All of sudden I'm seeing articles and videos about thorium, a radioactive metal once considered for nuclear power plants but rejected in favor of uranium. This article from Popular Mechanics actually has the best executive summary. A snippet, with my highlights:
Three to four times more plentiful than uranium, today's most common nuclear fuel, thorium packs a serious energetic punch: A single ton of it can generate as much energy as 200 tons of uranium, according to Nobel Prize-winning physicist Carlo Rubbia. In the mid-twentieth century, some U.S. physicists considered building the nuclear power landscape around thorium. But uranium-fueled reactors produced plutonium as a byproduct, a necessary ingredient for nuclear weapons production, and uranium ended up dominating through the Cold War and beyond.
In a traditional light water reactor, uranium-235 interacts with uranium-238 to produce plutonium-239 as a byproduct—a radioactive isotope that can be used for weapons. But when thorium is used instead of uranium-238 as a fertile material to kickstart nuclear fission, the thorium eventually "becomes uranium-233, which fissions almost instantaneously in the reactor, generating other isotopes that make power," Grae says. That means usable weapons-grade nuclear material is not produced, which would theoretically eliminate some security issues now associated with nuclear plants. Grae also claims thorium-powered light water reactors produce a much smaller volume of waste products that decay to relatively safe levels in just six to seven hundred years.