共查询到20条相似文献,搜索用时 31 毫秒
1.
《Journal of Nuclear Science and Technology》2013,50(11):1150-1154
Powder morphology evolution of recycled U3O8 according to the thermal treatments has been studied. The defective UO2 pellets are oxidized to U3O8 powders at a conventional temperature of 350 or 450°C in air. Those powders are pressed into green pellets and then sintered at 1,500 and 1,730°C in H2 gas flow. Final reoxidized U3O8 powers are obtained by reoxidizing those sintered pellets at 450°C in air. This paper shows that the reoxidized U3O8 powder morphology and the BET surface areas are greatly dependent on the density of sintered UO2 pellets before reoxidation. Reoxidized U3O8 powders are added to virgin UO2 powders to fabricate UO2 pellets and the effect of such addition on the UO2 pellet properties is investigated. The reoxidized U3O8 powders having a certain range of BET surface area significantly promote the grain growth of UO2 pellets. 相似文献
2.
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
3.
F.Y. Xi H.P. Liu X.M. Chen 《Nuclear instruments & methods in physics research. Section B, Beam interactions with materials and atoms》2010,268(13):2292-2294
We made an experimental study on ion guiding through capillaries in uncoated Al2O3 membranes using a variety of ions such as O1+, O3+, and O6+. The incident energy was varied within the range of 30-150 keV. The results were compared with others using coated PET and Al2O3 capillary membranes as well as with the so-called scaling law discovered by Stolterfoht and his co-workers. Good agreement of our results with the scaling law was found. However, our membranes showed extraordinarily strong guiding ability. The reason lies in that our membranes were uncoated. A slower charge drift speed along the insulating capillary wall and a much larger equilibrium charge Q∞ seems to exist in our experiment. 相似文献
4.
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
5.
《Journal of Nuclear Science and Technology》2013,50(11):849-855
Chemical form of radioiodine released from U3O8 will be UIx in helium and I2 in oxygen atmospheres. Relative reactivities of these iodines toward organic compounds have been studied at a temperature range of 250~500°C, by choosing propane as a reactant. The UIx has a higher reactivity than I2, particularly at a temperature range of 300~400°C. Above that temperature, both iodine species show a similar reactivity. In the reactions, CH3I, C2H5I, i, and n-C3H7I are formed: relative yields depend on both temperature and atmosphere. Two reaction processes participate in the formation of organic iodides. One is an iodine-initiation reaction and is relatively important at a lower temperature. The other is a radical-initiation reaction and become predominant as the temperature rises. 相似文献
6.
Takashi Kodama Hiroshi Kinuhata Yuki Shibata Mikio Kumagai Kazunori Suzuki Shin-Itiro Hayashi 《Journal of Nuclear Science and Technology》2020,57(9):1101-1110
ABSTRACT NO2 and NO generated during a boiling and drying accident, which affects the release of volatilized radioactive Ru into the atmosphere, were examined using various samples including simulated high-level liquid waste and a thermogravimetric analyzer. NO2 and NO in the gas flowing out of the analyzer were measured separately using a NOx analyzer equipped with NO2 and NO sensors. The samples were heated to 600°C at constant heating rates of mainly 0.2 and 1°C min?1 that was adopted taking into account the decay heat of high-level liquid waste. It was found that under 180°C some nitrates in the liquid waste mainly separated their nitrate groups as HNO3 without generating NOx (a mixture of NO and NO2) and above 300°C the residual HNO3 in the waste participated in thermal decomposition generating NOx. The generation rates of NO2 and NO were obtained as a function of time using Arrhenius type equations, and the O2 rate was derived from these equations using the stoichiometry of the reactions that generate NO2, NO, and O2. 相似文献
7.
