Electrochemical Extraction of Nd from NaCl-KCl Melt by Formation of Cu-Nd Alloys
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FULL recovery and reasonable treatment of spent nuclear fuel are key concerns for future nuclear power stations. To reduce the output and long-lived radiotoxicity of spent fuel and high-level waste, partitioning and transmutation (P&T) strategies have become a potential option for the advanced fuel cycle and an alternative for complementary waste management.[1] The first requirement of P&T is to extend the performance of Pu separation to 99.9 pct, separating Np, Am, and Cm, either as a group or individually, and in any case to remove lanthanide (Lns) contaminates as much as possible. The separated transuranium elements (TRUs) should then be ‘‘transmuted’’ (or ‘‘burned’’) in a neutron field.[2] However, Lns can effectively absorb neutrons and prevent neutron capture by TRUs. Therefore, TRUs have to be separated from Lns to avoid affecting
ZHONG-LIN ZHANG, DE-BIN JI, YONG-DE YAN, WEI HONG, YU-HUI LIU, PU WANG, TAI-QI YIN, JIA-NING ZHENG, and YUN XUE are with the Harbin Engineering University, Harbin 150001, China. Contact e-mails: [email protected], [email protected] LIN-ZONG ZHOU is with the Chu Xiong Normal University, Chuxiong 675000, China. YUAN-FENG YE is with the Jinling Institute of Technology, Nanjing 211169, China. Manuscript submitted November 9, 2015.
METALLURGICAL AND MATERIALS TRANSACTIONS B
their transmutation efficiency; molten salts employed as solvent media have been proposed as a promising option to achieve this.[3] On the other hand, the accumulation of Lns in the molten salts will modify their physical and chemical properties and contaminate the final cathodic product. When Lns concentration exceeds about 10 wt pct in the melt it must generally be regenerated to avoid lowering the TRUs/Lns separation efficiency[4] and to recycle the molten salts, because the reprocessing agent should be stable and immediately available for reuse, without further treatment.[5] Molten chlorides are reported to be convenient solvents for obtaining the detailed chemistry of fission products in molten salts due to their high radiation and thermal resistance, low neutron cross section, and high solubility of fuel components.[5] Nd is abundant in the fission products with a large transverse section of neutron capture and is one of the surrogate elements of Am3+ in molten salts.[6–8] The electrochemical behavior of Nd3+ has been widely studied in molten chloride. The reduction of Nd3+ takes place in two consecutive steps in LiCl-CaCl2, LiCl-BaCl2, CaCl2NaCl, LiCl-KCl melts.[6,9–12] In molten chlorides, like other valence Lns (Sm, Eu, Tm, and Yb), Nd has two stable electro-active forms, Nd2+ and Nd3+. However, for Nd and Tm, they are a little different from Sm, Eu, and Yb. This is because the deposition potentials of Nd2+ and Tm2+ are more positive than those of
Fig. 1—Cyclic voltammograms obtained at a W electrode (S = 0.32 cm2) in NaCl-KCl melt before (dotted line) and after (solid line) the addition of 2 wt pct NdCl3 at 988 K (715 C).
common solvents (Li+, Na+, and K+) while those of Sm2+, Eu2+, and Yb2+ are cl
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