The dependence of damage accumulation on irradiation dose rate in zirconium alloys: Rate theory, atomistic simulation and experimental validation

We present an approach to determine the sensitivity of irradiation damage accumulation to the irradiation dose rate in polycrystalline systems, when the internal and boundary sink strengths are the only microstructural components affecting defect accumulation. A rate theory of defect removal is introduced, and suggests that the impact of the irradiation rate on damage accumulation depends on the ratio of internal sink strength to the grain boundary sink strength. The validity of the model is tested with two different methodologies: i) proton irradiation of coarse grain commercial alloy, Zircaloy-4 and ii) atomistic simulation of electron irradiation of nano-size pure zirconium. In case (i), the removal of defects at the grain boundary is negligible, and the sensitivity to irradiation rate is minimal. In case (ii), defect annihilation at the boundary dominates. In that scenario, if the grain boundary density increases by a factor n, the irradiation rate should increase by a factor n2 times in order to achieve equivalent steady state damage accumulation.