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Now showing items 1 - 16 of 17

  • Anisotropic thermophysical properties of U3Si2 fuel:An atomic scale study

    Jossou, Ericmoore   Rahman, Md Jahidur   Oladimeji, Dotun   Beeler, Benjamin   Szpunar, Barbara   Szpunar, Jerzy  

    Due to renewed interest in uranium silicide compounds as a candidate for nuclear reactor fuels, there is a need for extensive investigations of their thermophysical properties as a function of temperature. In this work, we calculate the thermophysical properties of the U3Si2 compound within the framework of molecular dynamics (MD) using a semi-empirical modified Embedded-Atom Method (MEAM) potential and density functional theory (DFT). Thermal expansion, thermal conductivity, heat capacity, and elastic properties are presented as a function of temperature from 300 to 1800 K. The thermal conductivity of U3Si2 increases with temperature due to the electronic contribution while the phonon contribution decreases with increasing temperature. The phonon contribution to the thermal conductivity at 300 K is estimated at 2.03 W/mK and 1.41 W/mK using non-equilibrium molecular dynamics (NEMD) and equilibrium molecular dynamics (EMD), respectively. The electronic contribution is estimated to be 8.56 W/mK using the semi-classical Boltzmann transport theory at 300 K. Furthermore, we compared the thermal conductivity in two different crystallographic directions to shed light on the spatial anisotropy using NEMD and EMD methods. The inherent anisotropic thermophysical properties can be used to parametrize phase field models to incorporate anisotropic thermal conductivity and thermal expansion, allowing for a more accurate description of microstructural evolution under variable temperature and irradiation conditions. (c) 2019 Elsevier B.V. All rights reserved.
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  • Calculation of threshold displacement energies in UO2

    Dacus, Benjamin   Beeler, Benjamin   Schwen, Daniel  

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  • An atomistic study of grain boundaries and surfaces in γ U-Mo

    Beeler, Benjamin   Zhang, Yongfeng   Gao, Yipeng  

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  • Calculation of threshold displacement energies in UO2

    Dacus, Benjamin   Beeler, Benjamin   Schwen, Daniel  

    Despite the extensive utilization of uranium dioxide (UO2) as a fuel in commercial nuclear reactors, there is only minimal information regarding the fundamental nature of radiation damage at high temperatures, such as those experienced by the fuel under operation. In this work, molecular dynamics simulations have been performed to determine the threshold displacement energy (E-d) for oxygen and uranium in UO2 at 1500 K. Three definitions of displacement energy were employed to fully study the nature of low energy radiation damage: 1) the probability of having the primary knock-on atom (PKA) leave its original lattice site, 2) the probability that the PKA will permanently displace atoms from their original lattice site, and 3) the probability of forming a stable Frenkel pair. Additionally, four unique interatomic potentials were utilized to investigate uncertainties associated with potential choice in high temperature radiation damage studies in UO2. This work provides critical insight into the high temperature behavior of radiation damage in UO2, as well as the variation in behavior between oxygen and uranium PKAs. Published by Elsevier B.V.
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  • Molecular dynamics investigation of grain boundaries and surfaces in U3Si2

    Beeler, Benjamin   Baskes, Michael   Andersson, David   Cooper, Michael W. D.   Zhang, Yongfeng  

    Uranium-silicide (U-Si) fuels are being pursued as a possible accident tolerant fuel (ATF). This uranium alloy benefits from higher thermal conductivity and higher fissile density compared to uranium dioxide (UO2). In order to perform engineering scale nuclear fuel performance simulations, the material properties of the fuel must be known. Currently, the experimental data available for U-Si fuels is rather limited. Thus, multi-scale modeling efforts are underway to address this gap in knowledge. Interfaces play a critical role in the microstructural evolution of nuclear fuel under irradiation, acting both as sinks for point defects and as preferential nucleation sites for fission gas bubbles. In this study, a semiempirical modified Embedded-Atom Method (REAM) potential is utilized to investigate grain boundaries and free surfaces in U3Si2. The interfacial energy as a function of temperature is investigated for ten symmetric tilt grain boundaries, eight unique free surfaces and voids of radius up to 35 angstrom. The point defect segregation energy for both U and Si interstitials and vacancies is also determined for two grain boundary orientations. Finally, the entropy change and free energy change for grain boundaries is calculated as a function of temperature. This is the first study into grain boundary properties of U-Si nuclear fuel. Published by Elsevier B.V.
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  • Molecular dynamics investigation of grain boundaries and surfaces in U3Si2

    Beeler, Benjamin   Baskes, Michael   Andersson, David   Cooper, Michael WD.   Zhang, Yongfeng  

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  • A modified Embedded-Atom Method interatomic potential for uranium-silicide

    Beeler, Benjamin   Baskes, Michael   Andersson, David   Cooper, Michael W.D.   Zhang, Yongfeng  

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  • A molecular dynamics study of the behavior of Xe in U3Si2

