Electrochemistry of Uranium in the Molten LiCl-KCl Eutectic

The Institute for Transuranium Elements ITU is building up an accurate database of actinide behavior in chloride melts in support of its nuclear fuel reprocessing development program. The electrochemical properties of uranium, dissolved in LiCl-KCl eutectic melt, were investigated by transient electrochemical techniques, such as cyclic voltammetry CV and chronopotentiometry on an inert tungsten electrode. It was shown that U4+ is reduced to U0 by a two-step mechanism corresponding to U4+/U3+ and U3+/U0 transitions. In the 400-550 C s673-823 Kd range, the diffusion coefficients of U3+ and U4+ were similar and equal to: DsU3+d = 13.7 3 10−4 exph−24.2 3 103/RTsKdj and DsU4+d = 5.25 3 10−4 exph−19.8 3 103/RTsKdj cm2 s−1. The apparent standard potentials of U4+/U3+ and U3+/U0 redox systems were Eo sU4+/U3+dsVd = −1.902 + 0.0006104T sKd vs. Cl2/Cl− and Eo sU3+/U0dsVd = −3.099 + 0.0007689T sKd vs. Cl2/Cl−, respectively. Some thermochemical properties sDG,gd of uranium solutions were also derived from the electrochemical measurements. The Gibbs free energies of dilute solution of UCl3 and UCl4 in the LiCl-KCl were determined to be: DG = −897.09 + 0.226T sKd and −183.53 + 0.0589T sKd in kJ mol−1, respectively. In the 400-550C s673-823 Kd range, the activity coefficients g of UCl3 and UCl4 range between 0.3 − 4.5 3 10−3 and 17.1 − 12.7 3 10−3, respectively.

MASSET Patrick;  BOTTOMLEY Paul;  KONINGS Rudy;  MALMBECK Rikard;  RODRIGUES Alcide;  SERP Jerome;  GLATZ Jean-Paul; 

2005-09-12

ELECTROCHEMICAL SOC INC

JRC30471