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1.
Toyohiko Yano Hiroshi Konishi Saishun Yamazaki Mohd Idzat bin Idris Katsumi Yoshida 《Journal of Nuclear Science and Technology》2017,54(8):891-898
SiC fiber-reinforced SiC matrix composites (SiCf/SiC) are considered as one of the candidates for blanket materials in future fusion reactors and as an advanced fuel cladding material for next-generation fission reactors. Generally, the densification of SiC needs sintering additives and oxides such as Al2O3, Y2O3, and yttrium-aluminum garnet (YAG, Y3Al5O12), which are frequently added to SiC. However, the effects of neutron irradiation on sintering additives are still unclear. In this study, we performed the neutron irradiation of Al2O3, Y2O3, and YAG at fluences up to 2.0–2.5 × 1024 n/m2 (E > 0.1 MeV) at 60–90 °C. The isochronal recovery of the macroscopic volume of Al2O3 against annealing temperature showed smooth and continuous shrinkage at a temperature of up to 1200 °C, and the volume slightly increased above that temperature. In contrast, the volume of Y2O3 showed quick shrinkage at the low temperature range, and slower and smooth recovery was observed up to ~1100 °C. In the case of YAG, the recovery of volume occurred in a step-wise manner at 600–750 °C, and continuous shrinkage occurred at temperatures lower and higher than that temperature range. The activation energies for the macroscopic volume recoveries of three oxides were obtained from the Arrhenius plots of the rate coefficients. Two-stage recovery was observed for Al2O3, whereas more complicated recovery processes were suggested for Y2O3 and YAG. 相似文献
2.
Nano-crystalline W-1%Y2O3 (wt.%) powder was produced by a modified solution chemical reaction of ammonium paratungstate (APT) and yttrium nitrate. The precursor powder was found to consist of particles of bimodal morphology i.e. large APT-like particles up to 20 μm and rectangular yttrium containing ultrafine plates. After thermal processing tungsten crystals were evolved from W-O-Y plate like particles. spark plasma sintering (SPS) was used to consolidate the powder at 1100 and 1200 °C for different holding times in order to optimize the sintering conditions to yield high density but with reduced grain growth. Dispersion of yttrium oxide enhanced the sinterability of W powder with respect to lanthanum oxide. W-1%Y2O3 composites with sub-micron grain size showed improved density and mechanical properties as compared to W-La2O3 composites. Sample sintered in two steps showed improved density, due to longer holding time at lower temperature (900 °C) and less grain growth due to shorter holding time at higher temperature i.e. 1 min at 1100 °C. 相似文献
3.
X-ray powder diffraction, X-ray fluorescence, microscopy, X-ray absorption fine structure, and electron probe microanalysis were used to characterize ZrO2-MgO inert matrix fuel containing UO2 (as a fissile element and a Pu homolog) and Er2O3 as a burnable poison. A large composition range of MgO and ZrO2 was evaluated to determine total concentrations, local environment, phases present, phase mixing, and phase composition. It was found that most compositions of the material consist of two phases: MgO (periclase) and ZrO2 (cubic zirconia). The zirconia phase incorporates up to 5% (wt/wt) MgO and up to 20% and 10% (wt/wt) UO2 and Er2O3 respectively. This allows the fissile material and burnable poison to be incorporated into the zirconia crystal structure and defines the limits of this isomorphic substitution. The bond deformation due to the isomorphic substitution of uranium was determined by X-ray absorption fine structure. The MgO phase remains pure, which will enable design optimization of the overall thermophysical properties of the inert matrix fuel in regard to thermal diffusivity and thermal conductivity. This characterization data will be used in future studies to correlate the dissolution behavior of inert matrix material containing plutonium. 相似文献
4.
