abstract:A traveling-wave reactor (TWR) is a type of fourth-generation nuclear reactor that nuclear engineers anticipate can convert fertile material into usable fuel through nuclear transmutation in tandem with the burnup of fissile material. TWRs differ from other kinds of fast-neutron and breeder reactors in their ability to utilize fuel efficiently without uranium enrichment or reprocessing, instead directly using depleted uranium, natural uranium, thorium, spent fuel removed from light water reactors, or some combination of these materials.