Identifying the Roles of Irradiation and Stress in Dislocation-Mediated Grain Subdivision

High burnup structure (HBS) formation in nuclear fuels results from irradiation-driven grain subdivision coupled with stress-assisted dislocation motion. Because irradiation damage and mechanical deformation occur simultaneously during reactor operation, their individual contributions to dislocation evolution and grain boundary development cannot be separated from post-irradiation microstructures. This project isolates these effects by controlling the sequence of irradiation and deformation and examining how that sequence governs microstructural evolution relevant to HBS. The experimental approach combines self-ion irradiation and micro-mechanical compression applied independently and in controlled sequence. Four conditions will be examined: irradiation only, compression only, irradiation followed by compression, and compression followed by irradiation. Ion irradiation introduces controlled displacement damage without transmutation, while compression imposes plastic strain representative of swelling-induced mechanical constraint. Aluminum is used as a surrogate material to enable direct examination of dislocation-mediated grain subdivision without complications from fuel chemistry or fission products. Microstructural characterization will be performed using transmission electron microscopy and precession electron diffraction to quantify dislocation structures, subgrain size, and grain boundary misorientation distributions. Comparisons across damage sequences will determine how irradiation-produced dislocation networks influence subsequent deformation-driven subgrain evolution. The results will improve interpretation of HBS-related microstructures and provide data relevant to mesoscale models of irradiation-induced microstructural evolution. The expected period of performance is twelve months.