Two prethinned spinel specimens containing either Y 0 . 1 5 Zr 0 . 8 5 O 2 or Ce 0 . 5 Zr 0 . 5 O 2 particles were implanted with 200-400 keV Xe ions at 873 K using the IVEM-Tandem Facility at Argonne National Laboratory. In situ transmission electron microscopy (TEM) was conducted during the implantation in order to follow the evolution of the microstructure. At an ion fluence between 2.4x10 2 0 to 3x10 2 0 m - 2 (up to 50 dpa and 4.7 at %), large Xe bubbles of 50-100 nm developed at the boundaries of the small oxide particles, while a high density of dislocation loops (up to 8 nm in diameter) and much smaller bubbles (up to ~4 nm in diameter) formed in the spinel matrix. No large bubbles were observed at the boundaries between the spinel grains. These results suggest that the boundaries between spinel and oxide particles are preferred sites for fission gas accumulation.