Breeding reactorA reactor generating more fissile material than it uses. (Se... in which the fissionSee 'nuclear fission'. chain reactionSelf-perpetuating reaction. In a fission chain reaction, a f... is maintained by thermal neutrons. Thermal breedingConversion of non-fissionable into fissionable material, e.g... reactors convert non-fissionable Th-232 in fissionable U-233. (See breeding reactorA reactor generating more fissile material than it uses. (Se...).