Why China Is Building a Thorium Molten-Salt Reactor

After a half-century hiatus,thorium has returned to the front lines of nuclear power research as a source of fuel. In 2025, China plans to start building a demonstration thorium-based molten-salt reactor in the Gobi Desert.

The 10-megawatt reactor project, managed by the Chinese Academy of Sciences’ Shanghai Institute of Applied Physics (SINAP), is scheduled to be operational by 2030, according to an environmental-impact report released by the Academy in October. The project follows a 2-MW experimental version completed in 2021 and operated since then.

China’s efforts put it at the forefront of both thorium-based fuel breeding and molten-salt reactors. Several companies elsewhere in the world are developing plans for this kind of fuel or reactor, but none has yet operated one. Prior to China’s pilot project, the last operating molten-salt reactor was Oak Ridge National Laboratory’s Molten Salt Reactor Experiment, which ran on uranium. It shut down in 1969.

Thorium-232, found in igneous rocks and heavy mineral sands, is more abundant on Earth than the commonly used isotope in nuclear fuel, uranium-235. But this weakly radioactive metal isn’t directly fissile–it can’t undergo fission, the splitting of atomic nuclei that produces energy. So it must first be transformed into fissile uranium-233. That’s technically feasible, but whether it’s economical and practical is less clear.

China’s Thorium-Reactor Advances

The attraction of thorium is that it can help achieve energy self-sufficiency by reducing dependence on uranium, particularly for countries such as India with enormous thorium reserves. But China may source it in a different way: The element is a waste product of China’s huge rare earth mining industry. Harnessing it would provide a practically inexhaustible supply of fuel. Already, China’s Gansu province has maritime and aerospace applications in mind for this future energy supply, according to the state-run Xinhua News Agency.

Scant technical details of China’s reactor exist, and SINAP didn’t respond to IEEE Spectrum’s requests for information. The Chinese Academy of Sciences’ environmental-impact report states that the molten-salt reactor core will be 3 meters in height and 2.8 meters in diameter. It will operate at 700 °C and have a thermal output of 60 MW, along with 10 MW of electricity.

Molten-salt breeder reactors are the most viable designs for thorium fuel, says Charles Forsberg, a nuclear scientist at MIT. In this kind of reactor, thorium fluoride dissolves in molten salt in the reactor’s core. To turn thorium-232 into fuel, it is irradiated to thorium-233, which decays into an intermediate, protactinium-233, and then into uranium-233, which is fissile. During this fuel-breeding process, protactinium is removed from the reactor core while it decays, and then it is returned to the core as uranium-233. Fission occurs, generating heat and then steam, which drives a turbine to generate electricity.

But many challenges come along with thorium use. A big one is dealing with the risk of proliferation. When thorium is transformed into uranium-233, it becomes directly usable in nuclear weapons. “It’s of a quality comparable to separated plutonium and is thus very dangerous,” says Edwin Lyman, director of nuclear power safety at the Union of Concerned Scientists in Washington, D.C. If the fuel is circulating in and out of the reactor core during operation, this movement introduces routes for the theft of uranium-233, he says.

Thorium Fuel Charms Nuclear-Power Sector

Most groups developing molten-salt reactors are focused on uranium or uranium mixtures as a fuel, at least in the short term. Natura Resources and Abilene Christian University, both in Abilene, Texas, are collaborating on a 1-MW liquid-molten-salt reactor after receiving a construction permit in September from the U.S. Nuclear Regulatory Commission. Kairos Power is developing a fluoride-salt-cooled, high-temperature reactor in Oak Ridge, Tenn., that will use uranium-based tri-structural isotropic (TRISO) particle fuel. The company in October inked a deal with Google to provide a total of 500 MW by 2035 to power its data centers.

But China isn’t alone in its thorium aspirations. Japan, the United Kingdom, and the United States, in addition to India, have shown interest in the fuel at one point or another. The proliferation issue doesn’t seem to be a showstopper, and there are ways to mitigate the risk. Denmark’s Copenhagen Atomics, for example, currently aims to develop a thorium-based molten-salt reactor, with a 1-MW pilot planned for 2026. The company plans to weld it shut so that would-be thieves would have to break open a highly radioactive system to get at the weapon-ready material. Chicago-based Clean Core Thorium Energy developed a blended thorium and enriched uranium (including high-assay low-enriched uranium, or HALEU) fuel, which they say can’t be used in a weapon. The fuel is designed for heavy-water reactors.

Political and technical hurdles may have largely sidelined thorium fuel and molten-salt-reactor research for the last five decades, but both are definitely back on the drawing table.