The constitution of the uranium-tin-palladium system

The Pd-rich region of the isothermal section of the ternary U---Sn---Pd system at 1050°C was investigated by metallography, X-ray microanalysis and X-ray diffraction. The fcc -Pd(Sn, U) solid solution dissolves up to 16 at.% Sn and 15 at.% U. The AuCu₃ type phases SnPd₃ and UPd₄ are the end members of a single-phase region. SnPd₂ and UPd₃ are in equilibrium with this solid solution of the composition U_0.68Sn_0.32Pd₃ and with the ternary phase USnPd₂. The Gibbs energies of formation of SnPd₂, SnPd₃ and UPd₄ were used and ideal behaviour of the (Sn, U) Pd_3+x solid solution was assumed to calculate the Gibbs energy of formation of UPd₃ which gives Δ_fG° = −312 kJ/mol at 1050°C. In addition, the annealing experiments in the Pd-rich region of the binary U---Pd system were extended to 950°C which confirm the phase-field distribution established at 1050°C in earlier work.     

Some theoretical aspects in the spinodal decomposition and crystallization of silicate melts. Experimental results for the UO2-SiO2 system

In the first part of this paper the primary crystallization of quenched melts, in which the changes in composition involve the crossing of spinodal curves, is analysed. It is shown that the normal primary crystallization could be practically stopped when the temperature of the melt becomes lower than the temperature at which the corresponding liquidus concentration is lower than the corresponding spinodal concentration. In the second part experimental results are presented on the volume fraction and dimension of primary UO₂ crystal and spinodal decomposition widths (wavelength) for the UO₂-SiO₂ melts quenched by injection in copper and stainless steel moulds. The experimental data confirm the possibility of primary crystallization stopping at 2070°C which is the invariant point of the UO₂-SiO₂ system. The mean dimensions of UO₂ primary crystals depend on the rate of quenching as exponential $\text{?}\text{case1}\text{6}$. A similar ‘weak’ dependence on the quenching rate has been obtained for the spinodal decomposition wavelength.     

An inversion decomposition method for better energy resolution of NaI(Tl) scintillation detectors based on a Gaussian response matrix

NaI(T1) scintillation detectors have been widely applied for gamma-ray spectrum measurements owing to advantages such as high detection efficiency and low price.However,the mitigation of the limited energy resolution of these detectors,which detracts from an accurate analysis of the instrument spectra obtained,remains a crucial need.Based on the physical properties and spectrum formation processes of NaI(T1) scintillation detectors,the detector response to gamma photons with different energies is represented by photopeaks that are approximately Gaussian in shape with unique full-width-at-half-maximum(FWHM) values.The FWHM is established as a detector parameter based on resolution calibrations and is used in the construction of a general Gaussian response matrix,which is employed for the inverse decomposition of gamma spectra obtained from the detector.The Gold and Boosted Gold iterative algorithms are employed to accelerate the decomposition of the measured spectrum.Tests of the inverse decomposition method on multiple simulated overlapping peaks and on experimentally obtained U and Th radionuclide series spectra verify the practicability of the method,particularly in the low-energy region of the spectrum,providing for the accurate qualitative and quantitative analysis of radionuclides.     

The role of Fe on the solubility of Nb in α-Zr

The solid solubility of Nb in α-Zr is an important parameter that has a potential impact on the corrosion properties of Zr-Nb alloys at reactor operating temperatures, i.e. below the monotectoid temperature. Work on dilute Zr-Nb alloys has shown that Fe is a common impurity that confounds the assessment of the solid solubility limit for Nb in Zr. This is because Fe has a very low solubility limit and it forms precipitates with both Nb and Zr. To assess the effect of Fe on the phases formed in the binary Zr-Nb alloy system, alloys containing 0.1-0.7 wt% Nb and <11 to 470 wt ppm Fe were heat-treated at temperatures between 575 °C and 600 °C and examined by transmission electron microscopy. Results indicate that, even at a concentration ? 24 ppm, Fe readily combines with Nb to form precipitates in the alloys with Nb contents in the range of 0.20 to 0.29 wt%. However, β-Nb particles were not observed for these same alloys and were only seen when the Nb content was ? 0.49 wt%. Because β-Nb particles were not found in the 0.29 wt% Nb alloy and the precipitation was estimated to have a negligible effect on the amount of Nb remaining in solution (reduced by <0.001 wt%), it is proposed that the solubility limit of Nb in a true binary Zr-Nb alloy would be between 0.29 and 0.49 wt%.     

