US power utility Southern Company, TerraPower and Core Power have started pumped-salt operations in the Integrated Effects Test (IET), as a step towards development of Generation-IV molten salt reactor technology, namely TerraPower’s first-of-a-kind Molten Chloride Fast Reactor (MCFR).

Since installation of the IET at TerraPower’s laboratory in Everett, Washington in October 2022, the project team has completed mechanical, electrical and controls verification and commissioned all systems. The IET is a non-nuclear, externally heated, up to 1 MW multi-loop system – the world’s largest chloride salt system developed by the nuclear sector – and follows years of separate effects testing. The IET aims to inform the design, licensing and operation of an approximately 180 MW MCFR demonstration planned for the early 2030s.

The project was initiated by Southern Company and TerraPower under the US Department of Energy (DOE) Advanced Reactor Concepts (ARC-15) award, a multi-year effort to promote the design, construction and operation of Generation-IV nuclear reactors. ARC-15 involves a total project investment of $76m based on a 60-40% public-private cost share.

The project team also includes US and UK-based Core Power is a formed in 2018 to build marine-appropriate reactor plants, the US Electric Power Research Institute (EPRI), Idaho National Laboratory (INL), Oak Ridge National Laboratory (ORNL) and Vanderbilt University. The IET also supports the development and operation of the Molten Chloride Reactor Experiment at INL, a proof-of-concept critical fast-spectrum salt reactor. At less than 200 kW, the reactor will provide experimental and operational data.

Commissioning of the IET employed hot argon and chloride salts to confirm readiness, including filling and flushing of drain tanks and verifying operation of freeze valves – a unique and important component for salt systems. Chloride salt has now been loaded into the primary coolant salt loops and pumped-salt operations have begun. A multi-month test campaign will provide valuable salt operations data and know-how for the MCFR programme.

“Southern Company believes the next generation of nuclear power holds promise in providing an affordable and sustainable net-zero future that includes reliable, resilient and dispatchable clean energy for customers,” said Dr Mark S Berry, Southern Company Services Senior Vice President of Research & Development. “It’s exciting to see each new landmark in the Integrated Effects Test, as it helps our nation rebuild lost molten salt reactor knowledge.”

Jeff Latkowski, Senior Vice President for the MCFR said: “The Molten Chloride Fast Reactor has the potential to meet the carbon-free needs of hard-to-decarbonise industrial sectors including and beyond electricity. The IET will help us gather and evaluate data to support the development of our technology, and we are excited to launch pumped-salt operations.”

Mikal Bøe, President and CEO of Core Power described the start-up of the IET as “a milestone achievement in the development of the first fast-spectrum molten salt reactor”. He added that the IET “allows us to collect that crucial last-mile data for a design and build of the Molten Chloride Fast Reactor and takes the team one step closer to a genuinely unique way to do new nuclear that is appropriate for the commercial marine environment”.

TerraPower's MCFR technology uses molten chloride salt as both reactor coolant and fuel, which enables fast spectrum operation at higher temperatures than conventional reactors, generating electricity more efficiently. It also offers potential for process heat applications and thermal storage. A version of the MCFR – the m-MSR – is being developed for marine use. TerraPower is also developing Natrium technology – featuring a sodium fast reactor combined with a molten salt energy storage system – with a demonstration plant planned to be built at Kemmerer in Wyoming.

Image: The Integrated Effects Test (courtesy of Southern Company)