A nanoscale characterization study was carried out on SRA ZIRLO™ at various cycles, aiming to highlight the effect of irradiation-induced alloying element (Sn, Nb, Fe) redistribution on the in-reactor corrosion kinetics. Using a combination of scanning transmission electron microscopy (STEM), energy dispersive X-ray spectroscopy (EDS), and atom probe tomography (APT) in both oxide and metal, the results confirmed the existence of i) Nb-rich native precipitates and irradiation-induced platelets (IIPs)/nanoclusters in both metal and oxide, and ii) solute segregation to the metal and oxide grain boundaries. One of the most important findings is that the Nb/Zr ratio in the metal solid solution at high burnup is only about 0.2 at.%. All three alloying elements (Sn, Fe, Nb) have segregated to oxide grain boundaries at high burnup. The effects of these microstructural and microchemistry changes in SRA ZIRLO™ on its in-reactor corrosion mechanism are discussed.