Characterization of a Thermodynamic Reference Electrode for Molten LiF-BeF2 (FLiBe)

2LiF-BeF2 (FLiBe) is proposed as coolant for advanced nuclear fission and fusion reactors designs. Electrochemical techniques can be used to answer important research questions about the chemistry, mass transport, and corrosion behavior of FLiBe. The use of electrochemical techniques is predicated upon a thermodynamic reference electrode (RE) for FLiBe. This paper reports the design and characterization of a RE for FLiBe based on the Ni/Ni(II) redox couple, a boron nitride body, and a LaF3 ionic membrane. This electrode, tested in the range of 500 degrees C-600 degrees C shows stability of +/-1 mV for ten hours, good polarizability behavior, and Nernstian behavior. This data is comparable to other RE data reported for other fluoride salt mixtures. This paper also shows that beyond ten hours the RE potential drifts and there is evidence of Ni(II) depletion from the RE. We discuss some of the mechanisms that may cause this drift. (C) The Author(s) 2017. Published by ECS. All rights reserved.