High-Temperature Electronics for Real-Time, In-Line Impurity Monitoring for FLIBE-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 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 temperature near 700 °C. Continuous operation of a MSR heat-exchange loops requires monitoring of the molten salt as it ages. Normal operation of MSR loops over long periods of time can change the stoichiometry of the salt as components with different vapor pressures sublimate into the MSR low-pressure cover gas. As observed in the long-term operation of conventional salt heat- exchange loops, the loop components such as stainless steel pipes, flanges, pumps and reservoirs introduce impurities as they corrode[3],[4] producing flourides such as CrF2, FeF2 and NiF2 . More importantly, the electrical resistivity of these salts in their purest molten states is currently unknown. The innovation is to design and prototype a molten-salt conductance sensor with enough precision to differentiate a pure sample of FLiBe from a sample containing various 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 the geothermal well (350 ºC) and the surface of Venus (460 ºC), hypersonic vehicles (800 ºC)and now MSR research and development (700 ºC). The University of Wisconsin-Madison Thermal Hydraulics Laboratory will measure the conductivity profile of FLiBe from 800 C down to its freezing point near 458 C. This measurement will provide the key specification of a high-temperature module to make the same measurement remotely in a molten salt reactor. Commercial applications include the development of molten salt heat exchange loops, high-temperature chemical analysis, and geothermal well logging.