Determination of elastic moduli at high temperatures for uranium–vanadium alloy and pure plutonium by an ultrasonic method

Using a contact delay-line ultrasonic device, we measured the elastic properties particularly the shear modulus μ of pure plutonium and uranium–vanadium alloy from ambient temperature to 900 K. Several allotropes of these materials have been detected in the explored temperature range. For plutonium metal, measurements reveal a collapse of μ(T) of about 50% for the α → β phase change and a small increase of 0.2% for the β → γ phase change. For uranium–vanadium alloy, we observe a monotonic decrease of about 50% of μ(T) for the α → β phase change. In order to include the phase transition to describe the variation of μ(T), a model has been proposed and applied.