(288c) Uranium-Selective Membrane Adsorbers for Use in Nuclear Forensics Applications

Clandestine activities involving the manipulation of special nuclear material (SNM) with the intent of developing a weapon of mass destruction is likely to contaminate environmental waters. The capability to conduct isotopic analyses for waterborne SNM would be a powerful nuclear forensics tool. Despite widespread interest, there currently is no fieldable, separation technique capable of selectively concentrating uranium directly from groundwater for isotopic analysis.

This contribution describes our efforts to develop a high throughput analytical technique for waterborne isotopic analysis using reactive, functional membranes. In this work, we develop functional ultrafiltration membranes that (1) selectively concentrate uranium directly from neutral pH ground water and (2) serve as the substrate for isotopic analysis with alpha spectroscopy. Ultrafiltration alpha spectroscopy substrates were prepared by grafting ethylene glycol methacrylate phosphate from the surface of polyethersulfone membranes using (UV)-initiated polymerization. Membranes were characterized by Fourier-transform infrared spectroscopy before and after modification to support polymer grafting.

The effect of membrane pore size on peak resolution in the alpha spectrum was investigated for pure uranium containing solutions at pH 6. To mimic more realistic conditions, the selectivity of the membrane was tested using uranium-233 in simulated ground water. Membranes exhibited good resolution and fast preparation time. Membranes prepared from both distilled water and simulated ground water produced resolutions of 80-100 keV in the alpha spectrum. Furthermore, baseline resolution was observed for uranium-238 and uranium-233 using a membrane substrate loaded directly from neutral pH ground water. The permeability coefficient of 100 kDa UV-grafted ultrafiltration membranes was determined to be 566 ± 80 LMH/bar which means 3.6 L of contaminated ground water can be processed per hour at 414 kPa through a 45 mm ultrafiltration cell. Uranium recovery from DI and ground water were both 85-90%, supporting the selectivity of the membranes for uranium over common competitor ions. Since the membranes are not thermodynamically limited, recoveries less than 100% are indicative of a low Damköhler number and potential kinetic limitations in the system; consequently, kinetic studies were performed to support this hypothesis. Our porous, uranium-selective substrate design allows for the filtration of uranium-contaminated ground water through the uranium-selective membrane, leading to a high throughput separation and sample mounting process.