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Now showing items 1 - 3 of 3

  • 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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  • 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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