Decontamination of Carbonate Containing Process Streams in Nuclear Fuel Reprocessing by Ion Exchange Chromatography

A new procedure has been developed to decontaminate carbonate wash streams relevant to the Purex process from alpha-emitting actinides (²³⁸U, ²³⁷Np, ²⁴⁰Pu) and the fission products (⁹⁵Zr, ¹⁴⁴Ce, ¹⁰⁶Ru). The actinides, forming with Na₂CO₃ carbonato complexes, for example, [UO₂(CO₃)₃]^4-, [NpO₂(CO₃)₃]^4-, and unstable Pu(IV) complexes, are retained on the weakly basic anion exchanger resin Bio Rex 5. Plutonium(IV) forms complexes or precipitates nearly completely, when standing for some time or heating up to 70°C. The precipitate can be separated from the carbonate solution by a 2-µm filter mounted in front of the column. Neptunium and the fission products coprecipitate partially at the same time and therefore are also retained. Uranium and the species (neptunium and fission products) remaining in the filtrate are also removed by the Bio Rex 5 column, whereby the effluent of the column is decontaminated to >99%. The recovery of the actinides and fission products from the resin and the filter is performed with three column volumes of 4MHNO₃ >99%.