Chinese scientists have refuelled an experimental thorium-fueled molten salt reactor continuously without shutting it down. The Chinese prototype reached full operational power in June 2024, and in October researchers reloaded fuel while the reactor remained online, a world-first. This achievement was announced recently by Xu Hongjie, head of the scientific team responsible for the thorium reactor project, during a closed meeting of the Chinese Academy of Sciences (CAS). “We are now at the frontier of global nuclear innovation,” he said.
Xu and his team at the Shanghai Institute of Applied Physics (SINAP – part of CAS) developed the technology based on declassified research from the USA. He explained that researchers in the US had been building and testing early molten salt reactor technology since the 1960s, but did not develop it further, choosing to focus on uranium fuelled pressurised water reactor technology.
“The US left its research publicly available, waiting for the right successor. We were that successor,” he told the CAS meeting. “We mastered every technique in the literature – then pushed further.”
The Molten Salt Reactor Experiment (MSRE) at Oak Ridge National Laboratory (ORNL) was an experimental molten-salt research reactor which went critical in 1965, and was operated until 1969. It was closed after all the objectives of the experiment were achieved. The reactor was left in standby for nearly a year. A limited examination programme was then carried out after which the radioactive systems were closed pending ultimate disposal. It primarily used two fuels: first uranium-235 and later uranium-233. The 233 UF4 was the result of breeding from thorium in other reactors.
China has been quietly reviving this abandoned technology since 2011. Xu said construction of the experimental reactor in the Gobi Desert began in 2018. He noted that their team grew from initially several dozen people to more than 400.
The reactor design uses molten fluoride salts to dissolve the thorium fuel, functioning both as a coolant and as a carrier of fissile material. This allows the system to operate at high temperatures exceeding 700°C, but without the high pressures associated with traditional reactors. The use of thorium-232, which must be converted into fissile uranium-233, enables a completely different nuclear fuel cycle with a lower risk of proliferation and significantly fewer long-lived radioactive waste products.
Thorium is not only more abundant than uranium – available in three to four times greater quantities globally – but also less suitable for weapons production The reactor produces very low amounts of plutonium-239, the isotope commonly used in nuclear weapons, and the uranium-233 bred from thorium is more difficult to separate and utilise for military purposes. According to Chinese reports, the plutonium content of thorium reactor waste is “much lower” than in conventional nuclear systems.
The reactor also has passive safety features. In the event of overheating or power failure, the system uses a “frozen salt plug” at the bottom of the reactor vessel that melts automatically, allowing molten radioactive salt to drain into a secondary cooling chamber. This gravity-fed shutdown prevents meltdowns without requiring active control or external intervention.
China has already broken ground on a larger, 10 MWe demonstration reactor, also located near Wuwei in Gansu Province, which will generate both electricity and hydrogen. This facility, slated for completion by 2030, is designed to produce 60 MW of thermal energy, contributing to China’s larger goal of building a renewable and low-carbon energy hub in the desert.
The thorium molten salt system is also being eyed for non-electrical applications. The high temperatures of the reactor make it ideal for thermochemical hydrogen production, potentially transforming the economics of green hydrogen. There are also early-stage concepts for thorium-powered ships, particularly container vessels. These could run for years without refuelling, significantly reducing maritime emissions.
However, Chinese scientists point out that this is no instant victory. According to Guangming Daily, there are “no quick wins” and technical hurdles remain significant. The corrosive nature of molten salts, for instance, demands custom-built alloys like Hastelloy-N, capable of withstanding both radiation and chemical degradation. These materials must function reliably for decades, under extreme temperatures and in radioactive environments.
The SINAP team used the current 2 MW reactor as a materials testbed, experimenting with corrosion-resistant graphite and metals. These validations are essential before scaling up. Another challenge is thorium’s nature as a fertile, rather than fissile, material. The reactor needs an initial load of uranium-235 or plutonium-239 to start the chain reaction until enough uranium-233 is bred from the thorium.
Furthermore, the online chemical processing required to remove fission byproducts and balance salt chemistry adds another layer of complexity. Unlike conventional reactors that rely on solid fuel rods, thorium reactors must continuously manage liquid radioactive material, which presents unique engineering and safety challenges.
Even waste management remains an open issue. While thorium reactors generate far less long-lived waste, they produce a complex mix of fission products that must be handled with care. China plans to store this waste underground in the Gobi Desert, capitalising on the region’s geological stability and arid conditions.
Yet, despite these challenges, the message from Chinese researchers is clear. “The United States left their findings open to the world,” said Xu Hongjie told the CAS meeting, referencing the declassified American research. “We have been that successor.”
