b'few or no FGBs. Ongoing work is to determine if recrystallization / restructuring has occurred in these FGB-free grains. Medium-sized FGBs (5-40 nm) are present in grain interiors and on grain boundaries, usually in conjunction with simi-larly sized FMPs.Figure 1, as an example, shows the 0.55~0.57 r/r0 (approximately 1800 m from the cladding) region. This region is in the central restructured region of the pellet, near the border with the mid-radial region. In the top row of Figure 1(a)-(c), the general microstructures are seen. In the as-irradiated samples, bubbles are seen that were presumably filled with fission gas prior to FIB prepara-tion. Grain boundary cracking is also apparent (red arrow). Several smaller (~half micron) grain Figure 2. Comparison of NA1 as- transparency. Examination usingboundary or triple point bubbles irradiated and post-LOCA fission gasS/TEM X-ray spectrum imagingare also visible, i.e., yellow arrow bubble sizes at similar radial positions.(XSI) using energy dispersivein the NA1 as-irradiated figure. In Vertical lines are the median the post-LOCA, similarities and spectroscopy (EDS) finds thedifferences are noted. The number elemental distributions withinof small high-aspect, lenticular these complex structures, and FMPsbubbles appear higher, and they ranging from ~1-2 nm to a severalseem less associated with the grain hundred nm and found distributedboundaries and more intragranular; through the structures, with smallgreen arrow. EDS mapping, Figure FMPs primarily intragranularly1(d)-(i), show the polydispersity and larger FMPs scattered bothof the FMPs (yellow/white) and intragranularly, on grain bound- the FGBs (red). Also of note, and aries, and on the surfaces of thein need of further study, in the large open cavities. Further, smallmedium sized lenticular bubbles FGBswhich are pure Xe to thepost-LOCA sample show depletion detectivity of EDS, 1 wt%showof FGBs for ~100-200 nm around the a wide range of locations and sizes.lenticular bubbles. The denuded Small (~1-5 nm) FGBs are present inzone is interesting and in need of the interiors of many grains, oftenexploration. Other examined radial in association with similarly sizeddistances (~0.53, ~0.77 r/ro) showed FMPs; although, other grains show 118 2023|AFC ACCOMPLISHMENTS'