'Rabbits sometimes make mistakes or grow lazy. That's when the tortoise seizes its chance': Chinese scientists make nuclear power breakthrough using abandoned US research

For the first time ever, scientists in China have refueled an experimental nuclear reactor without shutting it down — a significant advance in weaning the world off fossil fuels and onto more efficient, low-carbon energy sources

The breakthrough, achieved using a prototype molten-salt design which runs on liquid thorium instead of uranium, means that China "now leads the global frontier" in nuclear innovation, the project's lead scientist, Xu Hongjie, said during an April 8 meeting at the Chinese Academy of Sciences.

Thorium reactors were first developed in the 1950s in the U.S., before it went all-in on uranium, according to the International Atomic Energy Agency. Following this decision, this early research was later declassified, and the Chinese researchers made use of it for the current project.

"The US left its research publicly available, waiting for the right successor. We were that successor," Xu said at the meeting, as reported by the South China Morning Post, which cites Guangming Daily. Drawing on Aesop's classic fable, he added: "Rabbits sometimes make mistakes or grow lazy. That's when the tortoise seizes its chance."

The secret facility housing the reactor, which came online in June 2024, is reportedly hidden away in the Gobi Desert in the north of the country near the Mongolian border. It can sustainably generate two megawatts (2MW) of energy — enough to power up to 2,000 households and about twice the minimum of standard utility-scale generators, which, according to the US Energy Information Administration (EIA), "have a nameplate generation capacity of at least 1 MW".

An abandoned technology, an abundant fuel

Thorium reactors are a type of molten salt reactor (MSR) that — as the name suggests — dissolve a fuel source into a molten salt, which can act as both a coolant and part of the fuel mix.

Once funneled inside the reactor chamber, this mixture is heated to temperatures above 1,112 Fahrenheit (600 degrees Celsius) and bombarded with high-energy neutrons, causing the thorium to form uranium-233 atoms that split and release energy via nuclear fission.

Molten salt nuclear reactors are considered significantly safer than their solid fuel counterparts as they can't suffer a meltdown — their already molten fuel simply cools and solidifies when exposed to air. This means that disasters such as those that happened at Chernobyl in 1986 and Fukushima in 2011 wouldn't be possible with a thorium reactor. The reactors also produce significantly less nuclear waste than standard uranium reactors. In fact, waste from solid fuel uranium reactors can be fed as fuel into molten salt reactors.

While uranium can be used in MSRs, scientists generally prefer thorium because it is easier to mine and three-times more abundant than uranium.

China has long targeted getting a fully-fledged thorium-powered power station online. The country contributes roughly 27% of the world's global carbon emissions, and Chinese President Xi Jinping intends to make it carbon-neutral by 2060.

Thorium is a particularly attractive way to meet this target for China because it recently discovered vast amounts of the element in its territory. A national geographical survey found the country has, by some estimates, enough of the material to satisfy its energy needs for 60,000 years, the South China Morning Post reported.

Molten-salt reactor concepts were first devised in 1946 as part of a plan by the United States Army Air Forces (the predecessor to the U.S. Air Force) to create a nuclear-powered supersonic jet.

But the experiments had too many snags, including the molten salt corroding the reactor metal, leading to their abandonment in 1954. Several groups have attempted to make viable thorium reactors since then, but the element's weak radioactivity made it difficult to build fission reactions up to sustainable levels.

It isn't yet clear how China, which has been working on thorium molten salt reactors since the 1970s, solved these technical problems. But Xu attributes it to consistent application.

"In the nuclear game, there are no quick wins," he said at the meeting. "You need to have strategic stamina, focusing on doing just one thing for 20, 30 years."