(559c) Anode Material Studies for Electrowinning Li2O in Molten LiCl

Pyroprocessing has gained widespread interest for closing the nuclear fuel cycle. It is a non-aqueous, high temperature process that can be very effective at extracting actinides from spent nuclear fuel for recycle via fabrication of new reactor fuel. It was originally developed for recycle of metallic spent fuel under the Integral Fast Reactor program at Argonne National Laboratory (ANL). ANL subsequently developed an electrochemical process for reducing commercial spent oxide fuel to metals that utilizes a molten LiCl-Li₂O electrolyte. The cathode consists of a steel basket loaded with the oxide fuel. An inert anode is needed to oxidize O^2- ions to O₂ gas. Finding a suitable anode material has proven to be very difficult, as the conditions in the electrochemical cell are very oxidizing. Platinum wires have widely been used for this purpose, but they are incompatible with metallic lithium, which can readily form during the process. The high cost of platinum makes it economically unattractive to use pure Pt rods as disposable anodes. Two approaches have been attempted to minimize the cost of anodes in the oxide reduction process. First, titanium rods with electroplated platinum coatings have been tested as alternatives to pure Pt wire or rods. These electroplated rods provide excellent surface area per cost of platinum. In initial testing using nitrate salts containing dissolved oxides, these electrodes have proven to be durable and effective as anodes. Second, metallic lithium activity within the molten salt can be minimized by using a liquid metal such as lead as the actual cathode rather than the fuel basket. Since metallic lithium reacts with platinum, this process modification is expected to significantly extend the lifetime of the platinum coating on the anodes. In this study, Pt-coated titanium rods were used as the anode for electrowinning Li₂O to Li metal and oxygen gas. The lithium metal formed at a molten lead cathode, while the oxygen gas evolved from the surface of the platinum anodes. Post-test examination of the Pt-coated rods was used to assess the rate of corrosion of the Pt layers and estimate the long-term cost of using these rods as anodes. Successful development of these cheaper anodes is expected to greatly improve the viability of applying pyroprocessing to commercial oxide fuel.