There are two main objectives in this study. One is to estimate atomic diffusion coefficients in eutectic reaction between metal fuel and cladding materials in order to establish the atomic diffusion model for the COMPASS code. The other is to estimate their material properties such as Young's modulus in high temperature up to near melting points in core disruptive accidents (CDAs) in Sodium-cooled Fast Reactors (SFRs). We used the first principle molecular dynamics (FPMD) code VASP to realize the two objectives. We tried to understand the initiation mechanism of eutectics based on change of electronic state energy accompanied by change of Kohn-Sham energy, including phonon effect. In this project , three methods, phase diagram calculation (CALPHAD), classical molecular dynamics (CMD), and FPMD, are employed to understand the mechanism of eutectics and to introduce dynamic characteristics in eutectic phenomena into the COMPASS code.