Aerodynamic and Dissolution Behavior of Fume Aerosols Produced During the Combustion of Laser-ignited Plutonium Droplets in Air

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Radioactive fume aerosols of plutonium oxide produced by condensation of vapors may be formed in conceivable accidents involving temperatures exceeding 2400°C, such as explosive fragmentation of plutonium metal or postulated breeder reactor accidents. These highly dispersed aerosols consist of ultrafine components (less than 0.1 μm in geometric diameter) and exhibit properties markedly different from the larger particles (larger than 0.1 μm) generally used for evaluation of inhalation toxicology. In this research, which was part of Sandia Laboratories' Plutonium Aerosol Generation Experiments (PAGE) program, studies have been conducted of the aerosols produced by high temperature burning in air of single 50–500μm-dia droplets of gallium-stabilized, delta-phase plutonium metal ignited with a laser. Mass balance and aerosol measurements demonstrated that essentially all the plutonium lost from the burning droplet (up to 40% of available plutonium) became aerosolized. These aerosols consisted primarily of weblike chains of ultrafine crystalline (cubical) particles (4–100 nm on side) and a few neatly spherical, discrete particles as large as 0.5 μm. These were respirable aerosols with measured activity median aerodynamic diameters of from 1 to 2 μm with geometric standard deviations about 1.5. In vitro dissolution studies demonstrated higher dissolution rates than normally exhibited by plutonium oxide; this apparent enhanced dissolution was related to the ready mobilization of small particulate components, as well as to the relatively large surface-to-volume ratios of the aerosol particles. Apparent dissolution half-times in the lung (which would be observed as translocation of plutonium from lung to blood and thence to bone and liver) were estimated to be about 200 days.

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