Author(s): Ander Fuller, Bryant Johnson, George Ankrah
Mentor(s): Devin Rappleye
Institution BYU
Nuclear waste, or used nuclear fuel (UNF), is one of the largest problems regarding nuclear reactors. However, over 95% of UNF still contains usable material. Recycling UNF not only reduces the amount of waste produced by a reactor but also increases the efficiency of the reactor. Molten salt electrorefining is a method to recycle UNF. Our research focused on designing and implementing a process to automate and optimize electrorefining of a surrogate for UNF. The biggest obstacle to effective implementation of electrorefining is its optimization. Optimal electrorefining happens as fast as possible while maintaining a pure product. To achieve this, we created a program that automatically determines the optimal current by applying a linear sweep of current and recording the resulting voltage of the electrorefining cell. The program then uses a second-derivative based model to find the highest current that does not reduce impurities. We electrorefined a tin anode with nickel as the impurity as a surrogate for plutonium. The anode was placed in a CaCl2-LiCl-KCl eutectic molten salt with some SnCl2 added to assist the refining process. We used a tungsten ring as the cathode. By passing current from the anode to the cathode, tin is oxidized from the impure anode into the salt and then reduced from the salt onto the cathode, forming a pure tin deposit. By analyzing experimental data, we developed a novel method to automatically terminate electrorefining. The program monitors the “static refining resistance,” which is a ratio of current-to-voltage. This ratio gradually increases as the tin is refined. When all the tin in the system is depleted by depositing on the cathode, the static refining resistance quickly and drastically increases. The program looks for this increase and automatically terminates the electrorefining procedure.