PNNL

Abstract

We investigate the oxidation of uranium (U) species, the physical conditions leading to uranium monoxide (UO) formation, and the interplay between plume hydrodynamics and plasma chemistry in a laser-produced uranium plasma. The plasmas are produced by ablation of metallic U using nanosecond laser pulses. An ambient gas environment with varying oxygen partial pressures in 100 Torr inert Ar gas is used for controlling the plasma oxidation chemistry. Optical emission spectroscopic analysis of U atomic and monoxide species shows a reduction of the emission intensity and persistence with increasing oxygen partial pressure. Spectral modeling is used for identifying the physical conditions in the plasma that favor UO formation. The optimal temperature for UO formation is found to be in the temperature range of ~1500–5000 K. The spectrally-integrated and spectrally-filtered (monochromatic) imaging of U atomic and molecular species reveal the evolutionary paths of oxidation U species in the plasma. Our results also highlight that oxidation in U plasmas predominantly happens at the cooler plasma periphery, is delayed with respect to plasma formation, and the dissipation of molecular species strongly depends on oxygen partial pressure.