Evaluation of deformation fields associated with irradiation-induced growth and grain boundary interactions in zirconium

Abstract

Irradiation growth is one of the deformation mechanisms which results in significant dimensional instability in nuclear reactor components over an extended service period. Therefore, understanding irradiation growth is essential for the cost-effective and safe design of nuclear reactors. Irradiation growth results from the preferential diffusion of irradiation-induced point defects, which makes it a macroscopic stress-independent volume-conservative shape change process. Macroscale experiments reveal that irradiation growth exhibits a strong dependence on the grain size of a specimen, i.e., small-sized grains escalate the irradiation growth. However, owing to the limitations in macroscale experiments, the mechanisms associated with such behaviour are not fully understood. The current work aims to investigate the irradiation growth mechanism over macro to micro scales. In order to examine the contributions of grain boundary in irradiation growth, irradiation growth deformation is investigated along different types of grain boundaries using high-resolution electron backscatter diffraction. Next, the results are compared with crystal plasticity-based finite element models to identify the effect of deformation incompatibility induced by the grain boundaries. A simplified yet novel field variable-based technique has been used to mimic the irradiation growth deformation into the finite element model. It is observed that the experimentally measured strains are more significant near the grain boundaries and distributed over a larger area as compared to the finite element results. This difference suggests that the localized strain/stress concentration is not only due to the deformation incompatibility at grain boundaries. The deformation incompatibility also activates additional mechanisms (e.g., irradiation creep), which enhance the deformation processes in the presence of grain boundaries.