Solubility of airborne uranium compounds at the Fernald Environmental Management Project

The in vitro solubility of airborne uranium dusts collected at a former uranium processing facility now undergoing safe shutdown, decontamination, and dismantling was evaluated by immersing air filters from high volume samplers in simulated lung fluid and measuring the 238U in sequential dissolution fractions using specific radiochemical analysis for uranium. X rays and photons from the decay of uranium and thorium remaining on the filter after each dissolution period were also directly measured using a planar germanium detector as a means for rapidly evaluating the solubility of the uranium-bearing dusts. Results of these analyses demonstrate that two distinct types of uranium-bearing dusts were collected on the filters depending upon the location of the air samplers. The first material exhibited a dissolution half-time much less than 1 d and was most likely UO3. The dissolution rate of the second material, which was most likely U3O8, exhibited two components. Approximately one-third of this material dissolved with a half time much less than 1 d. The remaining two-thirds of the material dissolved with half times between 230 +/- 16 d and 1,350 +/- 202 d. The dissolution rates for uranium determined by radiochemical analysis and by gamma spectrometry were similar. However, gamma spectrometry analysis suggested a difference between the half times of 238U and its initial decay product 234Th, which may have important implications for in vivo monitoring of uranium.