"Fission chain" refers to a process where the nucleus of an atom splits into two smaller nuclei, releasing a large amount of energy in the form of a chain reaction. Full definition
On December 2, 1942, scientists watched as the nuclear reactor that had been constructed beneath the University of Chicago's football stadium produced the first controlled, sustained fission chain reaction. (sciencenews.org)
Fast reactors, in contrast to thermal reactors, utilize fast neutrons for a sustained fission chain reaction. (nuclearstreet.com)
December 2 marks the semisesquicentennial (75th anniversary) of the first controlled and sustained nuclear fission chain reaction. (sciencenews.org)