The electrochemical measurement of concentration in molten chloride salts is a valuable tool for the control of existing and potential industrial processes, recycling of precious materials and energy production. The electrochemical techniques commonly used to measure concentration and each techniques’ associated theory are discussed. Practices which improve measurement accuracy and precision are set forth. Exceptionally accurate and precise measurements published in the literature are evaluated based on their performance in specified concentration ranges. The strengths and weaknesses of the most accurate measurements are briefly explored. Chronopotentiometry (CP) and square wave voltammetry (SWV) are accurate and precise with low concentration measurements. SWV was accurate at low concentrations, even in multi-analyte mixtures. CP was accurate for only single analyte mixtures. Open-circuit potentiometry (OCP) is accurate and precise in single-analyte mixtures but yields large errors in multianalyte mixtures. Cyclic voltammetry (CV), chronoamperometry (CA) and normal pulse voltammetry (NPV) are accurate and precise across all concentration ranges. NPV is exceptionally well suited for measurements in melts with multiple electroactive species.

Among electrochemical techniques, rotating electrodes are particularly useful for molten salt research due to their ability to precisely control the rate of mass transfer via the rotational rate of the electrode. Rotating electrodes create well-developed flow patterns with established mathematical relations for certain geometries. From these relations, it is possible to measure viscosities, diffusion coefficients, and other properties of molten salts relevant to nuclear material processing and molten salt reactors (MSR). Rotating electrodes have the potential to simulate the hydrodynamic conditions in a molten salt reactor and provide in situ feedback during corrosion testing. Additionally, rotating electrodes require significantly less material for corrosion testing than flow loops, offering a low-cost means to screen material and salt compositions for more expensive and larger flow loop experiments. Although rotating electrodes have been used extensively in aqueous solutions, there have been very few attempts to apply them to molten salts. The high efficiency electrochemical test (HEET) facility at Brigham Young University (BYU) has been designed and constructed specifically for rotating electrode tests in molten salts. The constructed cells will be presented along with initial test data to benchmark and validate the hydrodynamic relations in molten salts by comparing them to aqueous hydrodynamic relations for similar rotating electrode geometries.

No abstract