A traveling wave reactor is a type of Generation IV nuclear reactor that much of the nuclear industry anticipates can convert fertile material into nuclear fuel via nuclear transmutation in tandem with the burnup of fissile material. This particular design is very different from other kinds of fast-neutron and breeder reactors in their ability to utilize fuel efficiently without costly and impractical enrichment or reprocessing of uranium. TWRs instead directly use depleted uranium, natural (unenriched) uranium, thorium, spent fuel removed from light water reactors, or potentially a combination of these materials.
The “traveling wave” name refers to the fact that fission will not occur throughout the entire core, but remains confined to a boundary zone that slowly advances through the core over time. Theoretically, TWRs could run self-sustained for decades without having to remove and replace spent fuel from the reactor.
Some have criticized this implementation of the fast breeder reactor design as particularly difficult, especially given the fact that typical fast breeder reactors are already hard to build. Many have lauded the goal of addressing the global energy poverty with TWRs but have pointed out that its overall cost of construction is competitive with conventional nuclear power, and that isn’t as low as fossil fuels. Bill Gates has invested deeply into the development of TWRs not, as he stated in an interview, because he “expects to make a ton of money on it,” but because this Generation IV design is “very attractive from an economic point of view.”
Image: Conceptual design of the TWR.
GIF: A numeric simulation of a TWR. Red: Uranium-238. Light Green: Plutonium-239. Black: Fission products. The intensity of the blue color between the tiles indicates neutron density.