The chemical oxidation states of NpO2+, Np4+ and Np3+ in NaCl-CsCl eutectic were controlled by using Cl2, O2, H2 and Ar gas mixtures, and the redox behavior and electronic absorption properties of the Np ions were studied. The Np4+ was prepared from NpO2Cl by bubbling Cl2 gas into the melt in the presence of a carbon rod. The Np3+ was prepared by bubbling H2-Ar gas mixtures. In the electrochemical measurement of Np4+, the cathodic current for the reduction of Np4+ was found to be controlled by the diffusion of Np4+. The temperature dependence of the diffusion coefficient between 823 and 923K was described by: ln[D] = -4304/T - 6.172.

Spectrophotometric and Electrochemical Study of Neptunium Ions in Molten NaCl-CsCl Eutectic. A.Uehara, T.Nagai, T.Fujii, O.Shirai, H.Yamana: Journal of Nuclear Materials, 2013, 437[1-3], 166-70