[en] In addition to dissolution of the UO₂ matrix, the corrosion of spent nuclear fuel in groundwater appears to occur, at least in the short term, by the rapid dissolution of fission product phases formed during reactor irradiation, and by selective attack at zones or segregations in the fuel enriched in fission products. The Electron Probe Micro-Analysis (EPMA) technique offers the possibility of identifying and analyzing such phases and segregations in spent LWR fuel, although the small amounts expected to be present, and the background radiation, present a significant analytical challenge. This report describes preliminary work performed to examine the application of the EPMA technique to this problem. The fuel specimen examined had been power-bumped to a linear power rating somewhat higher than those generally experienced by commercial LWR fuel, so that fission product mobility had been enhanced. Steep concentration gradients for xenon and cesium within individual fuel grains, probably due to grain boundary sweeping during grain growth, were detected and measured. With changes in the analytical technique, it is possible that even strontium could be determined. (orig.)