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

Abstract

Radioactive fume aerosols of PuO2 produced by condensation of vapors may be formed in conceivable accidents involving temperatures exceeding 2400.degree. C, such as explosive fragmentation of Pu metal or postulated breeder reactor accidents. These highly dispersed aerosols consist of ultrafine components (less than 0.1 .mu.m in geometric diameter) and exhibit properties markedly different from the larger particles (larger than 0.1 .mu.m) generally used for evaluation of inhalation toxicology. In this research, which was part of Sandia Laboratories'' Plutonium Aerosol Generation Experiments (PAGE) program [Albuquerque, New Mexico, USA], studies were conducted of the aerosols produced by high temperature burning in air of single 50-500 .mu. m-diameter droplets of Ga-stabilized, .delta.-phase Pu metal ignited with a laser. Mass balance and aerosol measurements demonstrated that essentially all the Pu lost from the burning droplet (up to 40% of available Pu) became aerosolized. These aerosols consisted primarily of web-like chains of ultrafine crystalline (cubical) particles (4-100 nm on side) and a few nearly spherical, discrete particles as large as 0.5 .mu.m. These were respirable aerosols with measured activity median aerodynamic diameters of from 1-2 .mu.m with geometric SD about 1.5. In vitro dissolution studies demonstrated higher dissolution rates than normally exhibited by PuO2; this apparent enhanced dissolution was related to the ready mobilization of small particulate components, and 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 Pu from lung to blood and then to bone and liver) were estimated to be about 200 days.