China Built a Nuclear Power Plant That Technically Can’t Melt Down
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China Built a Nuclear Power Plant That Technically Can’t Melt Down
It stays cool on its own, even during a crisis.
- A new peer-reviewed paper details two tests of a nuclear plant that can’t melt down.
- The durability is due to natural qualities, like insulated fuel and the density of heated gas.
- China’s HTR-PM
reactor joins
planned pebble beds and other safe designs around the world.
Scientists in China have now designed and tested a nuclear fission power plant that can keep itself cool even during a power outage—meaning it completely avoids the runaway heating and disaster known as nuclear meltdown. This is not a design that can be retrofitted to existing nuclear fission plants, however, because it involves a new paradigm called a pebble bed reactor. The team’s findings appear now in the peer-reviewed journal Joule.
Traditional nuclear fission reactors hold fuel in a reservoir of water, typically diverted from a nearby river and pumped using electricity. The hot nuclear fuel heats the water and creates a lot of steam—hence the iconic nuclear tower with a fluffy steam plume coming out.
But if the plant loses power in an emergency and is not able to rely on backup power, the fuel can continue to heat past the point of boiling the water away (or trapping the superheated water if the reactor is pressurized). The nuclear fuel heats until it melts, then melts its containment and continues to breach the rest of the plant construction—it literally melts downward and takes the plant down with it. Deadly radiation and chemical pollution follow.
Scientists have been working toward safer nuclear plant designs for decades because of the seeming inevitability of risks like this. Many people can easily name Chernobyl, Fukushima, and Three Mile Island off the top of their heads. These disasters have cost hundreds of thousands of human lives over decades—from the emergencies themselves to the long tail of cancer and other illness. And cynically, they’ve set nuclear power back in the public eye. As more people in the energy industry turn to nuclear as a less environmentally impactful stopgap during the green transition, they also know that nuclear needs a safety and image upgrade.
This is where pebble bed plants, and the special fuel they use, enter the picture. The Chinese research team uses TRISO fuel (short for tristructural isotrope), which comes in a form similar to a layered jawbreaker or malt ball. Coated kernels of uranium fuel sit at the center of these pebbles of fuel, and outsides are coated and recoated with ceramic. While the fuel design is relatively new in the commercial and public sphere, it actually dates back decades to a time when nuclear researchers were trying a dozen or more very experimental designs to find the best way forward.
“The TRISO particles are able to prevent fission product release from fuel elements under a maximum temperature of 1620C, thereby determining the mean power density to be about [...] 1/30 of that of a commercial pressurized water reactor,” the researchers wrote. And the heat generated by this lower density fuel “can be dissipated to the environment naturally,” they explain, “by heat conduction, radiation, and natural convection.”
China’s working pebble bed reactor is called HTR-PM, and is located at Shidao Bay Nuclear Plant near the eastern tip of Shandong Province—the peninsula where a Chinese dissident was able to launch his 186-mile jet ski escape to South Korea last year. The reactor has been in service since 2022, and underwent two full tests of its ability to recover from total power loss—one in August of 2023 and one in September of 2023.
During the tests, the reactor worked as designed—transferring the excess heat to the surrounding structure that was specially designed to support it without power. Instead of overheating and melting through, the fuel reached a much lower maximum temperature dictated by its layered and insulated design. Inside the reactor space, helium gas circulated naturally as it was heated from below and cooled above. The reactor reached a maximum temperature of just 870°C after 3.5 hours without power. For context, the 2011 Fukushima meltdown reached 2800°C. 870°C, while incredibly hot, isn’t enough to melt stainless steel (of any grade), cast iron, or even brass.
This reactor is not the only TRISO game in town. Nuclear engineering powerhouse (pun intended) University of Illinois at Urbana Champaign and the Italy-based Ultra Safe Nuclear Corporation are also in the mix, collaborating on a TRISO-powered microreactor on the UIUC campus. But the project in China produces 200 MW of power, making it a small reactor instead of a microreactor (which only makes up to about 20 MW of power). Ultra Safe calls their design a “battery” because of its full, locked enclosure.
In 2021, Ultra Safe engineer and founder Francesco Venneri told Popular Mechanics that the ancestry of TRISO reactors like his isn’t on land at all—it’s in nuclear submarines. “A submarine,” he said, “is like a high-velocity sports car: It needs to go up and down in power very quickly.”
Indeed, careful and rigorous design can turn a brittle, meltdown-vulnerable traditional fission reactor into something more flexible and safe. And all it takes is a step down in power density and a smarter approach to materials. These scientists believe our future is worth the tradeoff.