The Experts below are selected from a list of 20964 Experts worldwide ranked by ideXlab platform
F Velasco - One of the best experts on this subject based on the ideXlab platform.
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effect of the boron content in the aluminium boron composite
Journal of Alloys and Compounds, 2006Co-Authors: Juana Abenojar, M. A. Martínez, F VelascoAbstract:Abstract Aluminium/boron metal–matrix composites (MMC) were fabricated and tested changing the boron content (10–50 wt.%) and using powder isostatic compaction and sintering as consolidation method. This high boron material can be used in nuclear applications, where boron gives Neutron Absorption properties, but not as structural material. The main objective was to study the influence of temperature on the reactivity of boron and aluminium and on the formation of new phases. By means of Differential Thermal Analysis (DTA), the formation of new phases was studied as well as sintering temperature was determined, finding that temperature was dependent on the boron content. Materials were characterized through density and mechanical properties (bending strength and hardness tests) finding, as expected, changes in properties with boron content. Furthermore, microstructural and fractographic studies have been performed by means of Scanning Electron Microscopy (SEM). Sintering process of these materials promoted the formation of borides, thus, X-ray diffraction (XRD) study was carried out in order to identify which kind of borides were formed.
Hiroshi Sekimoto - One of the best experts on this subject based on the ideXlab platform.
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simulation study on candle burnup applied to block type high temperature gas cooled reactor
Progress in Nuclear Energy, 2005Co-Authors: Yasunori Ohoka, Takashi Watanabe, Hiroshi SekimotoAbstract:Abstract The CANDLE burnup is a new reactor burnup concept, where the distributions of fuel nuclide densities, Neutron flux, and power density move with the same constant speed along the core axis from bottom to top (or from top to bottom) of the core and without any change in their shapes. It can be applied easily to a block-type high temperature gas cooled reactor (HTGR) using an appropriate burnable poison with a high Neutron Absorption cross section mixed with uranium oxide fuel. In this study, natural gadolinium is used as burnable poison. In the present paper, the simulation of the burnup for the steady state and the startup is performed. For the steady state simulation with direct solutions of steady state nuclide densities as inputs, the difference between the results of the steady state analysis and the simulation analysis is very small. It confirms that the steady state analysis is correct. When the initial core is constructed from easily available nuclides, the simulation result gives a reactivity change of 1.7% at a burnup time of 0.7 years.
Juana Abenojar - One of the best experts on this subject based on the ideXlab platform.
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effect of the boron content in the aluminium boron composite
Journal of Alloys and Compounds, 2006Co-Authors: Juana Abenojar, M. A. Martínez, F VelascoAbstract:Abstract Aluminium/boron metal–matrix composites (MMC) were fabricated and tested changing the boron content (10–50 wt.%) and using powder isostatic compaction and sintering as consolidation method. This high boron material can be used in nuclear applications, where boron gives Neutron Absorption properties, but not as structural material. The main objective was to study the influence of temperature on the reactivity of boron and aluminium and on the formation of new phases. By means of Differential Thermal Analysis (DTA), the formation of new phases was studied as well as sintering temperature was determined, finding that temperature was dependent on the boron content. Materials were characterized through density and mechanical properties (bending strength and hardness tests) finding, as expected, changes in properties with boron content. Furthermore, microstructural and fractographic studies have been performed by means of Scanning Electron Microscopy (SEM). Sintering process of these materials promoted the formation of borides, thus, X-ray diffraction (XRD) study was carried out in order to identify which kind of borides were formed.
T H Prettyman - One of the best experts on this subject based on the ideXlab platform.
