Rational and normative risk judgments are made based on information on a risk object's advantages and disadvantages, although many studies show that everyday heuristic risk judgment tends to be made based on limited information. I focused on the fact that affective heuristic (Slovic et al., 2004), one of the heuristic risk judgments, was affective judgment under "good-bad" criterion due to a trade-off in the perception of dangers and benefits, and showed by a social survey that female undergraduates in Japan and Eastern and Western Europe used the affect heuristic for various risk objects. In other words, an analysis of survey results on risk types perceived by female undergraduates in Osaka, London, Ljubljana, and Budapest showed that risk objects such as automobile driving, airplane travel, nuclear power plant, extremist group, and tobacco smoking were perceived as high-risk and low-return (Type 2) or low-risk and high-return (Type 3) [Study 1]. According to a tobacco smoking linguistic representation mail survey among university graduates of 24 to 71 years old in Japan, nonsmokers had relatively many adjectival and verbal linguistic representatives for tobacco smoking. This shows that affective risk judgment with a "good-bad" criterion was made by persons who perceived the risk object useless and the risk was taken involuntarily. [Study 2]

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When a heat transfer tube is failed in a steam generator (SG) of a sodium-cooled fast reactor (SFR), pressurized water and/or water vapor leaks into liquid sodium surrounding the tube and forms a reacting jet with high temperature. This reacting jet might cause the secondary failure of adjacent heat transfer tubes due to wastage or over-heating tube rapture resulting in undesirable development of the accident. Therefore, the sodium-water reaction phenomenon (SWR) is one of most important issues for the design and safety assessment of SFRs. This paper describes the R&D plan of a new multi-physics numerical simulation system which is based on mechanistic and theoretical modeling of the SWR rather than empirical modeling and can contribute to detailed and quantitative evaluations of the SWR in any types of SGs including commercial SFRs.

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In steam generator of sodium cooled fast reactor, a deterioration of neighbor tubes may happen due to a wastage phenomena when a sodium-water-reaction jet touches the neighbor tubes caused by a leakage of water into sodium. Since, there are so many parameters in the phenomena. Those parameters interact with each other complicatedly, it is necessary to understand the influence of those parameters and to evaluate correlations between the parameters in order to investigate the wastage phenomena. In the present study, we analyze the correlations using the DEMATEL method and coordinate a correlation chart of the parameters.

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In a sodium-cooled fast reactor (SFR), liquid sodium is used as a heat transfer fluid because of its excellent heat transport capability. On the other hand, it has strong chemical reactivity with water vapor. One of the design basis accidents of the SFR is the water leakage into the liquid sodium flow by a breach of heat transfer tubes. This process ends up damages on the heat transport equipment in the SFR. Therefore, the study on sodium-water chemical reactions is of paramount importance for security reasons. This study aims to clarify the sodium-water reaction mechanisms using an elementary reaction analysis. A quasi one-dimensional flame model is applied to a sodium-water counter-flow reaction field. The analysis contains 25 elementary reactions, which consist of 17 H_2-O_2 and 8 Na-H_2O reactions. Temperature and species concentrations in the counter-flow reaction field were measured using laser diagnostics such as LIF and CARS. The main reaction in the experimental conditions is Na+H_2O→NaOH+H, and OH is produced by H_2O+H→H_2+OH. It was demonstrated that the reaction model in this study well explains the structure of the sodium-water counter-flow diffusion flame.

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In the case of sodium-water reaction accident in a steam generator of sodium-cooled fast reactors (FRs), adjacent heat transfer tubes may be damaged due to high temperature environment of the reaction field. Therefore, it is integral to predict such event with high accuracy for the safety assessment of FRs. For the purpose of understanding the overheating tube rupture mechanism, an experimental study has been performed to clarify waterside heat transfer characteristics during up-flow in a vertical tube under the real plant part-load operation conditions in which safety margin is least. A test tube was heated rapidly and the time averaged heat flux was estimated using an inverse solution from the measured temperatures at two points on three different locations along the tube. It was conformed that the heat transfer on the wall changed from nucleate boiling to transient-film boiling all over the heating section and dried-out surface spread from downstream toward upstream. We improved the heat transfer correlations applied to RELAP5 code and made sure the adequacy of these correlations to evaluate tube overheating.

