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Diffusion Model for Electrolytic Reduction of Uranium Oxides in a Molten LiCl-Li2O Salt

Supathorn Phongikaroon, Steven D. Herrmann, Michael F. Simpson

Nuclear Technology / Volume 174 / Number 1 / April 2011 / Pages 85-93

Technical Paper / Reprocessing

In this study, a diffusion-based kinetic model essential for design and operational analysis of spent nuclear fuel reduction has been developed. The model considers the cathode side of the system to be rate limiting and deals with diffusion of lithium metal through the basket loaded with uranium oxide (UO2 or U3O8). Faraday's law was implemented into the model to observe the electrochemical effect on the model. Solutions with different conditions are developed, and detailed results are presented. These solutions were compared against experimental bench scale data. At high operating current conditions (I > 0.8 A), the model fits the data well. The fitting resulted in estimated effective lithium diffusion coefficients for high and low void fraction UO2 crushed fuels of 8.5 × 10-4 cm2/s and 2.2 × 10-4 cm2/s, respectively. The effective diffusion coefficient for U3O8 is estimated to be 8.6 × 10-4 cm2/s. In some experiments, a porous magnesium oxide basket was used for containing the U3O8. It was estimated that the lithium diffusion coefficient through this magnesia basket is 3.3 × 10-5 cm2/s.

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