Go with the flow

August 17, 2023, 12:00PMNuclear News

Nuclear thermal hydraulics—for light water reactors or advanced reactors cooled by gas, metal, or salt—is all about defining safety and performance margins as things heat up.

THETA’s primary system. (Photo: Argonne)

The Mechanisms Engineering Test Loop facility, as depicted in a 2021 Argonne video. (Photo: Argonne)

Test the metal

Meet THETA, the Thermal Hydraulic Experimental Test Article. Recently installed inside Argonne National Laboratory’s Mechanisms Engineering Test Loop (METL) facility, the 450-liter pool-type sodium vessel is equipped with sensors to provide real-time data and support liquid-metal fast reactor research and development. (Oklo’s Aurora is the first to benefit.)

THETA will serve as a test bed for both components and sensors, with a primary system submerged in liquid sodium and a secondary system outside the pool containing the major components of a sodium-­cooled fast reactor.

Multiphysics simulation

As a Maria Goeppert Mayer Fellow at Argonne, April Novak took the lead on a three-year team project to develop high-fidelity multiphysics simulation software to analyze advanced reactors and reduce uncertainties, with the aim of improving reactor economics and safety cases. Cardinal was the result, and the open-source software package was named a finalist for the 2022 R&D 100 awards.

Cardinal combines key areas of nuclear reactor physics, including neutron transport, fluid flow, and heat transfer, by integrating existing codes in the MOOSE framework. Cardinal’s geometric flexibility means it’s not limited to specific reactor types. In fact, Cardinal can even be used for fusion modeling.

ORNL recently installed the test stand in the Thermal Hydraulics High-Bay Laboratory. (Photo: Genevieve Martin/ORNL)

A molten chloride test loop known as the Facility to Alleviate Salt Technology Risks (FASTR) began flowing operations at ORNL in December 2022. (Photo: Kevin Robb/ORNL)

Bearing up in molten salt

Some advanced reactor developers plan to use molten fluoride or chloride salt as a coolant or a fuel-bearing salt, but so far those considering fluoride salts have more historical reactor data to work with.

A new molten chloride salt test stand recently installed in Oak Ridge National Laboratory’s Thermal Hydraulics High-Bay Laboratory is designed to reach temperatures of about 700 °C and may give molten chloride reactor developers some of the data they need to support modeling and design. Three bearing components inside the test stand will provide data on the material and design performance of bearings that would be subjected to a molten salt environment inside the full-size pump components of an operating power reactor.

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