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One of the design basis accidents in sodium-cooled fast reactor is sodium-water reaction at steam generator (SG). In case of a defect occurred on a heat transfer tube, the high-pressure water/vapor will spout into the low-pressure sodium surrounding outside the tube. As sodium is ordinarily quite reactive with water, this will initiate sodium-water reactions accompanied by high chemical heat generation. The liquid droplet in the reaction steam outflow would impinge on neighboring tubes to cause erosion, while the chemical reaction will cause corrosion, eventually may lead to secondary tube failure. Focusing on the erosion part, this study is to evaluate the liquid droplet impingement erosion (LDIE) rate on neighboring tubes caused by SG heat transfer tube rupture. In this paper, as a basic study, the pressure and temperature distribution of high-pressure two-phase free jet into the air is measured.

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For the purpose of elucidating the mechanism of the sodium-water surface reaction in a steam generator of sodium-cooled fast reactors, kinetic study of the sodium (Na)-sodium hydroxide (NaOH) reaction has been carried out by using Differential Thermal Analysis (DTA) technique. The parameters, including melting point of Na and NaOH, transition temperature of NaOH, Na-NaOH reaction temperature, and the decomposition temperature of sodium hydride (NaH) have been identified from DTA curves. Based on the measured reaction temperature, rate constant of Na_2O generation was obtained. Thermal analysis results indicated that Na_2O generation at the secondary overall reaction would be considered during the sodium-water reaction.

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The cracks detected by in-service inspection are not always removed when they are not hazardous according to fitness-for-service evaluations. In such cases, it is important to monitor the growth of these cracks in order to assess the validity of their integrity assessment. In previous study, a monitoring method using strain gage was proposed and its validity was shown by performing finite element analyses and experiments. In this study, this method was extended for estimating not only crack depth but also surface length. By using two strain gages, it was possible to identify the both size. Furthermore, by using several gages and averaging the estimated sizes from the gages, the accuracy of the estimation could be improved. By considering weights in the averaging, further improvement of the accuracy was achieved.

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Closed stress corrosion cracks (SCCs) in Ni-based alloy weld metal (NBAWM) lead to a problem of underestimation or overlook in ultrasonic inspection, resulting in catastrophic accidents such as radiation leaks. For application of new inspection methods to solve this problem, and for training/education of inspection, fabrication of realistic closed SCC specimens is required, though it takes many years. Here we propose a two-step process to form closed SCCs in NBAWM in relatively short time of several months. This method first forms an open SCC by accelerated chemical methods and then close it by a short time immersion in high temperature pressurized water (HTPW). The crack closure was verified by subharmonic phased array for crack evaluation (SPACE), capable of measuring closed SCC. In addition, we developed an FDTD (finite difference time domain) method with damped double node (DDN) model of closed crack for 2D simulation of subharmonic generation.

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This study proposes a signal processing method that significantly enhances the nondestructive evaluation of flaws appearing inside pipe wall from the reflection of microwaves propagating inside the pipe. The signal processing method modifies the phase of incident microwave as a function of frequency so that the reflection due to an anomaly at a certain distance is observed as a pulse. Validations are carried out both by experiments and finite element simulations using a straight brass pipe with a outer diameter of 25mm and a wall thickness of 3mm. This study considered wall thinning artificially introduced into the inner surface of the pipe. The results of the validations demonstrate the effectiveness of the signal processing method even when wall thinning have a complicated boundary profile.

