Distribution behavior of plutonium and americium in LiCl–KCl eutectic/liquid cadmium systems

Abstract The thermodynamics of plutonium and americium in LiCl–KCl eutectic/liquid cadmium systems was studied with interest in the oxidation state of americium in the salt phase. The standard potential of plutonium vs. the Ag/AgCl (1 wt% AgCl) electrode, E 0 Pu/Pu(III) , in the LiCl–KCl eutectic was measured in the temperature range of 400–500°C and given by the equation with a standard deviation, σ =0.0009 V: E 0 Pu/Pu(III) (V)=−2.204+0.000845 T (K). The Ag/AgCl electrode had been carefully calibrated using the Li–Al electrode. The potential of the cadmium containing plutonium and americium, E Cd , was measured at 500°C as a function of the distribution coefficient ( D : mole fraction in salt divided by mole fraction in cadmium), and represented by the following equations. over the range of E Cd >−1.45 V: E Cd =−1.360 (±0.004)+0.0511 log D Am =−1.348 (±0.002)+0.0511 log D Pu . It is indicated that americium as well as plutonium is present in the trivalent oxidation state in the salt under this condition. Based on the potential data, the activity coefficient of plutonium in liquid cadmium and the separation factor of americium relative to plutonium were determined to be (1.74±0.28)×10 −4 and 1.77±0.46, respectively. Under the reducing conditions (i.e. E Cd E Cd and log D Am , indicates that divalent americium is possibly present in the salt phase.