Scientists have built the first-ever thorium reactor.
Thorium is both more easily accessible and less dangerous than uranium—the most common fission fuel.
The system also uses molten salt instead of water to cool the fission reactor, which is reportedly much safer in the event of a meltdown.
Uranium (U) is the poster child for nuclear fission reactors—the most common type of nuclear reactor we have. Most fission reactors are fueled by the isotope uranium-235 (it even made its way into The Simpsons as the glowing green sludge that spawns mutant fish), but despite its star status in pop culture and nuclear physics, uranium is not the only heavy metal that can release a tremendous amount of power when its nuclei are split.
In the remote expanse of the Gobi desert stands the first thorium (Th) reactor ever built. Last year, researchers from the Chinese Academy of Sciences showed that this two-megawatt reactor could power up and operate without a glitch, and they have now achieved another first—successfully reloading it while it was still running. Thorium-232 (the isotope of thorium that most commonly occurs on its own) is not capable of undergoing fission by itself. By capturing an extra neutron, however, it can morph into protactinium, which decays into U-233. This can be achieved by exposing the thorium to extreme radiation, which bombards it with enough neutrons for the transmutation to happen. Protactinium is then extracted from the reactor’s active zone before too many neutrons can be lost.
It is possible to recycle the U-233 decay into new fuel, or continue fueling the machine with it as is, the latter of which is usually done with molten salt reactors like this new thorium reactor. These reactors are gaining traction again after a decades-long hiatus—almost $1 billion was spent on developing stealth bomber planes with molten salt reactors that used thorium for nuclear power at the dawn of the Cold War era. When the first functional molten salt reactor was developed by scientists at Oak Ridge National Laboratory, it ran at full power from 1965 though 1969 (over 13,000 hours), but the Department of Energy lost interest and no further work was done to advance the technology until the early 2000s.
But that research remained available to the public, which is how China eventually discovered it and used it as a backbone for their own reactor. And, as it turns out, molten salt is still an appealing option. Most nuclear reactors use water as a coolant, but because water is volatile—high pressure needs to be maintained so that it stays in its liquid state. Without that pressure, the water evaporates, and reactor fuel could overheat and suffer a meltdown. Using molten salt prevents radioactive sludge from leaking because the boiling point of salt is too high for it to evaporate at reactor temperatures. In case of overheating, the molten salt circling the reactor will expand and halt the reaction.
Molten salt reactors can can also use molten salt in the fuel, which makes it prone to freezing in case of a breach (a very good thing). The fuel in those vessels or pipes will spread and cool until it finally freezes in place. China’s reactor uses salt both as coolant and in its fuel.
Thorium is not only more abundant than uranium, but has the upside of not being as easy to weaponize. While the fission of Th-232 produces protinactium, which decays into U-233 and can be used in nuclear weapons, U-233 isn’t nearly as explosive as other isotopes (the isotope most commonly used in uranium explosives is U-235). There wouldn’t be much of a point in dealing it to create an illicit nuclear bomb.
Though China may currently be the world leader in molten salt reactors, the U.S. is catching up. Nuclear tech company Core Power is planning an enormous floating network of these power plants within the next decade. We’ll just have to wait and see where the molten salt take us.
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