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The First Nuclear Reactor Lived Under Some Bleachers by a Football Field

Happy birthday to Chicago Pile-1. Rest in peace.
Image: DOE

On Nov. 16, 1942, engineers began work on the world's first nuclear reactor, which was then known as an "atomic pile." Chicago Pile-1 was a relatively simple affair devised at the University of Chicago under the supervision of the great physicist Enrico Fermi and brought to life in a makeshift lab underneath the stands of Stagg Field. Crews worked night and day to construct what Fermi described as a "a crude pile of black bricks and wooden timbers." It lead to a successful nuclear reaction only weeks later.


Chicago Pile-1 was of course part of the Manhattan Project. Civilian nuclear power in 1942 would have been a non-sequitur.

The pile. Image: Department of Energy

Fermi was selling CP-1 a bit short. The reactor was a neat arrangement of uranium pellets and graphite bricks. The uranium served as the fuel by emitting neutrons that might go on to collide with the nuclei of other uranium atoms within the pile, which would cause a fission reaction and lead to the release of more neutrons, and these would in turn go on to induce more, secondary reactions. The graphite, meanwhile, served to slow the neutrons down, thus making collisions more likely.

The pile had no cooling system, nor did it offer bystanders any protection from radiation. The reaction could be controlled using rods made of cadmium and indium that, when inserted into the reactor, would absorb free neutrons, thus making fission reactions less likely. They would still be up against many bricks of black graphite all working toward the opposite effect.

A painting of the reactor going critical. Image: Department of Energy

"Fermi had convinced Arthur Compton that his calculations were reliable enough to rule out a runaway chain reaction or an explosion," explains a Department of Energy history of the event. "But, as the official historians of the Atomic Energy Commission later noted, the 'gamble' remained in conducting 'a possibly catastrophic experiment in one of the most densely populated areas of the nation!'"

Between Nov. 16 and Dec. 1 the pile grew brick by brick. Workers took 12 hour shifts and, due to the graphite dust smeared everywhere, came to resemble coal miners. On the first, tests revealed that the pile was almost ready for action. The next day, after a steady six hours of reactions, CP-1 went critical. The reaction was self-sustaining.

In January, the reactor was moved to a more reasonable location in Illinois' Red Gate Woods, at the site of what would become Argonne National Laboratory. It received an upgrade in the form of a protective radiation shield and was renamed Chicago Pile-2. Not much later it was buried where it stood, obsolete.