Uranium-based Alloys Research Articles

A prediction model for thermal conductivity of metallic nuclear fuel based on multiple machine learning models

In this work, the presence of the BCC phase and its thermal conductivity in uranium-based metallic nuclear fuels at higher temperatures were predicted by coupling a random forest classification model with a multilayer perceptron network model. To analyze the effect of phase constitution on thermal conductivity in uranium-based alloys, the pearson correlation coefficient was introduced. The data samples in the current small-sample database of metallic nuclear fuels, created by collecting experimental and computational data from the literature, were first pre-processed with the guide of professional knowledge before machine learning, involving data screening and data completion. Based on temperature and composition characteristics, the existence of the BCC phases and the thermal conductivities of the candidates were predicted by our models. The optimized thermal conductivities of the candidate alloys coincide well with the experimental results, which shows the reliability of our model.

Structures and properties of uranium–niobium intermetallic compounds under high pressure: A first principles study

Metallic uranium-based alloys, with d-transition metals such as Nb, Mo, and Zr, are promising candidates for actinide fuel. For this purpose, their behaviors under changing physical stimuli need to be understood. Here, we systematically investigate U–Nb intermetallic compounds and predict new compound formations under different pressures using the first-principles swarm-intelligence structure searching method. Two new compounds (U1Nb6 and U2Nb1) were identified to be thermodynamically stable at ambient and high pressures. U1Nb6 has a triclinic symmetry that is stable in the pressure range of 0–200 GPa, while U2Nb1 has a hexagonal closely packed structure at low pressure and transforms to a simple hexagonal lattice at 20 GPa. Other compounds, particularly U-rich ones (U3Nb1, U4Nb1, U5Nb1, and U6Nb1), are found metastable at ambient and high pressures, and all have orthorhombic structures. The structural, vibrational, electronic, and mechanical properties of predicted U-rich compounds were thoroughly studied using density-functional theory. The results of phonon spectra and elastic constant show that the predicted new structures are dynamically and mechanically stable in the corresponding pressure range. Also, these newly identified U-rich compounds exhibit strong composition dependence, and the pressure-induced enhancements of structural stability and mechanical performances are evident. These findings shall enrich the understanding of U-based alloys and serve as meaningful predictions for experimental research in the future.

Thermodynamic and diffusion databases for uranium-based alloys and their applications in materials design

Thermodynamic and diffusion databases are of fundamental importance for material design. In this work, the thermodynamic and diffusion databases for multicomponent U alloys are developed using the CALPHAD (CALculation of PHAse Diagram) method. Thermodynamic models are employed to describe all phases in the UNbZrTiMoC system in which 7 ternary systems (UNbZr, UZrTi, UMoZr, MoNbZr, MoTiZr, CNbZr, and CNbTi) are thermodynamically assessed. Thermodynamic descriptions of all sub-systems from both literature and present assessments are integrated into the database with a proper adjustment. The diffusion database is developed for bcc and liquid phases in the UNbZrTiMoC system. Applications of thermodynamic and diffusion databases are performed using two cases including (a) the stability of γU in the multicomponent system, and (b) discontinuous precipitation simulation in U-14 at.% Nb alloys. It is expected that further progress in CALPHAD-type nuclear materials databases will be an effective contribution to advanced metal fuels design.

Molecular dynamics studies of grain boundary mobility and anisotropy in BCC γ-uranium

Grain morphologies such as grain size and aspect ratio in uranium-based metallic fuels are important microstructural features that can impact various fuel performance properties such as fission-gas-induced swelling, thermal transport, high burnup structure formation, and radiation resistance. Accurate prediction of the fuel grain morphologies requires knowledge of critical grain growth parameters such as grain boundary (GB) mobility and anisotropy. In this work, molecular dynamics (MD) simulations were performed to study the GB mobility and its anisotropy in pure body-centered-cubic (BCC) γ uranium. Nine GBs with different combinations of misorientation angles (20°, 30°, 45°) and rotation axes (<100>, <110>, <111>), as well as an additional <111> 38.2° GB were studied using three interatomic potentials. It is found that the GB mobility anisotropy has complex trends, depending on both rotation axis and misorientation. However, in general the <110> rotation axis has the fastest GB mobility at the same misorientation. The results of this work can be used as not only a baseline for future studies of GB mobility in uranium-based alloys such as uranium-molybdenum (U-Mo) fuels, but also input for mesoscale modeling of grain growth in uranium-based alloys.

