First experiments in Argonne’s THETA aim to fill liquid sodium data gaps

May 13, 2022, 7:00AMNuclear News
THETA pictured in Argonne National Laboratory’s METL lab. (Photo: ANL)

The Thermal Hydraulic Experimental Test Article (THETA) at Argonne National Laboratory is now operating and providing data that could support the licensing of liquid-metal fast reactor designs by validating thermal-hydraulic and safety analysis codes. The new equipment has been installed in Argonne’s Mechanisms Engineering Test Loop (METL), and its first experiments are supporting data validation needs of Oklo, Inc., by simulating normal operating conditions as well as protected and unprotected loss-of-flow accidents in a sodium-cooled fast reactor.

What is THETA? THETA consists of a primary system submerged in a 450-liter liquid sodium pool, with a pump, electrically heated core, intermediate heat exchanger, and connected piping and thermal barriers, as well as a secondary system located outside the sodium pool that includes a pump, sodium-to-air heat exchanger, and connected piping and valves. A submersible flowmeter can measure the flow rate of sodium across the core.

THETA will provide real-time data to help researchers understand how sodium coolant flows through a reactor under different operating conditions to reduce uncertainties in systems-level modeling, especially modeling related to thermal stratification and the transition to natural circulation. The data and modeling could lead to more predictable safety margins, define higher operating temperatures, and provide more efficient power operation to support a wide range of advanced reactor designs.

“THETA represents a unique opportunity where experimental and computational researchers can collaborate closely on requirements and design of experiments with a strong focus on the industry needs for advanced reactor licensing,” said Lander Ibarra, principal nuclear engineer at Argonne.

Oklo gets support: Oklo wants to demonstrate and license a 1.5-MWe sodium fast reactor known as Aurora, and under a voucher granted by the Department of Energy’s Gateway for Accelerated Innovation in Nuclear (GAIN) initiative in March 2021, it is the first developer to use THETA. The testing planned under the GAIN voucher is expected to be complete by the end of 2022.

According to the GAIN voucher announcement, “The potential benefits of this project will include the ability to use higher temperatures and yield higher-power operations through reduced conservatism. This will improve economic competitiveness and reduce uncertainties associated with thermal-hydraulic modeling of these phenomena, which can lead to more efficient safety margins.”

More about METL: The METL facility was established in 2010 as an intermediate-scale liquid metal experimental facility that provides purified R-grade sodium to various experimental test vessels to test components that are required to operate in a prototypical advanced reactor environment, according to Argonne.

Technologies that can be tested in METL include components of an advanced fuel handling system, mechanisms for self-actuated control and shutdown systems, advanced sensors and instrumentation, in-service inspection and repair technologies, and thermal-hydraulic testing in a prototypic sodium environment.

METL’s testing facilities can bring its purified sodium to prototypic reactor temperatures of 650°C and include more than 1,000 sensors, as well as sodium purification and contamination monitoring equipment.

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