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This study reports a method to fabricate imitative stress corrosion cracking suitable for the development of nondestructive testing and evaluation methods. The method is to embed a partially-bonded region, which simulates the characteristics of stress corrosion cracking, inside a material by bonding together surfaces having artificial grooves. Since the sizes of the grooves are smaller than the spatial resolution of nondestructive testing method applied, the material property realized can be regarded as uniform as the actual stress corrosion cracking. The grooves are introduced using mechanical machining, which enables one to control the characteristics of the simulated flaw. Four specimens made of type 316L austenitic stainless steel are fabricated. The method is demonstrated by visual and eddy current examinations.

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Microwave microscopy was employed to detect stress corrosion cracking (SCC) and evaluate its depth on the Ni-base alloys. An open-ended coaxial line sensor was used to increase the spatial resolution. The working frequency was 110GHZ and the standoff distance between the sensor and the sample was 60μm. By measuring the amplitude of reflection coefficient, the detection of SCC was achieved and W-shaped characteristic signal was obtained. The distribution of SCC depth along crack length was evaluated by measuring the attenuation of microwave signal. The evaluated SCC depth was good agreement with the actual SCC depth obtained by a destructive testing.

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The thick welded part was conventionally inspected by the ultrasonic testing (UT) after welding. If the UT could be performed during welding, it should save time and cost of manufacture. Therefore, we have developed in-process Laser-Ultrasonic Testing (LUT) technique during welding at high temperature. LUT is applicable to structure with high temperature because of its non-contacting feature. In addition, to apply the LUT to thick welding parts having a thickness of more than 100mm we have developed Synthesis Aperture Focus Technique (SAFT) for sensitivity improvement of LUT. In this paper, we show the in-process testing result of drilled specimen and actual 150mm thickness pipe in high temperature more than 200 degrees C.

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Laser beam welding is one of the jointing processes by irradiating laser beam on the material surface locally and widely used at various industrial fields. Toshiba has developed various laser-based maintenance and repair technologies and already applied them to several existing nuclear power plants. Laser cladding is a technique to weld the corrosion resistant metal onto a substrate surface by feeding filler wire to improve the corrosion resistance. Temper-bead welding is the heat input process to provide the desired microstructure properties of welded low alloy steels without post weld heat treatment, by inducing proper heat cycle during laser welding. Both laser welding technologies would be performed underwater by blowing the shielding gas for creating the local dry area. In this report, some evaluation results of material characteristics by temper-bead welding to target at Reactor Coolant System nozzle of PWR are presented.

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Thermal transient stress analyses and pressure stress analyses were conducted using simplified turbine casing models with the variations of dimensional parameters. Thermal stress concentration factors were evaluated by the empirical formula and utilized for elastic-plastic strain analyses. Creep-fatigue damage was evaluated by the cumulative damage rule expressed in terms of cycle fraction and time fraction. The 2-dimensional probability function was used for calculating the failure probability under creep-fatigue damage, which was converted into time-based and cycle-based probability functions. The optimum dimensions were selected by equi-probability contours and the optimum maintenance intervals were determined using risk-cost functions. The proposed method was proved to be effective for the optimum design and maintenance decision making of high temperature components.

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High chromium steels are used as piping materials in a ultra-super-critical thermal power plant where operating temperature is nearly 600 degrees in Celsius. A current important issue in utilities is so-called "type IV" damage occurred in the heat affected zone (HAZ) of weld joints. In order to estimate this kind of damage quantitatively, it is necessary to consider not only internal pressure by steam but also thermal expansion of whole piping system. In this study, a three-dimensional finite element analysis program specialized for a plumbing stress analysis was developed and applied for thermal stress and creep analyses of a piping system of an actual thermal power plant.

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Proactive maintenance is effective to keep the normal operation of equipments and mechanical systems and so on. Early detection of anomalies followed by malfunction of the equipments and systems is essential for working order. This paper proposes a prognosis system that includes two functions. One is remote monitoring which detects anomalies by comparing sensor data with a threshold data, and another is data-mining which detects anomalies using statistical analysis. We have developed the prognosis system and have confirmed the effectiveness of preventing machine-trips.

