Deep in the Gobi Desert, China’s experimental thorium molten salt reactor has quietly achieved a milestone once thought decades away: refuelling while operating and converting thorium into uranium 233 inside a running liquid fuel core. This achievement, recently highlighted in a video by BeyondTheBuild (watch below), marks a meaningful step from theory into functioning technology.

The 2 megawatt thermal TMSR LF1 reactor near Wuwei reached full power in 2024. Though small, it represents the first modern liquid fuel thorium system brought online since the 1960s Oak Ridge experiments. Its molten fluoride salt fuel operates near atmospheric pressure and incorporates a thorium uranium fuel mix circulating at roughly 630 to 650 degrees Celsius.

Recent reports from Chinese institutions confirm that operators added thorium bearing salt while the reactor remained critical. Independent coverage also noted that the core produced uranium 233 from thorium during operation. These steps demonstrate core capabilities that had, until now, existed mainly on paper or in isolated lab loops.

TMSR LF1 is still a research machine with limited annual operating days and a ten year design life. But it is an active testbed for the materials, chemistry and neutron economy that full scale systems will require.

Traditional reactors pause every year or two to replace solid fuel assemblies. By contrast, molten salt reactors dissolve fuel in liquid form, allowing new material to be added and some waste products removed without shutting the core down. Reactors such as Canada’s CANDU already demonstrated online refuelling using solid channels, but liquid fuel makes the process far simpler and more continuous.

China’s demonstration was the first time a thorium molten salt reactor refuelled while operating. That does not make it a self sustaining breeder, and its conversion ratio remains modest. Still, it proves that the fundamental liquid fuel refuelling concept works in a real reactor at scale.

Thorium is abundant and globally distributed. When converted to uranium 233, it can sustain a fission chain reaction. India, which holds some of the world’s largest thorium reserves, built its three stage nuclear plan around this idea. International studies from the IAEA and research groups have long suggested that closed thorium cycles could extend global nuclear fuel supply for centuries.

China’s reactor does not yet close the fuel cycle, but it demonstrates a crucial step toward a system where fertile thorium can play a major long term role in clean energy production.

Molten salt reactors operate without the high pressure systems that underpin many severe accident scenarios in water cooled reactors. The liquid fuel expands as it heats, naturally reducing reactivity, and the design incorporates a freeze plug that drains the core into passively cooled tanks if temperatures rise too far. Studies of molten salt designs consistently show they avoid traditional meltdown routes and limit the potential for large radiological releases.

Thorium based cycles also generate significantly less long lived transuranic waste. With effective recycling, the radiotoxicity of the remaining waste can fall to near natural uranium levels in a few hundred years rather than tens of thousands.

China’s next step is a planned 10 megawatt electric molten salt reactor targeted for around 2030. Official documents outline long term goals for larger units capable of providing industrial heat, hydrogen production and high temperature process energy, all in regions where water cooled reactors cannot operate.

Whether this becomes a major industry or remains a specialised research path will depend on solving materials challenges, managing online fuel processing at scale and developing regulatory frameworks for reactors that do not resemble conventional nuclear plants. China’s advantage is that it is learning these lessons in hardware while most countries remain at the design stage.

The Gobi Desert reactor is small, and the challenges ahead are large. But for the first time in half a century, a thorium fuelled molten salt reactor is running, producing power and demonstrating capabilities needed for future commercial systems. The achievement does not rewrite global energy overnight, but it marks the first concrete step toward a technology long seen as promising and perpetually out of reach.