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 identified by determining the physical properties required to conduct electrorefining using a molten metal and molten salt in CaCl2 at 1123 K. More potential surrogates were identified by changing the matrix salt to be a LiCl-KCl-CaCl2 eutectic salt with electrorefining conducted at 673-773 K. Ce-CeCl3, In-InCl3, Zn-ZnCl2, Sn-SnCl2, and Bi-BiCl¬3 were investigated as potential plutonium electrorefining surrogates. Ce electrorefining in molten CaCl2 resulted in a difficult to separate colloid mixture of Ce, Ca and Cl. Electrorefining rates for In were too slow due to InCl3 volatilizing out of the molten salt. Zn was successfully electrorefined, but the metal obtained did not coalesce into one piece. Sn and Bi were successfully electrorefined and coalesced into solid 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 a eutectic LiCl-KCl-CaCl2 salt in place of CaCl2. Using this surrogate enables fundamental studies of aspects of plutonium electrorefining. One aspect of plutonium electrorefining research is to improve its efficiency and yield. Plutonium electrorefining is a time-intensive process which generates radioactive waste. Improvements in efficiency and yield can reduce process time and waste. One possible way of improving the efficiency of plutonium electrorefining is to study the impact of using an AC superimposed DC waveform. Four AC superimposed DC and two DC electrorefining runs were performed using bismuth as a plutonium surrogate. All six runs showed a high level of yield and coulombic efficiency. All six cathode rings were confirmed to be high-purity bismuth using scanning electron microscopy with energy dispersive x-ray analysis (SEM-EDS). While the results were inconclusive about the ability of AC superimposed DC waveforms to increase the efficiency of bismuth electrorefining, applying an AC superimposed DC waveform did not appear to decrease the efficiency or yield of the process. The change in waveform also did not result in impurities being present in the product cathode ring. Bismuth, in addition to being identified as a viable plutonium surrogate, has been investigated as a potential liquid electrode for molten salt electrorefining. Because of this, its electrochemical properties are of interest. However, bismuth's electrochemical behavior has received scant attention in eutectic LiCl-KCl melts and no studies were found in the ternary LiCl-KCl-CaCl2 melts. LiCl-KCl-CaCl2 melts offer some advantages over eutectic LiCl-KCl, such as lower melting point and higher oxide solubility. Cyclic voltammetry, square wave voltammetry, chronoamperometry, chronopotentiometry and open-circuit chronopotentiometry were used to measure electrochemical parameters, such as diffusivity and standard redox potential of bismuth electrodeposition in LiCl-KCl and LiCl-KCl-CaCl2 eutectics.

Degree

PhD

College and Department

Ira A. Fulton College of Engineering; Chemical Engineering

Rights

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