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Proactive maintenance is important to keep normal operation of plant and equipment systems. A prognosis system for such a system was developed that includes two functions: remote monitoring which detects anomalies by comparing sensor data with a threshold and data-mining which detects anomalies using statistical analysis. This paper proposes an automatic method of setting up criteria for remote monitoring. First, training data is generated based on the result of data-mining. Next, a decision tree is generated by learning the training data, and an if-then rule is extracted. Usefulness of the proposed method was evaluated using 4 data sets including one type of faults. In those data sets, anomalies are recognizable several days before the day of the fault. Two rules extracted using 2 of 4 data sets were different each other but the 2 sensor outputs corresponding with the 2 rules were highly correlated, and the extracted 2 rules can detect anomalies from the other data sets properly.

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As the motor's supply current changes with the load behavior, it is possible to analyze the motor condition through motor current signal analysis (MCSA). This paper examined the problem of the detection of the mechanical failures of the motor and its connected gear. From the result of the tests, the MCSA method is effective to monitor the dynamic model composed of motors and gear shaft.

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High power generating cost is a important problem in a sustainable energy. In order to reduce the cost for the power generation, passive power control using elastic turbine blade made of composites is adopted. In this study, the performance evaluation system with fluid-structure interaction analysis and water tank tests has been developed to design the passive power control property and evaluate its performance. First, we made rigid blade models and elastic blade models to compare the calculated deformation by fluid-structure interaction analysis. The deformation of blade is measured by a noncontact optical stereo camera. Consequently we confirmed that we can predict the deformation with fluid-structure interaction analysis. By using some numerical optimization methods, we try to design elastic turbine blade in actual sea condition.

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A new wave power generation system is proposed. Although existing wave power generation systems construct or float their facilities on sea, occupation of sea surface is restricted severely in Japan because of safety ensuring of ship course and securement of fishing grounds. To eliminate this problem, a new wave generation system has been developed. The system includes its facility inside a type of breakwater that is growing popular lately. The breakwater has water chambers for vanishing waves and water flow in/out to the chamber through the slits. The vortex produced behind the slits decay wave motion. In proposed system, a Savonius water mill was located behind the slits and was driven by reciprocating water flow. The generation power in this system was measured using a 1/12 scale model and practical realization of this system was proved by the measurement.

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The study of floating offshore wind turbines has recently been attractive to many research groups in the renewable energy. Because the area of shallow water along Japanese coast is limited, the development of floating base for wind turbine is inevitable for making large scale wind farms. There are some problems to be solved for floating offshore wind turbines. Besides the mechanical problems of turbines, the influence of the motion of the floater in wind and waves to the electric generation properties, the safeties of floating structures such as the fatigue of machines and structures or criteria of electric facilities should be studied. Several types of floating structures have been proposed such as SPAR, TLP, pontoon, and semi submersibles. The authors have focused on SPAR type because its simpler shape seems to have economical advantages. In this paper, the authors performed experiments in a wind tunnel and a water basin from the viewpoint of "wind turbines on a SPAR type floating structure". Firstly, forced pitching experiments were operated in a wind tunnel, and the difference in two types of wind turbines, upwind type and downwind type, is discussed. The former type is very popular and the latter type is thought to be suitable for floating structure. Secondly, experiments which thought to be more relevant for a floating wind turbine were carried out in a water basin. The relationship between the location of the attachment point of mooring lines and the motion of the SPAR in waves, and the influence of pitching angle of turbine blades to the motion of the SPAR in waves were inspected. In these experiments a PID control mechanism was used to control the pitch angle of the blades of the scale model of wind turbine.

