412770 Electrochemical Concentration Measurements for Online Monitoring of a Used Nuclear Fuel Electrorefiner

Wednesday, November 11, 2015: 8:55 AM
251C (Salt Palace Convention Center)
Devin Rappleye, University of Utah, Salt Lake City, UT and Michael Simpson, Metallurgical Engineering, University of Utah, Salt Lake City, UT

A high temperature, electrochemical process, commonly called pyroprocessing, is currently being developed by several countries as an option for managing used nuclear fuel (UNF). South Korea, most notably, has long term goals to use it to recycle actinides from their commercial UNF and minimize the volume of nuclear waste that will be placed in long term geologic disposal. The process consists of unit operations that have been tested using batches up to 20 kg with both surrogate and actual used nuclear fuel. In order for efficient operation at the industrial-scale, reliable online process monitoring needs to be developed for pyroprocessing. The UNF is separated into multiple product streams using an electrorefiner with molten LiCl-KCl eutectic as the electrolyte. The noble metal fission products remain with the UNF in anode baskets. The active metal fission products, transuranics, and lanthanides oxidize into the molten salt. Under normal operating conditions, uranium is electrodeposited at the cathode as the product. However, under the right conditions it is possible to co-deposit U/TRU actinides at the cathode. With each batch of UNF processed, transuranics, lanthanides and active fission products accumulate in the electrorefiner. If unmonitored, the accumulated elements could contaminate the uranium product, decrease process efficiency and, in the extreme case, achieve criticality. Electrochemical sensors are an ideal monitoring technology for the electrorefiner in the electrochemical treatment process. These sensors are simple, robust and would have minimal impact on process operations. To investigate the merits of an electrochemical sensor for online process monitoring, concentration predications were made in a small scale high temperature electrochemical cell. While the primary actinides of interest in electrorefiners are uranium and plutonium, it was not possible to run experiments with even very small quantities of plutonium in our lab. Thus, salts containing UCl3 and MgCl2 (as a surrogate for plutonium) were used. MgCl2 is deemed a good surrogate for PuCl3, due to the close proximity of their apparent standard reduction potentials. Electrochemical techniques such as cyclic voltammetry, chronoamperometry, chronopotentiometry and normal pulse voltammetry were performed at 500°C in eutectic LiCl-KCl with varying amounts of UCl3 and MgCl2. Several analytical techniques were applied to the collected data to predict the composition of the simulated electrorefiner salt. The merits and accuracy of each electrochemical and analytical technique were determined by comparing the predicted compositions to the ICP-OES measured compositions.

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See more of this Session: Fundamentals of Electrochemical Processes I
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