Multi-scales Simulation Of The Displacement Cascade In Iron And Vanadium

The crisis of energy is a sticky issue, and the nuclear energy has been predicted as one of the most potential energies in future. Especially the fusion energy, which is much safer than fission energy, is an environmentally friendly energy source. However, the commercial application of fusion energy is still under developing. Iron and vanadium-based alloys are two of the most important first-wall materials in fusion reactor. By applying molecular dynamics (MD) simulation, the low and high recoil energies have been introduced to model the cascade collision in iron and vanadium lattices in this thesis, respectively. And the evolution of the displacement cascade has only simulated in vanadium using object kinetic Monte Carlo (OKMC) method, which is suitable to simulate systems with large size and long time scale.By tracing every step of the atoms in simulation box, the displacement cascades in iron and vanadium have been studied with MD simulation. It has been found that the number of defects (including self-interstitial atoms and vacancies) increased sharply and reached the maximum at the primary tiny little time; then it declined significantly within 2ps. Most of vacancies and self-interstitial atoms recombined and at last only a few Frenkel Pairs were left. In these Frenkel Pairs, vacancy defects dominated by single vacancies located at the center of collision region, around by SIAs, which formed in the most stable configure -- dumbbells with <110> direction in iron and <111> direction in vanadium. The higher of PKA energy or temperature, the longer it will delay the occurrence of thermal peak stage and produce more atoms displaced away from their normal lattice sites at peak time. The cascade collision in iron was much more intense than that in vanadium.The input parameters for OKMC, consisting of the locations of surviving defects and migration energies, have been obtained by MD method and nudged elastic band (NEB), respectively. The migration energies of SIA and its clusters were much smaller than vacancy defects, which resulted to rather differently behaviors during the evolution. SIA and vacancy defects started to recombine as low as 4K in KMC. When temperature grew up to 289K, the second recombination happened. And above about 420K, if SIA defects still left in lattice will induce the third decline. Generally, SIA defects were annihilated completely, while only a few or none vacancies were left in a bunch of simulations. This research was prepared for further researches of the radiation damage in vanadium based alloys, or irradiation simulation with displacement per atom in metals, or the effects of helium bubbles introduced into fusion materials.