《Journal of Nuclear Science and Technology》2013,50(6):958-963
For the recovery of fuel materials from spent nuclear fuel, a novel reprocessing process based on the selective sulfurization of fission products (FP) has been proposed, where FP and minor actinides (MA) are first sulfurized by CS2 gas, and then, dissolved by a dilute nitric acid solution. Consequently, the fuel elements are recovered as UO2 and PuO2. As a basic research of this new concept, the sulfurization and dissolution behaviors of U, Pu, Np, Am, Eu, Cs, and Sr were investigated by γ-ray and α spectrometries in this paper using 236Pu-, 237Np-, 241Am-, 152Eu-, 137Cs-, and 85Sr-doped U3O8 samples. The dependence of the dissolution ratio of each element on the sulfurization temperature was studied and reasonably explained by combining the information of the sulfide phase analysis and the chemical thermodynamics of the dissolution reaction. The sulfurization temperature ranging from 350 to 450°C seems to be promising for the separation of FP and MA from U and Pu, since a clear difference in the dissolution ratio between FP and U was derived by the sulfurization treatment in this temperature range. 相似文献
8.
《Journal of Nuclear Science and Technology》2013,50(8):608-616
The compatibility of Eu3O3 and (Eu,Gd) 2O3 mixed oxides which contain 0, 1, 5, 10, 50 and 100 mol% of Gd2O3, with type 316 stainless steel was examined by out-of-pile heatings. The heating temperature ranged from 550 to 1,000°C and heating time from 500 h to up to 5,000 h. Metallographic examinations of the stainless steel indicated that chemical reaction between Eu2O3 and stainless steel occurred at 650°C and that grain boundary penetration extended up to 40 μ m after heating at 1,000°C for 500 h. The penetration depth Δ was expressed as a function of heating temperature T as Δ = 3.08 × 104 exp(?1.72 × 102RT) where R is the gas constant and the activation energy is given in cal/mol. Electron probe microanalysis and X-ray diffraction analysis indicated that main reaction product is europium silicate. When Gd, which is a decay product of Eu, is mixed with Eu2O3, the degree of reaction between (Eu,Gd) 2O3 and stainless steel decreases as increase in concentration of Gd2O3. It was found that actually no grain boundary attack was observed even after heating at 1,000°C for 500 h when concentration of Gd2O3;i in (Eu,Gd) 2O3 exceeded 10 Discussion was made of reaction mechanism of Eu2O3 and (Eu,Gd) 2O3 with stainless steel. 相似文献
9.
Bhushan Dhabekar S.N. MenonE. Alagu Raja A.K. BakshiA.K. Singh M.P. ChougaonkarY.S. Mayya 《Nuclear instruments & methods in physics research. Section B, Beam interactions with materials and atoms》2011,269(16):1844-1848
Optically Stimulated Luminescence (OSL) technique has emerged as a serious competitor to Thermally Stimulated Luminescence (TSL) technique in various dosimetric applications, especially after the development of crystalline alumina (Al2O3:C) doped with carbon. Since then, several attempts are being made to develop other possible materials for OSL based dosimetric applications. Efforts conducted in our laboratory in this direction have led to the development of a new phosphor, Lithium Magnesium Phosphate doped with terbium and boron (LiMgPO4:Tb,B). This phosphor is prepared by solid-state diffusion method involving conventional air furnaces with operating temperature 1000 °C and easily amenable to large scale production without compromising primary dosimetric advantages. In this work we present some of the dosimetric OSL characteristics of this phosphor. The phosphor exhibits a main TSL peak at 250 °C. The phosphor also emits OSL, when the irradiated phosphor is stimulated with 470 nm light with the OSL sensitivity 1.3 times that of commercially available Al2O3:C. Photoluminescence (PL) emission spectrum consists of sharp lines characteristics of Tb3+ emission. The OSL discs made out of this phosphor are reusable up to at least 50 cycles, the phosphor exhibits dose linearity up to 1 kGy. Minimum detectable dose is found to be 20 μGy and fading of the OSL signal is found to be about 16% in four days, after which the OSL signal stabilizes. 相似文献
10.
《Journal of Nuclear Science and Technology》2013,50(5):216-222
The phase equilibrium of non-stoichiometric U3O8-x has been studied by thermogravimetry in the range 765°≦T≦995°C and 10?4≦Po2≦1 atm. The results suggest the presence of six phases within U3O8-x the phase, separated by second (or higher) order transitions. The relative partial molar free energies, enthalpies and entropies within an each of the six phases, as well as the standard free energies, enthalpies and entropies for the phase changes are calculated and compared with previous works. 相似文献
11.