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Micro hydro power is suitable for Japan, which has many rivers, but it is not sufficiently spread in present. On the other hand, a lot of water wheels had been used for thread twisting in the region around Ashikaga city, which is home ground of our institute, exists until early Showa era. In this study, by using properties of traditional water wheels which existed in the region around Ashikaga city, the authors set to work to develop the micro hydro turbine generator which can be used at low head condition without major construction for installation. As the results of the performance test of a micro hydro turbine generator, Maximum power of 8.2W at 0.8m/s and 12.8W at 1.0m/s were obtained. Moreover, it was found that output power is also fairly increased by introduction of power augmentation unit such as a confuser and a diffuser.

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This paper describes a capability of the solar hybrid generation system consists of the existing amorphous silicon photovoltaic module and thermoelectric module. The optical long wavelength signal of solar light that transmitted by the optical cold mirror is introduced to thermoelectric module installed selective photo-absorption plate through Fresnel lens. The short wavelength signal that reflected by cold mirror is introduced to photovoltaic module. We demonstrated experimentally that the present solar hybrid generation unit could produce higher electric power than that of photovoltaic generation without cold mirror.

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Microgrid is noticed as the system that can reduce CO2 emission from residence area. Microgrid can absorbs the fluctuation of electricity power which might be originated with several kinds of renewable energy, therefore it doesn't negatively affect on the stability of utility grid. In addition, microgrid has a capability to control the heat-and-power ratio in demand and supply by optimizing the combination of several kinds of high efficiency residential devices in the area. However, here is few researches on this optimum combination of the eco-system devices. Therefore in this report, microgrid was evaluated in consideration for regional characteristics; those are 12 kinds of demand patterns and 3 kinds of electricity CO2 emission coefficient. As a result of analysis, the region that has high heat-to-power ratio, large demand, and large capacity of photovoltaics makes much advantage of microgrid relating to CO2 emission reduction.

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The thermosyphon can operate without an external power supply, and have simple structures. Therefore, thermosyphon can be expected to reduce energy consumption and consequently reduce CO_2 emissions. Ito et al. developed a device that the reservoir and the condenser are separate. Using this device, it was possible to drastically reduce the time before circulation commences. In this study, we examined unsteady characteristics of Ito's thermosyphon system. When the supplied power increased, the start-up time decreased. After the Working fluid has begun to flow, the fluctuation of flow velocity occurred. After several minutes, the flow in a top heat s thermosyphon became steady state.

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Ocean Thermal Energy Conversion (OTEC) is one of the renewable energy resources. Aiming to improvement of OTEC performance, an optimization of heat transfer area is important. For OTEC system using ammonia/water mixture as working fluid, effect of the heat transfer area on the system performance has not been clarified. Therefore, in this paper, the influence of the heat transfer area on the heat transfer performance of the heat exchangers, and subsequently on the entire system is experimentally investigated. Analysis of the power cycle using the experimental data was carried out and a maximum net power of 20.1kW was obtained at warm and cold water flow rates of 350m^3/h and working fluid flow rate of 6t/h.

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A Low-grade Thermal Energy Conversion (LTEC) which are Geothermal, Wasted Energy, Ocean Thermal Energy, is refocused on as one of the renewable energy to solve the global warming and the energy problem. In this paper, the evaluation method of LTEC as a renewable energy is proposed using maximum power with infinite heat transfer performance, The proposed evaluation method is used with the experimental data of 30kW Ocean Thermal Energy Conversion System. It is clarified that the proposed evaluation method is effective on LTEC as renewable energy system.

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This paper described a performance analysis of the power system using Uehara cycle utilizing warm wastewater as a heat source. Uehara cycle utilizes ammonia/water mixtures as working fluid. The facters in performance analysis consist of the inlet temperature of warm wastewater, the mass fraction of ammonia and each overall heat transfer coefficient of the heat exchangers. In this analysis, the thermal efficiency of Uehara cycle becames larger when the inlet temperature of warm wastewater is increased. Also, the thermal efficiency of Uehara cycle becames larger when the mass fraction of ammonia is increased because the rate of bleed of the turbine is increased. The thermal efficiency of Uehara cycle is compared with that Carnot cycle.