Fundamental experiments on phase stabilities of Fe–B–C ternary systems

To understanding the control blade degradation mechanism of a boiling-water reactor (BWR), a thermodynamic database for the fuel assembly materials is a useful tool. Although the iron, boron, and carbon ternary system is a dominant phase diagram, phase relation data are not sufficient for the region in which boron and carbon compositions are richer than the eutectic composition. The phase relations of three samples such as Fe_0.68B_0.06C_0.26 (at%), Fe_0.68B_0.16C_0.16 (at%), and Fe_0.76B_0.06C_0.18 (at%) were analyzed by X-ray diffraction, scanning electron microscopy, and energy–dispersive X-ray spectrometry. The results indicate that the Fe₃(B,C) phase exists only in the intermediate region at 1273 K and that the solidus temperature widely maintains at approximately 1400 K for all three samples; these results differ from the calculated data using the previous thermodynamic database. The difference might originate from the overestimation of the interaction parameter between boron and carbon in Fe₃(B,C). Proper titling was performed using the present data.     

Study on microstructural changes in thermally-aged stainless steel weld-overlay cladding of nuclear reactor pressure vessels by atom probe tomography

The effect of thermal aging on microstructural changes was investigated in stainless steel weld-overlay cladding composed of 90% austenite and 10% δ-ferrite phases using atom probe tomography (APT). In as-received materials subjected to cooling process after post-welding heat treatments (PWHT), a slight fluctuation of the Cr concentration was already observed due to spinodal decomposition in the ferrite phase but not in the austenitic phase. Thermal aging at 400 °C for 10,000 h caused not only an increase in the amplitude of spinodal decomposition but also the precipitation of G phases with composition ratios of Ni:Si:Mn = 16:7:6 in the ferrite phase. The chemical compositions of M₂₃C₆ type carbides seemed to be formed at the austenite/ferrite interface were analyzed. The analyses of the magnitude of the spinodal decomposition and the hardness implied that the spinodal decomposition was the main cause of the hardening.     

Investigation of thermodynamic properties of BCC solid solutions of uranium (II). The uranium-niobium system

The physical basis is presented of the model on which calculations of solid solution thermodynamic functions are based, and the relevant physical characteristics of γ-uranium-niobium solid solutions. The excess entropy and enthalpy of mixing at 1100 K are calculated for these alloys. Results are presented of an experimental study of the thermodynamic properties of U-Nb solid solutions in the temperature range from 1048 to 1173 K, by measuring EMF in a molten-salt electrolyte. For entropy of mixing the experimental data are closely consistent with the calculated curve, but there is no such agreement for the enthalpy of mixing. The reasons for this are considered. The possibility of the formation of an intermediate phase in the U-Nb system is briefly discussed.     

铀铌合金真空热氧化膜的俄歇电子能谱研究

用俄歇电子能谱(AES)研究了高真空下，环境温度对铀铌合金真空氧化膜的影响。当温度高于603K时，氧化膜表面结构发生明显改变，表面主要由铀碳化合物、金属态的U和Nb组成。利用Ar^ 溅射铀铌合金真空热氧化膜进行深度分布分析，发现在热氧化膜的表面氧含量很小，而在热氧化膜的内部有氧增多的现象。     

Phase diagram of the Rb-O system and disproportionation of rubidium suboxide

The phase diagram of the Rb-O system has been examined up to 28 at% oxygen and below 200°C. A eutectic point was found between rubidium and a rubidium suboxide (either Rb₆O or Rb₉O₂) at 10 at% oxygen and − 14°C. Three peritectic reactions were found: above 12 at% oxygen at − 11°C, above 14 at% oxygen at 20°C, and above 18 at% oxygen at 116°C. However, the composition of the rubidium suboxide that reveals the peritectic reaction could not be obtained. Oxygen solubility in rubidium above the melting point was equal to or greater than 3 wt%. With increasing oxygen concentration in the Rb-O mixture, the examination became more difficult. This difficulty appeared to be due to an intrinsic property of the Rb-O system, i.e. disproportionation of rubidium suboxide in the system. These results are in general agreement with those of Simon [4] but not with those of Touzain [3].     

