Radioactive wastes from a range of sources are of great concern for their potential to negatively affect the environment and human health. There is a substantial need to develop new methods and techniques for management and disposal that are economically feasible and environmentally suitable. Such methods require better characterization and chemical understanding of these wastes, including advancements pertaining to the interaction between radioactive elements and non-radioactive constituents within the complex waste matrix. This thesis focuses on the fundamental chemistry of three types of waste forms: (1) solid drill cuttings from hydraulic fracturing activities; (2) Weapons grade plutonium; and (3) solid aluminum hydroxide phases associated with Hanford Tank wastes.
The first study characterizes naturally occurring radioactive materials (NORM) in solid “drill cuttings” from hydraulic fracturing activities for natural gas extraction. NORM (uranium (U), thorium (Th), radium (Ra), lead (Pb), and polonium (Po) isotopes) associated with three samples from the Marcellus Shale formation were analyzed using radiometric techniques and found to have elevated radioactivity levels and isotopic disequilibria. NORM mobility within a landfill environment was also evaluated and these studies suggested some leaching of NORM from the solid waste form.
Nuclear weapons technologies have also produced significant amounts of wastes, including some forms can be processed into useable, mixed-oxide (MOX) nuclear fuels. MOX solids require a complete separation of the gallium (Ga) originally present in the original weapons materials from Pu and other actinides to ensure the conversion was effective. A radiochemical method for the separation of Ga, Pu, U, Th, and americium (Am) was developed using chromatographic resins and radiochemical tracers. The innovation within this study included the novel use of 68Ga, an isotope developed for nuclear medicine applications. This research can be translated to nuclear forensics applications because it provides isotope ratios that can be used to determine the method or location of production of the original nuclear weapons material.
The third research area focuses on the fundamental chemistry of the aluminum bearing wastes associated with the Hanford Site in Washington State. These mixed radioactive wastes have large quantities of aluminum (Al) that interferes with effective management and treatment strategies. There is a critical need to improve our fundamental understanding of Al chemistry in these systems to develop methods to improve our ability to work with the current waste streams. For example, Al is known to form oxyhydroxy polyaluminum species, or soluble molecular nanoclusters that exhibit different physical and chemical properties than isolated monomeric or dimeric forms of Al and contribute to much of the problematic chemistry in this system. There are significant challenges for the identification and characterization of these clusters in simple aqueous solutions and in more-complex solutions such as nuclear wastes. This body of work focuses on the isolation and identification of some of these clusters, including three Al30 clusters, and their interaction with other contaminants that are likely to be present in nuclear waste streams. Other clusters, including the elusive aluminum octamer, have also been synthesized and isolated, allowing for further characterization and understanding of these model clusters.