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A performance analysis of the power system utilizing waste heat energy from the industrial plants is conducted. The working fluid is used Trifluoroethanol (TFEA). A performance analysis of the power system is performed in the following two methods. Two methods estimated thermal efficiency of Rankine cycle and objective function for inlet and outlet temperature difference of exhaust gas. In the case of method of objective function, the maximum net power is given by minimizing of heat transfer area of the heat exchangers which consume most cost in total cost of the power system. The minimum value of objective function is about 7.6m^2/kW when the inlet and outlet temperature of exhaust gas is 45 degrees Celsius. The output power of power system utilizing waste heat energy is obtained from performance analysis.

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We have constructed a travelling wave thermoacoustic heat pump using a coaxial configuration with the regenerator positioned in the annulus. It was discovered that within the frequencies ranging from 100Hz to 400Hz a frequency dependent directional reversal of heat transport within the regenerator occurred. By decomposing the acoustic wave within the annulus for the tested frequencies, it was revealed that the cause of the reversal was due to the change of the acoustic field in regards to the magnitudes of the positive and negative direction travelling waves.

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The present study investigates experimentally the effects of the droplet diameter, its velocity and the surface roughness on the behavior of droplet impinging onto the hot surface. Cylindrical blocks made of SUS304 with different roughness, Ra0.04, 0.2, 3, 10 were used. The droplet diameter and velocity were independently controlled in ranges of 300-700μm and 1.0-4.0m/s, respectively. The cooling curve is drawn in the range of surface temperature from 500℃ to room temperature. The experimental results show that the cooling time decreases with increase roughness. In the case of quantity of water uniformity, a cooling rate becomes fast so that droplet diameter becomes small. It was demanded the number of We number and relations of the cooling time. A cooling time is the earliest with number of Weber around 50.

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An autonomous wireless sensor node using MEMS electret energy harvester has been prorotyped. With hybrid high-aspect ratio parylene springs and high-performance electret material based on perfluoro polymer CYTOP, more than 3μW output power can be generated in a broad range vibration frequency of 26-40Hz at 1.4G. By using a power management circuit, low-power-consumption CPU, and RF IC, we can also successfully drive the wireless sensor node with an interval of 80.6s and transmit temperature data intermittently.

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It is suggested that a steam injector (SI) is adjusted to heat pump systems to downscale the outdoor unit for the diffusion of them. The SI has high heat transfer performance due to the direct contact condensation and acts as a static jet pump. It is expected that the downsizing of the SI enable us to downsize a condenser and a compactor. And the feature to drive without any rotating power source may enable to reduce the total system energy. The objective of the present study is to investigate the operating condition of an ultra micro steam injector (UMSI) whose throat diameter is 600μm from the flow observation and the measurement of condensate. As the results, the backflow was confirmed due to the condensation in the mixing nozzle and the check valve in the drain. And heat transfer quantity of this device is approximately 500W.

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Experiments were carried out to explore boiling heat transfer during successive impacts of single nanofluid drops onto a hot solid surface. Nucleate boiling heat transfer and critical heat flux were improved when nanometer-sized titanium-dioxide particles were dispersed in water drops. In contrast, colloidal dispersion of the nanoparticles degraded the heat transfer in the film boiling regime at high wall temperatures. A thin nanoparticle layer was formed on the wall during the nanofluid drop impacts to improve the surface wettability. Observation of the impact process revealed that the droplet spreading area at low wall temperatures was wider for the nanofluid drops. An increase in the contact area was expected to be a primary cause of the nucleate boiling heat transfer improvement. At high wall temperatures, a central liquid jet was formed following the impact only in the case of pure water drops, which would be the evidence of a significant heat transfer. It was suggested that violent phase change induced immediately after the impact of nanofluid drop deteriorated the liquid-solid contact in the later stage.

