Molten salt reactors.
Running on 1960s salt.

The last molten salt reactor in the United States shut down in 1969. In September, the Department of Energy shipped some of its leftover salt to a startup in Texas that's trying to build the next one.

That's how far back the West is starting from. This summer, three startups in the Energy Department's reactor pilot program brought brand-new reactors to criticality, the point where a chain reaction sustains itself, by a July 4 target. None of them used molten salt. The two molten salt projects in the program both missed the date.

The gap is frustrating, because on paper this is the most elegant reactor ever designed. A molten salt reactor, or MSR, dissolves its fuel in liquid salt instead of packing it into solid rods. The salt runs hot at ordinary pressure, so there's no high-pressure steam system waiting to burst, and if things overheat, the fuel can drain into a tank where the reaction stops on its own. Some designs can even burn thorium, which is far more plentiful than uranium. Yet nobody in the West has run one in more than half a century. China has. Its small thorium test reactor in the Gobi desert went critical in 2023, and last November it reported turning thorium into usable uranium fuel.

Molten salt reactor stocks have paid for the gap. Terrestrial Energy, the only listed company developing a liquid-fuel molten salt reactor, is down about 80% since it went public a year ago, in a year that's been rough on small nuclear generally.

This list of molten salt reactor stocks is ordered by how close each company is to a reactor that actually runs: the one public developer, the government experiment, the bottleneck supplier, and the private companies doing most of the real work.

There's exactly one listed company building a liquid-fuel molten salt reactor.

Terrestrial Energy NASDAQ: IMSR

Terrestrial Energy went public through a SPAC last October with about $290 million. It still has $283 million, because it spends only a few million a quarter. The stock has fallen to under $4, which puts the company's market value only about $120 million above its cash.

That's the market saying Terrestrial's design is close to worthless until something gets built. The company has been in pre-application talks with the Nuclear Regulatory Commission since 2017 and hasn't filed for a construction permit. Its pilot reactor under the Energy Department program was supposed to reach criticality by July 2026. It didn't, and no new date has been given.

The case for it is that its reactor runs on standard low-enriched uranium, not the scarcer high-assay fuel most advanced designs need, and it has land under lease at Texas A&M's research campus. This is a binary bet with a cash cushion. If Terrestrial gets a reactor licensed, today's price looks absurd. If it doesn't, you're paying for a bank account that's slowly emptying.

The government is funding the first real Western test, and a utility is running it.

Southern Company NYSE: SO

Southern Company is the prime contractor on the Molten Chloride Reactor Experiment, a small reactor at Idaho National Laboratory built with TerraPower's technology. It's scheduled to run for about six months in 2028. It will be the world's first fast-spectrum molten salt reactor, a design meant to get far more energy out of its fuel than the 1960s version did.

It's also a reminder of how much work hides behind "liquid fuel." The experiment needs about 72 batches of fuel salt, made one at a time at the lab. The first came out in September 2025.

Southern is a giant utility, and this experiment won't move its earnings. It's still the lowest-risk seat at the first Western molten salt reactor since the 1960s.

Most molten salt designs use a salt made with lithium-7, a specific form of lithium that has to be separated from the natural mix. Most of the world's supply comes from China and Russia.

ASP Isotopes NASDAQ: ASPI

ASP Isotopes separates isotopes using lasers and other methods, and its Quantum Leap Energy subsidiary is working on lithium-7. It's early. In March it started designing a laser research facility for lithium enrichment with the University of Bristol.

If Western molten salt reactors ever get built at scale, someone has to make their salt, and right now nobody in the West does it commercially. That's the opportunity. The stock is down almost half this year, and ASP plans to list Quantum Leap separately. In July it swapped $109 million of the subsidiary's notes for new ASP shares, diluting holders by about 18%. This is a microcap that is funding itself as it goes.

The real work in Western molten salt reactors is happening at private companies, which is a problem for anyone shopping for molten salt reactor stocks.

Natura Resources (Private)

Natura Resources is building MSR-1, a small liquid-fuel research reactor at Abilene Christian University in Texas. In 2024 it became the first liquid-fuel reactor in the U.S. to get a construction permit from the NRC.

It's now on the Energy Department's faster approval track. The department signed off on its safety design agreement in July, and in September it delivered the coolant salt left over from the 1960s Oak Ridge reactor. Natura has a new CEO and a deal for high-assay fuel. It hasn't given a public date for first criticality. Whenever it comes, it'll probably be the first liquid-fuel reactor in the West since 1969.

Kairos Power (Private)

Kairos Power isn't a true molten salt reactor. Its fuel is solid pebbles, and the molten salt only cools them. It's here because it's the furthest along of anyone using salt.

Hermes, its first test reactor in Oak Ridge, Tennessee, has been under nuclear construction since May 2025. Its permitted completion date was pushed back to as late as 2029 in May. It broke ground on Hermes 2 in April, which will send 50 MW to the grid for Google starting in 2030. In September, Samsung C&T agreed to invest up to $100 million and join the construction team. Kairos shows that salt-cooled reactors can get built in the U.S. It also shows how long that takes.

TerraPower (Private)

TerraPower, the company Bill Gates backs, designed the molten chloride reactor that Southern is building in Idaho. Its main project, the Natrium plant in Wyoming, is a sodium-cooled reactor, not a salt reactor, and got its construction permit in March.

It's on this list because it has the money and the government relationships to take molten salt from experiment to product. It raised $650 million last year, with Nvidia's venture arm among the investors, and brought in Korea's state nuclear operator as an investor in January.

Copenhagen Atomics (Private)

Copenhagen Atomics wants to build thorium molten salt reactors the size of a shipping container and roll them off a production line. Its roadmap now calls for a subcritical prototype in 2027 and a 1-megawatt test reactor in 2028, later than an earlier plan.

It's a moonshot from a small Danish company that already markets itself to investors as "pre-IPO."

The first Western molten salt reactors will run short of salt before they run short of permits.

A conventional reactor runs on fuel assemblies that a handful of companies have been making for decades. A molten salt reactor runs on a custom chemical: highly purified salt, often with enriched lithium-7, with uranium or thorium dissolved in it. Today that chemistry happens in small batches at national labs. Idaho is making its experiment's fuel salt one batch at a time. Natura is using salt from 1969. China, which has spent a decade on this, already enriches its own lithium-7 to 99.95% for its test reactor.

So the pace of Western molten salt won't be set by regulators. It'll be set by chemistry plants. Whoever builds a reliable supply of reactor-grade salt in the U.S. or Europe will decide how fast everyone else can build, and no listed company does that at scale yet. Until one does, molten salt reactor stocks are a bet on someone else's chemistry plant.