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

The 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 or to have nuclear fuel dissolved within the salty fluid itself. All designs describe a chemically stable salt with a melting point below 500°C, heated by the nuclear reaction to a temperature near 700°C. Continuous healthy operation of an MSR heat-exchange loop requires monitoring of the molten salt as it ages. 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, a thermodynamic reference electrode (RE) measures electrode potentials on a thermodynamic scale, to associate measured potentials of known reactions to more durable electrode materials. Advantages of in-situ electronics include low-noise, removal of the effects of long wires and low-latency conversion of analog to digital data. Embedded electronics requires reliable, long-term operation without temperature management or active cooling. 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 Li2BeF4 (FLiBe) and LiF-NaF-KF (46.5-11.5-42 mol%) (FLiNaK) for determining molten salt properties, fission product retention, as well as molten salt components. Ozark IC and UWCE propose to develop an instrument for real-time comparison of reactive thermodynamic reference electrode potentials such as Ni coated graphite electrodes in FLiNaK+NiF2[3] to non-reactive electrode potentials such as a SiC/Au in FLiNaK. Ozark IC will manufacture a non-reactive probe using SiC and gold materials, which has a proven temperature cycling durability from 500°C to 800°C. UWCE will design a 4-electrode probe with a thermodynamic reference electrode and non-reactive 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. Ozark IC will manufacture the analog front-end for an electrode potential measurement instrument that will support short-term measurement (24 hours) of RE polarizability and cyclic voltammetry of up to 4 electrode potentials simultaneously. Commercial applications include the development of molten salt heat exchange loops, high-temperature chemical analysis, and geothermal well logging.