(401e) Microfluidic and Millifluidic Separations for Recovery of Plutonium from Residues

Operations within the plutonium facility at Los Alamos National Laboratory routinely generate residues that are too rich in plutonium to discard, but not pure enough to be used as feed for the electrorefining purification process. These residues are currently purified for electrorefining using either a nitric acid-based anion exchange process or a hydrochloric acid-based solvent extraction process. While historically successful, these processes were sized for higher throughputs rather than inherent criticality safety, and the flammable solvents and resins require risk management.

A multi-disciplinary team at Los Alamos is testing milli- and microfluidic contactors for use in the chemical separation of actinides. These highly efficient separations at short length-scales have the potential to purify plutonium residues with a smaller footprint than conventional aqueous processing. The slow flowrates required for millifluidic processing allows smaller volumes of solution to be used, which makes it easier to design a process that is inherently safe from a nuclear criticality accident. This in turn makes automation feasible. If a need for increased capacity returns, the process can be scaled up by adding parallel systems. By contacting the aqueous phase with a liquid anion exchanger (Aliquat 336) in an ionic liquid carrier, the flammable solvents and resins can be eliminated. Additionally, higher efficiency separations can result in a decreased volume of liquid transuranic waste requiring disposal.

Microfluidic contactors using co-current (slug flow) and counter-current (membrane separated) configurations were fabricated and tested. A higher throughput, commercially available milliliter-scale unit has been purchased for production scale testing. (LA-UR-16-23287)