The recent emphasis on profileration-resistant fuels for research and test reactors has resulted in additional investigations of well-established fuels, such as U3O8-Al dispersions, to determine their behavior at the higher fuel densities required for the lower uranium enrichment. Microstructural investigation of these irradiated fuels with modern techniques has provided insight into the fission gas behavior and its relationship to the U3O8-Al interaction during irradiation. These observations explain the observed limitations on fuel loading and safe levels of fission density achievable with these fuels.