After five years of trying to find the right ingredients, scientists at the Idaho National Laboratory (INL) believe they have created the perfect recipe to fuel the world’s first critical fast-spectrum molten salt reactor.
The Molten Chloride Reactor Experiment (MCRE) at INL will test a new type of nuclear reactor that uses a mixture of molten chloride salt and uranium as fuel and coolant. This experiment allows researchers and scientists to evaluate the safety and physics of a molten chloride fast reactor that Southern Company and TerraPower plan to build.
This type of advanced reactor is an attractive option to provide electricity and heat for communities and industry. They operate at higher temperatures for improved efficiency, potentially reduced waste generation and inherent safety features due to the liquid fuel design.
Making this special kind of salt requires a highly valuable ingredient – uranium. The process involves converting uranium metal into a compound that dissolves in the molten salt, forming the fuel.
“It’s like baking a cake,” said Bill Phillips, technical lead for MCRE. The key challenge was efficiency — converting over 90% of metal uranium feedstock into usable fuel salt. “Nobody has ever made this amount of uranium chloride before,” Phillips noted. “We had to develop the process from scratch.”
It began in 2020 when Phillips and his team began developing the process and equipment needed for salt synthesis at the Fuels and Applied Science Building at INL’s Materials and Fuels Complex.
It wasn’t easy, said Nick Smith, MCRE project director.
“We started out wasting too much of the uranium metal we have access to, and we would not be able to make enough fuel salt for the reactor to go critical,” Smith said. “After years of experimentation and revision, we finally found the right process to reach the perfect yield.
“It takes a special kind of perseverance to keep working the problem when there is no guarantee that you will find a solution,” Smith added.
Overcoming challenges
The team faced numerous technical challenges, including the need to develop a custom prototype furnace and specialized equipment to ensure safety.
“We’ve been doing experiments with different food names to help communicate the processes – like angel cake or stone soup,” Phillips said. “Even coffee-making approaches like a French press.”
Overcoming these hurdles was crucial. Phillips pointed out that highly enriched uranium is an extremely valuable and expensive resource. By using depleted uranium for experimentation, the team could test and refine its processes without wasting enriched material.
“When I joined the project, we were having success at making about 2-3 ounces of fuel at once,” said Jacob Yingling, research scientist and key figure in fuel salt technology development. “We were having serious difficulties at larger scale. Now we can make more than a dozen pounds of reactor fuel in a single batch.”
Other INL projects are in the works to build comprehensive molten salt reactor capabilities, including a molten salt characterization facility and fuel salt irradiation. In 2023, Phillips synthesized and irradiated enriched uranium-fueled molten chloride salt in the Molten Salt Research Temperature Controlled Irradiation experiment, advancing understanding of how such fuel will perform in commercial reactors.
The Molten Salt Flow Loop Test Bed, which recently became operational, allows for continuous, real-time monitoring and analysis that makes molten salt fuel research much more efficient and effective.
As INL continues to pioneer nuclear technology, the development of uranium chloride fuel salt for MCRE marks a significant milestone that could feed the energy needs of the future.
Next steps
Now, the project is at a crucial stage.
“We’re almost at the moment where we can bake the cake,” Phillips said with a smile. This means the team has all the ingredients and knows the precise conditions and methods needed.
The next goal is to demonstrate the full-scale production of enriched fuel MCRE salt and to make five batches by October 2025.
MCRE should be operational by 2028, running parallel to development of the Laboratory for Operation and Testing in the United States (LOTUS) test bed, where MCRE will be the first reactor experiment.
“We’re motivated by what molten chloride reactors can do that other energy technologies can’t,” Yingling said. “Everyone involved in MCRE is mission driven to get this world-changing technology deployed.”
