共查询到20条相似文献,搜索用时 0 毫秒
1.
The MnCl2-UCl4 system was studied employing differential thermal analysis, common thermal analysis and high-temperature cryometry. From the results obtained, both the phase diagram and the thermodynamic characteristics of liquid phases of the system have been determined. The results were discussed in terms of regularities found in the phase equilibria of binary salt systems with common anion and compared with those for other systems of the type MCln-UCl4. It appeared that the results confirmed earlier predictions on the title system. 相似文献
2.
The phase diagrams of the LiF-LnF3 series, where Ln = La-Sm, and of LiF-AnF3, where An = U, Pu, have been optimized using Redlich-Kister functions. The phase diagrams of LiF-AmF3 and LiF-PuF3-AmF3 have been calculated. The necessary Gibbs energy functions for americium trifluoride were defined by use of a semi-empirical method. The excess Gibbs energy terms, which are expressed as Redlich-Kister polynomials and describe the effect of interaction between the two fluoride components in the liquid phase, were obtained by translating the trends observed in the lanthanide trifluoride series into the actinide series. A single eutectic has been found in the LiF-AmF3 system with the eutectic point at ?33 mole% AmF3 and at ?951 K. 相似文献
3.
4.
The published data concerned with the determination of the composition ranges of uranium oxides, UO2+x, U4O9−y and U3O8−z, which have been determined using thermogravimetric, X-ray diffraction and electrochemical techniques are critically assessed. U4O9 and U3O8 have quite small domains of composition and the assessment of such data has carefully considered the uncertainties in the experimental determinations. In addition, the thermodynamic properties of U4O9 and U3O8, enthalpies of formation and transformation, entropies, and thermal capacities are analyzed and selected to build a primary data base for compounds. 相似文献
5.
The fuel of civil nuclear plants, UO2, melts at 3120 K. During an hypothetical severe accident, urania, submitted to high temperatures and various oxygen potentials, presents a wide non-stoichiometry range: the melting temperature of UO2±x, related to oxygen potential, decreases in all cases. In this scenario, urania could react with other materials, firstly zircaloy, and the melting temperature of (U, Zr)O2±x still decreases. That is why the critical assessment of the O-U binary system including the non-stoichiometry range of urania, is a major step to a correct thermodynamic modelling of multicomponent systems for nuclear safety. The very numerous experimental information has been compiled and analysed. The associate model was used for the liquid phase, and a sublattice model for UO2±x; U4O9−y, U3O8 and UO3 were treated as stoichiometric. Phase diagram and thermodynamic properties have been calculated from the optimised Gibbs energy parameters. The calculated consistency with the experimental ones is quite satisfactory. 相似文献
6.
A critical assessment of oxygen chemical potential of UO2+x, U4O9 and U3O8 oxide non-stoichiometric phases as well as of diphasic related domains has been performed in order to build up primary input data files used in a further optimization procedure of thermodynamic and phase diagram data for the uranium-oxygen system in the UO2-UO3 composition range. Owing to the fact that original data are very numerous, more than 500 publications, a twofold process is used for the assessment - (i) first a critical selection of data is performed for each method of measurement together with a careful estimate of their uncertainties, (ii) second a reduction of the total number of data on the basis of a chart with fixed intervals of temperature and composition that allows a comparison to be made of the results from the various experiments. Results are presented for chemical potentials of oxygen with their associated uncertainties. 相似文献
7.
K. Laaziri S. Roorda L. Cliche 《Nuclear instruments & methods in physics research. Section B, Beam interactions with materials and atoms》1994,90(1-4):438-441
The atomic density of amorphous SixGe1 − x alloys (x = 1, 0.85, 0.67, 0.50, 0.20 and 0) has been measured. Mono-crystalline SixGe1−x layers Were implanted with 1.50–2.75 MeV Si2+ and Ge2+ ions to produce the amorphous material. Using surface profilometry and RBS/channeling, it was found that amorphous alloys are less dense than the crystalline alloys, and that Vegard's law underestimates the a-SixGe1−x density. 相似文献
8.