Ying Zheng Ken Kurosaki Yuji Ohishi Hiroaki Muta Shinsuke Yamanaka 《Journal of Nuclear Science and Technology》2013,50(5):526-530
Y6UO12 was synthesized by solid-state reactions of Y2O3 and U3O8. The high-density pellet of Y6UO12 was prepared by the spark plasma sintering followed by heat treatment in air for oxygen supplementation. The thermal conductivity (κ) was evaluated using the laser flash method from room temperature to 1173 K. The κ of Y6UO12 decreased with increasing temperature in the whole temperature range, indicating that the phonon contribution was predominant. The room temperature κ value of Y6UO12 was 4.90 Wm?1K?1. The magnitude relationship of κ among Y6UO12, Y6WO12, and Yb6WO12, i.e. κ of Yb6WO12 < κ of Y6UO12 < κ of Y6WO12, was discussed based on the general lattice thermal conductivity theory. 相似文献
12.
《Journal of Nuclear Science and Technology》2013,50(8):317-325
Electrical conductivity and X-ray diffraction studies on non-stoichiometric U3O8-x phase were carried out simultaneously in the range 765°≦T≦995°C and 10?4≦Po2≦1 atm. The plot of logσ vs. logPo2 showed many refractions which corresponded with the phase transitions determined by thermogravimetry reported in the preceding paper. Based on the data of both electrical conductivity and thermogravimetry, the non-stoichiometric defect structures of various U3O8-x phases are interpreted as consisting of singly charged oxygen interstitials (Ol′) and doubly charged oxygen vacancies (Vo.)? Some of the X-ray diffraction lines were found to undergo splitting with decreasing oxygen partial pressure. These splits are qualitatively discussed in reference to the out-of-step structure model. The mechanism of electrical conduction in the high temperature hexagonal U3O8-x phases is surmised to be the hopping of small polarons. 相似文献
13.
Numan Salah Zishan H. KhanSami S. Habib 《Nuclear instruments & methods in physics research. Section B, Beam interactions with materials and atoms》2011,269(4):401-404
Aluminum Oxide (Al2O3) doped with proper activators is a highly sensitive phosphor commonly used for radiation dosimetry using thermoluminescence (TL) technique. Nanoparticles of this material activated with Chromium (Cr) have been synthesized using the propellant chemical combustion technique and studied for their TL response. They were characterized by X-ray diffraction and scanning electron microscope. The synthesized material has spherical nanoparticles with grain size around 25 nm. These nanoparticles were exposed to heavy doses from γ-rays of 137Cs. The TL glow curves show a prominent peak at around 474 K. This peak is found to be sensitive for high exposures of γ-rays and has linear response in the range of 100 Gy-20 kGy without showing saturation. This remarkable result suggests that Al2O3:Cr nanoparticles might be used for the dosimetry of food and seed irradiations. 相似文献
14.
M. Laitinen T. Sajavaara T. Ishida 《Nuclear instruments & methods in physics research. Section B, Beam interactions with materials and atoms》2011,269(24):3021-3024
Atomic layer deposition (ALD) is currently a widespread method to grow conformal thin films with a sub-nm thickness control. By using ALD for nanolaminate oxides, it is possible to fine tune the electrical, optical and mechanical properties of thin films. In this study the elemental depth profiles and surface roughnesses were determined for Al2O3 + TiO2 nanolaminates with nominal single-layer thicknesses of 1, 2, 5, 10 and 20 nm and total thickness between 40 nm and 60 nm. The depth profiles were measured by means of a time-of-flight elastic recoil detection analysis (ToF-ERDA) spectrometer recently installed at the University of Jyväskylä. In TOF-E measurements 63Cu, 35Cl, 12C and 4He ions with energies ranging from 0.5 to 10 MeV, were used and depth profiles of the whole nanolaminate film could be analyzed down to 5 nm individual layer thickness. 相似文献
15.
Y. TaharaB. Zhu S. KosugiN. Ishikawa Y. OkamotoF. Hori T. MatsuiA. Iwase 《Nuclear instruments & methods in physics research. Section B, Beam interactions with materials and atoms》2011,269(9):886-889
To simulate the effects of Gd2O3-doping and high-energy fission products in UO2, Gd2O3-doped CeO2 pellets were irradiated with 200-MeV Xe14+ ions. Doping and irradiation effects were analyzed using X-ray diffraction (XRD) and extended X-ray absorption fine structure (EXAFS). The lattice constant of CeO2 decreases and the local structure is disordered with increased doping levels. However, the irradiation induces an expansion of the lattice and a disordering of atomic arrangement near the Gd atoms. The effects of the irradiation become more pronounced with increasing Gd2O3-dopant levels. Our results are compared with those of a study involving Er2O3-doped CeO2. 相似文献
16.