High purity W and W-0.9La2O3 (wt.%) nanopowders were produced by a wet chemical route. The precursor was prepared by the reaction of ammonium paratungstate (APT) with lanthanum salt in aqueous solutions. High resolution electron microscopy investigations revealed that the tungstate particles were coated with oxide precipitates. The precursor powder was reduced to tungsten metal with dispersed lanthanum oxide. Powders were consolidated by spark plasma sintering (SPS) at 1300 and 1400 °C to suppress grain growth during sintering. The final grain size relates to the SPS conditions, i.e. temperature and heating rate, regardless of the starting powder particle size. Scanning electron microscopy revealed that oxide phases were mainly accumulated at grain boundaries while the tungsten matrix constituted of nanosized sub-grains. The transmission electron microscopy revealed that the tungsten grains consist of micron-scale grains and finer sub-grains. EDX analysis confirmed the presence of W in dispersed oxide phases with varying chemical composition, which evidenced the presence of complex oxide phases (W-O-La) in the sintered metals. 相似文献
5.
The Al2O3–Y2O3–ZrO2 eutectic composition samples were prepared using the Al2O3, Y2O3, ZrO2 powder treated at 900 °C for 30 min, pressed at 5 ton for 15 s and sintered at 1500 °C for 2 h. The locally made dense plasma focus (DPF) system with energy 2.8 kJ was used to surface modification of these samples. The samples, mounted at distance about 2 cm from the anode, were exposed to three shots of the DPF in Ar gas at a pressure of 0.8 mbar. The phase and elemental analysis of the untreated and plasma treated samples were conducted by the Raman and EDX spectroscopy. The Raman spectroscopy showed the formation of new phases (α-Al2O3 and c-ZrO2) in the treated samples. The micro-hardness of the plasma treated samples was increased by about 280 % in comparison with the untreated sample. 相似文献
6.
A technology has been developed for obtaining fuel tablets with the compositions (U, Th)O2, (U, Th, Ca)O2, and (U, Th)O2+MgO by combined precipitation of uranium, thorium, magnesium, or calcium components from inert solutions, followed by heat
treatment of the powders, compression into pellets, and sintering of the pellets. Work on optimizing the technological processes
for obtaining fuel pellets so as to obtain good pellet quality was performed. The effect of the properties of the precipitates
and powders, fabricated using different technological regimes on the properties of the finished objects was studied. The work
includes detailed investigations of powders (x-ray phase analysis, electron-microscopic investigation) and sintered fuel tablets
(change in the geometric dimensions as a result of sintering, determination of the density, and study of the microstructure).
The behavior of fuel compositions (U, Th)O2 and (U, Th)O2+MgO in contact, with coolants under conditions where the fuel elements become unsealed was studied: with water at 300°C and
sodium at 700°C. 3 figures, 3 tables, 6 references.
State Science Center of the Russian Federation-A. I. Leipunskii Physics and Power-Engineering Institute. Translated from Atomnaya
énergiya, Vol. 88, No. 5, pp. 346–353, May, 2000. 相似文献
7.
In this work, we have studied the impact of Y2O3 on the kinetics of oxidative dissolution of UO2 and the consumption of H2O2. The second order kinetics of catalytic consumption of H2O2 on Y2O3 was investigated in aqueous Y2O3 powder suspensions by varying the solid surface area to solution volume ratio. The resulting second order rate constant is 10−8 m s−1, which is of the same magnitude as for the reaction between H2O2 and UO2. Powder experiments with mixtures of UO2 and Y2O3 show that Y2O3 has no effect on the oxidative dissolution of UO2, whereas the consumption of H2O2 seems to be slightly slower in the presence of Y2O3 and H2 respectively. UO2 pellets with solid inclusions of Y2O3 show a decrease in oxidative dissolution by a factor of 3.3 and 5.3 under inert and hydrogen atmosphere, respectively. The rate of H2O2 consumption is similar for all cases and is well in line with kinetic data from powder experiments. The effects of H2 and Y2O3 on the oxidative dissolution of UO2 under gamma irradiation are similar to those found in experiments with H2O2. No significant difference in dissolution between inert and reducing atmosphere can be observed for pure UO2. 相似文献
8.
