Lately an unfamiliar type of advanced reactor has been getting more attention, because one Democratic presidential candidate has been talking about it. Andrew Yang, a tech entrepreneur, has put development of thorium reactors into his climate change platform.

But what is a thorium reactor?

Thorium is an abundant, lightly radioactive metal—named by its Swedish discoverer after the Norse god, Thor—that can be used in certain types of nuclear reactors. It isn’t really fuel, because it can’t be split like uranium can. But when thorium is placed in a reactor, it absorbs some of the neutrons that are given off by fission. A thorium atom that picks up a neutron becomes a new element—uranium 233, which is a reactor fuel. So, a reactor can cook thorium into reactor fuel, and then consume the fuel to make electricity.

Thorium is about three times more abundant than uranium. It’s already produced by mining companies as a byproduct, and it has a variety of non-nuclear uses. Plus, used fuel from thorium reactors contains minimal amounts of very long-lived radioactive materials compared to current uranium fuel, so disposing of waste is easier.

There are no thorium reactors running today, but Flibe Energy Inc., a startup based in Huntsville, Alabama, has an advanced reactor design that uses thorium and molten salt. Employing molten salt in place of water (to transfer heat from the fuel) allows a reactor to operate at a higher temperature and at lower pressure, which means it doesn’t need a super-strong and expensive reactor vessel and piping.

Heat from a high-temperature thorium reactor—whether molten salt or other—could be used in a variety of applications to displace fossil fuels, such as producing hydrogen for transportation or industrial use. Like all reactors, a thorium reactor would be carbon-free. And it would be dispatchable, meaning that it would run when needed and not simply when weather conditions permitted.

Thanks to work done in the U.S. national laboratories in the 1960s, the molten salt that Flibe proposes for a thorium reactor is already familiar to engineers. Still, deploying thorium reactors will require additional research and development, which is why Yang has proposed $50 billion dollars for thorium research (along with fusion).

Advanced nuclear technologies, including thorium reactors, are a promising component of a future with reduced carbon emissions and a stable climate.