The characterization of uranium mill tailings using alpha-sensitive nuclear emulsions

Alpha-sensitive nuclear-emulsion techniques have been used for the first time to supplement the traditional bulk chemical and radiometric measurements of uranium, radium, radon, and other radionuclide concentrations in uranium-mill-tailings samples. The work was undertaken in an effort to characterize the way these radionuclides are distributed, i.e., their modes of occurrence, mineralogy, and relative mobility. This preliminary investigation involved approximately 40 samples of drill core from the four tailings piles at the Monticello Mill, Monticello, Utah. The microautoradiographic technique that was used permits the direct observation of the alpha activity of uranium, Th-230, Ra-226, Rn-222, and some of the other alpha-emitting daughter products, as well as the association of these radionuclides with mineral grains and particles in the samples. These nuclear-emulsion studies suggest that there are four principal modes of occurrence involving U-238, U-234, and Th-230; and four principal modes of occurrence of Ra-226 and its immediate daughters Rn-222, Po-218, and Po-214. The qualitative, descriptive information on the localization of these radionuclides suggests that subsequent nuclear-emulsion studies combined with detailed mineralogical studies would contribute in several important ways to the uranium mill-tailings remedial action program. These contributions might include: Specific remedial actions based on the modes of occurrence of Ra-226 and Th-230; Assessment of both short-term and long-term effectiveness of certain remedial actions; Procedures to minimize further movement of Ra-226 and Rn-222 within tailings piles