Measurements of the positron annihilation coincidence count rate at the peak of the angular correlation curve (CCR) in uranium were performed as a function of temperature between 550 and 1350 K. The α → β and β → γ phase transformations are reflected by discontinuities of the CCR. The low temperature slope of the curve, the change at the α → β transition at 941 K, and the initial slope in the β phase can be very well described by linear thermal expansion. The jump of the CCR at 1048 K is predomi... »