Modelling of High-energy Radiation Damage in Materials relevant to Nuclear and Fusion Energy.

Abstract

The objective through my PhD has been to investigate radiation damage effects in materials related to fusion and to safe encapsulation of nuclear waste, using Molecular Dynamics (MD) methods. Particularly, using MD, we acquire essential information about the multi-scale phenomena that take place during irradiation of materials, and gain access at length and time-scales not possible to access experimentally. Computer simulations provide information at the microscopic level, acting as a bridge to the experimental observations and giving insights into processes that take place at small time and length-scales. The increasing computer capabilities in combination with recently developed scalable codes, and the availability of realistic potentials set the stage to perform large scale simulations, approaching phenomena that take place at the atomistic and mesoscopic scale (fractions of m for the first time) in a more realistic way. High-energy radiation damage effects have not been studied previously, yet it is important to simulate and reveal information about the properties of the materials under extreme irradiation conditions. Large scale MD simulations provide a detailed description of microstructural changes. Understanding of the primary stage of damage and short term annealing (scale of tens of picoseconds) will lead to better understanding of the materials properties, best possible long-term use of the materials and, importantly, new routes of optimization of their use. Systems of interest in my research are candidate fusion reactor structural materials (iron and tungsten) and materials related to the radioactive waste management (zirconia). High-energy events require large simulation box length in order for the damage to be contained in the system. This was a limitation for previous simulations, which was recently shifted with my radiation damage MD simulations. For the first time high-energy radiation damage effects were simulated, approaching new energy and length scales, giving a more realistic view of processes related to fusion and to high-energy ion irradiation of material