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We develop a deep neural network model capable of detecting the boiling inception and state transitions from boiling acoustic measurements. We characterize acoustic spectrums of water boiling with different heating surface geometries, heat flux, and degree of subcooling. Our measurement result shows that the feature extraction of the boiling inception and state transition is possible from the boiling-sound frequency dataset in each specific target system. Notably, the deep neural network can distinguish the boiling inception and the state transition more accurately even at the high-level white-noise intensity where human beings and traditional data analysis methods cannot distinguish. This result suggests that the acoustic diagnosis with the deep neural network algorithm has great potential to detect the boiling inception and to monitor the boiling states in quasi-real-time during an early stage of the boiling phenomena, in the nuclear power plants.

The lead-lithium eutectic alloy (PbLi) is a promising coolant for nuclear fusion reactors. Although PbLi flow and heat transfer in a nuclear fusion reactor condition needs to be comprehended, no ve...

Suspension state of a titanium nanoparticle in the liquid sodium was quantum chemically characterized by comparing physical characteristics, viz., electronic state, viscosity, and surface tension, with those of liquid sodium. The exterior titanium atoms on the topmost facet of the nanoparticle were found to constitute a stable Na-Ti layer, and the Brownian motion of a titanium nanoparticle could be seen in tandem with the surrounding sodium atoms. An electrochemical gradient due to the differences in electronegativity of both titanium and sodium causes electron flow from liquid sodium atoms to a titanium nanoparticle, Ti + Na → Ti(δ-) + Na(δ+), making the exothermic reaction possible. In other words, the titanium nanoparticle takes a role as electron-reservoir by withdrawing free electrons from sodium atoms and makes liquid sodium electropositive. The remaining electrons in the liquid sodium still make Na-Na bonds and become more stabilized. With increasing size of the titanium nanoparticle, the deeper electrostatic potential, the steeper electric field, and the larger Debye atmosphere are created in the electric double layer shell. Owing to electropositive sodium-to-sodium electrostatic repulsion between the external shells, naked titanium nanoparticles cannot approach each other, thus preventing the agglomeration.

Studies on the suppression of the reactivity of sodium itself have been performed on the basis of the concept of suspended nanoparticles in liquid sodium (sodium nanofluid). According to the theoretical and experimental results of studies for sodium nanofluid, velocity and heat of sodium nanofluid reaction with water (sodium nanofluid/water reaction) are lower than those of the pure sodium/water reaction. The analytical model for the peak temperature of a sodium nanofluid/water reaction jet has been developed by the authors in consideration of these suppression effects. In this paper, the prediction method for mitigation effects on damage of adjacent tubes in steam generator tube rupture (SGTR) accidents is developed by applying this analytical model for the peak temperature of the reaction jet. On the assumption that the sodium nanofluid is used for the secondary coolant of sodium-cooled fast reactor (SFR), mitigation effects under the design basis accident (DBA) condition and the design extension condition (DEC) of SGTR are estimated by using this method. The results indicate a clear possibility to reduce the number of damaged tubes and to suppress the pressure generated in SGTR accidents by using sodium nanofluid as the secondary coolant.

For ion radiation therapy, the measurement of effective atomic numbers, Z[eff], is necessary to know the material distribution in a human body; the range of ions entering the human body is influenced by the material distribution along their paths. Z[eff], however, cannot be measured at hospitals because monochromatic X-rays with different energies are necessary and are used only at synchrotron facilities. To make Z[eff] measurements at hand, we propose energy-resolved computed tomography (CT) using a “transXend detector”. By assigning two narrow energy ranges in the unfolding process of the data obtained by the transXend detector, Z[eff] for acrylic and aluminum can be estimated by energy-resolved CT. The estimated Z[eff] are compared with those obtained by dual-energy and monochromatic X-ray CT.

