Study on valence of Pu, Np and Tc in nitric acid after electrolytic reduction

• Published in: Journal of Alloys and Compounds Vol. 444; pp. 663 - 667
• Main Authors: Hoshi, H., Wei, Y.-Z., Kumagai, M., Asakura, T., Morita, Y.
• Format: Journal Article Conference Proceeding
• Language: English
• Published: Lausanne Elsevier B.V 01.10.2007; Elsevier BV; Elsevier
• Subjects: Applied sciences; Electrolysis; Energy; Exact sciences and technology; Fuels; Hydrazine; Nuclear fuels; Preparation and processing of nuclear fuels; Reduction; Reduction; Np; Ru; Electrolysis; Hydrazine; Pu; Chemical reduction; Fission reactor fuel reprocessing; Valence; Fast breeder; Ion exchange; Nitric acid
• ISSN: 0925-8388; 1873-4669
• DOI: 10.1016/j.jallcom.2007.02.060

The adjustment of valence of actinides, e.g. U(VI) to U(IV), is one of the most important subject to increase its affinity onto anion exchanger for quantitative recovery of U, Pu and Np in ERIX Process for advanced FBR reprocessing system. For this purpose, nitric acid concentration of spent fuel solution is adjusted to 6 M and then reduced at −300 mV (versus Ag/AgCl) through a novel flow-type electrolysis cell. In this work, valence of Pu, Np and Tc in concentrated nitric acid solution after the electroreduction was studied. Electroreduction of 6 M HNO 3 solution containing Pu, Np and Tc through flow-type electrolysis cell was examined. According to the UV–vis spectra, Pu and Np were reduced to Pu(III) and Np(IV), respectively. With existence of hydrazine, Pu stably existed as Pu(III) in 6 M HNO 3 solution after electroreduction. However, Pu(III) was liable to be oxidized to Pu(IV) in case of coexisting with Tc or Ru by their catalytic reaction. Especially, oxidation ratio of Pu(III) to Pu(IV) with Ru was faster than that with Tc. Anion exchanger column separation of the reduced solution was also performed. Tc was reduced and separated from Pu and Np which were quantitatively recovered from the column by dilute nitric acid solution. Since Pu was eluted together with the Np(IV), it is presumed that the Pu(III) was oxidized to Pu(IV) inside the anion exchanger column. U, Pu and Np were well separated from fission product elements and this is a promising result for recovering these elements together in FBR reprocessing system.