Material informatics for uranium-bearing equiatomic disordered solid solution alloys

Near-equiatomic, multi-component alloys with disordered solid solution phase (DSSP) are associated with outstanding performance in phase stability, mechanical properties and irradiation resistance, and may provide a feasible solution for developing novel uranium-based alloys with better fuel capacity. In this work, we build a machine learning (ML) model of disordered solid solution alloys (DSSAs) based on about 6000 known multi-component alloys and several materials descriptors to efficiently predict the DSSAs formation ability. To fully optimize the ML model, we develop a multi-algorithm cross-verification approach in combination with the SHapley Additive exPlanations value (SHAP value). We find that the ΔSC, Λ, Φs, γ and 1∕Ω, corresponding to the former two Hume − Rothery (H − R) rules, are the most important materials descriptors affecting DSSAs formation ability. When the ML model is applied to the 375 uranium-bearing DSSAs, 190 of them are predicted to be the DSSAs never known before. 20 of these alloys were randomly synthesized and characterized. Our predictions are in-line with experiments with 3 inconsistent cases, suggesting that our strategy offers a fast and accurate way to predict novel multi-component alloys with high DSSAs formation ability. These findings shed considerable light on the mapping between the material descriptors and DSSAs formation ability.

High entropy uranium-based alloys: Thermodynamics, characterization and mechanical properties

Uranium is traditionally stabilized in its ductile γ (BCC) phase by the addition of elements such as Mo, Nb or Zr (Mo is used in metallic fuel for reactor applications). Due to the resemblance of uranium alloys to ferrous alloys, an attempt was made to synthesize single phase U-based high entropy alloys (HEAs) in the U-Mo-Nb-Zr system, following empirical rules related to enthalpies of mixing and atomic radius differences. Microstructure, phase and elemental compositional were characterized, and mechanical properties were measured. This research showed that despite the expectation that a single γ (BCC) phase would be formed, these alloys usually presented two-phase structures; a U-rich γ phase and a Mo-Nb rich BCC phase or a Laves phase. Thermodynamic calculations were successful in predicting the content of phases in the alloys but were not in full agreement with the experimental results. Small punch tests (SPT) showed that most of the studied samples were hard and brittle, which could be attributed to the presence of the Laves phases or alternatively, could be correlated with the multi-component γ (BCC) phase, since other BCC HEAs also tend to be hard and brittle.

Hydrogen absorption in uranium-based alloys with cubic γ -U structure3

UH3-type hydrides were formed by hydrogenation of splat-cooled U-based alloys upon applying high H2 pressures (>2.5 bar). Hydrogenation of U1−xMox alloys (with x ⩾ 0.12 (12 at.% Mo) containing the cubic γ-U phase leads to a formation of nanocrystalline β-UH3, why those of U1−xZrx alloys (with x ⩾15 at.% Zr) implies a pure α-UH3. The Curie temperature of hydride (UH3)0.85Mo0.15 reaches 200 K; it may be the first U-based ferromagnet with such high TC. The results reflect the dominant U–H interaction.

Thermophysical Properties of Uranium-Based Niobium and Zirconium Alloys from 23 °C to 175 °C

The thermal diffusivities of uranium alloys were measured by the laser-flash method between room temperature and 448 K. In recent years, several UZrNb alloys have been studied by many researchers and it was shown that additions of niobium and zirconium improve the properties of uranium-based alloys. The purpose of this article is to summarize the thermophysical properties of two uranium alloys that have been studied by CDTN in a program of development of fuel for low-power reactors. The nominal compositions of the studied alloys are U4Zr6Nb and U3Zr9Nb. The results obtained by the original laser-flash method and by the mathematical model developed by the laboratory were compared to the literature data. The adaptive Monte Carlo method was used to obtain the endpoints of the probabilistically symmetric 95% coverage interval for estimates of the output quantities and its uncertainties.

Effect of molybdenum addition on metastability of cubic γ-uranium

Abstract Over the years U 3 Si 2 compound dispersed in aluminium matrix has been used successfully as the potential low enriched uranium (LEU 235 ) base dispersion fuel for use in new research and test reactors and also for converting high enriched uranium (HEU > 85%U 235 ) cores to LEU for most of the existing research and test reactors world over, though maximum 4.8 g U cm −3 density is achievable with U 3 Si 2 –Al dispersion fuel. To achieve a uranium density of 8.0–9.0 g U cm −3 in dispersion fuel with aluminium as matrix material, it is required to use γ-stabilized uranium metal powders. At Bhabha Atomic Research Centre (BARC), R & D efforts are on to develop these high density uranium base alloys. This paper describes the alloying behaviour of uranium with varying amount of molybdenum. The U–Mo alloys with different molybdenum content have been prepared by using an induction melting furnace with uranium and molybdenum metal pellets as starting materials. U–Mo alloys with different molybdenum content were characterized by X-ray diffraction (XRD) for phase identification and lattice parameter measurements. The optical microstructure of different U–Mo alloy composition has also been discussed in this paper. Quantitative image analysis was also carried out to determine the amount of various phases in each composition.

