fukushima Dai-ichi Nuclear Power Station (NPS), investigations of NPS condition are conducted to retrieve fuel debris to achieve the decommissioning. In this study, we focused on the ultrasonic measurement technique for the survey, because ultrasonic technique can overcome the environment such as a cloudy and highly-dosed environment. However, when we use ultrasound in air, the attenuation of ultrasound in air is large. Therefore, 3D measurement technology using parametric ultrasound source is expected to long distance measurement. Because it’s characteristics are lower attenuation in the air and lower side robe causing noise signal compared to single frequency ultrasound. For measurement application inside of nuclear reactor using this technique, we investigated the measurable length and conducted measurement of the shapes of simulated the fuel debris models under mist environment.
After the Fukushima Dai-ichi NPP accident, a significant amount of radioactive material was released into the atmosphere, and three of the plant's six reactors suffered core meltdowns (unit 1, 2 and 3). The long-term goal is to decommission the damaged vessels. Nevertheless, before starting the decommissioning process, the highly radioactive fuel debris must be retrieved from the PCV and RPV. Through the many inspections in the NPP, some information about the state of the vessels and the location and distribution of the fuel debris is gradually being obtained. In this study, we proposed an integrated system of the robot and ultrasonic measurement. Ultrasonic measurement is considered as a promising non-optical inspection method since it can be used in opaque liquids. Furthermore, ultrasonic transducers are suited to high radiation environment. In this study, identifying simulated leakage points and determining the distribution of simulated fuel debris using ultrasound and robot were conducted．
A flow measurement system using ultrasonic pulses was developed to inspect inside the primary containment vessels (PCVs) of Fukushima Daiichi, especially for identifying leakage points from flow behavior. As a method of an ultrasonic flow measurement technique, we focused on an ultrasonic velocity profiler (UVP), and we have combined with a phased array technique to realize a two-dimensional and vector velocities measurement. The UVP has however difficulty to observe low and high velocities simultaneously due to the velocity resolution and the maximum detectable velocity limitation in a conventional signal processing algorithm. A novel signal processing algorithm, wideband phase difference method, was devised to overcome the narrow velocity range measurement in the conventional method. The method can extend the lower and higher velocity limitation. To verify the lower velocity extension, a wall velocity which moves low speed was captured. In addition, to confirm the higher velocity extension, a pipe flow velocity measurement was carried out. The method was suggested that the lower velocity limit was extended to one over tenth and the higher velocity limit was extended to eight times compared with the conventional method.
This is the research on a debris removal robot for the Fukushima Daiichi nuclear power plant. The creative robot contest is based on problem-based learning (PBL) education and was held at the decommissioning Fukushima Daiichi Nuclear Power Station. It aims to encourage student interest in decommissioning and to simultaneously discover problem-solving abilities. Our debris removal robot development began with this contest. The robot can travel in a pipe, has a 3 meter telescopic arm, and has a debris removal device called a spiral catcher. This report introduce an overview of this robot.
By using the FCVS technology, we had started to develop a high decontamination air cleaning system to remove multi-nuclides for radiation protection to conduct decommissioning the Fukushima NPP. High efficiency multi-nuclide aerosol filters for radiation protection during a process of cutting core debris has been developed at Hokkaido University. A plasma cutter, laser cutter, wire cutter, drilling machine, etc., will be used and will generate aerosols. Therefore, the air cleaning system should be needed for removing core debris. In order to develop an air clean up system, a metal fiver filter test was conducted. Measured DF were analyzed using FE-SEM and particle diameter analyzer was used to breakdown DF for each diameter range, it is possible to develop the high efficiency filters by multi-layer filters. Integral filter system will be consisted, such as a wet-type aerosol filter, multi-stage metal fiber filters and a silver zeolite to remove organic iodine. In order to develop an air clean up system, a metal fiver filter test was conducted. Measured DF were analyzed using FE-SEM and particle diameter analyzer was used to breakdown DF for each diameter range. Integral filter system was designed, by using the wet-type aerosol filter, multi-stage metal fiber filters to maintain the PCV or Reactor buildings. This paper describes the results of improvement of metal fiber filter for and total system test.
