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Electrorefining of uranium was studied for developing pyrometallurgical reprocessing technology of metal fuel cycle. After concentration dependence of polarization curve was measured, uranium was electrodeposited either on solid iron cathode or in liquid cadmium cathode. Design and operational conditions of the cathode were improved for obtaining much greater quantity of deposit, resulting in recovery of 732g of dendritic uranium on a single solid cathode, and of 232 g of uranium in 2,344 g of a liquid cadmium cathode. The behaviors of electro-codeposition of rare earth elements with uranium were observed for liquid cadmium cathode, and were found to follow the local equilibrium between salt electrolyte and cathode. The decontamination factors of FP simulating elements from uranium were tentatively determined as >2,000 for deposition to solid cathode and as >7 for deposition to liquid cadmium cathode, respectively. KEYWORDS: nuclear metal fuels, molten salts, electrorefining, pyrometallurgy, uranium, FBR type reactors, fuel cycle, pyroprocess, partition, Concentration dependence, electrodepositionand the noble FPs such as ruthenium and palladium are not oxidized from the spent fuels and are retained in the anode basket as a sludge or fall into cadmium pool.The original concept of this type electrorefiner was first proposed by Miller et al. of ANL at 1986'"). In the beginning, they studied the deposition behaviors of uranium and plutonium by using laboratory scale elec-

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The diffusion coefficients of Ce(III) and Gd(III) in LiCl-KC1 eutectic melt were determined in the temperature range between 673 and 823 K by chronopotentiometry. A new method was devised to minimize the error in defining the surface area of the working electrode. The immersed depth of the working electrode was changed by stages, and the relation between the change in the square root of the transition time and that in the surface area of the working electrode was substituted into the Sand equation instead of their absolute values. Diffusion coefficients obtained were written in following equations 1670(±l08) 2 log D = -2.69(±O.145) -(D : cm Is)T log DG4 = -2.78(±O.128) -1670(±94.3) (DGd: cm7s)The activation energies for diffusion and the diffusion coefficients of lanthanide ions in LiCl-KC1 are discussed in connection with their ionic radii and the stability of their complex ions.

Electrorefining of uranium was studied for developing pyrometallurgical reprocessing technology of metal fuel cycle. After concentration dependence of polarization curve was measured, uranium was electrodeposited either on solid iron cathode or in liquid cadmium cathode. Design and operational conditions of the cathode were improved for obtaining much greater quantity of deposit, resulting in recovery of 732g of dendritic uranium on a single solid cathode, and of 232 g of uranium in 2,344 g of a liquid cadmium cathode. The behaviors of electro-codeposition of rare earth elements with uranium were observed for liquid cadmium cathode, and were found to follow the local equilibrium between salt electrolyte and cathode. The decontamination factors of FP simulating elements from uranium were tentatively determined as >2,000 for deposition to solid cathode and as >7 for deposition to liquid cadmium cathode, respectively.