(374e) A New Co Conversion Technology Based on Liquid/Liquid Extraction Column

The current objective of fabricating nonproliferating nuclear fuel by ?direct? coprecipitation of uranium, plutonium and minor actinides requires a new process to replace the (co)precipitation step. It was necessary to examine its adaptability to a plant flowsheet implementing devices capable of ensuring this function at suitable continuous flow rates. Coprecipitation of a uranium fraction together with plutonium results in an appreciable increase in the process flow rates for this step. The technological impact of the increased capacity on the work zone could require the development of a different concept for a continuous device capable of ensuring the proposed throughput, as the flow rate of the Vortex effect reactors currently used for plutonium precipitation at La Hague appears too limited.

A new type of device designed and patented by the CEA was tested in 2007. The patent is for organic confinement in a pulsed column (PC) or Couette column (CC). The precipitation reaction between the oxalate complexing agent and a surrogate nitrate?cerium(II) or neodymium(III) alone, or coprecipitated uranium(IV) and cerium(III)?occurs within an emulsion created in the device by these two phases flowing with a counter-current chemically inert organic phase (for example TPH) produced by the stirring action of the pulsator (PC) or the central rotor (CC). The precipitate is confined and thus does not form deposits on the vessel walls (which are also water-repellent); it flows downward by gravity and exits the column continuously into a settling tank.

The results obtained for precipitation of cerium or neodymium alone in a short column of small diameter have demonstrated that high throughputs are feasible without system malfunctions. The measured particle sizes of the precipitates range from 20 to 40 µm on average, and the measured device outflow indicates that the precipitation reaction is complete. These results suggest that this laboratory design can be extrapolated to an industrial column. Moreover, a recent test campaign demonstrated that a uranium-cerium coprecipitate easily forms when the two nitrates are mixed in a pulsed column of the same size operating under very similar process conditions. Qualitatively, the coprecipitate meets the process requirements.