Proposal for ultrasonic technique for evaluation elastic constants in UO₂ pellets

ABSTRACT

Uranium dioxide pellets (UO₂) used as fuel in nuclear power reactors are subjected to high thermal gradients and may undergo swelling during reactor operation. The swelling of UO₂ pellets, resulting from the fission products, causes cracking of the material and it is thus critical to study their behaviour. This study evaluated the application of the ultrasonic method in obtaining the elastic constants of UO₂ pellets. Due to the difficulties in handling nuclear material, we used tablets of alumina (Al₂O₃) for a comparative study. For this, two sets of 10 Al₂O₃pellets with densities of 92% and 96% were fabricated. Ultrasonic transmission technique was used for obtaining measurements of the travel time of longitudinal and transverse ultrasonic waves. Equations relating material density and velocity of the ultrasonic wave to the elasticity, shear and Poisson’s modules allowed the determination of these elastic constants, whose values showed excellent agreement with those available in the literature for Al₂O₃.

Keywords
Ultrasound; Ultrasonic Wave; Elastic Constants; Alumina