High-Temperature Electronics for Real-Time, In-Line Monitoring of Molten Salt Reduction and Oxidation (RedOx)

C53-20b-271305The prospect of nuclear power produced with advanced molten salt-cooled reactor (MSR) designs has garnered the attention of the Department of Energy in conjunction with the private sector. The salts are used to transfer heat from the reacting fuel. All designs describe a chemically stable salt with a melting point near 500°C, heated by the nuclear reaction to a temperature near 700°C. Operation of a heat- exchange loop requires monitoring salt properties. The oxidizing chemical environment corrodes reactor components, conduits, vessels, and valves. Real-time measurement of the salt reduction and oxidation (RedOx) is needed as a “health monitor”. To monitor corrosion, thermodynamic reference electrode (RE) potentials must be correlated to potentials produced by durable electrode materials. A rugged health monitoring instrument that measures and compares multiple RE potentials accelerates the study of electrode behaviors to produce a reliable, long-term measurement of the salt RedOx state. Ozark IC is a leader in the development of extreme-environment electronics, making breakthroughs for high-temperature environments with recent demonstrations up to 800°C. The University of Wisconsin, College of Engineering (UWCE) is uniquely capable of, and an acknowledged expert in, producing high- purity salts such as LiF-NaF-KF (46.5-11.5-42 mol%) (FLiNaK) for determining molten salt properties. Ozark IC and UWCE propose to develop an instrument for real-time comparison of reactive thermodynamic reference electrode potentials in FLiNaK+NiF2[3] to non-reactive electrode potentials such as a AlN/Au. Advanced salt oxidation-reduction measurement designs, techniques, and best practices will be provided by Argonne National Labs (ANL). Creation of a miniaturized and temperature- hardened reduction-oxidation state measurement instrument is the objective of Phase II. UCWE identified two electrically insulating materials that are suitable for conventional electrode fabrication. This result intersected with a material study performed by Ozark IC using thick film printed electrode conductors on the same material, determining the key feasibility of creating both conventionally machined and film-miniaturized electrodes for a comparative study in Phase II. Ozark IC was able to manufacture a suitable electrode potential amplification circuit that was successfully temperature- hardened to 200°C validating the efficacy of the readout. Ozark IC will incrementally harden the electronics to temperature through Year-1 to Year-2. UWCE/ANL will design conventional electrodes and measure the potentials to confirm feasibility of the instrument. Short-term measurements (24-48 hours) of electrode potentials will be performed to validate Nernstian behavior in FLiNaK. Commercial applications include the development of molten salt heat exchange loops, high-temperature chemical analysis, and geothermal well logging.