Study of the plutonium (IV) electrochemical behavior in nitric acid at a platinum electrode. Application to the cathodic reduction of Pu(IV) in a plate electrolyzer

• Determination of Pu(IV) and Pu(III) diffusion coefficients in 1 M HNO3.
• Validation of the quasi-reversibility of Pu(IV)/Pu(III) system.
• Estimation of the charge transfer rate of Pu(IV)/Pu(III) redox pair at Pt electrode.
• Quantitative reduction of Pu(IV) nitrate solutions at platinised Ti electrode.

Spent fuel reprocessing and notably plutonium recycling contributes in enhancing the sustainability of nuclear energy by preserving uranium natural resources and decreasing the long term radiotoxicity of the final waste. After initial dissolution of the spent nuclear fuel in nitric acid, uranium and plutonium recovery from ultimate waste (fission products and minor actinides) is operated by a liquid–liquid extraction process (PUREX process) and plutonium partitioning from uranium is run on the basis of the selective reduction of Pu and its back extraction. Therefore, the redox properties of Pu in nitric acid are of prime importance and the stabilization of Pu at its lower redox state + III is to be mastered. This study then deals with the characterization of Pu(IV)/Pu(III) redox couple in aqueous nitric acid solution. It was aimed at measuring physico-chemical features of the redox couple such as half-wave and conditional standard potentials, diffusion coefficients and charge transfer rate constant in nitric acid medium. These features have been used in modeling experimental results of preparative Pu(IV) reduction tests in nitrate medium in a laboratory parallel plate electrode cell.