C. O'Raifeartaigh R. C. Barklie A. Nylandsted Larsen F. Priolo G. Franz G. Lulli M. Bianconi J. K. N. Lindner F. Cristiano P. L. F. Hemment 《Nuclear instruments & methods in physics research. Section B, Beam interactions with materials and atoms》1996,120(1-4):165-168
The damage produced by implanting, at room temperature, 3 μm thick relaxed Si1−xGex layers with 2 MeV Si+ ions has been measured as a function of Ge content (x = 0.04, 0.13, 0.24 or 0.36) and Si dose in the dose range 1010–1015 cm−2. The accumulation of damage with increasing dose has been studied as a function of Ge content by Rutherford Backscattering Spectrometry, Optical Reflectivity Depth Profiling and Transmission Electron Microscopy and an increased damage efficiency in Si1−xGex with increasing x is observed. The characteristics of implantation-induced defects have been investigated by Electron Paramagnetic Resonance. The results are discussed in the context of a model of the damage process in SiGe. 相似文献
9.
A. Nylandsted Larsen S. Yu. Shiryaev P. Gaiduk V. S. Tishkov 《Nuclear instruments & methods in physics research. Section B, Beam interactions with materials and atoms》1996,120(1-4):161-164
The electrical activity and redistribution during rapid thermal annealing (RTA) of high concentrations of As implanted into epitaxially grown, relaxed Si1−xGex for x≤0.5 have been studied as a function of composition x and RTA parameters. At a given RTA temperature the maximum carrier concentration decreases and the redistribution increases with increasing x. Maximum carrier concentrations and junction depths as a function of composition and RTA parameters are given. 相似文献
10.
L. Calcagno G. Compagnini G. Foti M. G. Grimaldi P. Musumeci 《Nuclear instruments & methods in physics research. Section B, Beam interactions with materials and atoms》1996,120(1-4):121-124
Silicon-carbon alloys were formed by multiple energy implantation of C+ ions in silicon and in Silicon on Sapphire (SOS). The ion fluence ranged between 5 × 1016 − 3 × 1017 ions/cm2 and the energy between 10–30 keV in order to obtain constant carbon concentration into a depth of 100 nm. The carbon atomic fraction (x) was in the range 0.22–0.59 as tested by Rutherford backscattering spectrometry (RBS). Thermal annealing of the implanted films induced a transition from amorphous to a polycrystalline structure at temperatures above 850°C as detected by Infrared spectrometry (IR) in the wavenumber range 600–900 cm−1. The optical energy gap and the intensity of the infrared signal after annealing at 1000°C depended on the film composition: they both increased linearly with carbon concentration reaching a maximum at the stoichiometric composition (x = 0.5). At higher carbon concentration the IR intensity saturated and the optical energy gap decreased from the maximum value of 2.2 to 1.8 eV. The behaviour at the high carbon content has been related to the formation of graphitic clusters as detected by Raman spectroscopy. 相似文献
11.
A new chlorination method using ZrCl4 in a molten salt bath has been investigated for the pyrometallurgical reprocessing of nuclear fuels. ZrCl4 has a high reactivity with oxygen but is not corrosive to refractory metals such as steel. Rare earth oxides (La2O3, CeO2, Nd2O3 and Y2O3) and actinide oxides (UO2 and PuO2) were allowed to react with ZrCl4 in a LiCl-KCl eutectic salt at 773 K to give a metal chloride solution and a precipitate of ZrO2. An addition of zirconium metal as a reductant was effective in chlorinating the dioxides. When the oxides were in powder form, the reaction was observed to progress rapidly. Cyclic voltammetry provided a convenient way of establishing when the reaction was completed. It was demonstrated that the ZrCl4 chlorination method, free from corrosive gas, was very simple and useful. 相似文献
12.
