The first successful experiment with a self-cooling nuclear reactor in emergency situations has proven that it is possible to build a nuclear power plant without the risk of a meltdown.
The large-scale nuclear power plant in Shandong, China, is the first in the world to have no risk of meltdown, even in the event of a complete power outage. This design cannot be applied to existing nuclear reactors worldwide, but it may pave the way for future versions, according to New Scientist on July 19.
The HTR-PM reactor located in Shandong. (Photo: China Huaneng Group).
All modern nuclear power plants rely on cooling mechanisms that use electricity to remove excess heat from the reactor or depend on human intervention to shut down the plant in emergencies. Water or liquid carbon dioxide is commonly used as a coolant, but they often depend on external power supplies for operation.
If these systems fail, the reactor can overheat, leading to an explosion or overheating which can result in a meltdown due to excess heat. This factor contributed to the Fukushima nuclear disaster in Japan in 2011, where both standard and emergency power systems were lost, resulting in a meltdown.
The relatively new reactor design known as the Pebble Bed Reactor (PBR) offers a safety advantage, meaning that if cooling system power is lost, the reactor can safely shut down. Instead of using high-density fuel rods like many other reactor designs, the PBR utilizes a large number of low-density “pebbles” as fuel. These pebbles contain small amounts of uranium surrounded by graphite. This design can help slow down the nuclear reaction and withstand high temperatures. The low energy density means that any excess heat will disperse across all the pebbles, making it easier to dissipate through natural cooling processes such as heat conduction and convection, according to researcher Zhe Dong from Tsinghua University, China.
While small prototypes of PBRs have been developed in Germany and China, there has yet to be a full-sized PBR operating safely. Dong and colleagues demonstrated the system’s operation with the full-sized nuclear power plant through the High-Temperature Gas-Cooled Reactor Pebble Bed Module (HTR-PM) in Shandong. Previously, all commercial reactors except for the HTR-PM had emergency core cooling systems. However, due to its inherent safety, the HTR-PM plant does not require such systems.
To test the commercial reactor, in December 2023, Dong and colleagues shut down both modules of the HTR-PM while they were operating at full capacity, measuring and monitoring the temperatures of various parts of the plant afterwards. They found that the HTR-PM naturally cooled down and reached a stable temperature within 35 hours after the power outage.
