Various types of machine oil are used for analysis and utility equipment, and these organic liquid wastes are stored in nuclear facilities and laboratories due to a lack of appropriate treatment processes. Treatment of organic liquid waste is one of the principal tasks since radiolysis of organic material generates various hazardous products. Perfluoro oil, generally used in vacuum pumps, is difficult to decompose because of its chemical stability. Calcination of fluorine compounds is possible to generate toxic and corrosive gas products. In order to achieve complete mineralization of the organic liquid wastes, the application of a subcritical water reaction was examined. In this study, the effect of introducing a functional group into a perfluoro compound on its decomposition performance was experimentally evaluated. First, we carried out the transformation of perfluorohexane to perfluorohexyl iodide or perfluoroheptanoic acid based on reported procedures. Next, laboratory scale batch-wise decomposition tests with subcritical water on perfluorohexyl iodide and on perfluoro heptanoic acid were carried out. Analyses of degraded organic products remaining in the aqueous phase by atmospheric pressure ionization mass spectrometry and liquid chromatography-mass spectrometry were carried out. The decomposition products of each fluorine compound were identified, confirming that subcritical treatment is a promising treatment method.

The accident at the Fukushima Daiichi Nuclear Power Plant in 2011 led to a core meltdown, resulting in the significant release of radioactive materials into the environment, revealing the urgent need for further in-depth development of Level 2 probabilistic safety assessment technology. To help establish an effective source-term migration evaluation method, this study investigates fission product migration behavior across leak pathways. Specifically, an experimental line is developed, and experiments are performed under conditions that simulate the environmental and flow conditions in containment vessel penetrations and failure locations during a severe accident. The experiments are conducted in narrow circular pipes, which represent the leak pathways in the containment vessel and reactor building, to determine the impact of flow rate, particle size, and flow path size on the decontamination factors. Additionally, a turbulent deposition model that accounts for re-entrainment effects has been developed, and the experimentally obtained decontamination factors are compared with the developed model, as well as a conventional model. The predicted decontamination factors from the present model exhibit similar trends and values to the experimental results.

The objective of the current study is to investigate the mechanical properties of the 180° bending edge of a hot-dip galvanized steel panel with a flat surface edge (as the JISG3302 stander). Our study investigated the relationship between hardness and strain at the cross-section of the panel through numerical simulations. Hardness tests are carried out on the machined cross-sections of the panel, subsequently further hardness and strain conversion equations (based on the ASTM-E140.19(2013) standard), The hardness and strain tests offer valuable insights into the materials’ deformation resistance and its capacity to withstand external loads. The results obtained from these tests, including the hardness and strain values, can be used to develop conversion equations that facilitate the evaluation of the hemmed panel's strength with respect to the metal material used. In addition, the strain results are compared with the numerically simulated strain results (utilized DEFORM Ver.11) to provide a basis for subsequent simulation works. This approach allows for a more comprehensive understanding of the mechanical properties of the cross-section panel and could also validate simulation results: on the reliability and accuracy of the hardness test work. Consequently, this approach allows to predict the behavior of panel material under specific loading conditions in the hemming process. which can be of utmost importance in industrial applications.

This paper describes the visualization of defect regions in a structure via hammering test that employs the level set type topology optimization based on the concept of the phase-field method. In this study, the residual between the calculated displacement and the observed displacement is defined as the performance function, with the identification problem of defect regions being formulated based on the adjoint variable and finite element methods. Numerical experiments were performed to investigate the effect of the regularization parameter, the number of observation point, the evaluation equation of convergence and the application of the weighted gradient. Consequently, it was found that the number, position and size of defect can be adjusted using the regularization parameter τ. In addition, it was seen that if the number of observation points and the evaluation equation in the iterative computation of topology update are appropriately given, the identified defect topology is close to the exact defect topology. Furthermore, it was found that defect topologies can be more accurately identified by applying weighted sensitivities.

The free-cutting steel is one of the essential structural steels in electrical appliance industry and automotive industry. Most of the steel contains Pb, as solid lubricant, chip breaker, tool edge stabilizer and tool life extender. MnS grains also play the same role of Pb. However, Pb is toxic so that it will be prohibited to add to the steel in near future. Steel industry has tried to replace Pb with other element(s) and/or compound(s). The trials are still going on. This study proposes a candidate of the workability parameters for free-cutting steels with/without Pb. Investigated steels were loaded quasi-statically (strain rate: 1×10-3 s-1) and dynamically (1×103 s-1) up to fracture. Half of the specimens were pre-fatigued to form easier slip situation in steel matrix. After fracture, thin steel matrix penetrated into plenty of MnS grains. For the steel with Pb, the ratios of the number of such penetrations to those of total grains maintained almost the same value for all loading conditions. The ratios were varied with the loading conditions for the steel without Pb. These facts meant that Pb was a key element for easier slip of steel matrix. Therefore, this ratio had a feasibility to be one of the workability parameters for the free-cutting steel.

