Characterization and Modeling of Effective Density of Uranium Particles

The effective density of uranyl aerosol produced from UF6 and environmental moisture is one of the most important properties affecting the fate and transport of the aerosol particles. Literature data for uranyl aerosols have been severely limited. We applied a fractal-geometry model and recent advances in our understanding of the chemical pathways to help estimate and explain the density of uranyl aerosol particles that were produced during the UF6 hydrolysis reaction. Our modeling analysis provides quantitative evidence that particle density impacts the performance of aggregation models. The modeling results were supported by experimental data showing particles of the same mobility diameter could have a lower density if the aerosol structure becomes fractal. The model also indicates that where the measured density of UO2F2was approximately 300% lower than the documented bulk density, the volumetric growth rate of particles using a density of 2 g cm-3 was more than 700% faster as when the bulk density (~ 6 g cm-3) of anhydrous UO2F2 was used. The results imply that removal of uranyl aerosol particles from the air by settling mechanism alone would be much faster than previously estimated when a large aerosol density value was used as the model input. The measured uranyl aerosol density was found to be in between 2 and 4 g cm-3. This range is more than 50% lower than the density value commonly used by previous modelling applications. Finally, using a higher aerosol density is expected to significantly impact modeling of atmospheric transport and transformation and aerosol dynamics simulation.