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 normalΔGnormalUCl3normalo=−844.2+0.1681T false(normalkJ/normalmolfalse),normalΔGnormalNpCl3normalo=−902.9+0.1688T false(normalkJ/normalmolfalse) , and normalΔGnormalPuCl3normalo=−960.6+0.2039T false(normalkJ/normalmolfalse) when T is in K. The Gibbs free energy of formation for AmCl2 was −548.7 kJ/mol at 450°C. The activity coefficients for U and Pu in LiCl‐KCl ranged from 1 to 4×10−3 . Activity coefficients in Cd at 450°C were 15, 2.8×10−3,3.1×10−5 , and 1.1×10−4 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.

A pyrochemical process is being developed to recover the longlived alpha-decaying radioactive nuclides from PUREX (plutonium uranium extraction), high-level wastes generated by the reprocessing of spent nuclear fuel. 1 These aqueous wastes contain fission products (noble metals, rare earths, transition metals, rubidium, strontium, cesium, barium, cadmium, tin, selenium) and actinides, the former being predominately short-lived, the latter containing many long-lived radionuclides. Removal of these alpha-decaying actinides from the residues reduces the long-term radiotoxicity and simplifies waste management. 2,3 Molten LiCl-KCl eutectic salt, cadmium and bismuth are used as solvents in the TRUMP-S (transuranic management by pyropartitioning separation) process. Process goals are to remove 99% of the actinides (U, Np, Pu, Am, and Cm) from chlorinated PUREX residues and to recover a product that is greater than 90% actinides by weight. The process separates the waste 4 into four fractions: actinides, rare earths, metals more noble than actinides, and metals more active than the rare earths. Separation of actinides and rare earths as a group from noble and active metals is accomplished by reductive extraction from the chlorinated high-level waste (HLW) residues into liquid Cd. The actinides are separated from the rare earths by electrorefining and countercurrent reductive extraction into liquid bismuth. A full set of consistent thermodynamic property measurements for the actinides and rare earths in the process solvents is required to predict actinide/rare earth separation. Data for the major trivalent actinides were reported previously. 5 Thermodynamic data obtained from measurements for the trivalent rare earths and americium are reported in this paper.Electrochemical potentials were measured and used to calculate the standard Gibbs free energy of formation of the metal chlorides in LiCl-KCl eutectic. Potential measurements at the LiCl-KCl/Cd and LiCl-KCl/Bi interfaces were made to calculate the activity coefficients for Am in the liquid Cd and Bi phases. These thermodynamic properties provide a basis for predicting composition in the salt and metal phases and of the separation products from electrorefining and extraction processes.Equilibrium potential measurements in LiCl-KCl eutectic have been reported previously for the actinides 5 and rare earths. 6 The previously reported rare earth data did not show the same degree of consistency with theory (i.e., calculated ion valence, standard potential temperature dependence) as for the reported actinide results.New data for the rare earths and Am are reported here. Improvements to the electrochemical cell design and experimental procedures were implemented for the experiments reported. For the rare earth chlorides, rare earth metal was deposited onto a Ta cathode to ensure a reliable electrical contact to the rare earth metal in equilibrium with the salt. A thoroughly characterized AgCl-LiCl-KCl salt was used in the reference electrodes. Relatively large amounts of Am a...

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A pyrometallurgical partitioning process is being developed for recovering transuranic elements (TRUs) from high-level liquid waste. For estimating the separation efficiencies of TRUs from rare earth elements (REs), preliminary measurements were made of the distribution coefficients of TRUs in an LiCl-KCl/Bi system at 773 K. Actual separation of TRUs from REs was experimented by multiple-batch extraction in LiCl-KCl/Bi system. The experimental results agreed well with estimates obtained from measured separation factors for single-step reductive extraction. A simulation study was performed in counter-current extraction, for which the TRU recovery yields and separation efficiencies were derived from the measured distribution coefficients. The results indicated that counter-current extraction should permit recovering more than 99% of every actinide contained in the high-level liquid waste, while ensuring a mass ratio of TRUs to REs high enough for deriving metallic fuels for FBR.

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