Structural study of (N2H5,H)2.9U1.1Ce0.9(C2O4)5·10H2O from a conventional X-ray diffraction diagram obtained on a powder synthesized by a fast vortex process

Abstract

In the context of research on U/minor actinides for nuclear fuel reprocessing in the transmutation process, developments are first studied with surrogates containing uranium and lanthanides to facilitate testing. The tests consist of precipitating and calcining a hydrazinium uranium/cerium oxalate. The structure of this oxalate had not been previously determined, but was necessary to validate the physicochemical mechanisms involved.The present study, firstly demonstrates the structural similarity of the U/Ce oxalate phase (N2H5,H)2.9U1.1Ce0.9(C2O4)5·10H2O, synthesized using a vortex precipitator for continuous synthesis of actinide oxalates, with previously known oxalates, crystallizing in P63/mmc symmetry, obtained by more classical methods.This fast precipitation process induces massive nucleation of fine powders. Their structural and microstructural determination confirms that the raw and dried phases belong to the same structural family as (NH4)2U2(C2O4)5·0.7H2O whose structure was described by Chapelet-Arab in P63/mmc symmetry, using single crystal data. However, they present an extended disorder inside the tunnels of the structure, even after drying at 100°C, between water and hydrazinium ions. This disorder is directly related to the fast vortex method.This structure determination can be used as a basis for further semi-quantitative analysis on the U/minor actinides products formed under various experimental conditions.