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Due to ongoing progress in material surface treatments and in micro/nano scale processing, it is feasible to fabricate various structures at micro/nanometer scale on a solid surface. The molecular dynamics simulations have been applied to understand static structures and transport phenomena at the molecular scale at a liquid-solid interface, and a substantial thermal resistance was found at the liquid-solid interface. In the present study, the effects of nanoparticles adherent to a surface on the thermal resistance at a liquid molecule-solid interface were investigated directly by the nonequilibrium classical molecular dynamics simulations. The reduction of the interfacial thermal resistance caused by the nanoparticle adhesion can be observed only when the high wettability nanoparticles are adherent to the low wettability surface.

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Fullerenes were generated and observed in the combustion processes of hydrocarbon fuel under low pressure conditions although the fullerene formation mechanism from PAHs in fuel rich hydrocarbon flames under low pressure conditions has not been clarified yet. The experimental results show that the fullerene content in the total soot increases or decreases under the reduced pressure conditions when argon gas is added to the toluene and oxygen premixed gas at the constant flow rate of the premixed gas. The effects of the temperature in the combustion chamber and the argon dilution rate on the fullerene formation mechanism are discussed under various experimental conditions. The experimental results show that the fullerene contents in the total soot increase substantially by the argon dilution when the heat supply from an electric tubular heater is sufficient.

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Collapse of a water jet flowing out from a nozzle to the atmosphere was examined. The flow state of the water jet was recorded with a high speed video camera. The collapse length was derived from recorded images. The radial void fraction distribution in the water jet was also measured with a conduction void probe. The measured results of the void fraction distribution indicated that the region that contains gas phase was formed near the water jet interface. The region spread toward the center of the water jet as the water jet flowed downstream. However, the recorded pictures with the high speed camera revealed that the gas phase was not rolled into the water jet and the gas-water two-phase region was not formed until the water jet disrupted into the lumps of water. The water jet showed the winding shape. The void probe came out of the water jet intermittently since the water jet wound. As a result of it, the void probe superficially detected the existence of the gas-water two-phase region in the water jet. This situation is largely different from what has been believed about the variation of the water jet structure.

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The Japan Atomic Energy Agency has developed TPFIT, a detailed two-phase flow analysis code with an advanced interface tracking method, as part of development of a new method of thermal hydraulic design for nuclear reactor cores based on large-scale numerical simulation. In past studies, most attempts to validate TPFIT have been performed under bubbly, slug and churn flow conditions. However, to apply TPFIT to a two-phase flow in fuel assemblies, TPFIT must also be validated for annular and dispersed flow. In this study, TPFIT was applied to a water jet experiment as a first step in validating TPFIT for annular and dispersed flow conditions. The liquid film flowing on fuel rods in an annular two-phase flow was imitated as a water jet. To simulate jet, boundary conditions are important especially for high velocity conditions. In this paper, appropriate boundary condition for high flow rate (high velocity) simulations was evaluated.

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In order to evaluate CCFL (countercurrent flow limitation) characteristics in a PWR hot leg under reflux condensation, numerical simulations have been done using a two-fluid (2F) model and a VOF (volume of fluid) method implemented in the CFD software, FLUENT6.3.26. The 2F model gave good agreement with CCFL data under low pressure conditions but did not give good results under high pressure steam-water conditions. On the other hand, the VOF method gave good agreement with CCFL data for tests with a rectangular channel but did not give good results for calculations in a circular channel. Therefore, in this study, the computational grid and schemes were improved in the VOF method, numerical simulations were done for steam-water flows at 1.5MPa under PWR full-scale conditions with the inner diameter of 0.75m, and the calculated results were compared with the UPTF data at 1.5MPa. As a result, the calculated CCFL characteristics agreed well with the UPTF data at 1.5MPa.

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