Development, preparation and characterization of uranium molybdenum alloys for dispersion fuel application

Most of the research and test reactors worldwide have undergone core conversion from high enriched uranium base fuel to low enriched uranium base fuel under the Reduced Enrichment for Research and Test Reactor (RERTR) program, which was launched in the late 1970s to reduce the risk of nuclear proliferation. To realize this goal, high density uranium compounds and γ-stabilized uranium alloy powder were identified. In Metallic Fuels Division of BARC, R&D efforts are on to develop these high density uranium base alloys. This paper describes the preparation flow sheet for different compositions of Uranium and molybdenum alloys by an innovative powder processing route with uranium and molybdenum metal powders as starting materials. The same composition of U–Mo alloys were also fabricated by conventional method i.e. ingot metallurgy route. The U–Mo alloys prepared by both the methods were then characterized by XRD for phase analysis. The photomicrographs of alloys with different compositions prepared by powder metallurgy and ingot metallurgy routes are also included in the paper. The paper also covers the comparison of properties of the alloys prepared by powder metallurgy and ingot metallurgy routes.

Stress relaxation of elastic precursor for unalloyed uranium and some uranium-based alloys

The new data are presented on relaxation of an elastic precursor in unalloyed depleted uranium and two its alloys. Results were obtained under low-intense explosive loading. Statistic thermofluctuational model was used for approximation of experimental data. The inversion of strength properties of the tested U-Mo and U-Fe-Ge alloys at their quasi-static and high-rate loading was revealed.

Stress relaxation of elastic precursor for unalloyed uranium and some uranium-based alloys

The new data are presented on relaxation of an elastic precursor in unalloyed depleted uranium and two its alloys. Results were obtained under low-intense explosive loading. Statistic thermofluctuational model was used for approximation of experimental data. The inversion of strength properties of the tested U-Mo and U-Fe-Ge alloys at their quasi-static and high-rate loading was revealed.

Effect of finite concentration in Kondo alloys: Approach to the heavy-fermion problem.

By using Nozieres' Fermi-liquid formulation for magnetic impurities as scattering centers at low temperatures ([ital T][lt][ital T][sub [ital K]]), we calculate the [ital x][sup 2] correction terms (in the impurity concentration) to the thermodynamic potential. We interpret the difference in the low-temperature properties between some cerium- and uranium-based alloys in terms of how close the scattering phase shift [delta] for an isolated impurity center is to the unitary limit ([delta]=[pi]/2). We apply a picture of independent impurity centers for a large range of [ital x] in some Ce-based alloys, but only for [ital x][much lt]1 in U-based alloys. This is due to the Ce-based alloys being much closer to the unitary limit than the U-based alloys, suggesting that in the formation of a collective ground state the change in the density of states is the dominant effect in a dense [ital Kondo] [ital lattice] where the single-center phase shift is close to the unitary limit, while the magnetic interaction between local-impurity centers becomes important in a system where the phase shift differs from [pi]/2.

Phase equilibria in the UU 3Si 2-UAl 2 system

The phase equilibria in high purity electrolytic uranium base alloys of the system UU 3Si 2-UAl 2 near the composition of the lowest uranium silicide U 3Si were investigated by microstructural, X-ray and differential thermal analyses at temperatures up to 980°C. Using the experimental results and the available literature data, eight topologically non-equivalent isothermal sections and the polythermal sections in the 1360-765°C temperature range were constructed. Three non-variant four-phase equilibria at 976, 973 and 765°C have been revealed. The constructed partial phase diagram UU 3Si 2-UAl 2 is significantly different from that known in literature. The cause of this difference is discussed.

