Molecular Dynamics Simulation of Irradiation Damage in α-Zirconium

Abstract

Zirconium alloys, due to their good corrosion resistance and low neutron absorption cross section, are widely used in heavy and light water nuclear reactors. Irradiation induced defects and deformation lead to mechanical property degradation and potentially lead to accidents. In this study, molecular dynamics method, as a powerful atomic-level simulation tool, is applied to investigate and characterize the formation and evolution of point defects in irradiated alpha-zirconium by using a recent updated many-body interatomic potential. The effects of strain field on point defects, the formation of dislocation loops and the effects of niobium in zirconium-niobium system have been also explored. This dissertation has focused on understanding the atomic-level mechanism of irradiation damages and defect formation in zirconium. After a brief introduction in Chapter 1, Chapter 2 is the literature review including topics of displacement cascade, irradiation induced deformation, importance of zirconium in nuclear reactors and possible simulation methods. Chapter 3 reports a comparison of previous potential and current potential in a displacement cascade simulation in alpha zirconium. In Chapter 4, the shape of irradiation cascades in alpha zirconium has been studied, and the threshold displacement energy in zirconium has been calculated. Chapter 5 studies the strain effects (up to 1%) on defects in zirconium. Chapter 6 extends the work in Chapter 5 with tensile strain up to 5%; a void has been found in the displacement cascades in alpha zirconium under the applied strain field. In Chapter 7, simulations have been conducted to study the effects of irradiation cascades in alpha zirconium within one vacancy type < a > loop. In Chapter 8, other than most work in literature focused on alpha phase in zirconium alloy (hexagonal close-packed crystal structure), we have considered irradiation effects on beta phase (body centered cubic structure) using MD calculations. The impact of niobium in zirconium-niobium system is also studied. Chapter 9 contains a summary of present thesis and possible future work. Appendixes in the end contain the basic description of parallel programming, various methods of defect analysis, some related input files and programs.