Ultrasonic Doppler velocimetry (UDV) with a titanium-tipped transducer has been successfully demonstrated for measuring a velocity profile of molten lead–lithium eutectic alloy (PbLi) with a concentration of oxygen and moisture lower than 1 ppm. In contrast, it is found that UDV does not work for PbLi flows in a more oxygen-rich environment. This paper presents UDV measurements of PbLi flows at different levels of ambient oxygen concentration, and then discusses the measurement deterioration, based on a thermodynamic consideration of oxides formation in molten PbLi. In summary, it can be concluded that in an oxygen-rich environment, titanium oxidation occurs and consequently deteriorates the acoustic coupling between the transducer tip and the molten PbLi.

X-ray computed tomography (CT) with iodine contrast agent is widely employed to locate cancers. However, this method has shortcomings such as high-radiation dose exposure, iodine side effects, and ...

The authors invented the transXend detector, which measures X-rays as electric currents, and then gives the energy distribution of the X-rays after an unfolding process. In a previous paper, it was shown that the material thickness distributions can be estimated with the transXend detector by using reference points plotted from the electric current ratios, such as the I 2/I 1 − I 3/I 1 graph, where Ii denotes the electric current measured by the i-th segment of the transXend detector. In this paper, the tomographic images of iodine, aluminum, and the acrylic those surround the other two materials are reconstructed from their material thickness distributions, which are estimated from two X-ray incidence directions. The X-ray event ratios are also used to estimate the material thickness distributions.

To measure the iron concentration in the human liver, which comprises soft tissue and adipose as well as iron, energy-resolved computed tomography (CT) is applied using a transXend detector. The transXend detector measures X-rays as electric current and gives an energy distribution after analysis. Energy-resolved CT clearly separates iron solution from acrylic, a substitute for soft tissue, whereas conventional current-measurement CT cannot. Using CT values obtained in two different energy ranges, a two-dimensional map of iron, adipose and soft tissue is plotted. With this map, the components in the liver can be identified.

The present authors developed the transXend detector, which measures incident X-rays as current and also gives their energy distribution after an unfolding process with using previously obtained response functions. This detector enables X-ray energy-resolved computed tomography (CT). To incorporate the transXend detector into a third-generation CT scanner, a flat panel detector (FPD) made of CdTe pixels is employed with placing a variable number of aluminum absorbers in front of the FPD. Although changing the number of absorbers can be time consuming, the time necessary to generate a CT image is much less when compared with image acquisition by first-generation CT.

The energy resolved computed tomography (CT), which had advantage over conventional CT (twofold higher CT value for iodine contrast agent and being free from beam hardening effect), was shown practical by employing the transXend detector: it measured X-rays as electric current and gave energy distribution of incident X-rays after analysis. This article shows a new application of the transXend detector for estimating the thicknesses of acrylic, iodine, and aluminum in a phantom. For this purpose, the responses of the segment detectors in the transXend detector are changed intentionally with inserting filters. With previously obtained two-dimensional maps for acrylic–iodine and acrylic–aluminum thicknesses, which are shown by the ratios of electric currents measured by the segment detectors, the thickness of materials on the path of the X-rays are obtained by a transmission measurement.

Liquid sodium is used as coolant in fast reactors (FRs), because of its high thermal conductivity and wide temperature range of liquid phase. It has superior thermal medium properties but its chemical reactivity with water and oxygen is very high. Hence, FR plants have to take safety measures regarding these reactions. To develop FR systems for practical use, a better physical and chemical understanding of reaction phenomena and more mechanistic analyses for accidents are desired. Oxidation in the early stage of sodium combustion is especially important regarding the aspect of reaction continuity. The purpose of this study is to understand the sodium reaction precisely in order to apply the knowledge of the sodium reaction to promoting further safety of FRs. In the authors' previous study, it was recognized that dendritic oxide had an important role in the sodium oxidation reaction such as supplying unreacted sodium to the reaction interface. In this study, a mechanistic model for supplying sodium through...

