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

The thermodynamics of plutonium and americium in LiCl-KCl eutectic/liquid c admium systems was studied with interest in the oxidation state of americiu m in the salt phase. The standard potential of plutonium vs, the Ag/AgCl (1 wt% AgCl) electrode, E-Pu/Pu(III)(0), in the LiCl-KCl eutectic was measure d in the temperature range of 400-500 degreesC and given by the equation wi th a standard deviation, sigma =0.0009 V: E-Pu/Pu(III)(0) (V) = -2.204+0.00 0845 T (K). The Ag/AgCl electrode had been carefully calibrated using the L i-Al electrode, The potential of the cadmium containing plutonium and ameri cium, E-Cd, was measured at 500 degreesC 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) + 0.05 11 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 o n the potential data, the activity coefficient of plutonium in liquid cadmi um and the separation factor of americium relative to plutonium were determ ined to be (1.74 +/-0.28)x10(-4) and 1.77 +/-0.46, respectively. Under the reducing conditions (i.e. E-Cd < - 1.45 V), the relationship between E-Cd a nd log D-Am, indicates that divalent americium is possibly present in the s alt phase. (C) 2001 Elsevier Science B.V. All rights reserved.