Thermodynamic properties of U, Np, Pu and Am in molten LiCl-KCl eutectic and liquid cadmium

Thermodynamic property measurements for actinides in the LiCl-KCl/Cd system have been obtained as part of the development of an electrochemical pyropartitioning process to remove actinides from PUREX waste residues. Electrochemical potential measurements and distribution ratios were employed to obtain standard Gibbs free energies of formation for actinide chlorides in LiCl-KCl, activity coefficients of reduced actinides in Cd, and distribution coefficients for actinides in the LiCl-KCl/Cd system relative to neodymium. The temperature-dependent free energies of formation for U, Np, and Pu were {Delta}G{degree}{sub UCl{sub 3}} = {minus}844.2 + 0.1681T (kJ/mol), {Delta}G{degree}{sub NpCl{sub 3}} = {minus}902.9 + 0.1688T (kJ/mol), and {Delta}G{degree}{sub PuCl{sub 3}} = {minus}960.6 + 0.2039T (kJ/mol) when T is in K. The Gibbs free energy of formation for AmCl{sub 2} was {minus}548.7 kJ/mol at 450 C. The activity coefficients for U and Pu in LiCl-KCl ranged from 1 to 4 {times} 10{sup {minus}3}. Activity coefficients in Cd at 450 C were 15, 2.8 {times} 10{sup {minus}3}, 3.1 {times} 10{sup {minus}5}, and 1.1 {times} 10{sup {minus}4} for U, Np, Pu, and Am, respectively. The distribution coefficients between the salt and metal phases relative to Nd were 0.022, 0.056, 0.040, and 0.024 to 0.067 for U, Np, Pu, and Am in the LiCl-KCl/Cd system at 450 C.