Lee states, "One important comparison for the three major fissile nuclides, U, U, and Pu, is their breeding potential. A breeder is by definition a reactor that produces more fissile material than it consumes and needs a minimum of two neutrons produced for each neutron absorbed in a fissile nucleus. Thus, in general, the conversion ratio (CR) is defined as the ratio of fissile material produced to that destroyed...when the CR is greater than 1.0, it is called the breeding ratio (BR)... U offers a superior breeding potential for both thermal and fast reactors, while Pu offers a superior breeding potential for fast reactors."