[en] A fast reactor, which uses sodium as a coolant, has a lot of merits as a next generation nuclear reactor. However, the possibility of a sodium-water reaction occurrence hinders the commercialization of this reactor. As one way to improve the reliability of a steam generator, a double-wall tube steam generator is being developed in GEN-4 program. In this report, the current state of the technical developments for a double-wall tube steam generator are reviewed and a future plan for the development of a double-wall tube steam generator is established. The current focuses of this research are an improvement of the heat transfer capability for a double-wall tube and the development of a proper leak detection method for the failure of a double-wall tube during a reactor operation. The ideal goal is an on-line leak detection of a double wall tube to prevent the sodium-water reaction. However, such a method is not developed as yet. An alternative method is being used to improve the reliability of a steam generator by performing a non-destructive test of a double wall tube during the refueling period of a reactor. In this method a straight double wall tube is employed to perform this test easily, but has a difficulty regarding an absorption of a thermal expansion of the used materials. If an on-line leak detection method is developed, the demerits of a straight double-wall tube are avoided by using a helical type double-wall tube, and the probability of a sodium-water reaction can be reduced to a level less than the design-based accident

[en] This paper reports a class of compact low-voltage-actuated micromechanical radio-frequency (RF) switches with a piezoelectric micro-cantilever and a signal transmission line in an integrated form. Perovskite lead zirconate titanate (PZT) thin film was prepared by using a facile sol-gel process in a programmable manner. The proposed RF switch was demonstrated without significant structural deformation by optimization of both the structural design and batch fabrication with various micromachining techniques. The proposed compact RF switch was experimentally found to be actuated with an applied voltage as low as 2 V. The switch also showed high isolation and moderate insertion loss for frequencies up to 5 GHz.

[en] The sodium is widely used as one of the coolants in the liquid metal reactor system since it has important safety features such as a long thermal response time, a large margin to coolant boiling, and operating in near atmospheric pressure, etc. The state-of-the-art on the flow and pressure measurement techniques in the piping system worldwide is investigated and reviewed to utilize it as a basis for developing a new technique applying for the high temperature sodium flow environment

[en] Polydiacetylene (PDAs) have received great attention as colorimetric sensors since these conjugated polymers undergo a blue-to-red color change upon various chemical/biochemical and physical stimuli. PDAs have been reported to display thermochromism (heat), solvatochromism (solvent), mechanochromism (mechanical strain) as well as magnetochromism (magnetic force) electrochromism (electric current), and affinochromism (ligand-receptor interaction). The solvent induced color change of PDA is generally non-specific and irreversible. For instance, the PDA derived from 10,12-pentacosadiynoic acid (PCDA) undergoes a blue-to-red (or purple) color change upon exposure to many common organic solvents including tetrahydrofuran (THF), chloroform, dichloromethane, acetone, methanol (MeOH), ethyl acetate (EA), and diethyl ether. The results obtained from Raman spectral analysis suggests that exposure to THF causes the distortion of the backbone of the polymer main chain and some conformational changes in the aliphatic side chain. Solvatochromism of a PDA is closely related to the solubility of a diacetylene monomer. PDA undergoes a color change when the dissolution of unpolymerized monomers causes some void in the PDA supramolecules. Since PCDA-mBzA has a good solubility only in THF, colorimetric transition of PDA occurs only in response to THF. Since solubility of a diacetylene monomer can be manipulated by structural change of the monomer, we believe the strategy described in current investigation should be useful for the development of solvent-specific PDA sensor systems

No abstract available

[en] As a treatment method of the waste sodium which was produced from a sodium facility, an investigation for a reaction procedure of the waste sodium with the sodium hydroxide has been developed. The sodium was injected into a reaction vessel filled with a caustic soda through an atomizing nozzle to maintain the reaction uniformly. There were complex reacting phenomena in the system to observe with a naked eye. Therefore, a water mock-up was carried out for a practical use the data got in the waste sodium treatment test. The major experimental parameters are the flowrate of water through an atomizing nozzle and the recirculation rate. In addition, the positions and flow directions of the nozzles are important parameters, also. From this experiment, 300 sets of data were obtained by analyses of the phenomena of the photographic records, and the optimum flowing conditions

