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Tamura K.,Wakasa - Wan Energy Research Center | Yamagishi R.,Wakasa - Wan Energy Research Center
Journal of Nuclear Science and Technology | Year: 2017

Molten metal behaviors during the laser cutting of carbon steel and stainless steel specimens up to 300 mm in thickness were observed to dismantle large steel objects for the nuclear decommissioning, where attenuated process images from both steels were observed for detailed process analysis. Circular and rod-like molten metal structures were observed at the laser irradiated region depending on the assist gas flow conditions. Molten metal blow-off and flow processes were observed as cutting processes. The observations were explained by the aerodynamic interaction of the melted surface layer. The method is useful for the detailed observation of the molten metal behaviors, and the results are informative to understand and optimize the laser cutting process of very thick steel specimens. © 2017 Atomic Energy Society of Japan. All rights reserved.


Sasase M.,Wakasa - Wan Energy Research Center | Suiya N.,NESI Inc.
Tribology International | Year: 2010

Sliding friction tests of pin-on-disc type were carried out for carbon steel, pure iron and pure copper, and the microstructure and hardness near the sliding surfaces were investigated in detail. It was found that patchy transfer layers with ultra-fine (<200 nm) structures were produced on the disc surfaces. Nanocrystalline grains of 30-50 nm were identified for carbon steel, and submicron sized grains of 100-150 nm were observed in pure copper. The thicknesses of the ultra-fine structures were in the range of 10-50 μm, depending on the specimen material, sliding speed and applied load. The hardness near the sliding surface of pure iron was increased compared with the matrix. It was suggested that the hardening was due to the very fine structure formed by severe plastic deformation, but not due to phase transformation caused by thermal effects. © 2009 Elsevier Ltd. All rights reserved.


Matsumoto H.,University of Fukui | Tomita M.,Japan Central Research Institute of Electric Power Industry | Otsuka K.,Japan Central Research Institute of Electric Power Industry | Hatashita M.,Wakasa - Wan Energy Research Center | Hamada N.,Japan Central Research Institute of Electric Power Industry
Current Molecular Pharmacology | Year: 2011

A classical paradigm of radiation biology asserts "targeted effect" that all radiation effects on cells, tissues and organisms are due to the direct action of radiation. However, over the past two decades, a paradigm of radiation biology has undergone a shift away from "targeted effect" relationships and towards complex ongoing "intra- and inter-cellular responses", which involve not only targeted but also non-targeted ones. These responses include now familiar, but still fully unknown, phenomena associated with low-dose/low-dose-rate radiation exposure such as adaptive responses, bystander responses, low-dose hypersensitivity, and genomic instability. The mechanisms underlying these responses often involve biochemical/molecular signals that respond to targeted and non-targeted events. Matsumoto et al. have previously found that nitric oxide functions as initiators of radiation-induced bystander and adaptive responses. These findings suggest correlations between the radioadaptive and bystander responses. The present review focuses on these two phenomena by summarizing observations supporting their existence, and discussing the linkage between them from the aspect of production of reactive nitrogen species. © 2011 Bentham Science Publishers Ltd.


Shukla P.K.,Ruhr University Bochum | Shukla P.K.,Wakasa - Wan Energy Research Center
Physics of Plasmas | Year: 2012

We examine linear dust acoustic waves (DAWs) in a dusty plasma with strongly correlated dust grains, and discuss possibility of a twisted DA vortex beam carrying orbital angular momentum (OAM). For our purposes, we use the Boltzmann distributed electron and ion density perturbations, the dust continuity and generalized viscoelastic dust momentum equations, and Poisson's equation to obtain a dispersion relation for the modified DAWs. The effects of the polarization force, strong dust couplings, and dust charge fluctuations on the DAW spectrum are examined. Furthermore, we demonstrate that the DAW can propagate as a twisted vortex beam carrying OAM. A twisted DA vortex structure can trap and transport dust particles in dusty plasmas. © 2012 American Institute of Physics.


Tane M.,Osaka University | Mayama T.,Kumamoto University | Oda A.,Osaka University | Nakajima H.,Osaka University | Nakajima H.,Wakasa - Wan Energy Research Center
Acta Materialia | Year: 2014

The tensile and compressive deformation in porous Mg with unidirectionally oriented cylindrical pores and a unique fiber texture in which the normal direction of the {1 0 1¯ 3} plane was preferentially oriented was studied. Porous Mg specimens with unidirectional pores and texture were prepared by unidirectional solidification in a hydrogen atmosphere using a continuous-casting technique and their quasi-static tensile deformation and quasi-static and dynamic compressions were investigated. In tensile loading parallel to the orientation direction of the pores (the "pore direction"), the porous Mg exhibited a large tensile elongation of ∼60% strain despite the presence of ∼42% porosity, whereas it showed high energy absorption of ∼30 kJ kg-1 along the same direction. To clarify these superior mechanical properties, the underlying operative deformation modes and rotation of crystallographic orientation during loadings were analyzed by X-ray pole figures, optical microscopy and crystal plasticity finite-element modeling. The analyses revealed that in the initial stage of both the compression and tensile loadings along the pore direction, basal slip mainly operated. Importantly, the activity of basal slip was enhanced during the tensile loading by rotation of the crystallographic orientation, which resulted in high tensile elongation. On the other hand, the activation of basal slip was initially suppressed by the crystal rotation during compression. However, the localization of basal slip originating from the elongated grains with the unique texture subsequently enhanced the activity of basal slip, which suppressed the steep increase in the flow stress. This unique localized deformation gave rise to the superior impact energy absorption. © 2014 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.


