(13d) Uranium-Selective Polymer Materials for Water Quality Monitoring and Isotopic Identification

The manipulation of special nuclear material (i.e. uranium or plutonium) for the express purpose of assembling a weapon of mass destruction will likely result in the contamination of the environment. The ability to monitor environmental waters for gross-activity and perform isotopic analysis would help determine if there is an elevated concentration of actinides present in the environment or an abnormal isotopic distribution; both of which may indicate illicit nuclear activities nearby. Currently, there is no fieldable technique capable of conducting these analyses directlyfrom environmental waters. In the past 4 years, I have been involved with 2 projects funded by the Defense Threat Reduction Agency seeking to fill these needs. The goal of these projects has been to develop fieldable techniques to analyze environmental waters for uranium by focusing on near-neutral pH separations that minimize consumables.

In the first project, we synthesized extractive scintillating resins to monitor the activity of radionuclides in groundwater in a continuous, online system. Extractive scintillating resin serves two purposes: (1) selectively concentrate the desired radionuclide and (2) serve as a radiation transducer by emitting light in the presence of a radioactive decay. Through this research, I gained experience in the following technical areas: (1) synthesis and functionalization of polymer resins; (2) characterization of ion-exchange resins; (3) theory and practice of scintillating counting for both liquid and solid-phase scintillators and (4) proper techniques and safety for handling radioactive materials. Specifically, we studied how the physical properties of the resin (pore structure, ligand type, resin diameter, degree of crosslinking and composition) affect the capacity, selectivity and detection efficiency of the material.

In the second project, we developed a rapid sample preparation method for alpha spectroscopy using ultrafiltration membranes. Alpha spectroscopy is an analytical technique that can distinguish isotopes of alpha-emitting radionuclides by the characteristic energy of the alpha particle. Through this research, I gained experience in the following technical areas: (1) Bulk polymerization and purification; (2) Membrane modification by UV-polymerization and other chemistries; (3) Characterization of membranes for molecular weight cut-off, permeability, surface morphology and (4) theory and practice of alpha spectroscopy. Here, we studied how the membrane properties (pore structure, ligand type, method of grafting, degree of grafting, composition and membrane material) affect the capacity, selectivity, detection efficiency and peak resolution in the alpha spectrum.

Proposed future research will apply my expertise in uranium selective-polymeric materials to the field of nuclear fuel reprocessing. Nuclear fuel reprocessing uses the liquid-liquid extraction process called PUREX to separation uranium and plutonium from other fission products. There are many opportunities for membrane technologies downstream from the initial extraction stage. I plan to focus my research around the implementation of polymer inclusion membranes, supported liquid membranes and membrane contactors in the PUREX process. Specially designed membrane technologies can provide low-energy separations that are capable of selectively removing trace-levels of actinides or fission products. Challenges of this research will be choosing ligands with moderate binding affinities to facilitate the "catch and release" of radioisotopes on either side of the membarne as well as desinging membranes with sufficient radiolytic stability for a given waste stream. The results of this research will have implications in the field of membrane science, nuclear fuel reprocessing as well as nuclear waste processing and storage.

Teaching Interests:  Introduction to Chemical Engineering (mass and energy balances), transport phenomena, membrane separations, nuclear engineering

Teaching experience: Co-instructor for Introduction to Chemical Engineering (2 semesters), Instructor for Membrane Separations for Clean Water and Energy (3 semesters), Undergraduate research mentor (4 years, 3 students)