In order to improve the homogeneity of the distributed U3Si fuel particles in the Al matrix of a high density research reactor fuel, the effect of the U3Si particle shape and size on the homogeneity of research reactor fuels has been investigated. The homogeneity of the distributed U3Si fuel particles in the Al matrix was evaluated by the apparent density measurement method. The homogeneity of a mixture consisting of comminuted irregular shaped U3Si particles and Al powders is superior to that of a mixture consisting of atomized U3Si particles and Al powders. From the measurement of the repose angle of the U3Si particles, it was noted that the cohesive strength of comminuted U3Si particles is higher than that of atomized U3Si particles, The homogeneity of a mixture consisting of finely atomized U3Si particles and Al powders is higher than that of a mixture consisting of coarsely atomized U3Si particles and Al powders, This result indicates that the cohesive strength of fine U3Si particles is higher than that of coarse U3Si particles. The homogeneity of U3Si/Al nuclear reactor fuel is improved by the formation of the an adsorbed layers between the U3Si and the Al powders. (C) 2001 Published by Elsevier Science B.V.