ReviewUse of a pulsed column contactor as a continuous oxalate precipitation reactor

Add time:09/09/2019    Source:sciencedirect.com

The current objective of coprecipitating uranium, and minor actinides in order to fabricate a new nuclear fuel by direct (co)precipitation for further transmutation, requires to develop specific technology in order to meet the following requirements: nuclear maintenance, criticity, and potentially high flowrates due to global coprecipitation. A new type of device designed and patented by the CEA was then tested in 2007 under inactive conditions and with uranium. The patent is for organic confinement in a pulsed column (PC). Actually, pulsed columns have been working for a long time in a nuclear environment, as they allow high capacity, sub-critical design (annular geometry) and easy high activity maintenance. The precipitation reaction between the oxalate complexing agent and a surrogate nitrate – cerium(III) 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 tetrapropylene hydrogen—TPH) produced by the stirring action of the column pulsator. 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 size of the precipitates ranges 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 to filter, calcine and fabricate the new nuclear fuel in the downstream steps.

► A new type of continuous precipitating device was patented by CEA and tested with reaction between a surrogate nitrate cerium(III) or neodymium(III) and oxalate complexing agent. ► Precipitate is confined in aqueous phase emulsion in tetrapropylene hydrogen and does not form deposit on the vessel walls. ► Measure size of the precipitate ranges from 20 to 40 μm, it meets the process requirements to filter, and the precipitation reaction is complete. ► The laboratory design can be extrapolated to an industrial uranium(IV) and minor actinide(III) coprecipitating column.

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