During the decommissioning of the Fukushima Nuclear Power Plant after severe accident, the process of cutting the core debris (using a laser cutter, wire cutter or drilling machine) will generate a large amount of radioactive aerosol. Therefore, the air cleaning system should be needed to prevent the release of radioactive materials into the environment. For this purpose, an integral filter system including three filter layers has been developed: the wet-type aerosol filter, multi-stage metal fiber filter and the zeolite filter for organic iodine removal. The wet-type filter plays an important role in effective removal the aerosol particles from the venting system and it should be properly investigated. In this study, the behavior of bubble distribution in the two-phase flow of the wet-type filter layer was investigated for the difference of the air injection flow rate.
It is necessary to simulate a eutectic melting reaction and relocation behavior of boron carbide (B4C) as a control rod material and stainless steel (SS) during a core disruptive accident in an advanced sodium-cooled fast reactor designed in Japan. To validate a physical model simulating the eutectic melting reaction and relocation, the visualization experiments of SS-B4C eutectic reaction was carried out by contacting SS melts of several kg with a B4C pellet heated up to about 1500 °C. This paper describes chemical analysis results of eutectic materials formed in the experiment, which are served as interpretation of the experiments and code validation.
When severe accident occurs in nuclear power plant, irradiated iodine would be formed. The irradiated iodine is basically trapped into the cooling water by existing in the ionized condition. However, it is assumed that the gaseous iodine might be re-volatilized from the cooling water in suppression pool chamber by the irradiation effect. The iodine volatilize behavior is said to be affected by pH control of the pool water. In this study, volatilize behavior of inorganic/organic iodine with pH control under gamma-ray irradiation is evaluated, based on simulated actual plant environments. The pH control to alkaline environment is effective to the inhibition of re-volatilization of inorganic/organic iodine. It is also confirmed that the emission behavior of organic iodine gas is mainly due to the reaction between the epoxy paint of gaseous phase in PCV inner wall and volatilized inorganic iodine gas with irradiation effect.
Preventing filter clogging of emergency diesel generators of nuclear power plants in volcanic ash fall by eructation, we develop new equipment to remove volcanic ash from air. The equipment, called ‘Louver-Spray System (LSS)’, is composed of spray nozzles and weather louvers at air supply of emergency diesel generators. It is necessary the spraying droplet size is enough large to catch by the weather louver. Spraying large droplets, volcanic ashes collide droplets, and removed by sedimentation before the weather louver or trapping at the weather louver with droplets. Additionally, the weather louvers become wet by spraying, so volcanic ashes are trapped at the wet weather louvers. We evaluate performance of the equipment, ex. dust removal efficiency, by numerical analysis and mock-up tests. In the mock-up tests, we used an actual weather louver and a single fluid spray nozzle. Test particles are glass beads, which are smaller particles than the removal targets of volcanic ashes (aerodynamic dimeters are several hundred μm). Spraying 480-660μm droplets at 50 L/min per 1 m2 of the weather louver opening, the equipment removed over 90% test particles of aerodynamic dimeter 16-32 μm, and over 97% test particles of aerodynamic dimeter 79-184 μm. The results show that LSS can remove volcanic ashes very efficiently.
The aim of this study is to understand the precise cross sections of collision processes between spray water drop and volcanic ash and also investigate the validity of water spray for the ash removal. We reproduce the accurate cross sections by considering six major collision processes and carried out a simple two-dimensional simulation for roughly estimating the survival rate of volcanic ashes. Firstly, we confirmed that the effective cross section is almost identical to two hard sphere core collisions if the size of volcanic ash is larger than 10μm. Secondly, we found that the ash removal via water spray shows remarkable high efficiency, i.e. the removal rates are more than 80%. The simulation will be further more improved and enabled to compare with mockup-tests of a new volcanic ash removal system which has currently been developed by TEPCO.