I.R. Shein 《Journal of Nuclear Materials》2007,361(1):69-77
First-principle calculations in the framework of the full-potential linearized-augmented-plane-wave method (FLAPW, as implemented into the WIEN-2k code) have been performed to understand the structural, elastic, cohesive and electronic properties of the meta-stable cubic strontium thorate SrThO3. The optimized lattice parameters, elastic parameters, formation energies, densities of states, band structures and charge density distributions are obtained and discussed in comparison with those of cubic SrZrO3 and ThO2. 相似文献
13.
Jae Ho Yang Young Woo Rhee Keon Sik Kim Seung Jae Lee 《Journal of Nuclear Materials》2007,360(2):208-213
The reduction of U3O8 pellets to UO2+x has been investigated at 1300 °C in H2, Ar and CO2 gas atmospheres by TGA, SEM, and X-ray diffraction. The selected U3O8 pellet was prepared by sintering a U3O8 powder compact. The TGA results show that the reduction rate is fastest in H2 gas, and X-ray diffraction indicates that U3O8 reduces to UO2+x without any intermediate phase. The reduced pellet, UO2+x, has a special grain structure that consists of equiaxed grains at the surface, columnar grains in the middle, and equiaxed grains in the center. The equiaxed grains and columnar grains are much smaller in H2 gas than in Ar or CO2 gas. The reducing gases significantly influence the morphology of the grain structure. This difference can be explained in terms of a relation between oxygen potential and critical nucleus size during the reduction. 相似文献
14.
Kinya Nakamura Takanari OgataMasaki Kurata Takeshi YokooMichael A Mignanelli 《Journal of Nuclear Materials》2002,304(1):63-72
The phase diagram in the quaternary Fe-Pu-U-Zr system was established at 923 K in the uranium-rich region to understand better the compatibility between the metal fuel and stainless steel cladding in a fast reactor. The experimental phase relation data obtained in this study was applied to the thermodynamic methodology for construction of the phase diagram. The calculated phase diagram was consistent and well within the experimental data. The applicability of the thermodynamic model to other temperatures was confirmed by comparing the present results of differential thermal analysis with the calculated phase diagrams. These consistencies mean that both the thermodynamic model and the assessed parameters in the binary and ternary subsystems developed so far are reasonable. The calculated phase diagram established in this study was also in good agreement with the analysis of the diffusion zone in tests on Pu-U-Zr/Fe couples. This suggests that the diffusion zone formed at the fuel-cladding interface in the reactor system can be assessed using the phase diagram in the quaternary Fe-Pu-U-Zr system. 相似文献
15.
ThO2 containing around 2-3% 233UO2 is the proposed fuel for the forthcoming Indian Advanced Heavy Water Reactor (AHWR). This fuel is prepared by powder metallurgy technique using ThO2 and U3O8 powders as the starting material. The densification behaviour of the fuel was evaluated using a high temperature dilatometer in four different atmospheres Ar, Ar-8%H2, CO2 and air. Air was found to be the best medium for sintering among them. For Ar and Ar-8%H2 atmospheres, the former gave a slightly higher densification. Thermogravimetric studies carried out on ThO2-2%U3O8 granules in air showed a continuous decrease in weight up to 1500 °C. The effectiveness of U3O8 in enhancing the sintering of ThO2 has been established. 相似文献
16.
The reversible adsorption of water from actinide oxide surfaces is examined from several viewpoints in this article. A reinterpretation and critical look at the previously published thermodynamic values for desorption of water from PuO2 [J. Phys. Chem. 77 (1973) 581] are reexamined in light of more recent mathematical treatments of thermal desorption data from high surface area materials. In addition, the time and temperature dependent process of water adsorption/desorption in closed system experiments is examined using chemical kinetics modeling. A simple experimental method and mathematical treatment of determining adsorption enthalpies based upon a closed system is also described. The desorption enthalpy for reversibly adsorbed water from PuO2 is determined to be a function of adsorbate coverage with values ranging from 51 to 44 kJ mol−1 for coverages of one to several monolayers (MLs). Consistent desorption enthalpy values are obtained using either approach thus highlighting the importance of proper interpretation of adsorption parameters determined from high surface area powders. Reversible adsorption/desorption equilibrium of water with actinide oxide materials is discussed from the practical standpoint of storage and subsequent pressurization of containers. These results obtained from PuO2 surfaces are consistent with desorption enthalpies of water from a low surface area UO2 that has been measured using ultra-high vacuum thermal desorption mass spectroscopy to be 42.2 kJ mol−1. 相似文献
17.