Point defect properties in hcp and bcc Zr with trace solute Nb revealed by ab initio calculations

The properties of simple point defect (i.e. vacancy, self and foreign interstitial atoms) in the hcp (alpha) and bcc (beta) Zr with trace solute Nb have been studied by ab initio calculations with VASP codes. The calculations indicate that the formation energies of vacancy and substitutional Nb atom are 1.94 eV and 0.68 eV in alpha Zr and 0.36 eV and 0.07 eV in beta Zr, respectively, while the binding energies of the nearest neighbor vacancy-substitutional Nb pair and the nearest neighbor substitutional Nb-Nb pair are 0.09 eV and 0.03 eV in alpha Zr and 2.78 eV and 0.72 eV in beta Zr, respectively. These results suggest that the Nb atoms are more likely to agglomerate and form precipitates in the beta Zr than in the alpha Zr. Thus, the α-Zr-β-Zr-β-Nb transition mechanism through in situ α to β transformation of Zr and the vacancy-assisted Nb diffusion for Nb conglomeration in beta Zr under irradiation is proposed to explain the existence of beta Nb and Zr precipitate mixtures observed in the experiments for the Zr-Nb alloy. In addition, the defect formation energies in bcc Nb are also presented.     

The solubility of hydrogen,deuterium and tritium in liquid lead-lithium alloys

The solubility of H₂, D₂ and T₂ in liquid Pb-Li alloys was calculated, as a function of composition and temperature, using the thermodynamic data of the binary systems. In the 17 at% Li alloy, at 600 K the D₂ solubility is log K = ?4.20 ± 0.076, K in appm. torr^{?$\text{1}\text{2}$}, that of H₂ is ?4.125 ± 0.076, and that of T₂ is ?4.244 ± 0.076. The calculated values give a much lower solubility than the experimental data. A ternary H-Li-Pb interaction term must be postulated to get agreement between experimental and calculated results.     

Thermodynamic analysis of phase equilibria in the iron-uranium-zirconium system

Thermodynamic analysis of phase equilibria in metallic nuclear reactor systems has progressed to the study of the iron-uranium-zirconium ternary system. This work is based on our previous assessments and optimizations of the constituent binary subsystems iron-uranium, iron-zirconium, and uranium-zirconium.     

Study of the zirconium apex op the Zr-Ta-Nb phase diagram

Metallographical examination thermal analysis and electrical resistance measurements have been applied to a study of the zirconium apex, up to 82% zirconium and a temperature of 1200C, of the ternary system Zr-Ta-Nb, with limited solubility of tantalum and niobium in -zirconium ( phase), limited solubility and complete solubility of niobium in -zirconium, with eutectoid decomposition of the \ solid solution and three-phase eutectoid equilibrium + between - and-zirconium. In the investigated portion of the Zr-Ta-Nb phase diagram, the following phase regions were found: a) two one-phase regions and ; b) three two-phase regions + , + and + : c) one three-phase region + + ; the region contracts as the temperature falls below 1200 C.The solubility of tantalum and niobium in -zirconium in the system Zr—Ta—Nb is about 0.5%. On passing from Zr—Ta to Zr—Nb, the + and + regions are displaced toward lower temperature and high niobium concentrations; the boundaries of the + and + + regions are lowered from 790 for Zr—Ta to 612 C for Zr-Nb. Passing between the + and + regions is a binary eutectoid line which, from Zr-Ta to Zr-Nb is displaced toward lower temperatures and higher niobium concentrations. The solubility of niobium in ot zirconium in the Zr-Nb system is about 0.5%by weight. Eutectoid decomposition in the Zr-Ta system shifts the maximum of the martensitic-like transformation to the left and results in an increase in the stability of the phase at room temperature in quenched alloys.     