To enable practical computed tomography (CT) that uses the energy information of X-rays, the “transXend detector” was developed to provide energy information about incident X-rays by measuring them as an electric current. The transXend detector requires a spectrum survey method in the unfolding process for measuring the energy distribution of incident X-rays, when the response functions of segment detectors have nearly the same behavior. When employing various scintillators with different effective atomic numbers and densities as the substrates of the segment detectors, better convergence is obtained in the unfolding process by using only one initial guess spectrum. Additionally, less dose exposure is possible when using the transXend detector with various segment detectors, compared with the transXend detector that consists of the segment detectors with the same substrate.

Measurements of the contact angles at the different temperatures of a molten lead–lithium eutectic alloy (PbLi) droplet on a silicon carbide (SiC) wall are needed for the research and development both of a magnetic confinement fusion (MCF) and an inertia confinement fusion (ICF) blankets. PbLi coolant/breeder flows in the coolant channel, which is made of the SiC walls, and will experience a flow slip at the wall, called as a magnetohydrodynamic (MHD) slip flow. The ICF blanket adopts a molten PbLi film flow along the first wall made of SiC. The PbLi contact angle database is necessary as the thermal property for numerically predicting the behavior of the flowing molten PbLi film. This study attempts the measurement of the contact angles between the molten PbLi and the various SiC surfaces. For example, in order to examine the initial PbLi wettability, we measured the contact angles of a chemical vapor deposition (CVD) SiC, a nano-infiltration and transient eutectic-phase (NITE) SiC/SiC composites, and a NITE SiC in an inert atmosphere. We obtained the contact angle database of the molten PbLi, varying the temperature of PbLi from 250 to 400 °C, on a surface-polished as well as an unpolished SiC.

An electromagnetic pump (EMP) has superior potential to improve the economic performance and ease of maintenance of sodium-cooled fast reactors. This study investigates the adequateness of a modular-type EMP system for large-sized (1,500MWe class) sodium-cooled fast reactors. A flow rate of over 500 m3/min is required for the main circulating pump of such reactors. There is concern that such a large EMP will cause flow instability. A modular-type EMP system can solve this issue since smaller EMPs are arranged in parallel and the flow rate of each EMP is reduced. Parallel-module EMP systems have been investigated as the primary and secondary circulating pumps. The results of the design study and electromagnetic analysis of the primary main pump confirmed that flow instability does not occur under all operational conditions. From a safety viewpoint, a reliable flow-coast-down system has been proposed, comprising an electric supply system with a permanent magnet synchronous motor and a reliable circuit break...

X-ray computed tomography (CT) using X-ray energy information has been studied by the present authors on acrylic phantoms containing an iodine contrast medium. To observe a human body, however, it is necessary to consider the bone. In this paper, CT measurements were made on a phantom with regions of both iodine and aluminum, which was used as a substitute for the bone. A filtered back-projection method and a maximum likelihood-expectation maximization method were employed for image reconstruction.

A study on the chemical reactivity control of sodium utilizing the atomic interaction of sodium with suspended nanoparticles was carried out. The atomic interaction between nanoparticles and sodium was estimated by theoretical calculations and verified by fundamental physical property measurements. Results showed that the bond between the sodium atom and the nanoparticle atom was significantly stronger than that between sodium atoms, when the transition metals that have large electronegativity are applied as nanoparticles. From the theoretical calculation results, it was suggested that charge transfer occurs from the sodium atom to the nanoparticle atom. The fundamental physical properties of sodium with suspended nanoparticles were examined in comparison with that of sodium to verify the change of the atomic interaction. From the experimental results, it became clear that surface tension increases and evaporation rate decreases. These changes in fundamental physical properties were measured to verify the...

To exploit the energy information of X-rays in computed tomography (CT), we developed a current-mode detector that gave the energy distribution of incident X-rays. The CT value obtained for a given material in a phantom depended on the X-ray path length through the phantom. To ensure a constant CT value for a given material, we prepared response functions as a function of X-ray path length and applied these response functions in the unfolding process. When using response functions that depended on X-ray path length, the CT values obtained were constant for a given material. In addition, the CT values obtained for iodine contrast media were greater than the values obtained using conventional current CT, especially for higher X-ray tube voltages.

