Thorium-uranium Conversion Makes Breakthrough

In early November, the experimental operation of a 2-megawatt liquid-fuel thorium-based molten salt reactor (TMSR), led by the Shanghai Institute of Applied Physics, Chinese Academy of Sciences (CAS), achieved the world's first thorium-uranium nuclear fuel conversion in Wuwei, Gansu province.

This landmark breakthrough has provided core technical support and feasible solutions for the future large-scale exploration and utilization of thorium resources in China, as well as for the development of fourth-generation advanced nuclear energy systems.

Abundant thorium resources

Energy security is a fundamental and strategic issue that affects the overall development of a country's economy and society. The shortage of energy supply caused by the rapid growth in electricity demand means that nuclear energy has become an important new energy option for resolving the energy crisis.

At present, the main fissile isotopes used as nuclear fuel in reactors include uranium-235, plutonium-239, and uranium-233. Although these resources are limited, thorium — a fertile rather than fissile element — is more abundant in nature and can be converted into uranium-233 for use in nuclear power generation. China possesses significant thorium reserves, largely associated with its rare-earth mining industry. The TMSR is a fourth-generation nuclear energy system that uses thorium fuel and high-temperature molten salt as the coolant. It operates at near-atmospheric pressure without the need for water cooling and offers high thermal efficiency and enhanced safety features.

This technology is designed to integrate with industries such as solar and wind power, high-temperature molten salt energy storage, hydrogen production, and coal-to-chemical processes. By doing so, it aims to form a multi-energy complementary, low-carbon composite energy system that enhances efficiency and reduces emissions.

TMSR convenient and safe

Most conventional nuclear power plants are located along the coast, because a large amount of water is needed for cooling the reactor core. "Unlike the currently widely used pressurized water reactors, the TMSR uses high-temperature liquid molten salt as the coolant.

There is no need for huge pressure vessels or a large amount of water for cooling. It's like generating electricity by flowing 'nuclear fuel' through 'high-temperature salt,' which is both safe and efficient," according to researchers of the Shanghai Institute of Applied Physics, CAS.

Because there is no need of water as a coolant, the TMSR is expected to enable the construction of safe and highly efficient nuclear power plants in inland areas.

According to researchers, when a reactor needs to add nuclear fuel, conventional pressurized water reactors need to be shut down regularly and the top cover of the pressure vessel needs to be opened to replace the nuclear fuel. However, the TMSR uses liquid fuel. The nuclear fuel is uniformly dissolved in the molten salt coolant and circulates along with it, allowing for fuel replenishment without shutting down the reactor.

The TMSR also has many safety features. When the temperature of the TMSR inside the reactor exceeds the predetermined threshold, the bottom freezing plug will automatically melt, and the molten salt carrying the nuclear fuel will all flow into the molten salt storage tank, thereby terminating the nuclear reaction. Meanwhile, the reactor operates under a normal pressure environment, with simple and safe operation. The fluoride salt coolant turns into a solid state after cooling, effectively preventing the leakage and spread of nuclear fuel, and also preventing it from interacting with groundwater and causing ecological disasters.

Tackling key tech barriers

In 2011, CAS initiated the TMSR nuclear energy system technology project, systematically overcoming a series of technical challenges such as the design of the experimental reactor, the development of key materials and equipment, installation and commissioning, as well as reactor safety. Ultimately, the overall self-made rate of the experimental reactor exceeded 90 percent, and all key core equipment was domestically produced, establishing an independent and controllable supply chain system.

From the implementation of the project to its stable operation, the construction of the experimental reactor has been advancing steadily. In June 2024, it achieved full-power operation for the first time, and in October 2024, it completed the world's first molten salt reactor with thorium. It was the first in the world to build a unique MSR and thorium-uranium fuel cycle research platform.

Now, the research team is conducting systematic studies on the key scientific issues related to adding thorium, and aims to complete the construction of a 100-megawatt TMSR demonstration project, and begin operation by 2035.

Source: Science and Technology Daily