Absorption spectra of neptunium and plutonium in spent fuel reprocessing active test

The recovery of neptunium and plutonium play an important role in the spent nuclear fuel reprocessing process. Neptunium and plutonium are multiple oxidation states stable in solution and the varying conditions of the involved processes make it very difficult to effectively restrict them within desired streams in the relevant separation processes, and to precisely depict their species and ideally control their distribution in the environment. In order to control the valence of neptunium and plutonium in nitric acid and 30% TBP-nd, the structures and properties need to be deeply understood, especially the coordination behavior with nitrate. The special 5f orbital electron transition of actinides results in the characteristic absorption spectra of neptunium and plutonium in the visible-near infrared region, therefore, the valence and species structure of neptunium and plutonium in the relevant process points can be studied by absorption spectroscopy. In this paper, the species composition of neptunium in spent fuel reprocessing process, especially the distribution of Np (IV), (V), (VI) in the aqueous and organic phase in dissolution and co-decontamination unit were studied by absorption spectroscopy, the coordination structure of neptunium with nitrate and the spectra in 30% TBP- n-dodecane were also studied. On the other hand, the distribution of Pu (III), (IV), (VI) in the process were studied by absorption spectroscopy method. (author)