The computed tomography (CT) values obtained by the energy subtraction method with a transXend detector, which measured X-rays as current and gave the corresponding X-ray energy information, show the disadvantage that the CT values are dependent on the thickness of a homogeneous phantom. In order to obtain constant CT values for a uniform material, a new unfolding method is proposed using variable response functions of the transXend detector according to the X-ray path length in the phantom. The CT values measured using the new unfolding method are discussed with respect to the energy range used in the unfolding process, the number of segment detectors, and the substrate of the segment detectors.

A feasibility study of suppression of the chemical reactivity of sodium itself using an atomic interaction between nanoparticles and sodium atoms has been carried out. We expected that the atomic interaction strengthens when the nanoparticle metal is the transition element which has a major difference in electronegativity from sodium. We also calculated the atomic interaction between nanoparticle and sodium atoms. It became clear that the atomic bond between the nanoparticle atom and the sodium atom is larger than that between sodium atoms, and the charge transfer takes place to the nanoparticle atom from the sodium atom. Using sodium with suspended nanoparticles, the fundamental physical properties related to the atomic interaction were investigated to verify the atomic bond. The surface tension of sodium with suspended nanoparticles increased, and the evaporation rate of sodium with suspended nanoparticles also decreased compared with that of sodium. Therefore the presence of the atomic interaction between nanoparticles and sodium was verified from these experiments. Because the fundamental physical property changes by the atomic interaction, we expected changes in the chemical reactivity characteristics. The chemical reaction properties of sodium with suspended nanoparticles with water were investigated experimentally. The released reaction heat and the reaction rate of sodium with suspended nanoparticles were reduced than those of sodium. The influence of the charge state of nanoparticle on the chemical process with water was theoretically investigated to speculate on the cause of reaction suppression. The potential energy in both primary and side reactions changed by the charge transfer, and the free energy of activation of the reaction with water increased. Accordingly, the reaction barrier also increased. This suggests there is a possibility of the reduction in the reaction of sodium by the suspension of nanoparticles. Consequently the possibility of the reaction suppression of sodium itself by the atomic interaction between nanoparticles and sodium atoms, which occurs by suspension of nanoparticles into sodium, was discovered.

In International Fusion Materials Irradiation Facility (IFMIF), intense neutron flux (4.5 × 1017 n/m2 s) with a peak energy of 14 MeV are produced by means of two deuteron beams with a total current of 250 mA and maximum energy of 40 MeV that strike a liquid Li target circulating in a Li loop. Major design requirement is to provide a stable Li jet at a speed of 10–20 m/s with a surface wave amplitude on the Li flow less than 1 mm for handling of an averaged heat flux of 1 GW/m2 under a continuous 10 MW deuterium beam deposition. The target system consists of a target assembly, a replaceable back-plate, a Li main loop and a Li purification loop. In July 2007, Engineering Validation and Engineering Design Activities (EVEDA) started under Broader Approach. In this paper, status of the engineering design of the IFMIF Li target system performed in 2007/2008 is described. The future EVEDA tasks to develop the target system are also summarized.

A photon detector operating in current mode that can sense X-ray energy distribution has been reported. This detector consists of a row of several segment detectors. The energy distribution is derived using an unfolding technique. In this paper, comparisons of the unfolding techniques among error reduction, spectrum surveillance, and neural network methods are discussed through simulation studies on the detection of diagnostic X-rays and gamma rays emitted by a mixture of 137Cs and 60Co. For diagnostic X-ray measurement, the spectrum surveillance and neural network methods appeared promising, while the error reduction method yielded poor results. However, in the case of measuring mixtures of gamma rays, the error reduction method was both sufficient and effective.

