b'oxidizing and inert atmospheres. The oxidizing atmosphere was used to preferentially attack the grain bound-aries of the samples and thus force the release of the grain boundary retained fission gas without inducing any significant transport or release of intra-granular retained fission gas. This was performed at the Hot Fuel Examination Facility (HFEF) at INL. After the heat treatments, the gas was collected and analyzed using gamma spectroscopy and gas mass spectrom-etry. That analysis is still ongoing.Radial composition and burnup characterization were also attempted using atom probe tomography (APT). The shielded FIB at IMCL was used to remove APT tips and APT was performed using the LEAP system at the Center for Advanced Energy Studies (CAES). Performing APT on highly irradiated fuel is exceptionally challenging as porosity within the sample can cause the tip to fail catastrophically during mounting or measurement. A few tips were successfully measured from all three regions; however, additional investigation is required in order to corroborate present results and confirm identification of fission products. The presence of many fission products causes significant overlaps inFigure 4. APT count corrected spectrum: a) shows the full mass to charge the spectra collected, and the thermalspectrum (excluding hydrogen peaks). b) through d) show fission product and U/Pu tails in the fissile materials makespeaks. e) & f) show UO & UO 2peaks.signal deconvolution challenging.2019|AFC ACCOMPLISHMENTS 137'