Scientists have built the first-ever thorium reactor. 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. 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.