This paper describes the latest design of liquid lithium (Li) target system in International Fusion Materials Irradiation Facility (IFMIF). IFMIF is an accelerator-driven intense neutron source for fusion reactor materials testing. Two 40 MeV deuteron beams with a total current of 250 mA strikes a liquid Li target circulating in a Li loop. The Li target is to provide a stable Li jet at a speed of 10–20 m/s to handle an averaged heat flux of 1 GW/m 2 . A concaved Li flow is applied to avoid Li boiling. A cold trap and two kinds of hot trap are applied to control impurities (T, 7 Be, C, O, N) below permissible levels. A back wall made of RAFM is located in the most severe region of neutron irradiation (50 dpa/year). System availability requires more than 95% during plant lifetime. EVEDA tasks including Li loop are now being performed under the Broader Approach.

To turn the advantage of energy measurement in x-ray transmission diagnosis into practice, we propose a novel detector for the estimation of x-ray energy distribution. This detector consists of several segment detectors arrayed in the direction of x-ray incidence. Each segment detector measures x-rays as current. With unfolding measured currents, the x-ray energy distribution is obtained. The practical application of this detector was verified by estimating the iodine thickness in an acryl phantom.

In the nuclear industries, a visual inspection is required to confirm the integrity of the facilities and components. Recently, a silica-based image fiber has been used for visual inspection in the nuclear facilities. As the emphasis on visual inspection increases, an image fiber which can function in harsh environments, such as under high dose rate, narrow spaces and high temperature is required. It is thus necessary to study the transmission and mechanical characteristics of a silica-based image fiber exposed to γ-ray irradiation and elevated temperatures. We investigated the transmission loss characteristics and mechanical strength under γ-ray irradiation at high temperature with the objective of identifying the causes of deterioration of the image fiber. The induced loss of the transmission in the visible wavelength region was caused by E center and NBOHC (non-bridging oxygen hole center), and their annealing effect by thermal energy was confirmed. We believe that a high radiation resistant image fibe...

For the reduction of exposure dose in contrast media detection with X-ray transmission measurements, the energy measurement of X-rays and the energy subtraction (ES) method have been shown to be effective. To make the ES method applicable, a novel detector for unfolding the X-ray energy distribution was proposed by the authors. As an application of this novel detector, a CT image was reconstructed with ES data and compared with the image reconstructed using electric current data.

Liquid sodium containing titanium nanoparticles (LSnanop) of 10-nm diameter was prepared by dispersing titanium nanoparticles (2 at.% Ti) into liquid sodium with the addition of stirring and ultrasonic sound wave. The titanium nanoparticles themselves were prepared by the vapor deposition method. This new liquid metal, LSnanop, shows a remarkable stability due to the Brownian motion of nanoparticles in liquid sodium medium. In addition, the difference of measured heat of reaction to water between this LSnanop and liquid sodium indicates the existence of cohesive energy between the liquid sodium medium and dispersed titanium nanoparticles. The origin of the cohesive energy, which serves to stabilize this new liquid metal, was explained by the model of screened nanoparticles in liquid sodium. In this model, negatively charged nanoparticles with transferred electrons from liquid sodium are surrounded by the positively charged screening shell, which may inhibit the gathering of nanoparticles by the “Coulombic repulsion coating.” The atomic volume of LSnanop shows the shrinkage from the linear law, which also suggests the existence of cohesive energy. The viscosity of LSnanop is almost the same as that of liquid sodium. This behavior was explained by the Einstein equation. The surface tension of LSnanop is 17 % larger than that of liquid sodium. The cohesive energy and the negative adsorption may be responsible to this increase. Titanium nanoparticles in liquid sodium seem to be free from the Coulomb fission. This new liquid metal containing nanoparticles suggests the possibility to prepare various stable suspensions with new properties.

For the energy-resolved computed tomography (CT), the authors developed a current mode X-ray detector, a "transXend detector", which measures X-rays as electric current and gives X-ray energy distribution after analysis. As an application of the transXend detector, thickness distributions of materials are estimated with one transmission measurement, with using two-dimensional map made of the ratio of measured electric currents. With two transmission measurements, a tomography is reconstructed. Large reduction of dose exposure in CT is expected with this method.

