Experiments have been performed recently at Sandia Laboratories to investigate and characterize potential fuel materials for fast burst reactors. A novel technique has been developed to determine the thermomechanical properties of fuel materials under actual use conditions. The Sandia Pulsed Reactor II is used to rapidly fission heat a thin rod of the sample material, supported at its center, thereby inducing longitudinal stress waves in the sample. The dilation history at the ends of the rod and the temperature of the rod are recorded. A measure of the internal friction is determined from the decay of the longitudinal oscillations induced in the sample. The materials examined include uranium, U—0.78 wt% Ti, U— 6 wt% Mo, and U—10 wt% Mo. The first two are alpha-phase materials in a wrought condition, while the second two are gamma-phase-stabilized materials in an “as cast” condition. The alpha-phase wrought materials had higher internal friction than the gamma-phase “as cast” materials, with uranium being the highest by approximately two orders of magnitude as compared to U— 10 wt% Mo, the lowest.