We propose to use scanning transmission electron microscopy ((S)TEM) with Super-X EDS to study the evolution of microstructure and microchemistry of neutron irradiated ZIRLO® and AXIOM X2® alloys at different irradiation doses (1 cycle and 4 cycles). The major research objective of this study is to provide knowledge on neutron irradiation induced Nb redistribution in Zr-Nb alloys and its correlation with irradiation induced dislocation loops. The overall research program aims at precisely characterizing the size, density, microchemistry and crystallography of irradiation induced platelets (IIPs) and the density of dislocation loops of neutron irradiated samples, to better understand the in-reactor irradiation induced growth (IIG) and corrosion behavior of Zr-Nb alloys. The two main hypothesis tested here are that (i) reduced irradiation induced growth of Zr-Nb alloys is due to the precipitation of IIPs that prevents the nucleation of <c> loops by lattice compression, and (ii) the precipitation of Nb-rich IIPs, and the associated decrease in Nb solute concentration, is responsible for the low corrosion rates experienced by Zr-Nb alloys. Our recently published paper on proton irradiated Zr-Nb alloys has, to some extent, proved the second hypothesis. The next step is to examine the microstructure and microchemistry of neutron irradiated Zr-Nb alloys using (S)TEM/EDS. This study will primarily use Titan Themis 200 with Super-X Energy Dispersive Spectroscopy (EDS) at Irradiated Materials Characterization Laboratory (IMCL) to perform (S)TEM/EDS characterization. To effectively study the precipitates and dislocation loops in the metal and to avoid ZrH contamination from FIB milling, electropolished 3mm disc of neutron irradiated samples will be prepared from the metallic region of the fuel rod at IMCL. To characterize the precipitates in the oxidized region of neutron irradiated samples, shielded Plasma-FIB will be used to prepare TEM lamella in a much faster pace than using conventional gallium source FIB. The primary focus of (S)TEM/EDS is to investigate size, microchemistry, and crystallography of irradiation induced Nb-rich platelets in both metal and oxide neutron irradiated samples. The characterization of dislocation loops using the 3mm disc will be performed under TEM mode using specific g vectors. Since Titan Themis 200 is equipped with EELS, the thickness of each imaging area will be measured to compute the precipitate and loop density.