    Beeler, Benjamin   Andersson, David   Cooper, Michael W. D.   Zhang, Yongfeng  

    Uranium-silicide (U-Si) fuels are being pursued as a possible accident tolerant fuel (ATF). This uranium alloy fuel benefits from higher thermal conductivity and higher fissile density compared to uranium dioxide (UO2). The role of fission gas swelling on the operational performance of U-Si fuels remains an open question, however, fission gas swelling is a critical phenomenon in UO2, U-Zr and U-Mo nuclear fuels. Given the lack of experimental data, in order to study the fundamentals of bubble formation and evolution in U-Si, it is critical that there be an atomistic description of Xe within the U-Si system. In this work, a recently developed U-Si MEAM interatomic potential is leveraged to generate a description of the U-Si-Xe system fit to density functional theory data. The point defect energies of Xe in U3Si2 are determined, in addition to the point defect segregation energy for Xe with respect to two grain boundary orientations. Finally, the properties of small Xe bubbles are analyzed and an equation of state is developed. Published by Elsevier B.V.
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  • Atomistic properties of γ uranium

    Beeler, Benjamin   Deo, Chaitanya   Baskes, Michael   Okuniewski, Maria  

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  • A improved equation of state for Xe gas bubbles in gamma U-Mo fuels

    Beeler, Benjamin   Hu, Shenyang   Zhang, Yongfeng   Gao, Yipeng  

    A monolithic fuel design based on a U-Mo alloy has been selected as the fuel type for conversion of the United States High-Performance Research Reactors (HPRRs). An issue with U-Mo monolithic fuel is the large amount of swelling that takes place during operation. The accurate prediction of fuel evolution under irradiation requires implementation of correct thermodynamic properties into mesoscale and continuum level fuel performance modeling codes. However, the thermodynamic properties of the fission gas bubbles (such as the relationship among bubble size, equilibrium Xe concentration, and bubble pressure) are not well known. This work studies Xe bubbles in gamma U-Mo from a diameter of 3 nm up to 8.5 nm and from 400 K up to 700 K. The energetic relationship of Xe bubbles with regard to voids and Xe substitutional atoms is described. The transition is also determined for when a bubble becomes over-pressurized. Finally, an equation of state is fit to the pressure as a function of molar volume and temperature. Published by Elsevier B.V.
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  • Effects of applied strain on radiation damage generation in body centered cubic iron

    Beeler, Benjamin   Asta, Mark   Hosemann, Peter   Gronbech-Jensen, Niels  

    Radiation damage in body-centered cubic (BCC) Fe has been extensively studied by computer simulations to quantify effects of temperature, impinging particle energy, and the presence of extrinsic particles. However, limited investigation has been conducted into the effects of mechanical stresses and strain. In a reactor environment, structural materials are often mechanically strained, and an expanded understanding of how this strain affects the generation of defects may be important for predicting microstructural evolution and damage accumulation under such conditions. In this study, we have performed molecular dynamics simulations in which various types of homogeneous strains are applied to BCC Fe and the effect on defect generation is examined. It is found that volume-conserving shear strains yield no statistically significant variations in the stable number of defects created via cascades in BCC Fe. However, strains that result in volume changes are found to produce significant effects on defect generation. (C) 2015 Elsevier B.V. All rights reserved.
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  • Effects of applied strain on radiation damage generation in body-centered cubic iron

    Beeler, Benjamin   Asta, Mark   Hosemann, Peter   Gr?nbech-Jensen, Niels  

    Radiation damage in body-centered cubic (BCC) Fe has been extensively studied by computer simulations to quantify effects of temperature, impinging particle energy, and the presence of extrinsic particles. However, limited investigation has been conducted into the effects of mechanical stresses and strain. In a reactor environment, structural materials are often mechanically strained, and an expanded understanding of how this strain affects the generation of defects may be important for predicting microstructural evolution and damage accumulation under such conditions. In this study, we have performed molecular dynamics simulations in which various types of homogeneous strains are applied to BCC Fe and the effect on defect generation is examined. It is found that volume-conserving shear strains yield no statistically significant variations in the stable number of defects created via cascades in BCC Fe. However, strains that result in volume changes are found to produce significant effects on defect generation. (C) 2015 Elsevier B.V. All rights reserved.
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  • uranium

    Beeler, Benjamin   Zhang, Yongfeng   Okuniewski, Maria   Deo, Chaitanya  

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  • First principles calculations of the structure and elastic constants of α, β and γ uranium

    Beeler, Benjamin   Deo, Chaitanya   Baskes, Michael   Okuniewski, Maria  

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  • Effect of strain and temperature on the threshold displacement energy in body-centered cubic iron

    Beeler, Benjamin   Asta, Mark   Hosemann, Peter   Gr?nbech-Jensen, Niels  

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  • First principles calculations of the structure and elastic constants of alpha, beta and gamma uranium

    Beeler, Benjamin   Deo, Chaitanya   Baskes, Michael   Okuniewski, Maria  

    This study analyzes structural and elastic properties of five uranium crystal structures: the face centered orthorhombic A20 (alpha phase), the tetragonal D8(b) (beta phase), body centered tetragonal (bct), body centered cubic (gamma phase) and face centered cubic structures. Calculations are performed within the density functional theory framework employing the Projector Augmented Wave method and the Perdew-Burke-Ernzerhof generalized gradient approximation (PBE-GGA) of the exchange correlation. The elastic constants are used to compute polycrystalline elastic moduli, Poisson's ratio and the Debye temperature for all five structures. The alpha and gamma phase properties are compared with theoretical and experimental results. The complex tetragonal 30 atom beta phase is examined in detail. Representation of the beta phase by a bct structure is examined; we find that the structure of the beta phase is significantly different from the bct phase but exhibits similar elastic properties. This is the first comprehensive investigation into the elastic constants of uranium utilizing the PBE-GGA. (c) 2012 Elsevier B.V. All rights reserved.
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