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Neutron Absorption constraints on the composition of 4 vesta
Meteoritics & Planetary Science, 2013Co-Authors: T H Prettyman, David W Mittlefehldt, N Yamashita, Andrew W Beck, W C Feldman, John S Hendricks, D J Lawrence, T J Mccoy, H Y Mcsween, P N PeplowskiAbstract:Global maps of the macroscopic thermal Neutron Absorption cross section of Vesta's regolith by the Gamma Ray and Neutron Detector (GRaND) on board the NASA Dawn spacecraft provide constraints on the abundance and distribution of Fe, Ca, Al, Mg, and other rock-forming elements. From a circular, polar low-altitude mapping orbit, GRaND sampled the regolith to decimeter depths with a spatial resolution of about 300 km. At this spatial scale, the variation in Neutron Absorption is about seven times lower than that of the Moon. The observed variation is consistent with the range of Absorption for howardite whole-rock compositions, which further supports the connection between Vesta and the howardite, eucrite, and diogenite meteorites. We find a strong correlation between Neutron Absorption and the percentage of eucritic materials in howardites and polymict breccias, which enables petrologic mapping of Vesta's surface. The distribution of basaltic eucrite and diogenite determined from Neutron Absorption measurements is qualitatively similar to that indicated by visible and near infrared spectroscopy. The Rheasilvia basin and ejecta blanket has relatively low Absorption, consistent with Mg-rich orthopyroxene. Based on a combination of Fe and Neutron Absorption measurements, olivine-rich lithologies are not detected on the spatial scales sampled by GRaND. The sensitivity of GRaND to the presence of mantle material is described and implications for the absence of an olivine signature are discussed. High Absorption values found in Vesta's “dark” hemisphere, where exogenic hydrogen has accumulated, indicate that this region is richer in basaltic eucrite, representative of Vesta's ancient upper crust.
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Neutron Absorption measurements constrain eucrite diogenite mixing in
2013Co-Authors: T H Prettyman, N Yamashita, Andrew W Beck, H Mizzon, V Reddy, Max PlanckAbstract:The NASA Dawn Mission’s Gam-ma Ray and Neutron Detector (GRaND) [1] acquired mapping data during 5 months in a polar, low altitude mapping orbit (LAMO) with ~460-km mean radius around main-belt asteroid Vesta (264-km mean radius) [2]. Neutrons and gamma rays are produced by galac-tic cosmic ray interactions and by the decay of natural radioelements (K, Th, U), providing information about the elemental composition of Vesta’s regolith to depths of a few decimeters beneath the surface. From the data acquired in LAMO, maps of vestan Neutron and gam-ma ray signatures were determined with a spatial reso-lution of ~300 km full-width-at-half-maximum (FWHM), comparable in scale to the Rheasilvia impact basin (~500 km diameter). The data from Vesta en-counter are available from the NASA Planetary Data System. Based on an analysis of gamma-ray spectra, Vesta’s global-average regolith composition was found to be consistent with the Howardite, Eucrite, and Diogenite (HED) meteorites, reinforcing the HED-Vesta connec-tion [2-7]. Further, an analysis of epithermal Neutrons revealed variations in the abundance of hydrogen on Vesta’s surface, reaching values up to 400 g/g [2]. The association of high concentrations of hydrogen with equatorial, low-albedo surface regions indicated exogenic delivery of hydrogen by the infall of carbona-ceous chondrite (CC) materials. This finding was but-tressed by the presence of minimally-altered CC clasts in howardites, with inferred bulk hydrogen abundances similar to that found by GRaND, and by studies using data from Dawn’s Framing Camera (FC) and VIR in-struments [8-10]. In addition, from an analysis of neu-tron Absorption, spatial-variations in the abundance of elements other than hydrogen were detected [2]. Ongoing mapping studies with GRaND data in-clude the determination Fe abundances from the 7.6 MeV
Yasunori Ohoka - One of the best experts on this subject based on the ideXlab platform.
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simulation study on candle burnup applied to block type high temperature gas cooled reactor
Progress in Nuclear Energy, 2005Co-Authors: Yasunori Ohoka, Takashi Watanabe, Hiroshi SekimotoAbstract:Abstract The CANDLE burnup is a new reactor burnup concept, where the distributions of fuel nuclide densities, Neutron flux, and power density move with the same constant speed along the core axis from bottom to top (or from top to bottom) of the core and without any change in their shapes. It can be applied easily to a block-type high temperature gas cooled reactor (HTGR) using an appropriate burnable poison with a high Neutron Absorption cross section mixed with uranium oxide fuel. In this study, natural gadolinium is used as burnable poison. In the present paper, the simulation of the burnup for the steady state and the startup is performed. For the steady state simulation with direct solutions of steady state nuclide densities as inputs, the difference between the results of the steady state analysis and the simulation analysis is very small. It confirms that the steady state analysis is correct. When the initial core is constructed from easily available nuclides, the simulation result gives a reactivity change of 1.7% at a burnup time of 0.7 years.