Particle-Size Distribution in Capacitor Discharge Vaporization of Uranium Dioxide

A homogeneous nucleation-condensation growth model was developed for calculating particle-size distributions measured in capacitor discharge vaporization (CDV) experiments conducted at the Oak Ridge National Laboratory. Uranium dioxide pellets were partially vaporized in an argon environment by rapid energy deposition through capacitor discharge. This was followed by rapid expansion and subsequent condensation of the UO₂ vapor. Measured primary particle-size distributions of the resulting aerosols were lognormal, with a geometric mean particle diameter of (0.014 ± 0.002) µm and a geometric standard deviation of 1.7 ± 0.1. It was postulated that the expanding UO₂ vapor compressed the surrounding argon as in a spherical shock tube and that the aerosol was generated by homogeneous nucleation and condensation growth in the resulting rarefaction wave. The calculated motion of the U0²-argon interface is in approximate agreement with the movies of the expansion process. The calculated particle-size distributions are in agreement with the measured distributions except at the large particle end. This agreement indicates that the small primary particles from the CDV tests resulted from homogeneous nucleation and condensation growth, as assumed in the analytical model.