Nuclear fusion reactors are a promising candidate of the future power source. Magnetic confinement fusion (MCF) blankets adopt high-temperature liquid metals (LM) such as the lead-lithium eutectic alloy (PbLi), as a coolant/tritium breeder. Developments of the LM-MCF blankets require comprehensive understanding of the high-temperature LM flows under the influence of the plasma-confining magnetic field. A high-temperature ultrasonic Doppler velocimetry (HT-UDV) has been developed as a flow diagnostic technique to acquire local velocity profiles of the opaque, high-temperature LM flow. This paper describes HT-UDV technique that has been successfully applied to measure velocity profiles of PbLi flows. The impact of tracer particles is investigated to determine requirements for HT-UDV measurement of PbLi flows. The HT-UDV system is tested on a PbLi flow driven by a rotating-disk in an inert atmosphere. We find that a sufficient amount of particles contained in the molten PbLi are required to successfully measure PbLi velocity profiles by HT-UDV. An X-ray diffraction analysis is performed to identify those particles in PbLi, and indicates that those particles were made of the lead mono-oxide (PbO). Since the specific densities of PbLi and PbO are close to each other, the PbO particles are expected to be well-dispersed in the bulk of molten PbLi. We conclude that the excellent dispersion of PbO particles enables the HT-UDV to obtain reliable velocity profiles for operation times of around 12 h.

A contact angle database of a molten lead–lithium eutectic alloy (PbLi) droplet on a silicon carbide (SiC) is basic information for research and development both of magnetic confinement fusion (MCF) and inertia confinement fusion (ICF) blankets. PbLi coolant/breeder flows in the coolant channel made of the SiC walls will experience a flow slip at the wall, called as a magnetohydrodynamic (MHD) slip flow. An ICF blanket adopts a molten PbLi film flow along the SiC first wall. The PbLi contact angle database is necessary for numerically predicting the molten PbLi film flow behaviors. The present study is attempted to measure the contact angles formed between the molten PbLi and the various SiC surfaces, e.g. a chemical vapor deposition (CVD) SiC and a nano-infiltration and transient eutectic-phase (NITE) SiC/SiC composite in an inert atmosphere in order to examine an initial PbLi wettability. As the results, the molten PbLi contact angle database is obtained, which covers the PbLi temperature from 250 to 400°C on the surface-polished and unpolished SiC, respectively.

Liquid sodium is used as the coolant of the fast breeder reactor (FBR). A weak point of sodium is a high chemical reactivity with water or oxygen. So an idea of chemical reactivity suppression of liquid sodium itself is proposed. The idea is that nano-meter size particles (hereafter called nano-particles) are dispersed in liquid sodium, and an atomic interaction which is generated between nano-particle and sodium atoms is applied to suppress the chemical reactivity. We call sodium that has dispersed the nano-particle a Nano-fluid. Three key technologies which are the trial manufacture of Nano-fluid, the reaction property of the Nano-fluid and applicability of Nano-fluid to FBR Plant have been carried out to develop the Nano-fluid.Copyright © 2008 by ASME

In conventional X-ray computed tomography (CT), X-rays are measured as electric current. Materials inside a subject are described by the linear attenuation coefficients averaged by the energy spectrum of the X-rays. A CT image cannot distinguish materials such as iodine and calcium, because the linear attenuation coefficient is not inherent to a material, but the product of X-ray mass attenuation coefficient and the density of the material. Materials such as iodine and calcium can be distinguished using an energy-resolved CT technique, with a current-mode detector system, using segment detectors aligned in the direction of X-ray incidence: the energy-resolved CT images are reconstructed by the X-rays with the energy of interest, by unfolding electric currents measured by the segment detectors.

The temperature dependence of the loss of a silica-based image fiber induced by γ-ray irradiation was examined and the deterioration of transmitted image quality was discussed.