This report describes the development of and experimental measurements made with the thermal conductivity and viscosity measurement systems for molten salts at Oak Ridge National Laboratory. The thermal conductivity system is based on a steady-state measurement technique in which a heat flux is driven across a variable gap, and the changes in temperature difference across the gap are measured as the gap size is varied. The system comprises an inner containment, which possesses the heating element, and an outer containment, which possesses the salt specimen and cooling channels. The gap is formed between the outer bottom of the inner containment and the inner bottom of the outer containment. The viscosity system is based on the falling-ball technique in which a salt-filled tubular crucible is fixed at an angle and a ball rolls through the salt. The terminal velocity of the ball can be converted into viscosity via a calibration factor calculated for crucible-ball combinations which account for thermal expansion and flow characteristics. Modifications were made to both systems this fiscal year. Modifications to the thermal conductivity system included adding guard heaters to prevent axial heating losses, and modifications to the viscosity system included changing the crucible design to prevent air pocket formation and providing the ability to conduct measurements with a glass or steel crucible.

This report presents the current status of the Molten Salt Thermal Properties Database-Thermophysical (MSTDB-TP). Building off of MSTDB-TP and through the direction of the Roadmap for Thermal Property Measurement of Molten Salt Reactor Systems [1], MSTDB-TP v2.1.1 has now been released, containing a total 448 salt entries (data from 140+ independent studies), an increase compared with the original commit of 62 [2, 3], and containing thermophysical properties, including density, viscosity, thermal conductivity, and heat capacity. Along with the new database release, the further advancement of Saline, which is a C++ application programming interface, and a graphical user interface have facilitated increased user/developer interaction with the database. Furthermore, estimation techniques, first principles calculations (ab initio), and interpolation/extrapolation methods (Redlich-Kister/Muggianu) have shown great promise in the future of thermophysical property determination for filling out compositional spaces and investigating experimentally difficult salts (hazardous and/or expensive). This report describes the database composition, the development and advancement of database tools, and the strategy of advancing and implementing estimation data into future iterations of the database for MSTDB-TP.