Compositional changes in Fe-Cr-Ni alloys under proton bombardment at elevated temperatures

Compositional redistribution in austenitic Fe-Cr-Ni alloys during energetic proton bombardment has been calculated as a function of time, temperature, and ion energy, using a kinetic model of radiation-induced segregation recently developed for ternary alloys. The effect of spatial nonuniformity in damage rates was taken into account and found to have a peculiar effect on the redistribution of the alloying elements. Enrichment of Ni occurs at the bombarded surface and in the bulk beyond the damage range, whereas Fe and Cr are enriched in the peak-damage region at the expense of their depletion in regions near the surface and beyond the damage range. These compositional changes can lead to local phase transformation, since the composition of local regions of the alloy is shifted away from the initial composition into different parts of the multicomponent phase diagram. The stability of the austenite phase in the sub-surface and post-range regions is enhanced by irradiation, while the austenite-to-ferrite transformation takes place in the peak-damage region.     

Fission products stability in uranium dioxide

Fission product stability in nuclear fuels is investigated using density functional theory (DFT). In particular, incorporation and solution energies of He, Kr, Xe, I, Te, Ru, Sr and Ce in pre-existing trap sites of UO₂ (vacancies, interstitials, U-O divacancy, and Schottky trio defects) are calculated using the projector-augmented-wave method as implemented in the Vienna ab initio simulation package. Correlation effects are taken into account within the DFT+U approach. The stability of many binary and ternary compounds in comparison to soluted atoms is also explored. Finally the involvement of FP in the formation of metallic and oxide precipitates in oxide fuels is discussed in the light of experimental results.     

A New Instrument Concept for Gamma Ray Astronomy

A new instrument concept that utilizes the principle of the Total Absorption Shower Cascade (TASC) detector is proposed for gamma ray astronomy in space. Using the TASC detector to measure the gamma ray energy and wire chamber arrays to measure the incident angle, an instrument package designed to measure gamma rays having energies greater than 100 MeV is being proposed for a large satellite such as NASA's proposed High Energy Astronomy Observatory. The proposed instrument has a minimal flux sensitivity of 2 × 10-10 photons/cm2 sr sec which will allow gamma rays with energies up to 104 GeV to be measured. An energy resolution (FWHM) for the TASC detector of ~l percent at 10 GeV has been measured and an angular resolution of ~1 degree appears to be obtainable for the wire chamber arrays.     

Thermodynamics of the uranium-zirconium system

Renewed interest in metallic fuel for nuclear reactors has prompted new studies of the thermodynamics and phase equilibria in binary alloys containing uranium, plutonium, and zirconium so that the ternary phase diagram might be calculated. An analysis of the uranium-zirconium alloy system has been performed. Thermodynamic functions for all existing uranium-zirconium phases have been derived and a phase diagram was calculated. These results are compared with the available thermodynamic data and accepted phase diagrams and general agreement was found. Disagreements generally occurred where experimental data were sparse and when previously drawn phase boundaries were found to be inconsistent with theory.     

Multidimensional effects in laminar filmwise condensation of water vapour in binary and ternary mixtures with noncondensable gases

This paper is dealing with the multidimensional modelling of gravity driven water vapour free convection condensation from binary and ternary mixtures of condensable and noncondensable gases. In the case of ternary mixtures, a special attention is paid to the influence of the light gas on the transport phenomena in the gaseous phase. Two solution methods have been applied: an analytical solution employing the boundary layer similarity approximation and a numerical solution of multi-fluid, multi-component formulation of the conservation equations. It has been demonstrated that the two methods are equivalent when applied to binary mixtures in simple geometries. However, to capture the spatial effects and the ternary mixture phenomena the latter method must be used.     

铀铌合金中铌的测定

本文介绍了氯代磺酚Ｓ直接分光光度法测定铀铌合金中的铌．方法具有简便、快速、灵敏度高等优点。可测铀铌合金中１％～１０％的铌．回收率为９９％～１０２％。