Remembering the Chicago Pile, the First Nuclear Reactor

On December 2, 1942, a team from the Metallurgical Laboratory assembled and started the Chicago Pile beneath the Stagg Field stands, achieving the first self-sustaining nuclear chain reaction. Built from some forty thousand graphite blocks in a wooden frame roughly twenty-five feet by twenty feet, the Pile contained holes packed with uranium oxide and a few nuggets of refined uranium metal. It had almost no engineered safety systems: control rods of cadmium were handled by hand, and reliance rested on untested calculations and secrecy. The experiment reached criticality, ran for about half an hour, and was deliberately shut down; it was later rebuilt with shielding at a more remote site as Chicago Pile-2 and provided operational data used to design reactors that produced plutonium for Trinity and the Nagasaki bomb.

The Pile was an operational node of the Manhattan Project, focused on producing fissile material rather than power. Wartime security classified many staff as risks or “enemy aliens,” prompting tighter control and the creation of Los Alamos for the most sensitive work. Some Chicago scientists - while contributing to weapon development - channeled their energies into policy and ethics: the Franck Report urged warning before using atomic bombs (its recommendation was ignored), and advocates pressed for “nucleonics,” national laboratories, and public engagement. Those efforts spawned organizations like the Bulletin of the Atomic Scientists and a persistent legacy of scientific activism; a University of Chicago plaque commemorates the achievement, while a suggested addendum - “for better or worse” - was declined.