Ilaria Rosella Pagliaro China inaugurates the world's first fusion-resistant nuclear reactor, a breakthrough technology that promises a safer future for nuclear energy
©Tsinghua University
A large-scale nuclear plant in China has become the first in the world to be completely immune to dangerous core meltdown incidents, even in the event of a total loss of external power. While this design cannot be retrofitted to existing nuclear reactors worldwide, it may serve as a model for future developments.
How modern nuclear plants operate
Modern nuclear power plants are designed with numerous safety systems to prevent catastrophic explosions. While older nuclear plants have experienced steam explosions caused by positive void reactions, as seen in Chernobyl, modern plants, especially third and fourth-generation ones, are equipped with multiple passive and active safety systems. These systems include:
- Emergency Cooling Systems: To prevent the core from overheating.
- Multiple Containment Barriers: To prevent the release of radioactive materials.
- Inherently Safe Designs: Reactors designed to shut down automatically in the event of anomalies.
Though it cannot be said with absolute certainty that an explosion is impossible, the likelihood of such an event is extremely low due to technological advancements and stringent safety protocols. Water or liquid carbon dioxide is often used as coolants, but these typically rely on external power sources to function.
If these systems fail, reactors can overheat, leading to explosions or overheating, causing the plant to melt down due to excess heat. In a world-first achievement, researchers at Tsinghua University in China successfully demonstrated a fusion-resistant nuclear fission reactor. The twin-reactor design can generate 105 MW of power each and has been in development since 2016. This technology is a positive step for the nuclear energy industry after the meltdown at Fukushima in Japan over a decade ago.
Advantages of the pebble-bed nuclear reactor
Conventional nuclear reactors use high-energy-density fuel rods, containing large amounts of uranium with small amounts of graphite. In the HTR-PM reactor design, the fuel rod is inverted, and a large amount of graphite encapsulates the uranium. This makes the fuel’s energy density much lower, resembling pebbles in a larger body of water.
This approach has two main advantages. First, the nuclear fission reaction occurs much more slowly than in a conventional reactor and can withstand higher temperatures for longer periods. The second advantage is that the excess heat generated during the process is dispersed over a larger fuel area and can be cooled using passive or non-energy-consuming methods, such as conduction and convection.
However, the Chinese reactor is not the first with self-moderating capabilities: there are other technologies like MRS (Molten Salt Reactors), FNRs (Fast Neutron Reactors), and iPWRs (integral Pressurized Water Reactors), known for features that allow them to reduce or control the nuclear reaction under abnormal conditions.
China’s ambitious nuclear effort
China is constructing nuclear reactors at an unprecedented pace, but attempting to build a commercial-scale nuclear reactor for a new technology is a first for the country.
The Institute of Nuclear and New Energy Technology began constructing the commercial-scale HTR-PM at a Shandong facility in 2016, with the expectation that the site would be ready for testing a year later. The reactor began commercial operation only in December 2023. To demonstrate that it could cool itself without an external power source, the team shut down both modules while they were running at full power and began monitoring temperature changes inside the reactor.
As expected, the reactors naturally cooled down and reached a stable temperature 35 hours after the shutdown. However, this technology cannot be retrofitted to existing nuclear reactors. To build a future where nuclear reactors are meltdown-proof, the nuclear energy industry will first need to construct HTR-PM reactors.
Source: Tsinghua University
