Novel Molten Salt Electrode and Insulating Material Development and Testing

Molten salts including fluoride, chloride and other high-temperature variants are preferred candidates for fuel salts, coolants, and electrolytes in molten salt advanced nuclear reactors. To reduce corrosion of structural materials, the redox state of the salt can be monitored to indicate the need for chemical modification of the salt. A thermodynamic reference electrode is a standard that can be used to measure the redox state of the molten salt. There is a challenge to maintain the operational lifetime of molten salt reference electrodes. The electrodes must survive in a high-temperature corrosive environment, be inert to the molten salt chemistry, and be able to survive in a radioactively hot environment. A review of molten salt reference electrodes indicates that state-of-the-art systems have lifetimes limited from a few days to a maximum of 2-3 weeks. These short lifetimes imply that the electrodes would have to be routinely inspected, recalibrated, and/or replaced every two weeks or less; thus creating the need to often move electrodes in and out of the radioactive salt, leading to potential risk in radiation exposure, corrosion damage of the structural materials, increased cost, and production of radioactive waste of the expired electrodes. For these reasons there is a need to develop robust thermodynamic reference electrodes capable of extended use in nuclear-relevant molten salts. Developments in manufacturing techniques, novel metal alloys, and in carbon-based materials have created classes of new materials that may enable order of magnitude improvements in corrosion resistance and lifetimes of electrodes and insulating materials for molten salt electrode applications. The selected materials will be procured, characterized, and tested at the high temperature chloride molten salt system at the Virginia Commonwealth University Radiochemistry Laboratory. The proven materials will then be used to construct an electrochemical cell that will also be tested in the chloride molten salt system. In Phase II, additional characterization will be carried out at Pacific Northwest National Radiochemistry Processing Laboratory where the samples can be tested in fluoride based molten salts. The successful outcome will lead to the design of an electrochemical device targeted to applications in molten salt advanced reactors, molten salt energy storage units, concentrated solar plants and potentially downhole applications.