The Effects of Fission Gas and Radiation Collision on UO2 Melting: A Molecular Dynamics Simulation

Xiangyu Wang, Bin Wu, Fei Gao Gao, Xin Li, Xin Sun, Mohammed A. Khaleel, Ademola V. Akinlalu, Fallon Laliberte, Lauren Boldon, Emily Liu

Department of Mechanical, Aerospace & Nuclear Engineering, Rensselaer Polytechnic Institute, Troy, NY 12180, USA. Fundamental Science Directory, Pacific Northwest National Laboratory, P. O. Box 999, Richland, WA 99352, USA

The melting point of Uranium Dioxide (UO2) has previously been evaluated through molecular dynamics (MD) simulations by employing the empirical interaction potential. The interaction potential is analyzed in terms of the pure UO2 lattice, fission gas atoms (Xenon), and radiation collisions. A preliminary study of the melting point of UO2 is presented in this paper in order to analyze the effects of fission gas atoms and radiation collision. Utilizing molecular dynamics simulation with a two-phase method, the melting point for pure UO2 and UO2 with fission gas was observed to be 3175 K ± 12.5 K and 3150 K ± 12.5 K, respectively, as the temperature increased from 2800 K to 3400 K. The calculated melting point for UO2 using two-phase method was close to experimental measurements observed for the melting point. From the study of the relationship between melting point and fission gas density, the melting point of UO2 decreased while the density of Xe increased. The two-phase method also demonstrated a decrease in the melting point of approximately 15 K/Xe gas atom. This may result from a reduction in the nucleation barrier due to the presence of Xenon. From the study of the relationship between melting point and defects generated by various primary knock-on atoms (PKAs) for different Xe concentrations, there was no direct relationship determined between the melting point of UO2 and the number of defects generated by PKAs. However, the creation of point defects may indirectly influence the melting point, especially in the case where both fission gas and radiation collisions are included. Journal of Nature and Science, 1(7):e133, 2015.

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