Implementation and Application of a Coupling Method between Molecular Dynamics and Kinetic Monte Carlo for the Evolution of Helium Bubbles in Nuclear Structural Steel

The research and development of structural materials for fourth-generation advanced reactors, such as accelerator-driven subcritical reactors and ultrahigh-temperature gas-cooled reactors, urgently requires the use of numerical simulation methods to shorten the research and development cycle and enhance the efficiency of research and development. Currently, various existing numerical simulation methods are only applicable to specific time and space scales, while the high-temperature irradiation effect of nuclear structural materials for advanced reactors involves multiple time and space scales from the irradiated microstructure evolution to the macroscopic mechanical properties. It is of great significance to develop coupling methods and codes between simulation methods at various scales, and to construct a multi-scale simulation and computation platform for the rapid research and development and service performance prediction of structural materials for advanced reactors. Based on the mutual conversion between atomic configuration and defect configuration, this paper proposes and implements a simulation method that temporally couples the microscale simulation method (molecular dynamics) with the mesoscale simulation method dynamics (Monte Carlo). By this method, the irradiation cascade process can be simulated by molecular dynamics, while the further evolution of defects is simulated by kinetic Monte Carlo, thus simulating the microstructural evolution of nuclear structural materials under the accumulation of irradiation dose. The reliability of this coupling method is demonstrated by using it to simulate the evolution of helium bubbles in the nuclear structural steel matrix material α-Fe under neutron irradiation and comparing it with experimental data.