Sang Pill Lee Jin Kyung Lee In Soo Son Dong Su Bae Akira Kohyama 《Fusion Engineering and Design》2012,87(7-8):1244-1248
This paper dealt with the thermal shock properties of SiCf/SiC composites reinforced with two dimensional SiC fabrics. SiCf/SiC composites were fabricated by a liquid phase sintering process, using a commercial nano-size SiC powder and oxide additive materials. An Al2O3–Y2O3–SiO2 powder mixture was used as a sintering additive for the consolidation of SiC matrix region. In this composite system, Tyranno SA SiC fabrics were also utilized as a reinforcing material. The thermal shock test for SiCf/SiC composites was carried out at the elevated temperature. Both mechanical strength and microstructure of SiCf/SiC composites were investigated by means of optical microscopy, SEM and three point bending test. SiCf/SiC composites represented a dense morphology with a porosity of about 8.2% and a flexural strength of about 160 MPs. The characterization of SiCf/SiC composites was greatly affected by the history of cyclic thermal shock. Especially, SiCf/SiC composites represented a reduction of flexural strength at the thermal shock temperature difference higher than 800 °C. 相似文献
9.
The incorporation of gadolinium directly into nuclear fuel is important regarding reactivity compensation, which enables longer fuel cycles. The incorporation of Gd2O3 powder directly into the UO2 powder by dry mechanical blending is the most attractive process, because of its simplicity. Nevertheless, processing by this method leads to difficulties while obtaining sintered pellets with the minimum required density. This is due to the bad sintering behavior of the UO2-Gd2O3 mixed fuel, which shows a blockage in the sintering process that hinder the densification process. Minimal information exists regarding the possible mechanisms for this blockage and this is restricted to the hypothesis based on the formation of a low diffusivity Gd rich (U,Gd)O2 phase. The objective of this investigation was to study the phase formation in this system, thus contributing to clarifying the causes of the blockage. Experimental evidence indicated the existence of phases in the (U,Gd)O2 system that revealed structures different from the fluorite-type UO2 structure. These phases appear to be isostructural to the phases observed in the rare earth-oxygen system. 相似文献
10.
Zirconia sphere particles were synthesized through the gelation process of Na-alginate, and cermet (ZrO2-Mo) pellets were fabricated under several conditions. In this process, a zirconia slurry was prepared by mixing oxide powders (ZrO2, Y2O3, Er2O3, CeO2), distilled water and Na-alginate, and subsequently dropped into CaCl2 solution. As a result, zirconia sphere particles coated with a gelled film were synthesized. The slurry density (zirconia content in slurry) of 30-64 wt.% and Na-alginate concentration of a few% were good for gelation for up to 10 wt.% CaCl2 solution. Sphere particles with smaller diameter were obtained by dropping slurry with a mechanical vibration. The prolongation of the ball milling time for mixture of oxide powders was effective to increase the sintered density of zirconia sphere particles, especially for higher CeO2 concentration. The dense cermet pellets were fabricated for max. 50% volume ratio of zirconia phase for Mo matrix using zirconia particles covered with Mo powder by a rotating granulation method. 相似文献
11.
Diffuse reflectance measurements were made over the wavenumber range of 4000-20,000 cm−1 at room temperature on monoclinic and stabilised ZrO2, together with Y2Ti2O7 having the pyrochlore structure, all of which were doped with U and sintered in various atmospheres. X-ray photoelectron spectroscopy measurements were also carried out on selected samples. In monoclinic and stabilised zirconia, U exhibited valence states of +4 and/or +5, depending on the sintering atmosphere and the presence of appropriate charge compensators. Using both diffuse reflectance and X-ray photoelectron spectroscopy, U was also observed as mainly U4+ and/or U5+ in U-doped Y2Ti2O7 sintered at 1400 °C in air or Ar, although a small amount of U6+ also appeared to be present in some U-doped Y2Ti2O7 samples heated in air. 相似文献
12.
