Back to the Future: A New Experiment for Molten Salt

The promise of Molten Salt has launched dozens of startups in the US without splitting a single atom. A new experimental reactor licensed by the NRC is looking to accelerate the progress.

The new MSR research facility at Abilene Christian University

The last time we had a molten salt reactor running in the United States was in 1969, when the Molten Salt Reactor Experiment (MRSE) went offline. That tantalizing run of an alternate nuclear technology at Oak Ridge National Laboratory (ONRL) was enough to get a hundred reactor startups to dream a thousand dreams all around the world about a whole new class of nuclear power plants. But in all this time, nobody has managed to convinced a nuclear regulator (outside of China) to let them split an atom in a molten salt system.

The last time around: Control panel at the Molten Salt Reactor Experiment which ended in 1969

The best they can do so far is the approach of Copenhagen Atomics and many others: go as far as they can on the basis of basic data from the MRSE using computer modeling, and even building mockup reactors. In the case of Copenhagen Atomics, they zoned in on the problem of purifying the salt that would be used in their reactors, reducing the problem of corrosion. But no artificially heated molten salt loop would truly replicate the harsh chemical and radiation environment of a molten-salt reactor (MSR).

All of that is about to change.

Introducing the Molten Salt Research Reactor (MSRR)

The US Nuclear Regulatory Commission (NRC) just issued a Construction Permit to Abilene Christian University to build its Molten Salt Research Reactor (MSRR) facility on the university’s campus in Abilene, Texas. The students at ACU might have lost an intramural field, but they will be gaining the first research reactor of any kind going up in the US for decades.

The permit only authorizes construction and ACU will need to apply for a separate operating license in the future.

The process appears to be smooth and speedy: the NRC began regulatory review in November 2022 and issued the final safety evaluation for the permit on September 16, 2024, meaning it took less than two years for ACU from submitting its application to build the reactor and receiving the construction permit.

“We believe this technology will make the world a better place and we’re not interested in doing it in our grandchildren’s lifetime…we’d like to do it soon,” said Dr. Rusty Towell, director of Nuclear Energy eXperimental Testing (NEXT) lab at ACU.

Ready Reactor One

Given the fact that the construction license was approved just hours ago, I was expecting the site for the MSRR to look like something ACU students can still play field hockey on. So imagine my surprise when I found a video on YouTube featuring Dr. Towell giving a tour of the $23 million dollar facility that the reactor that is going to be housed in. (Same facility as in the photo on the top of the post.)

Dr. Rusty Towell in the multiuse facility that will house the MSRR at ACU. Note the concrete “pit” that will accommodate the reactor.

How is this possible? Turns out the Atomic Energy Act of 1954 allows for research reactors to be housed in “multi-use facilities.” After an “a-ha” moment in 2019 and a lot of back-and-forth with the NRC, the ACU team figured out that you can build the “multi-use” facility with the reactor in mind ahead of getting the construction license from the NRC.

“We’re going to build a building and have it classified as pre-existing…are we all on the same page that that works?”

May I suggest some ping-pong tables so that the ACU students can still use the site for intramural sports? After all, it is a multi-use building, right?

The main space for the housing of the reactor is a hall with a 25-foot concrete trench, a large door at the South end, and a 40-ton overhead crane. The reactor is actually going to be built off-site in a factory and rolled into site in a flatbed truck. With concrete blocks in place, the concrete trench becomes a concrete box that seals off the radioactivity in case of an accident.

Replicating the experiment

The surprises just keep on coming. When I heard that they were going to use the same molten salt as the MSRE experiment at Oak Ridge, I figured they meant the same kind of salt. No. They mean the same batch!

“Our plan is to use the same enriched Lithium-7 that Oak Ridge used in the 60’s. We want to recycle that old FLiBe that’s been sitting at Oak Ridge. They’ve been trying to throw it out for years.”

While more enriched uranium fuel will need to be added, the MSRR will literally be using the same salts that ran the MSRE half a century ago. It’s a smart way to reduce the startup cost of the reactor (otherwise isotopically separating the lithium is going to be another cost).

I simultaneously felt a sense of loss for the half-century of development that’s been wasted while we kind of forgot about atomic power, and a sense of hope: the progress of the past was not lost. Like the old batch of FLiBe at Oak Ridge, it’s just been sitting quietly, waiting to be rediscovered.

With today’s new technology, the MSRR will be able to validate the results of the MSRE and help us learn a lot more.

“We take a little sample of the salt, we’ll see how the fuel is evolving, how the buildup of fission fragments is occurring, how corrosion is happening…if we can monitor the salt, we’ve got the health of the reactor,” said Towell.

THE ELEMENTAL TAKE

The reason why molten salt captures the imagination of so many entrepreneurs is because it’s easy to see the vision: with a liquid-fueled reactor not under pressure we can create a new class of reactors that are way smaller and more economical than traditional light-water reactors. In the case of the accident, the reactor does the opposite of melting down. The already-molten fuel freezes up, meaning the resulting mess is contained.

What the team at ACU managed to see was not the potential of molten salt that anyone can see, but the golden path hiding in plain sight in the Atomic Energy Act of 1954 that allows them to build the housing for the reactor before the reactor itself is licensed for construction. This insight, combined with the new spirit of urgency rising in the NRC, is getting us — half a century later — back to where we were at in Oak Ridge, 1969, but with more sophisticated equipment, materials and testing.

It’s a huge milestone for the molten salt community. There’s only so much you can do with modeling, old data and dry runs in mock reactors without radiation. We need data like precise rates different materials corrode in the harsh conditions of the reactor, just one of the many experiments they plan to conduct when the MSRR is up and running.

I believe there is no time to lose. The Chinese have been building a Thorium molten salt reactor in the Gobi desert that looks to operate by 2025. While that is a slightly different technology, it’s safe to say the race is on to unlock the next generation of nuclear power.

In a way, the first experiment this reactor is running is already a success. Is the “US NRC ready to license a molten salt reactor?” The answer is YES!