A long-abandoned US nuclear technology is making a comeback in China

You can basically copy and paste that line into countless stories about today’s advanced reactor technology. Molten-salt cooling systems? Invented in the mid-20th century but never commercialized. Same for several alternative fuels, like TRISO. And, of course, there’s thorium.

This one research reactor in China running with an alternative fuel says a lot about this moment for nuclear energy technology: Many groups are looking into the past for technologies, with a new appetite for building them.

First, it’s important to note that China is the hot spot for nuclear energy right now. While the US still has the most operational reactors in the world, China is catching up quickly. The country is building reactors at a remarkable clip and currently has more reactors under construction than any other country by far. Just this week, China approved 10 new reactors, totaling over $27 billion in investment.

China is also leading the way for some advanced reactor technologies (that category includes basically anything that deviates from the standard blueprint of what’s on the grid today: large reactors that use enriched uranium for fuel and high-pressure water to keep the reactor cool). High-temperature reactors that use gas as a coolant are one major area of focus for China—a few reactors that use this technology have recently started up, and more are in the planning stages or under construction.

Now, Chinese state media is reporting that scientists in the country reached a milestone with a thorium-based reactor. The reactor came online in June 2024, but researchers say it recently went through refueling without shutting down. (Conventional reactors generally need to be stopped to replenish the fuel supply.) The project’s lead scientists shared the results during a closed meeting at the Chinese Academy of Sciences.

I’ll emphasize here that this isn’t some massive power plant: This reactor is tiny. It generates just two megawatts of heat—less than the research reactor on MIT’s campus, which rings in at six megawatts. (To be fair, MIT’s is one of the largest university research reactors in the US, but still … it’s small.)

Regardless, progress is progress for thorium reactors, as the world has been entirely focused on uranium for the last 50 years or so.

Much of the original research on thorium came out of the US, which pumped resources into all sorts of different reactor technologies in the 1950s and ’60s. A reactor at Oak Ridge National Laboratory in Tennessee that ran in the 1960s used Uranium-233 fuel (which can be generated when thorium is bombarded with radiation).