X-ray powder diffraction, microscopy, thermal analysis and electron probe microanalysis were used to characterize a ZrO2-MgO inert matrix containing CeO2 as a homolog for PuO2 and Er2O3 as a burnable poison. The synthesis was carried out using a precipitation method. A large composition range of MgO to ZrO2 was evaluated to determine phases present, phase mixing, phase composition, microstructure and thermal properties. It was found that most compositions of the material consist of two phases: MgO (periclase) and ZrO2 (cubic zirconia). The zirconia phase incorporates 5% (wt/wt) MgO and up to 14% and 12% (wt/wt) CeO2 and Er2O3, respectively. The MgO phase remains pure, which will enable it to retain its heat transfer and solubility properties and will improve the overall thermal conductivity and reprocessing component of the inert matrix fuel. The results with Ce will be used as the basis of future studies with actinides. 相似文献
13.
《Journal of Nuclear Science and Technology》2013,50(7):597-603
A high purity Al powder was directly reacted with isotopically enriched 15N2 gas at 1,200°C in a vacuum furnace to synthesize Al15N. In the initial reaction process, a small amount of AlF3, was mixed with the Al powder to suppress excess temperature rise due to the heat of formation of the nitride. Then, the Al15N thus formed was used as the diluent for the second run, and the same procedure was repeated. A total of 100g of Al15N powder with 15N isotopic content 99.6 at% was formed with average gas efficiency of 75.6%. Then the Al15N powder was pressureless-sintered at 1,830°C in an argon atmosphere by adding a small amount of Y2O3 as the sintering agent. An Al15N ceramic plate with dimensions 50mm × 50mm × 1.6 mm and relative density 97.3% was obtained with the 15N isotopic content 99.2 at%. Some physical properties and stability in air of an Al15N ceramic plate were studied. 相似文献
14.
Chromium sesquioxide doped uranium dioxide systems with a variety of initially added Cr2O3 amounts were prepared under different sintering conditions. The solubility limit of Cr for each sintering condition is derived from the measured content of the dopant dissolved in the UO2 matrix using electron probe microanalysis (EPMA). It is found that the solubility of chromium in a uranium dioxide system for these series sintered at 1600, 1660 and 1760 °C is limited to respectively 0.065±0.002, 0.086±0.003 and 0.102±0.004 wt% Cr. The lattice parameters of the different Cr2O3 doped fuels have been examined with X-ray diffraction (XRD). The XRD peaks of the samples sintered at 1760 °C as well as a UO2 reference without Cr, prepared under the same conditions, were measured and a value for the lattice parameter a for each sample was obtained using the unit cell refinement method. A slight contraction of the lattice parameter is observed with increasing dopant content. 相似文献
15.
Pellets of sintered ZrN were studied to optimize the mechanical properties and microstructures needed in nitride fuel pellets, using ZrN as a surrogate for actinide nitrides and as potential component in low fertile and inert matrix fuels. Samples were prepared via sintering in either Ar or N2 (with and without 6% H2) and at 1300 °C or 1600 °C. A significant difference in the hardness was measured ranging from 1000 (Kg/mm2) in samples sintered at 1600 °C in argon to 100 (Kg/mm2) in samples sintered at 1300 °C in nitrogen. Samples with 6% hydrogen added to the sintering environment experienced a decrease in hardness, as well as an increase in intergranular cracking as compared to samples sintered without hydrogen, suggesting hydrogen embrittlement. Grain size was more uniform in samples sintered in pure Ar as compared to Ar-H2, while the latter had a larger fraction of high angle grain boundaries than the former. Cracking around indents had a clear tendency to follow high angle boundaries, which were found to be intrinsically weak in ZrN. 相似文献
16.
Jae Hwan Yang Hwan-Seo Park Yung-Zun Cho 《Journal of Nuclear Science and Technology》2017,54(12):1330-1337
Al2O3-containing silver phosphate glasses were synthesized to investigate the feasibility of phosphate glasses for the immobilization of radioactive iodine (129I) present in spent nuclear fuel. Characterizations were performed by X-ray diffraction, Fourier transformed infrared spectroscopy, and scanning electron microscopy coupled with energy dispersive spectroscopy to examine structures, bonding properties, surface morphology, and elemental distribution of the synthesized glasses. The principal results showed that iodine became more strongly immobilized in the phosphate glasses with the addition of Al2O3, which was confirmed by the decrease of iodine leaching rates with approximately one order of magnitude. The present study would be helpful to decide whether Al2O3-containing silver phosphate glasses could be used as a candidate matrix to incorporate 129I. 相似文献
17.
