Conventional approaches for the isotopic screening of aqueous Pu at trace-levels requires time-consuming sample preparation methods performed in offsite laboratories. An onsite analytical method that can concentrate Pu and subsequently provide isotopic ratios would be an invaluable tool for the real-time surveying of Pu in groundwater samples, as well as for nonproliferation efforts where the rapid screening of special nuclear materials is a critical need.

This presentation will cover the development of thin-film composite membranes for the concentration and isotopic screening of Pu from water at concentrations from 10^-10 to 10^-12 M Pu. The first defining feature of the membranes is a thin film (30-250 nm) active layer composed of chelation or ion-exchange groups that capture Pu during filtration. The active layers were applied to ultrafiltration support membranes by two methodologies: casting a Pu-selective ligands physically immobilized within a polymer-matrix, and casting polymers with Pu-selective side chains. The second defining feature of the membranes is their ability to serve as samples for the direct isotopic analysis by alpha spectroscopy.

Ligand screening studies were carried out for films developed by the first method. While films composed of bis(2-ethylhexyl) phosphoric acid (HDEHP) were able to extract Pu at high recoveries of 35.8 ± 1.8 % and 10.6 ± 0.6 % from low (2.3) and circumneutral (6.3) pH conditions, and exhibited alpha peak FWHM values ranging from 20 to 35 keV. A surface excess of non-immobilized HDEHP lead to the leaching of the ligand from the film after long-term contact with water. The second method was developed to overcome this drawback. Castable Pu-selective polymers were developed using monomers with phosphate terminal groups and tested for their ability to extract Pu from solutions at pH 4.2 and 6.8. Copolymers of 4-methylstyrene (MS) and ethylene glycol methacrylate phosphate (EGMP) recovered up to 93 ± 8 % and 94 ± 4 %, respectively, for the low and circumneutral pH conditions. Poly(EGMP-co-MS) polymers prepared with 5% (w/w) EGMP were suitable for spin coating on membrane supports. Detailed findings will be presented on Pu recoveries and alpha peak resolutions using ultrafiltration membranes coated with poly(EGMP-co-MS) active layers.

James Foster

Appearances