Molecular dynamics simulation of thermomechanical properties of nulcear fuel

Abstract

Many new kinds of nuclear reactor fuel are under development-to-testing stage for enhancing the efficiency and safety of existing reactors and new generation reactors. Molecular dynamics (MD) as a important computational method calculating the time dependent behavior of a molecular system at atomic or molecular level is very useful to predict thermal and mechanical properties of the material. The simulation analyzed fuel behaviors can point a direction for experiment, thus to reduce the expense of research. In present study, the MD simulations by using the MXDORTO code are performed in NPT and NVT. Morse-type potential equation is chosen. Quantum correction for kinetic energy is also taken into account. The equations of the motion are integrated with the modified Verlet algorithm. The time step is $0.5×10^{-15}s$, the initial velocity is set to $1.0pm/fs$. The UN and PUN are performed with 4×4×4 cells in the same structure of $NaCl$ type crystal and $UO_2$ with 3×3×3 cells in the same structure of $CaF_2$ type crystal. Before simulation is started, an initial NVT running is performed at desired temperature for 100000 steps. With the results of lattice parameter, linear thermal expansion coefficient and the compressibilities of UN, PUN and $UO_2$ are evaluated. Further the heat capacities of UN and PUN are calculated from the energy data by NVT simulation. The results are in close agreement with the experimental values.