Determination of a surrogate for plutonium electrorefining

Abstract

Conducting research experiments on plutonium electrorefining is difficult due to the significant hazards and regulations associated with nuclear materials. Finding a surrogate for plutonium electrorefining studies would enable more fundamental research to be conducted. Potential surrogates were first identified by determining the physical properties required to conduct electrorefining at the same conditions commonly used in plutonium electrorefining, a molten metal and molten CaCl2 at 1123 K. Ce-CeCl3, In-InCl3, and Pb-PbCl2 were the only potential surrogates identified using these constraints. Sn-SnCl2 was also tested at these same conditions. More potential surrogates were identified by changing the matrix salt and operating temperature. This expanded the potential surrogate list to also include Zn-ZnCl2, Sn-SnCl2, and Bi-BiCl3. Zn-ZnCl2 was used with the LiCl-CaCl2 (65:35 mol%) eutectic at 773 K. Sn-SnCl2 and Bi-BiCl3 were used with the LiCl-KCl-CaCl2 (50.5:44.2:5.3 mol%) eutectic at 673–773 K. Ce electrorefining in molten CaCl2 resulted in a difficult to separate colloid mixture of Ce, Ca and Cl. Electrorefining rates for In in molten CaCl2 were too slow due to InCl3 volatilizing out of the molten salt. Only trace amounts of SnCl2 was retained in the CaCl2 at 1123 K resulting in impractical electrorefining rates. Zn metal product was successfully collected in the LiCl-CaCl2 eutectic molten salt, but the metal obtained did not coalesce into one piece. Sn and Bi were successfully electrorefined in the LiCl-KCl-CaCl2 eutectic molten salt and coalesced into product rings with high yields and coulombic efficiencies. While a surrogate could not be identified using the same conditions as plutonium electrorefining, two possible surrogates, Sn-SnCl2 and Bi-BiCl3, were found that could imitate the physical configuration (i.e., molten salt on top of molten metal) of plutonium electrorefining at a reduced temperature using the eutectic LiCl-KCl-CaCl2 salt at 673–773 K in place of CaCl2 at 1123 K.