China’s TMSR-LF1 fuses two nuclear breakthroughs in one reactor

Posted: March 27, 2026

In a remote corner of the Gobi Desert, near the city of Wuwei in China’s Gansu Province, a tiny 2 MW experimental nuclear reactor is humming along, quietly changing the course of nuclear power history. The reactor, called TMSR-LF1, is the first to combine two long-sought advances: molten salt cooling and a working thorium fuel cycle.

Benefits of molten salt-cooled reactors

TMSR-LF1 uses molten salt for cooling and as a fuel carrier, making it significantly safer than traditional water-cooled uranium reactors, which make up roughly 95% of the world’s operating reactor fleet. Salt-cooled reactors are, for instance, much less likely to melt down—some even claim it’s impossible for them to do so. If the reactor overheats, the fuel salt expands, naturally slowing the chain reaction. In an emergency, a frozen salt plug at the base of the reactor vessel melts, allowing the fuel to drain by gravity into a containment chamber where it solidifies, halting the reaction automatically—no pumps, no operator intervention, no external power required.

Because molten salt reactors do not require water for cooling or to moderate the nuclear fission process, they do not need to be located on coastlines or next to major bodies of water like most of the rest of the world’s nuclear fleet. A molten salt reactor can operate in water-poor regions or arid deserts thousands of miles from the coast.

The benefits of thorium-fueled reactors

TMSR-LF1 also burns no uranium fuel rods, though it does require a small amount of uranium to drive the fuel reaction. Instead, TMSR-LF1’s main fuel input is designed to be thorium, an abundant, slightly radioactive element named, perhaps fittingly, after Thor, the Norse god of thunder. Thorium is three to four times more abundant in the Earth’s crust than uranium, with significant deposits in India, Brazil, Australia, the U.S., and China. Given that those deposits are often found with the rare earth element monazite, it's possible that thorium could be produced economically—if there was sufficient demand for it.  

For all their promise, salt-cooled thorium reactors only recently moved from the dungeon of theoretical reports and abandoned experiments into the light of a working model. China first broke ground on TMSR-LF1 in 2018, achieved criticality in October 2023, and reached full operational power in June 2024. In October that year, the experimental machine made headlines when it successfully refueled without shutting down. Imagine watching a car refuel itself without stopping while traveling at 70 mph down the highway. Watching a nuclear plant refuel while still operating might feel something like that.

Late last year, the reactor marked another major milestone when scientists finally detected Uranium-233, securing the reactor’s position as the first on Earth to demonstrate the successful conversion of thorium into fissile uranium fuel. Today, it is still the only operational molten salt reactor in the world to “have successfully incorporated thorium fuel,” according to the Shanghai Institute of Applied Physics.

History of molten salt reactors

While salt-cooled thorium reactors may have only recently gained traction, the story of molten salt reactors is decades old. The story begins, like so many stories in nuclear energy, at Oak Ridge National Laboratory, established as part of the Manhattan Project in 1943 and the site where uranium-235 was first enriched at an industrial scale for the atomic bomb. In the 1950s, engineers were trying to build a reactor compact enough to fit inside a plane—part of a Cold War program to develop nuclear-powered aircraft.

Scientists experimented with using molten fluoride salts, which could carry tremendous heat at low pressures. The molten salts served both as a fuel carrier for the uranium and a coolant. The results were promising enough that even after the aircraft program was shelved, the research continued with an eye toward civilian power generation. The result was the Molten-Salt Reactor Experiment, or MSRE, which went critical in June 1965 and remained operational for four years. The MSRE used a mixture of lithium, beryllium and zirconium fluoride salts that flowed through a graphite-moderated core, transferring heat through a secondary salt loop to an air-cooled radiator.

When the reactor was finally shut down in 1969, the graphite bars that lined the reactor core showed little to no heat or radiation damage. Nonetheless, the technology was largely abandoned in favor of the now more widespread water-cooled reactor models. For decades, the technology languished. The research was declassified and made available to the public, but hardly anyone seemed interested.

Then, in 2011, a team of Chinese scientists began combing through the data, reigniting interest in the abandoned technology. “The U.S. left its research publicly available, waiting for the right successor. We were that successor,” Xu Hongjie, head of the scientific team responsible for the thorium reactor project, said during a closed meeting of the Chinese Academy of Sciences (CAS). “We mastered every technique in the literature – then pushed further.”

TMSR-LF1 goes far beyond what Oak Ridge’s MSRE achieved. Where the MSRE ran on uranium alone, TMSR-LF1 was designed from the outset to use the thorium fuel cycle. Thorium-232 is not itself fissile—it cannot sustain the chain reaction on its own. But when it absorbs a neutron inside the reactor, it transmutes into uranium-233, which is fissile. The reactor, in other words, can breed its own fuel.

Molten-salt reactor alternatives

China is not the only country exploring the potential benefits of molten-salt reactor designs. U.S.-based Kairos Power is building Hermes, a salt-cooled test reactor at Oak Ridge, Tennessee, on ground not far from where the original MSRE operated. In December 2023, the U.S. Nuclear Regulatory Commission granted Kairos a construction permit for Hermes, making it the first non-light-water reactor approved for construction in the United States in over 50 years.

Other companies designing reactors with salt cooling include TerraPower, the Bill Gates-backed venture which broke ground in 2024 on its Natrium reactor demonstration project; Terrestrial Energy in Canada; and Copenhagen Atomics in Denmark, which is developing 100-MWth thorium molten salt reactors for deployment by 2030.  In August of last year, Indonesia’s ThorCon International received the first stage of approvals for its ThorCon 500 molten-salt reactor.

Still, as of publication, TMSR-LF1 remains the only operational molten-salt reactor on the planet since Oak Ridge, and is the only reactor to have successfully incorporated thorium fuel. That designation won’t last. China has already broken ground on a larger, 10 MWe demonstration reactor, also slated for completion by 2030. Located near TMSR-LF1 in Gansu Province, the new facility will aim to produce 60 MW of thermal energy, generating both electricity and hydrogen.

Hurdles to the scaling of thorium-fuel reactors

Plenty of technical, economic, and political hurdles remain, however. For all its abundance, thorium is difficult and expensive to extract, requiring harsh, energy-intensive, and costly chemical processing to isolate it from rare-earth minerals like monazite. The world also currently lacks regulatory frameworks for thorium fuel cycles and established thorium fuel-fabrication facilities and supply chains. Critics also point out that thorium-fueled reactors still require uranium or plutonium as a driver to initiate and maintain the necessary chain reaction. None of the available drivers are easy to supply.

Waste management also remains an issue. Thorium reactors do create much less long-lasting radioactive waste than their uranium counterparts. But they still generate a complex mix of fission products that must be handled properly.

Nevertheless, China appears confident in its claim as one of the leaders in the next era of nuclear energy. As one Beijing-based geologist put it to the South China Morning Post, “For over a century, nations have been engaging in wars over fossil fuels. It turns out the endless energy source lies right under our feet.” A 100-megawatt commercial prototype is planned for 2035.

Further reading 

^{Nuclear Engineering International: China refuels thorium reactor without shutdown
Southern Nuclear: Water—precious for life and important for generating electricity
Power Mag: China’s molten salt reactor reaches thorium-uranium conversion milestone
Power Mag: China’s advanced nuclear efforts are pushing frontiers
The Breakthrough Institute: Nuclear reactors don’t need to be so thirsty
World Nuclear Association: Thorium}