Spectroscopic characterization of neptunium(vi), plutonium(vi), americium(vi) and neptunium(v) encapsulated in uranyl nitrate hexahydrate

The coordination of crystalline products resulting from the co-crystallization of Np(vi), Pu(vi), Am(vi), and Np(v) with uranyl nitrate hexahydrate (UNH) has been revealed through solid-state spectroscopic characterization via diffuse reflectance UV-Vis-NIR spectroscopy, SEM-EDS, and extended X-ray absorption fine structure (EXAFS) spectroscopy. Density functional and multireference wavefunction calculations were performed to analyze the An(vi/v)O-2(NO3)(2)center dot 2H(2)O electronic structures and to help assign the observed transitions in the absorption spectra. EXAFS show a similar coordination between the U(VI) in UNH and Np(vi) and Pu(vi); while Am resulted in a similar coordination to Am(iii), as reduction of Am(vi) occurred prior to EXAFS data being obtained. The co-crystallization of the oxidized transuranic species-penta- and hexavalent-with UNH, represents a significant advance from not only a practical standpoint in providing an elegant solution for used nuclear fuel recycle, but also as an avenue to expand the fundamental understanding of the 5f electronic behavior in the solid-state.

Automated summary

The coordination of crystalline products resulting from the co-crystallization of Np(vi), Pu(vi), Am(vi), and Np(v) with uranyl nitrate hexahydrate (UNH) was revealed through solid-state spectroscopic characterization. EXAFS spectroscopy showed similar coordination patterns between U(VI) in UNH and Np(vi) and Pu(vi), while Am exhibited similar coordination to Am(iii) due to reduction of Am(vi). The co-crystallization of oxidized transuranic species with UNH represents a significant advancement in nuclear fuel recycle and expands fundamental understanding of 5f electronic behavior in the solid-state.