China has been working on its pebble reactor, the HTR-PM, testing if the technology can operate without danger of nuclear meltdown. According to an Aug. 8, 2024 feature in Popular Mechanics, the reactor is located at the Shidao Bay Nuclear Plant, near the eastern tip of Shandong Province, and is one of several types of reactors that China is experimenting on as a part of its extensive nuclear energy program. The reactor uses TRISO fuel, which consists of coated kernels of uranium surrounded by several coats of ceramics.
In two tests, one in August 2023 and one in September 2023, power to the reactor was shut off completely. The reactor worked as designed, transferring the excess heat to the surrounding structure, which was developed 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, helium gas circulated naturally as it was heated from below and cooled above, reaching a maximum temperature of just 870°C. While this is very hot, it isn’t enough to melt stainless steel, cast iron, or even brass.