The previous research of speech separation has significantly improved separation performance based on the time-domain method: encoder, separator, and decoder. Most research has focused on revising the architecture of the separator. In contrast, a single 1-D convolution layer and 1-D transposed convolution layer have been used as encoder and decoder, respectively. This study proposes deep encoder and decoder architectures, consisting of stacked 1-D convolution layers, 1-D transposed convolution layers, or residual blocks, for the time-domain speech separation. The intentions of revising them are to improve separation performance and overcome the tradeoff between separation performance and computational cost due to their stride by enhancing their mapping ability. We applied them to Conv-TasNet, the typical model in the time-domain speech separation. Our results indicate that the better separation performance is archived as the number of their layers increases and that changing the number of their layers from 1 to 12 results in more than 1 dB improvement of SI-SDR on WSJ0-2mix. Additionally, it is suggested that the encoder and decoder should be deeper, corresponding to their stride since their task may be more difficult as the stride becomes larger. This study represents the importance of improving these architectures as well as separators.

To develop rationalized maintenance plans for nuclear power plants, the characteristics of each plant must be considered. For sodium-cooled fast reactor (SFR) plants, constraints on inspections exist due to the specialty that equipment retaining sodium must be handled, which is one of the important points that must be considered in maintenance rationalization. In this study, we propose a maintenance optimization scheme, which is a design support tool, using risk information to develop a maintenance strategy based on the system based code (SBC) concept. The SBC concept intends to provide a theoretical procedure to optimize the reliability of structure, system and components (SSCs) by administrating every related engineering requirements throughout the life of the SSCs from design to decommissioning. “The American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel Code, Code Case, N-875, Alternative In-service Inspection Requirements for Liquid-Metal Reactor Passive Components” was developed based on the SBC concept. The basic procedure of the Code Case has also been implemented in “The ASME Boiler and Pressure Vessel Code, Section XI, Division 2,” which provides requirements for Reliability and Integrity Management programs for nuclear power plants, including advanced reactors. The purpose of this study is to establish detailed procedures for the maintenance optimization scheme based on the procedure in Code Case N-875. Furthermore, a quantitative trial evaluation of the core support structure of the next SFR under development in Japan is also performed using the maintenance optimization scheme.

A multi-material structure that is composed of several different material properties is promising for achieving an ideal functionality that can outperform a single material structure. In the course of automotive design, the combination of lightweight and stiff materials can reduce the weight of a car body without sacrificing its performance. This paper proposes a multi-material topology optimization (MMTO) framework for the eigenfrequency maximization problem based on the Multi-material level set (MMLS) based topology optimization. The key idea of MMLS is to use M level set functions to represent M material regions and one void region without overlap. To demonstrate the proposed method, first, we formulate an MMTO problem for maximizing the eigenfrequency based on the shape representation by the MMLS method. Next, we derive the topological derivatives of multiple materials in the eigenfrequency problem and construct an optimization algorithm in which the level set functions are evolved by solving a reaction-diffusion equation (RDE) based on the topological derivatives. Several numerical examples are provided to validate the proposed methodology.

In this study, we will report the efficiency of hybrid filler for the mechanical properties and the thermal conductivity of Polyamide-6 (PA6) composite. One of the ways to improve the thermal conductivity of the composite is to add fillers to the matrix, but the excessive filler causes the composite to form aggregation and void. They make the mechanical properties and thermal conductivity decline. As the solution to this problem, to use of hybrid filler is expected to realize the lower filler content of composite with keeping the properties. However, the most efficient ratio of hybrid filler is unclear. In this study, PA6 and filler were composited using a twin-shaft melt-mixing machine. A manual injection molding machine was then used to produce test specimens for thermal conductivity measurement and tensile test specimens. Thermal conductivity was measured based on the laser flash method. The structure of the composite was also investigated by fracture surface observation after tensile testing. It is revealed that two types of fillers were composited with PA6 to obtain higher thermal conductivity than that of a single filler with the same filler content. This is because the different shapes of the two fillers made the thermally conductive path.

CVT chains are widely used in vehicles because the slip between parts is small, which enables efficient power transmission. However, the intermittent motion of CVT chain pins entering and leaving the pulleys causes undesirable vibration in the whole chain, and affects the basic performance of the CVT. Therefore, it is important to investigate the influence of the geometrical specifications of the chain on this vibratory motion. This study focused on the pin-pulley slip length when the pins enter and leave the pulleys, and a mathematical model for the power loss of a CVT chain was developed. The validity of this model was verified and confirmed experimentally. In addition, the influence of the shape of chain components on power loss was also investigated. In particular, the influence of the position of the contact point between the pins and pulleys on power loss was investigated both theoretically and experimentally, and geometric parameters were optimized. As a result, the model formulated in this paper can be used to investigate measures for reducing CVT power loss.