: The fate and transport of radionuclides at a nuclear waste repository or environmentally-contaminated site is the major component of a risk assessment model. Long-lived radionuclides, such as 237Np (τ½ = 2.1 million years), are of particular concern due to their radiotoxicity and relatively high mobility in oxidized, carbonated water. The mobility of such radionuclides may be inhibited due to incorporation into mineral phases and/or sorption onto mineral surfaces. Of particular interest is the role of mineral surfaces on the sorption and reduction of actinyl complexes. Mineral surfaces appear to catalyze the sorption and reduction of actinyl complexes; however, the particular mechanism is not yet understood. Dr. Shuller-Nickles (Clemson University) uses quantum-mechanical calculations to characterize changes in electron density associated with sorption and reduction in these systems. For example, quantum-mechanical calculations have shown that the passing of electron density through the weakly semiconducting surface of UO2 is the reason for enhanced corrosion of UO2 in the presence of O2 and H2O with respect to the corrosion of ThO2 (an insulator). Further evaluation of the sorption and reduction of actinyl complexes on mineral surfaces, such as Fe-oxide and silica, are necessary to enhance our understanding of results from batch sorption experiments. Integration of experimental and computational methods will allow scientists to fully evaluate complex systems at an atomistic to microscopic level.
The REU student involved in this project will explore the role of mineral surfaces on the sorption of actinide complexes. The student will compare sorption of uranyl, neptunyl, and plutonyl on different mineral surfaces to help identify the role of surface elemental and electronic structure on sorption phenomena. Their research will be computational in nature; thus, the student will have hands-on experience learning computer languages, such as Linux and bash, and a range of atomistic simulation software, such as VASP and Gaussian09. The student will be challenged to visualize mineral surfaces at an atomic level in order to construct a conceptual model of the sorption phenomena under investigation. In addition, the student will interface with experimentalists to gain a more comprehensive understanding of the nature of mineral surfaces and contaminant transport.