Nishio S.,Wakasa - Wan Energy Research Center
Corrosion Science | Year: 2012

Zr metal readily dissolved in a mixture of H 2SO 4 and HNO 3. The solubility of Zr in a 10% mixture (96wt% H 2SO 4:61wt% HNO 3=9:1 volumetric mixture) reached approximately 34g/L. It was found that NO2+ and H 2SO 4 are consumed to form NO 2, NO +, and HSO4- upon the dissolution of Zr. Finally, two possible dissolution mechanisms are discussed. © 2012 Elsevier Ltd.


Shy S.S.,Wakasa - Wan Energy Research Center | Liu C.C.,Wakasa - Wan Energy Research Center | Shih W.T.,Wakasa - Wan Energy Research Center
Combustion and Flame | Year: 2010

Recently, Shy and his co-workers reported a turbulent ignition transition based on measurements of minimum ignition energies (MIE) of lean premixed turbulent methane combustion in a centrally-ignited, fan-stirred cruciform burner capable of generating intense isotropic turbulence. Using the same methodology, this paper presents new complete MIE data sets for stoichiometric and rich cases at three different equivalence ratios φ{symbol} = 1.0, 1.2 and 1.3, each covering a wide range of a turbulent Karlovitz number (Ka) indicating a time ratio between chemical reaction and turbulence. Thus, ignition transition in premixed turbulent combustion depending on both Ka and φ{symbol} can be identified for the first time. It is found that there are two distinct modes on ignition in randomly stirred methane-air mixtures (ignition transition) separated by a critical Ka where values of Kac ≈ 8-26 depending on φ{symbol} with the minimum Kac occurring near φ{symbol} = 1. For Ka < Kac, MIE increases gradually with Ka, flame kernel formation is similar to laminar ignition remaining a torus, and 2D laser tomography images of subsequent outwardly-propagating turbulent flames show sharp fronts. For Ka > Kac, MIE increases abruptly with Ka, flame kernel is disrupted, and subsequent randomly-propagating turbulent flames reveal distributed-like fronts. Moreover, we introduce a reaction zone Péclet number (PRZ) indicating the diffusivity ratio between turbulence and chemical reaction, such that the aforementioned very scattering MIE data depending on Ka and φ{symbol} can be collapsed into a single curve having two drastically different increasing slopes with PRZ which are separated by a critical PRZ ≈ 4.5 showing ignition transition. Finally, a physical model is proposed to explain these results. © 2009 The Combustion Institute.


Fekete T.,Wakasa - Wan Energy Research Center
Frattura ed Integrita Strutturale | Year: 2016

Buildings, structures and systems of large scale and high value (e.g. conventional and nuclear power plants, etc.) are designed for a certain, limited service lifetime. If the standards and guidelines of the time are taken into account during the design process, the resulting structures will operate safely in most cases. However, in the course of technical history there were examples of unusual, catastrophic failures of structures, even resulting in human casualties. Although the concept of Structural Integrity first appeared in industrial applications only two-three decades ago, its pertinence has been growing higher ever since. Four nuclear power generation units have been constructed in Hungary, more than 30 years ago. In every unit, VVER-440 V213 type light-water cooled, light-water moderated, pressurized water reactors are in operation. Since the mid-1980s, Pressurized Thermal Shock (PTS) analyses of Reactor Pressure Vessels (RPV) have been conducted in Hungary, where the concept of structural integrity was the basis of research and development. In the first part of the paper, a short historic overview is given, where the origins of the Structural Integrity concept are presented, and the beginnings of Structural Integrity in Hungary are summarized. In the second part, a new conceptual model of Structural Integrity is introduced. In the third part, a brief description of the VVER-440 V213 type RPV and its surrounding primary system is presented. In the fourth part, a conceptual model developed for PTS Structural Integrity Analyses is explained. © 2016 Gruppo Italiano Frattura. All Rights Reserved.


Fekete T.,Wakasa - Wan Energy Research Center
Frattura ed Integrita Strutturale | Year: 2016

In Hungary, four nuclear power units were constructed more than 30 years ago; they are operating to this day. In every unit, VVER-440 V213-type light-water cooled, light-water moderated, pressurized water reactors are in operation. Since the mid-1980s, numerous researches in the field of Pressurized Thermal Shock (PTS) analyses of Reactor Pressure Vessels (RPVs) have been conducted in Hungary; in all of them, the concept of structural integrity was the basis of research and development. During this time, four large PTS studies with industrial relevance have been completed in Hungary. Each used different objectives and guides, and the analysis methodology was also changing. This paper gives a comparative review of the methodologies used in these large PTS Structural Integrity Analysis projects, presenting the latest results as well. © 2016 Gruppo Italiano Frattura. All Rights Reserved.


Kurita T.,Wakasa - Wan Energy Research Center
Nuclear Instruments and Methods in Physics Research, Section A: Accelerators, Spectrometers, Detectors and Associated Equipment | Year: 2014

I developed a beam current transformer (CT) for monitoring the beam of a slow-cycling accelerator. The beam monitor is a new type of CT that measures the average current of a circulating beam using a negative impedance circuit (NIC). Adding an NIC can extend the low-frequency cutoff of a CT down to 0 Hz (Ninomiya et al., 2006 [1]). This report presents the detail of our proposed beam-monitoring system. The measurable band width of the CT is 30 kHz. The stability of the droop time constant of the square pulse response is ~2%/s. This beam monitor was developed for the synchrotron at the Wakasa-Wan Energy Research Center (WERC) and is currently installed there. © 2014 Elsevier Ltd. All rights reserved.

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