In this paper, a thermal–hydraulic analysis of nanofluid as the coolant is performed in a typical VVER-1000 reactor with internally and externally cooled annular fuel. The fuel assembly for annular case with 8 × 8 arrays is considered for annular pin configuration. The considered nanofluid is a mixture composed of water and particles of Al2O3 with various volume percentages. The fuel rod is modeled using a CFD code. To validate the calculated results, the present results of solid fuel with nanofluid and pure water are compared with other studies which have been done with visual FORTRAN language, DRAGON/DONJON code, COBRA-EN code and the mentioned analytical approaches have been validated by comparing with the final safety analysis report (FSAR). The comparison of the calculated results shows that the results are in good agreement with other studies. Thus, the accuracy of the validation is satisfactory. Moreover, the temperature distributions of the fuel, clad and coolant are described for water/Al2O3 nanofluid in solid fuel and annular fuel. It is observed that as the concentration of Al2O3 nanoparticles increases, due to higher heat transfer coefficient of Al2O3 nanofluid, the temperature of the coolant is increased and the central fuel temperature is reduced. Thus, it improves margin from peak fuel temperature to melting. Finally, it is illustrated the use of the annular fuel instead of solid fuel in core of the reactor, security and efficiency of the nuclear power plant will be increased. 相似文献
18.
In connection with improving the retention of solid fission products in gas-cooled high-temperature reactor fuels, the vaporization of Ba from UO2 model nuclear fuel particles with and without a pyrocarbon coating was studied by high-temperature mass spectrometry using a Knudsen cell. The UO2 kernels of the particles were doped with BaO. In addition, some of them contained Al2O3. Whereas BaO mainly evaporated from the surface of the kernels as BaO, only Ba could be observed over the coated particles. Moreover, the BaO vapor pressure over kernels with and without the addition of Al2O3 was determined. From this it was determined that the BaO vapor pressure could be diminished by approximately two orders of magnitude by the admixture of Al2O3. Finally it was proved that the diminution of the BaO vapor pressure was caused by the formation of the compound BaAl2O4. 相似文献
19.
《Nuclear instruments & methods in physics research. Section B, Beam interactions with materials and atoms》2004,225(3):392-396
For the application of the computed tomography (CT) scanner, Gd1.94−xYxEu0.06O3 ceramic scintillator was prepared. We investigated the effect of the relative contents of Y2O3 for Gd2O3 matrix on the light output properties by the measurements of the emitted light spectra, relative light output, and X-ray diffraction (XRD) patterns. From the measurement results, it was found that maintaining the crystalline structure as cubic phase after sintering process is important to achieve high light output properties on (Gd,Y)2O3 ceramic scintillators, and the scintillation conversion process is more dominant for high light output of cubic phase than the optical transparency. 相似文献
20.
Diffuse reflectance spectroscopy (DRS) measurements were made over the wavenumber range of 4000–20,000 cm?1 at room temperature on monoclinic and stabilized zirconia and pyrochlore-structured Y2Ti2O7, which were doped with Np or Pu and sintered at ~1400 °C in various atmospheres. Np4+ was present in uncompensated monoclinic zirconia samples sintered in air, Ar or H2/N2. Np6+ was obtained in air/Ar-sintered monoclinic zirconia that also contained Y3+ as charge compensators, and Np4+ was formed on sintering in H2/N2. Np4+ was present in Y-stabilized zirconia after firing in air, Ar or H2/N2. Pu4+ was observed in air-fired Pu-doped monoclinic zirconia, and sintering in Ar or H2/N2 produced Pu3+ while only Pu4+ was identified in Y-stabilized zirconia sintered in air, Ar or H2/N2. Only Pu4+ and Np4+ were observed in Y2Ti2O7 after sintering in air or argon, even when Ca was substituted for Y to try to encourage the formation of higher valence states of Pu and Np. 相似文献