(376b) Development of Functional Membranes for Use in Nuclear Forensics Applications

Clandestine activities involving the separation or manipulation of special nuclear material (SNM) for the purpose of developing a weapon of mass destruction is likely to result in the contamination of 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 by using reactive, functional membranes as alpha spectroscopy substrates. Alpha spectroscopy is an analytical technique that allows for the discrimination of isotopes of uranium based on differences in characteristic energies for emitted alpha particles. In this work, alpha spectroscopy substrates were prepared by two methods: (1) physical deposition of a uranium-selective, water-soluble polymer film on ultrafiltration membranes and (2) grafting uranium-selective ligands from the surface of ultrafiltration membranes. Uranium was loaded onto the substrates by filtering uranium-contaminated water through the ultrafiltration membranes. The uranium-selective, water-soluble polymer was prepared by the copolymerization of 2-hydroxyethyl methacrylate and ethylene glycol methacrylate phosphate. The ligand-grafted membrane was prepared by the UV-polymerization of ethylene glycol methacrylate phosphate with N,N-methylene bisacrylimide. Membranes were characterized by Fourier-transform infrared spectroscopy before and after modification to support the deposition or grafting of the polymer on the membrane surface. The capacity for uranium, 1.9 mmol U/ g, was determined from equilibrium binding experiments.

The effect of membrane preparation method and 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 groundwater. Both uranium-coated membranes prepared from distilled water and groundwater showed resolutions of 40-60 keV in the alpha spectrum and detection efficiencies of 12% for uranium-233. The membranes showed both high resolution and fast preparation time. The permeability of the polymer-coated, ultrafiltration membranes (MWCO 100 kDa) was determined to be 3.74 LMH/kPa which means 2 L of contaminated groundwater can be processed per hour at 345 kPa (50 psi) in a 45 mm ultrafiltration cell. The results of this research are laying the foundation for the development of a novel rapid, field portable method for the separation and isotopic identification of waterborne SNM.