Coprecipitation of actinide peroxide salts in the U-Th and U-Pu systems and their thermal decomposition

• Published in: Dalton transactions : an international journal of inorganic chemistry Vol. 51; no. 34; pp. 12928 - 12942
• Main Authors: Hibert, Nicolas, Arab-Chapelet, Bénédicte, Rivenet, Murielle, Venault, Laurent, Tamain, Christelle, Tougait, Olivier
• Format: Journal Article
• Language: English
• Published: Cambridge Royal Society of Chemistry 30.08.2022
• Subjects: Actinides; Chemical precipitation; Chemical Sciences; Coprecipitation; Decomposition; Hydrogen peroxide; Infrared spectroscopy; Low temperature; Material chemistry; Nitrates; Plutonium; Precursors; Raman spectroscopy; Salt effect; Solid phases; Thermal decomposition; Thorium; Uranium
• ISSN: 1477-9226; 1477-9234; 1477-9234
• DOI: 10.1039/d2dt02376h

The uranium and plutonium co-conversion process constitutes a continuous subject of interest for MOx fuel fabrication. Among the various routes considered, chemical coprecipitation by the salt effect has been widely investigated regarding its simplicity of integration between the partitioning and purification steps of the PUREX process, and the straightforward recovery of precursors that are easily converted into oxide phases by thermal decomposition. The present study focuses on the coprecipitation behavior of U-Th and U-Pu actinide peroxide mixed systems by examining the precipitation yields and settling properties for nitric acidity in the range of 1 to 3 M and hydrogen peroxide concentration in the range of 4.5 to 7 M. The precipitated solids have been characterized by powder XRD, IR and Raman spectroscopy, laser granulometry and SEM-EDS analyses revealing the synthesis of studtite and actinide( iv ) peroxo-nitrates as aggregated particles. The actinide solid phases are uniformly distributed within the filtered cakes. The precursor thermal decomposition results in the formation of oxide phases at low temperature according to a sequential release of water molecules, peroxide ligands and nitrate ions. The calcination step has a limited effect on the morphology of the powders which remain highly divided. The high precipitation rate of actinides makes this chemical route potentially interesting as a co-precipitation process. Efficient coprecipation conditions using peroxide ligand were determined for the two U-Th and U-Pu mixed systems. The resulting solids are composed of studtite and actinide( iv ) peroxonitrates which readily decompose to oxide phases at low temperature.