A. Meftah W. AssmannN. Khalfaoui J.P. StoquertF. Studer M. ToulemondeC. Trautmann K.-O. Voss 《Nuclear instruments & methods in physics research. Section B, Beam interactions with materials and atoms》2011,269(9):955-958
The results of present paper have shown that sputtering of yttrium iron garnet (Y3Fe5O12) under swift heavy ions in the electronic energy loss regime is non-stoichiometric. Here we are presenting additional experimental results for gadolinium gallium garnet (Gd3Ga5O12) as target. The irradiations were performed with different ions (50Cr (589 MeV), 86Kr (195 MeV) and 181Ta (400 MeV)) impinging perpendicularly to the surface. As earlier, the sputtering yield was determined by collecting the emitted gadolinium and gallium atoms on a thin aluminium foil, placed upstream above the target and analyzing the Al catcher by Rutherford backscattering. Also for Gd3Ga5O12, the emission of Gd and Ga is non-stoichiometric. Sputtering appears above a critical electronic stopping power of Sth = 11.6 ± 1.5 keV/nm, which is larger than the threshold for track formation, in agreement with other amorphisable materials. In addition, the angular distribution of the sputtered species was measured for Y3Fe5O12 and Gd3Ga5O12 using 200 MeV Au ions impinging the surface at 20° relatively to the surface. For the two garnets the ratio of Y/Fe (and Gd/Ga) varies with the angle of emitted species and the stoichiometry seems to be preserved only for an emission perpendicular to the surface. 相似文献
17.
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
18.
Al2O3–14 wt%B4C composites with 0–1 wt% C addition were sintered in Ar at 1550–1650 °C. The influence of the C additive on the B loss, densification behavior, and microstructure of the Al2O3–B4C composites were investigated. The results show that there are B2O3, H3BO3 and Al18B4O33 exist between Al2O3 and B4C interface, which result in B loss because of B2O3's high vapor tension at above 1500 °C. The presence of Al18B4O33 grains formed by chemical reaction of Al2O3 with surface oxides on B4C inhibit the densification of pellets by reducing the specific free surface energy of the Al2O3. However, the added C eliminates those oxides to reduce B loss because of its higher activity than B4C, and it also coarsens Al2O3 grain although the density of pellets is decreased by gas products. 相似文献
19.
《Journal of Nuclear Materials》1987,150(2):182-185
Volume change of Al2O3 and MgAl2O4 induced by irradiation with 14-MeV neutrons at 50°C has been measured. It is shown that the volume change of A12O3 is anisotropic and is larger than that of MgAl2O4 about a factor of five. The result for MgAl2O4 is compared with that of fission neutron irradiation. 相似文献
20.
《Journal of Nuclear Science and Technology》2013,50(10):445-451
The oxidation of UO2 was studied by thermogravimetry and X-ray diffraction. It was clarified that the thermal history covering the first stage of the oxidation from UO2 to U3O UO7 significantly influenced the rate of the oxidation of the second stage from U3O7 to U3 O8. The entire oxidation reaction proceeded in what to all appearances, was a single stage when the specimen temperature was raised rapidly, whereas at slower rates of heating up, two distinct stages of oxidation were observed, separated by an intermediate induction period. These findings suggest the existence of a close connection between the rate of formation of the U3O7 phase and the rate of the subsequent oxidation of this phase: A slow formation of U3O7 would tend to prolong the induction period preceding the second stage of the oxidation. A similar effect was observed also with annealing of the intermediate U3O7 at 200°C: The increase of annealing time prolonged the induction stage. The rate of the second stage oxidation was fairly well expressed by Johnson & Mehl's equation, log (1/(1-y/)=(1/2.303)kntn . The time exponent n in this equation varied in the range of 1.0~2.5, and the rate constant k of 1.15×10?4~2.04 ×10?1 min?1, depending on the experimental conditions. 相似文献