An investigation of the γ → α martensitic transformation in uranium alloys

A detailed study of the γ → α martensitic transformation in uranium alloys is presented. Five binary uranium-base alloys containing 0.77Ti, 1.2 Mo, 2.2 Mo, 4.3 Mo and 5.0 Mo, respectively, were examined. As quenched, the U-0.77 Ti and U-1.2 Mo alloys consisted of an orthorhombic a/ a , martensite phase with an acicular morphology. The acicular martensite plates contain deformation twins which result from transformation stresses. The U-2.2 Mo and U-4.3 Mo alloys transformed during quenching to orthorhombic α/ b and monoclinic α/ b , martensite phases, respectively. The banded morphology observed in these two alloys consists of long, parallel martensite plates containing fine arrays of transformation twins. The type I transformation twinning modes were identified as {021},{130} and {131}. There was also evidence for a type II 〈512〉 {111} mode. It was found that adjacent bands could contain different kinds of transformation twins. In the U-5.0 Mo alloy, some of the cubic parent phase was retained during water quenching, and the α γ orientation relationship was determined. The γ phase was completely retained in this alloy by slow cooling from the solution treatment temperature of 800°C, and it was found that a martensitic reaction could be induced by deformation. The strain-induced martensite plates contained {021} transformation twins. The α γ orientation relationship was found to be different than the one determined in the quenched condition, and both orientation relationships are irrational. The invariant plane strain theory of martensite crystallography was applied to the twinned martensites, and a number of different parent/product lattice correspondences were considered for the γ → α transformations. It was concluded that more than one correspondence may be operative during these transformations. The single-shear theory was not able to explain the occurrence of all of the observed transformation twinning modes, although the theory was quite successful in predicting the observed crystallography for the strain-induced transformation.

Magnetic properties of two new uranium-based alloys: UAuCu4and UPdCu4

Two new uranium-based alloys UAuCu4 and UPdCu4 have been prepared and their magnetic properties studied. The NMR of the isotope 63Cu in these alloys suggests that they are well ordered ternary materials. There is a strong correlation between the occupancy of the (4c) sites in the structure and the relative size of the two non-uranium atoms in these alloys.

Anomalous glass-forming ability of uranium-based alloys

Using a melt spinning technique glassy UCo alloys were produced over the range 10–58 at.% cobalt. Glassy UFe and UNi alloys were also produced containing as little as 14.3% iron or nickel. Metallic glass formation at concentrations as low as 10% of the smaller atoms is unusual and particularly so in the case of these uranium alloys; this is because their composition is far from the eutectic composition (34% for UCo) and the corresponding equilibrium liquidus temperature is closer to the melting point of pure uranium than to the eutectic temperature. Based on X-ray diffraction data on a series of UCo glasses, a qualitative structural model is proposed which predicts that glass formation becomes much more difficult as the cobalt concentration decreases below 14%. Calorimetric and diffraction data together imply that the equilibrium phase diagram cannot be used as a guide for judging glass formability in the case of uranium-based metallic glasses.

アルミニウム,クロム,鉄,モリブデン,ニオブ,ニッケル,チタン,バナジウム,ジルコニウム各ウラン合金の分析

The preparation of many kinds of uranium base alloys by the Metallurgy Research Group of the Japan Atomic Energy Research Institute necessitated a rapid and accurate analytical method for the determination of the additive element in each alloy. The alloys are binary uranium base alloys of Al, Cr, Fe, Mo, Nb, Ni, Ti, V and Zr, and the additives are contained 0.15 a/o in the alloys, respectively.In the determination of the additives, “the extraction-photometric method” was used and the following reagents were used: 8-quinolinol for Al, Fe, Mo, Nb and V, 2-methyl-8-quinolinol for Cr and Ti and dimethylglyoxime for Ni.In each case, masking agent for uranium, optimum pH range for extraction, washing of the extract and the wavelength of absorbance measurement were closely studied.The reproducibility and the accuracy of all the methods were satisfactory, and some of the methods have been and are used for the routine analysis in the Institute.

Spectrophotometric determination of niobium with Xylenol Orange.

A method is described for the spectrophotometric determination of niobium with Xylenol Orange. The sample solution containing 5 approximates 60 mu g of niobium is transferred to a 25 ml volumetric flask. Sulfuric acid concentration is adjusted to make the acidity 0.05 approximates 0.25N after diluting to volume. Ascorbic acid is then added to reduce iron(III). Sodium sulfate is added to mask small amounts of thorium. Xylenol Orange is added, followed by aluminum sulfate. The aluminum is added to eliminate the interference of fluoride that is presnet in the sample solution. After diluting to the mark and allowing to stand for 1 hr, the absorbance is measured in a 1 cm cell at 53 m mu , using the reagent blank as the reference. Beer's law is obeyed, and the molar absorptivity is 2.3 x 10/sup 4/. According to the continuous variation and slope ratio methods, the composition of the colored products corresponds to a mixture of NbXO and Nb(XO)/sub 2/, where XO is Xylenol Orange. The proposed method was applied to uranium-base alloys, and favorable results were obtained. (auth)

Spectrophotometric Determination of Niobium and molybdenum with 8-Quinolinol in Uranium-Base Alloys

Spectrophotometric Determination of Niobium and molybdenum with 8-Quinolinol in Uranium-Base Alloys