Synthesis of plutonium trichloride and measurement of redox potentials for the Pu/Pu couple in NaCl-2CsCl melt

Hayashi, Hirokazu ; Minato, Kazuo*

Anhydrous plutonium trichloride (PuCl) was synthesized by a solid-state reaction of plutonium nitride with cadmium chloride. The lattice constants of hexagonal PuCl were refined from its powder X-ray diffraction pattern to be a = 0.7394 0.0006 nm and c = 0.4244 0.0006 nm, which are close to the reported values. Using the synthesized PuCl sample, electrochemical behavior of plutonium in NaCl-2CsCl melt at 823-923 K was investigated by cyclic voltammetry and open-circuit chronopotentiometry after polarization. The results show that Pu ions are reduced to Pu metal by single-step mechanism in the NaCl-2CsCl melt. The apparent standard potentials of Pu/Pu redox couple were determined to be E(Pu/Pu) = -3.514 + 8.6010 T vs. Cl/Cl (V). The activity coefficients of Pu ions were determined using the previously reported Gibbs free energy of formation for PuCl in the supercooled liquid state.