The interaction between atomized U3Si2 and aluminum in dispersion fuel samples has been characterized and compared with that of comminuted U3Si2. Fuel samples with atomized powder showed a smaller volume increase compared to those with the comminuted powder, irrespective of heat treatment, and volume fraction of U3Si2 powder. The possible reasons for this seem to be as follows: (1) the smaller specific surface area of the atomized spherical powder compared to the irregular comminuted powder translating in a smaller U3Si2-Al interface area for the former affecting what appears to be a diffusion-controlled interaction process, (2) the atomized fuel samples also contain lower fraction of as-fabricated porosity than the comminuted fuel samples, which may enhance the restraint force in the swelling fuel meat, (3) the comminuted powder particles have distinctive aluminum penetration paths in the form of deformation zones that originated from the comminution process. There appear to be two pronounced penetration paths of aluminum into atomized U3Si2 powder; (1) through the phase interface, leaving a central unreacted island, (2) along grain boundaries, leaving several unreacted islands. (C) 1999 Elsevier Science B.V. All rights reserved.