[en] In the liquid metal reactor using sodium as a coolant, there exists a free surface in the upper plenum of the reactor vessel where the hot coolant contacts with a cold cover gas. The fluctuation of the free surface causes two important phenomena in the reactor. One is to induce a thermal stress to the reactor vessel due to the free surface fluctuation of sodium. Another is the cover gas entrainment at the free surface. If a significant amount of gas is entrained by the fluctuation of sodium, the entrained gas causes a change in the reactivity and also reduces the heat removal capability of the coolant in the core. Therefore it is an important parameter in the design of a liquid metal reactor. An experimental study will be carried out for measuring the fluctuating frequency and amplitude of the free surface in a cylindrical annular vessel where the inner vessel is simulated as a UIS of a reactor. Since the hydraulic property of sodium is similar to that of water, water is used as a working fluid instead of sodium. Because the range of the estimated frequency is about 0.5∼5 Hz in this experiment, a conductivity type wire sensor is used as a level meter in order to get an accurate enough response. But the characteristic of this type level sensor have not been reported in the literature so far. Owing to this reason, an experiment is carried out to find the characteristics of the level sensor before the surface fluctuation measuring experiment. In the present paper the characteristics of the level sensor are described through an experiment

[en] The protection of a water/steam leak into a sodium in the SFR SG at an early phase of a leak origin depends on a fast response and sensitivity of a leak detection system not to a response against the several kinds of noises. The subject in this study is to introduce a detection performance by using our developed acoustic leak detection methodology discriminated by a backpropagation neural network according to a preprocessing of the 1/6 Octave band analysis or 1/12 Octave band analysis and the xⁿ method defined by us. It was used for the acoustic signals generated from the simulation works which are the noises of an artificial background such as a scratching, a hammering on a steel structure and so on. In a previous study, we showed that the performance of a LabVIEW tool embedded with the developed acoustic leak detection methodology detected the SWR leak signals

[en] We performed DFT calculations on an amide/urea system. A weak interaction was found between these species in the neutral state. Urea dimer formation energy is also comparable to that of the amide/urea complex. However, the oxidation of the urea into its radical cation induces a strong hydrogen bonding interaction with the amide guest. The responses of chemical systems to changes in external stimuli such as pressure, temperature, electrons, photons, and chemicals are important aspects of supramolecular chemistry, which has found applications in the sensor, molecular electronics, and molecular machine fields, to name a few. Furthermore, hydrogen bonding is one of the most important molecular interactions in terms of these applications. Generally, the reduction of a receptor leads to the formation of a radical anion, which binds more strongly to substrates than the neutral parent molecule. We previously reported the results of a theoretical study on nitrobenzene/urea hydrogen bonding, in which it was found that a computational model based on density functional theory (DFT) produced an excellent correlation with experimental data. Recently, Woods et al. described redox-switched hydrogen bonding between amide and diaryl-urea. Unlike other studies on redox-dependent hydrogen bonding, their system is based on oxidation rather than reduction. 1,4-dimethylpiperizine-2,3-dione (PZD), which has two pre-organized hydrogen acceptor atoms, can form intermolecular hydrogen bonds with both urea NH's. In the context of redox-switching, the dependence of strength of bonding upon changes in external stimuli is of great importance. We performed DFT calculations on these hydrogen bonding pairs and correlated the results with the experimental data

[en] The development of efficient chemosensors based on the conjugated polymers has been the central focus of a large number of recent research programs. The presence of extensively delocalized electrons and conformational restrictions of the backbone structures make conjugated polymers attractive sensory materials. In these polymers, molecular recognition events influence electronic absorption and emission properties. Thus, a wide variety of conjugated polymer-based sensors have been investigated. However, the majority of the conjugated polymer sensors described to date have been explored in the form of solutions or thin films. Most biologically interesting target molecules, such as proteins, carbohydrates, nucleic acids, or ions, are only soluble in water. Thus, it is desirable to use water-soluble conjugated polymers as sensor matrices. In general, in order to make water-soluble conjugated polymers tedious procedures are required since most synthetic methods developed for this purpose are incompatible with sidechain functionalities. Accordingly, protecting group strategies are required to prepare polymers with requisite functional groups that foster water solubility