High-Temperature Electronics for Low-Cost, In-Line Impurity Monitoring of Salt-Cooled Reactors

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. Modern designs describe a chemically stable salt such as FLiNaK with a melting point below 500°C, heated by the nuclear reaction to a temperature near 700°C. Continuous operation of MSR heat-exchange loops requires monitoring of the molten salt as it ages. Normal operation of salt heat-exchanges loops over long periods can consume the loop components such as stainless-steel pipes, flanges, pumps, and reservoirs. This introduces impurities, producing fluorides such as CrF2, FeF2 and NiF2. The electrical conductivity of these salts has been identified as a low-cost, real-time leading indicator of changes in salt impurity and system health. The innovation is to prototype a molten-salt conductance sensor with enough precision to differentiate a pure sample of FLiNaK from a sample containing concentrations of impurities. 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 for DARPA with novel integrated circuit (IC) processes, high-density IC connectivity/packaging, and high-temperature connectors and cabling. These electronic solutions serve environments where temperature management of the electronics is not possible, such as in geothermal wells (350°C), the surface of Venus (460°C), hypersonic vehicles (800°C), and now MSR research and development (700°C). The University of Wisconsin-Madison (UW) extended the measurement of the conductivity profile of molten FLiNaK with a range of impurity species and concentrations thereby enriching the datasets needed to correlate impurity concentration with measured specific conductivity. Ozark IC migrated a lowtemperature printed circuit board prototype to a high-temperature ceramic implementation. The manufacturing and test of these circuit functions completed the analog front end hardware validation of the instrument. These parallel activities at Wisconsin and Ozark IC have paved the way for completing the temperature-hardened precision conductivity instrument in Phase II. Ozark IC will complete a fully-enclosed instrument hardware design (Year 1) and will complete embedded software design of the instrument to include impurity calculations in Year 2. UW will continue collecting conductivity VS impurity data in Year 1 and support measurement with the temperature hardened instrument in Year 2. Commercial applications include the development of molten salt heat health monitoring, exchange loops, high-temperature chemical analysis, and geothermal well logging.