The Thermal Hydraulic Experimental Test Article (THETA) is a 500 L liquid sodium facility that is used to develop components and instrumentation as well as acquire experimental data for validation of reactor thermal hydraulic and safety analysis codes. THETA is a Mechanisms Engineering Test Loop (METL) test article installed in one of the 71 cm (28 in) nominal diameter METL test vessels. The facility can be used to simulate normal conditions as well as a variety of accident conditions characteristic of a liquid metal cooled nuclear reactor. 

THETA is comprised of a traditional primary coolant and secondary coolant system. The primary system is submerged in the pool of sodium and consists of a pump, electrically heated core, intermediate heat exchanger, flowmeter, and connected piping and thermal barriers (redan). The secondary system, located outside of the sodium pool, consists of a pump, flowmeter, sodium to air heat exchanger, and connected piping and valves. Cutting edge instrumentation such as Rayleigh backscatter based optical fiber temperature sensors and high temperature rated (550 °C) electromagnetic flowmeters are being used to characterize THETA thermal hydraulics. The facility was designed in partnership with systems code experts to tailor the experiment to ensure the most relevant and highest quality data for code validation. The THETA primary and secondary systems are both operational and providing experimental data for sodium cooled reactor thermal hydraulic characterization.