P.R. Vasudeva Rao S. Anthonysamy M.V. Krishnaiah V. Chandramouli 《Journal of Nuclear Materials》2006,348(3):329-334
(U, Pu) mixed oxides, (U1−yPuy)O2−x, with y = 0.21 and 0.28 are being considered as fuels for the Prototype Fast Breeder Reactor (PFBR) in India. The use of urania-plutonia solid solutions in PFBR calls for accurate measurement of physicochemical properties of these materials. Hence, in the present study, oxygen potentials of (U1−yPuy)O2−x, with y = 0.21 and 0.28 were measured over the temperature range 1073-1473 K covering an oxygen potential range of −550 to −300 kJ mol−1 (O/M ratio from 1.96 to 2.000) by employing a H2/H2O gas equilibration technique followed by solid electrolyte EMFmeasurement. (U1−yPuy)O2−x, with y = 0.40 is being used in the Fast Breeder Test Reactor (FBTR) in India to test the behaviour of fuels with high plutonium content. However, data on the oxygen potential as well as thermal conductivity of the mixed oxides with high plutonium content are scanty. Hence, the thermal diffusivity of (U1−yPuy)O2, with y = 0.21, 0.28 and 0.40 was measured and the results of the measurements are reported. 相似文献
18.
The temperature variation of UV-VIS-NIR optical spectra of UO2 have been investigated from room temperature up to 1173 K with careful in situ oxygen partial pressure control. The deduced optical absorption edge exhibits a strong temperature dependence. Its value decreases from ∼2 eV at room temperature to ∼0.8 eV at 1173 K. Such thermal behaviour is interpreted as the consequence of the existence of a strong electron-phonon coupling (small polaron). In the temperature range 300-1173 K, the model yields a hopping radius of ∼2 Å and a polaron self-energy of Ep=−0.38 eV. 相似文献
19.
R. Pankajavalli 《Journal of Nuclear Materials》2007,362(1):128-131
A horizontal thermal analysis instrument was adapted as a transpiration apparatus for the measurement of vapour pressure of solid boric acid, H3BO3. The experimental parameters necessary for establishing a dynamic isothermal congruent vapourisation equilibrium of H3BO3 were identified. Using these optimized transpiration experiments, the vapour pressures were measured in the temperature range 326-363 K. The temperature dependence of the measured values of vapour pressures could be expressed using the expression, log(p/Pa) = 26.83(±0.09) − 9094(±246)/T (K). The standard enthalpy of sublimation, , of H3BO3 was estimated to be 174.1 ± 4.7 kJ mol−1 at the mean temperature of the present measurements, viz., 345 K. 相似文献
20.
The dissolution of different mixed oxide (U, Th)O2 particles under reducing conditions has been studied using a continuous flow-through reactor. The U/Th ratio seems to have no or little influence on the normalised leaching rate of thorium or uranium, The release rate of uranium from the outer surface of a Th rich matrix seems to follow the behaviour of pure UO2 even though U is a minor component in these phases and the dissolution rate of Th is much lower. After long time U concentrations will become depleted at the solids surface and it will be expected that U release rates will become controlled by the release rates of thorium (rates at neutral pH < 10−6 g m−2 d−1). Under reducing conditions, the matrix of HTR fuel particles presents significant intrinsic radionuclide confinement properties. 相似文献