Effect of Ce 4+ and Th 4+ Ion Substitution in Uranium Dioxide
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Effect of Ce4+ and Th4+ Ion Substitution in Uranium Dioxide Rakesh K. Behera1, and Chaitanya S. Deo1 1 Nuclear and Radiological Engineering Program, George W. Woodruff School of Mechanical Engineering, Georgia Institute of Technology, Atlanta, GA 30332, U.S.A.
ABSTRACT Uranium dioxide is the most common fuel used in commercial light water nuclear reactors. The fission of the fuel generates fission products (FPs) and minor actinides (MAs), which affects the thermo-physical properties of the fuel. The understanding of the physical and chemical properties of the FPs and MAs is still limited. In this study we have used atomic level simulations to estimate the effect of Ce4+ and Th4+ ions in urania matrix. Our results show that the structural variation depends on the elastic effect, which is guided by the ionic radius of the substituted ion. Ce4+ (ionic radius 0.97 Å) reduces the overall lattice parameter, while Th4+ (ionic radius 1.05 Å) increases the overall lattice parameter of the urania matrix (U4+ ionic radius 1.00 Å). In addition bulk modulus of the U1-xCexO2 system does not change with substitution while the modulus of U1-xThxO2 reduces with an increase in Th4+ ion concentration. This observation is in accordance with Vegard’s law prediction based on the modulus values of bulk UO2, CeO2 and ThO2 systems. INTRODUCTION Uranium dioxide is the most common fuel used in commercial light water nuclear reactors. The fission of uranium based fuels in a light water reactor generates more than 20 fission products (FPs) [1]. In addition, the neutron capture and decay reactions during the fuel cycle produces minor actinides (MAs). These FPs and MAs affect the thermo-physical properties, e.g., thermal conductivity, swelling, creep of the fuel. Lanthanides and actinides are usually dissolved in the host UO2 matrix. This paper studies the effect of these elements on structure and elastic constants of the host UO2 matrix using atomistic simulations. Considering the FPs and MAs, uranium-based fuels can generate Ce, Nd, Pm, Sm, Eu, and Gd in the Lanthanide series and Th, Np, Pu, Am, and Cm in the Actinide series. In this study we have investigated the structural and mechanical properties of UO2 for 4+ ion (Ce4+ or Th4+) substituted urania-systems using atomistic models. Atomic level simulations are successfully used to simulate nuclear materials [2]. In addition it is possible to define the substitution of the species of interest with atomic precision. Since we are interested in investigating the structural and elastic properties of UO2 and substitution of Ce4+ and Th4+ in the urania matrix, we have collected relevant interatomic potentials from the literature. METHODOLOGY In order to simulate the urania systems with Ce4+ and Th4+, we employ the transferable interatomic potentials from the literature which are described in table I. The
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overall interactions in urania systems are calculated by a combination of long-range and short-range interactions. The long-range interactions for all the potentials are described by the Coulom
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