Date of Award

Fall 2014

Degree Type


Degree Name

Doctor of Philosophy (PhD)


Nuclear Engineering

First Advisor

Audeen Fentiman

Committee Chair

Audeen Fentiman

Committee Member 1

Ahmed Hassanein

Committee Member 2

Anter El-Azab

Committee Member 3

Mark Williamson


A uranium molybdenum alloy fuel has been proposed to convert research and test reactors from highly enriched uranium to low enriched uranium to increase the proliferation resistance at such reactors. Pyroprocessing has been selected to recover uranium from the scrap produced in the manufacture of this novel fuel type. Electrorefining, the main separation process of pyroprocessing, is modeled through a novel approach using corrosion theory. To use corrosion theory, knowledge of uranium polarization and kinetic parameters such as Tafel constant, transfer coefficient and exchange current density are required. Uranium polarization was investigated at five temperatures and three scan rates in both the anodic and cathodic directions. Anodic polarization of uranium revealed complex behavior caused by a buildup of a film-like material. This material was identified as a precipitate, K2UCl5, which forms as U3+ ion concentration exceeds a solubility limit in the diffusion layer adjacent to the electrode surface. The presence of the film material on the anode caused the polarization to experience reduced current density and a passive region of overpotential where current density was independent of overpotential. At large overpotentials, >250mV, active dissolution behavior was observed. The temperature dependence of the polarization behavior was examined and supports the conclusion that precipitation of K2UCl 5 is the cause for the behavior. ^ Kinetic parameters were obtained from polarization data taken carefully in the pre-Tafel region to avoid film formation interference. The Oldham-Mansfeld method was used to analyze the data and obtain polarization resistance, Tafel constant, transfer coefficient and exchange current density values of high precision. The data were compared to the values available in the literature. Tafel constant values agreed reasonably well, while exchange current density did not. Errors in the methodology used in the literature to produce the exchange current density values were identified as the potential cause of the disagreement. ^ The complex uranium polarization behavior observed in the experimental work was modeled empirically and the empirical polarization model implemented in an electrorefiner model constructed in MatLab using corrosion theory. The model was compared to data obtained by experiment at laboratory-scale. The comparison demonstrated that the empirical polarization model developed is a good first approximation of the electrochemical behavior of the system, but a physically meaningful model should be developed in the future to better elucidate the chemistry in the system.