Breeder Reaction: Fast neutrons convert the (238U) uranium isotope, which does not directly undergo fission, to (239Pu) plutonium. A breeder reactor is a nuclear reactor that is designed to produce more fissile material than it uses up.
Fast neutrons convert the (238U) uranium isotope, which does not directly undergo fission, to (239Pu) plutonium.
source: Beyond Oil and Gas