Simulating radiation damage accumulation in α-Fe: A spatially resolved stochastic cluster dynamics approach

Neutron irradiation of high purity α-Fe to 10-1 DPA is simulated using spatially resolved stochastic cluster dynamics (SRSCD). In doing so, a novel scheme is developed that addresses the following challenges to simulations of defect accumulation in bulk materials: how to introduce displacement cascades in a numerically efficient manner while maintaining the spatial resolution necessary for accurate defect evolution within cascades; how to account for interactions between defects already present in the material and cascades during the thermal spike phase; and how to choose appropriate cascade energies that reflect damage accumulation due to high-energy neutrons. The spatial resolution necessary for displacement cascade implantation is maintained via an accelerated adaptive meshing scheme. Direct cascade mixing with point defects present in the material is studied and shown to be necessary for defect saturation above 10-3 DPA. Defect population evolution is shown to only weakly depend on the cascade energy used in this study, allowing the use of a single cascade energy for simulating high energy neutron irradiation. Using this scheme, traps for mobile one-dimensional diffusing SIA loops are shown to strongly affect the final defect microstructure, and simulated defect accumulation results are compared to experimental results over the range of DPA studied here. The computational efficiency and accuracy of this technique make it a good candidate for inclusion in multi-scale models of radiation-induced material behavior changes.