Abstract
High-temperature operation and the presence of oxidizing impurities in molten chloride and fluoride salts pose significant corrosion risks to structural alloys in molten salt nuclear reactors. Electrochemical impedance spectroscopy (EIS) offers an operando, real-time method to study the instantaneous corrosion behavior of these materials non-destructively. However, signal noises may originate from sources extraneous to the electrochemical systems that limit the ability to perform quality impedance measurements in low-frequency regime where polarization resistance (Rp) dominates. Using the exposure of pure Cr in molten LiF-NaF-KF containing 1 wt% EuF3 at 600 °C as a model corrosion system, the extent of Non-Uniform Current and Potential (NUCP) distribution during an AC perturbation associate with the disk electrodes is evaluated in terms of two dimensionless correction factors kfRct(=Rct/Reff) and kfCdl(=Cdl/Ceff). Results show that a small area Cr disk electrode increases the transition frequency that marks the dominance of Rp to a conventional terminational frequency above 10−2 Hz, enabling a reliable charge-transfer resistance (Rct) value to be determined via circle fitting of an electrical equivalent circuit model (ECM) model. Experimental results were supported by EIS simulations considering commonly used ECM models that factor in the NUCP effect of disk geometries.
Published Version
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