The first test of a nuclear reactor that cools itself in case of emergency was successful, proving that it is possible to build a nuclear power plant without the risk of a meltdown.
The massive nuclear power plant in Shandong, China, is the world’s first to be completely free of the risk of meltdown, even in the event of a total power outage. The design is not applicable to any of the world’s operating nuclear reactors, but it could pave the way for future versions, New Scientist July 19 news.
All modern nuclear power plants rely on electrical cooling to remove excess heat from the reactors or on human intervention to shut down the plant in an emergency. Water or liquid carbon dioxide are often used as coolants, but they often rely on external power supplies to operate.
If these systems fail, the reactor could overheat, leading to an explosion, or overheat, causing the plant to melt down from the excess heat. This was a contributing factor to the 2011 Fukushima nuclear disaster in Japan, where both standard and emergency power systems were lost, leading to a meltdown.
The relatively new reactor design, called the gravel bed reactor (PBR), has a safety advantage, meaning that if the power to the cooling system is lost, the reactor can safely shut itself down. Instead of using high-energy-density fuel rods like many other reactor designs, the PBR uses large quantities of low-energy-density “gravel” as fuel. The gravel contains a small amount of uranium, surrounded by graphite. This can help slow down the nuclear reaction and withstand high temperatures. The low energy density means that any excess heat is spread out over all the gravel, making it easier to move away by natural cooling processes such as conduction and convection, according to researcher Zhe Dong of Tsinghua University in China.
While small reactor prototypes have been built in Germany and China, no full-scale PBR has been shown to operate safely to date. Dong and his colleagues demonstrated the system in action with a full-scale nuclear plant using the High-Temperature Gas-Cooled Gravel Bed Modular Reactor (HTR-PM) in Shandong. All commercial reactors except the HTR-PM have had an emergency core cooling system. However, because of its inherent safety, the HTR-PM plant does not need such a system.
To test the reactor for commercial operation in December 2023, Dong and his colleagues shut down both modules of the HTR-PM while they were running at full power, then measured and monitored the temperatures of various parts of the plant. They found that the HTR-PM cooled naturally and reached a stable temperature within 35 hours of the power failure.