Synthesis of U 3+ with Cd 2+ or Bi 3+ was investigated in a LiCl-KCl eutectic melt at 500°C by using cyclic voltammetry ͑CV͒ and ultraviolet-visible ͑UV-vis͒ spectroscopy. CV results showed that the equilibrium potentials of the species are larger in sequence of U 0/3+ Ͻ Cd 0/2+ Ͻ U 3+/4+ Ͻ Bi 0+/3+ . UV-vis spectroscopy results exhibited that U 3+ was directly produced in the eutectic melt containing Cd 2+ . In BiCl 3 , U metal was oxidized to U 4+ by Bi 3+ , and then U 4+ was reduced to U 3+ by additional U. From these results, the reaction mechanisms taking place during the synthesis are proposed.Pyrochemical processing of nuclear fuels using a molten salt as a solvent is regarded as a promising option for future spent nuclear fuel management. 1-3 Molten salts are known as suitable media for electrorefining and electrowinning of metals especially in the pyrochemical process of spent fuels. 1-3 In the electrorefining step, a small amount of U 3+ is added to a LiCl-KCl eutectic bath to initiate electrodeposition of U onto a working electrode. 4 U 3+ can be prepared by chemical synthesis in the molten salt melt by using reagents such as BiCl 3 5 or CdCl 2 . 4 The reactions that take place during U 3+ synthesis involve the following redox events 4,5However, details about the reactions occurring during the synthesis of U 3+ in the molten salt have not been reported yet. In this work, changes in the oxidation states of U during the synthesis of UCl 3 with BiCl 3 and CdCl 2 in the LiCl-KCl eutectic melt were investigated by using ultraviolet-visible ͑UV-vis͒ spectroscopy to understand the reaction mechanism of the synthesis. ExperimentalLithium chloride ͑LiCl͒/potassium chloride ͑KCl͒ eutectic salts ͑anhydrous beads͒, bismuth chloride ͑BiCl 3 ͒, and cadmium ͑CdCl 2 ͒ were obtained from Aldrich Co., Ltd. ͑purity Ն 99.99%͒. U metal was supplied from KAERI stock material. Silver chloride ͑AgCl͒ was purchased from Alfa Aesar ͑purity Ն 99.998%͒. All chemicals were used without further purification.The electrochemical reaction vessel was made from a quartz tube ͑350 mm long, 20 mm outer diameter, and 2 mm in wall thickness͒ using a conventional glass blowing technique. Tungsten wire was used as the working and counter electrodes. The electrodes were encased in quartz tubes to prevent electrical contact with other electrodes and the ends were exposed to the melt. The surface of the electrodes was polished thoroughly with sand paper before every use. The Ag͉Ag + reference electrode contains 1.00 wt % of AgCl in the LiCl-KCl eutectic melt. A silver wire was then inserted into a Pyrex glass, immersing the Ag wire into the molten salts. All the potential values reported hereafter are with respect to the Ag͉Ag + reference electrode unless otherwise specified. More details can be found in our previous article. 6 The spectrometric measurement system was interfaced with an integrated glove box furnace. A rectangular quartz cell ͑path length 1 cm͒ attached to a 350 mm long quartz tube ͑outside diameter of 10 mm͒ was placed at the ce...

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