We propose to investigate the porosity development and evolution in zirconium-niobium alloys, samples of irradiated and non-irradiated Zr-xNb (x = 0.2, 0.4, 0.5, 1.0) and Zircaloy-4 irradiated under 2-MeV rastering proton beam to 1.0 dpa at 350 °C at the University of Wisconsin Ion Beam Laboratory. These samples were then corroded in water at 320 °C for up to 120 days total exposure. Samples were archived at varying total exposures, resulting in a range of catalogued pre-transition oxide thicknesses for each irradiated alloy. As part of the proposed RTE, Positron Annihilation Lifetime Spectroscopy (PALS) and Doppler Broadening Spectroscopy (DBS) will be performed on these prepared samples at the Positron Intense Beam Facility at North Carolina State University. These results will be used to characterize and compare the pore density between the irradiated and non-irradiated samples at different depths within the thin oxide layer. It is noted that this would be the first time that PAS is used on pre-irradiated, corroded, specimen. Preliminary study performed by PI’s group at the NCSU facility confirmed that the sensitivity to the thin film oxide layer is too low using a positron point source because most of the annihilation events occur within the bulk material, resulting in a low signal-to-noise ratio. By using a positron beam condition, long-lifetime positronium can be detected with better resolution and sensitivity to investigate porosity in thin-film zirconium oxides. 12 samples will be analyzed, 4 pre-irradiated ZrNb samples corroded up to 120 days, 4 pre-irradiated Zircaloy-4 samples corroded up to 120 days and 4 unirradiated ZrNb and Zircaloy-4 samples corroded up to 120 days to serve as benchmark. The samples are already available and, after discussion with the NCSU PAS group, 4 weeks of beamtime are required to accommodate these 12 samples.