b'(EBSD) patterns as well as electron probe microanalysis (EPMA). The goal of this characterization will be to identify the fuel microstructure and porosity of each region. It is important to understand the statistics of the porosity, such as pore volume fraction and number density, so that the fission gas analysis can be mean-ingful. Understanding both enables researchers to analyze the pressures experienced by the fuel microstruc-ture during an accident scenario.Accomplishments: In order to provide a thorough description of the as-irradiated microstructure, a combination of experimental techniques has been used to gather data from a polished cross section of LWR UO 2fuel irradi-ated at 72 GWd/tHM average burnup. Detailed image analysis from SEM images acquired with the Backscat-tered Electron Detector has been performed along the pellet radius. At the same time EBSD patterns have been collected radially and correlated to the local gas inventory.The plasma focused ion beam (PFIB) at the Irradiated Materials Characterization Laboratory (IMCL) at Idaho National Laboratory (INL) was successfully used to mill out and remove large (~300 m) cubes for fission gas examination. The team also successfully designed and fabricated air tight capsules capable of retaining the fuel samples during heat treat-Figure 3. Kr-85 measured from oxidation study: a) shows the comparison betweenment. The cubes were placed within capsules heat treated with O 2 -He mixture and pure He. b) shows the relativethe capsules and subjected todifference in the release quantity. The lines indicate the relative separation between300 C heat treatments in both the HBS, DZ, and center regions.136 2019|AFC ACCOMPLISHMENTS'