The Power Energy Systems Division of JSME established a "Study Group on Optimum Nuclear Safety Regulation for Risk Reduction". This association is aimed at bringing together stakeholders from industry, government and academia, investigating and examining the latest knowledge on nuclear safety regulations, and contributing to the advancement of future safety regulations. We set the followings as research subjects for overseas visit. Plant Life Extension; we investigated the safety assessment at nuclear power plant in the US and the status of utilization of risk information to improve the safety of Long-Term Operation of nuclear power plant in Japan and to reflect the learned insights into our Code/Standards, Risk informed ISI; we investigated the US Risk-Informed Inspection approach and by proposing the utilization of the method to our regulator in Japan to optimize the inspection while reducing the unnecessary load of inspection and Classification of importance of FLEX equipment; we would like to investigate the approach method of safety classification of FLEX equipment so as to reflect this concept in the optimization of maintenance of SA equipment / DB equipment.
Fukushima Daiichi NPP accident would be terminated, if sufficient accident countermeasures, such as water proof door, mobile power, etc. In case of Europe, it had already installed the heat removal system and filtered containment venting system (FCVS) from the lessons of TMI and Chernobyl Accidents. The new regulatory standard, the FCVS should be installed, and prevent the radioactive material in case of the severe accident and the overpressure breakage prevention of a primary containment vessel (PCV) and also stabilize the FCVS. The authors examined the severe accident process in the 2nd unit of Fukushima Daiichi NPS, and found the vent by FCVS should be done before water injection into the core. Upon occurrence of a SA, vent gas with radioactive fission products is blown out to a scrubbing pool through numerous venturi nozzles. Mist in steam moves upward to a metal fiber filter through a multi-hole baffle plate. After the mist is removed by that filter, radioactive methyl iodine (CH3I) is captured on the surface of a molecular sieve or AgX, made from zeolite particles with silver coating. Even if the severe accident occurred, FCVS will keep the radiation dose very low, and people who live in UPZ zone need not evacuation out of their home.
At Fukushima Daiichi Nuclear Power Station, flange-type tanks which could be deployed in a short time were installed at the time of the disaster because it was necessary to store the increasing number of contaminated water securely. After a while, replacement of flange-type tanks to more reliable welded-type tanks has been carried out. In dismantling the flange-type tanks, loose radioactive material is fixed and prevented from scattering by coating of inner surface before the dismantling. This paper describes the development status of the method to prevent scattering of radioactive material by reducing (decontaminating) the loose radioactive material with irradiating the laser to inner surface of the flange type tanks instead of the coating carried out so far.
For the safety enhancement of the nuclear power plant, the safety equipment is constructing additionally under the new regulatory requirements. With the increase of safety equipment, the amount of inspection during the outage may increase. Accordingly, increase of the outage lead to prolong maintenance schedule period. To perform the outage efficiently, we developed health visualization system for the equipment while operations. The health visualization system consists of database, health diagnosis engine and visualization engine. In this health diagnosis engine, the diagnosis technique that integrated a statistical model, which can detect the change of the process value early, with a physical model, which can identify equipment, the parts and phenomenon, was applied. With a constant monitoring of the process value, it is possible to estimate the phenomenon and equipment immediately when the process value shows different behavior than usual. Besides, by understanding that the equipment is healthy while operations, it is possible to optimize the amount of inspected equipment in the outage.
Two-phase flow regime identification in internal flow system is crucial for various energy systems involving phase-change. Closure of several conservation equations often times require proper selection of interfacial transfer models, which are highly dependent on flow regime. In the current study, non-intrusive methodology to identify two-phase flow regime is proposed using vibration signals acquired from the force transducers attached on the external piping structure. For the objective flow regime identification, machine learning techniques are adopted for the flow regime clustering.