Some oxidation states ͑0, ϩ1, ϩ2, and ϩ4͒ of zirconium exist in a LiCl-KCl eutectic system over the temperature range 450-550°C, and the behavior is complicated. In cyclic voltammograms at 500°C, a cathodic peak was observed at about Ϫ1.2 V vs. Ag/AgCl reference electrode, which might be due to the reduction of Zr͑IV͒ to ZrCl and zirconium metal. Two anodic peaks might correspond to the oxidation of ZrCl and zirconium metal, respectively. The electrolysis at a cathode potential of about Ϫ1.1 V yielded a nodular deposit identified as ZrCl, which appeared to be a metastable compound in this system. When the potential was sufficiently negative ͑i.e., ϽϪ1.35 V͒, zirconium metal was obtained. The deposited zirconium metal was fine black powder, and adhesion to the cathode wire was poor. In the presence of cadmium metal at the cathode, an intermetallic compound that might be Cd 3 Zr was obtained. The collection efficiency of zirconium is improved using cadmium because the adhesion of the intermetallic compound was much better. Zirconium metal reacted with Zr͑IV͒ to give Zr͑II͒ whose solution was light brown, and Zr͑II͒ was easily disproportionated into Zr͑IV͒ and zirconium metal. The anodic dissolution test indicated that the zirconium metal primarily dissolved into the electrolyte salt as Zr͑IV͒. The Zr͑II͒/Zr͑IV͒ ratio seemed to be very low and to increase with increasing temperature.

To develop an electrochemical reduction technique for the reprocessing of nuclear fuels, the reduction behavior of UO 2 at the cathode and the anode reactions were investigated in both CaCl 2 and LiCl salt baths. In the CaCl 2 at about 800°C, UO 2 was reduced into metal over the potential range Ͻ0.6 V vs the Ca 2+ /Ca. The reduced uranium metal cohered due to the high temperature and a dense metal skin covered the surface of the UO 2 disk sample. It prevented the transportation of oxygen from the inside to the bulk salt and the reduction often stopped with UO 2 remaining inside. A significant underpotential deposition of calcium metal was observed. In the LiCl at 650°C, UO 2 was reduced into metal over the potential range Ͻ0.15 V vs the Li + /Li. The UO 2 disk sample was satisfactorily reduced because the LiCl melt could permeate into the sample. The current efficiency of UO 2 reduction in the LiCl was much better than in the CaCl 2 . The anodic currents for oxygen and carbon oxide gas evolutions were verified in cyclic voltammograms of the platinum and glassy carbon electrodes. At the platinum surface, Pt 3 O 4 and Li 2 PtO 3 yielded in the CaCl 2 and LiCl, respectively. The next generation nuclear fuel cycle must not only deliver economic advantages but must also be environmentally safe and highly resistant to proliferation. Combining the metal fuel fast reactor with excellent safety features and pyrometallurgical reprocessing that provides simple and compact facilities is one of the promising options. [1][2][3] In the pyrometallurgical reprocessing, uranium, plutonium, and the other actinides are recovered by the electrorefining process in a LiCl-KCl eutectic salt at 500°C. 4-10 The actinides in the spent metal fuels ͑i.e., irradiated U-Zr or U-Pu-Zr͒ are anodically dissolved into the electrolyte. 4,5 At the same time, highly pure uranium is collected onto the iron cathode. 6,7 A mixture of plutonium, uranium, and the other actinides is collected by employing a liquid cadmium cathode. 5,8-10 Active fission products such as cesium, strontium, and rare earths accumulate in the electrolyte salt, while noble fission products such as molybdenum, palladium, and ruthenium do not dissolve and remain at the anode.The electrorefining process cannot accept oxide nuclear fuels directly, because the actinide oxides do not dissolve into the chloride salt. Therefore, a pretreatment step is necessary for reducing the oxides to the metallic form. The metal products are then loaded at the anode in the electrorefiner.The lithium reduction process using a lithium metal reductant in a molten LiCl bath has been developed to reduce oxide fuels. [11][12][13][14][15] The operation is carried out at 650°C, as the melting point of LiCl is 606°C. The reduction of MO 2 that denotes actinide dioxide is described as followswhere ͑LiCl͒ denotes the molten salt phase. The by-product of Li 2 O, of which solubility in the molten LiCl is 12.0 mol % at 650°C, 12 accumulates in the salt bath as the oxide fuels are processed. It was reported that u...

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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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