The world's first nuclear reactor was a pile of bricks built under a stadium.

Countries & Cities · Published 29 September 2026 Swipe more like this →

In short: In 1942, Enrico Fermi led a team to construct Chicago Pile-1, the first artificial nuclear reactor. Built beneath the west viewing stands of Stagg Field, this crude assembly of graphite and uranium proved that a self-sustaining chain reaction was possible, changing the course of World War II and nuclear science forever.

The development of Chicago Pile-1 was a desperate race against the perceived scientific lead of Nazi Germany. While German researchers struggled with the belief that expensive heavy water was essential for a moderator, Fermi and Leo Szilard identified that high-purity graphite could serve the same purpose. They discovered that common contaminants like boron and cadmium were neutron poisons, leading to the production of ultra-pure AGOT graphite by National Carbon. This innovation was critical to the reactor's success.

The construction was an immense logistical undertaking, involving 45,000 graphite blocks and over 50 tons of uranium fuel. Because the project was under intense pressure, the team built the reactor in a squash court beneath the stands of the University of Chicago’s Stagg Field. Despite the inherent danger of operating a critical reactor in a densely populated urban area, Fermi’s safety calculations convinced leaders like Arthur Compton that the experiment could be controlled. The reactor operated at a mere half-watt, requiring no cooling system or radiation shielding.

The physics of the reactor relied on delayed neutrons, which provided a critical margin of safety. By monitoring the reaction, operators could inject neutron absorbers if the power spiked, preventing a runaway disaster. On 2 December 1942, this design successfully achieved the first human-made self-sustaining nuclear chain reaction. The success of the pile provided the first vivid demonstration that nuclear energy could be harnessed for military use, directly fueling the Manhattan Project’s goal of creating atomic weapons.

Following its success, the reactor was reconfigured into Chicago Pile-2 at Site A in 1943. It remained in operation until 1954, when it was dismantled and buried. Today, the original site at Stagg Field is marked by a memorial quadrangle, serving as a National Historic Landmark that commemorates the birth of the nuclear age.

General information, not professional advice. Spotted an error? Flag the card or see corrections and complaints.

Intellect Plus is a visual educational discovery platform for exploring fascinating facts and ideas. Brain Food, Not Brain Rot. What is Intellect Plus?

Related

• The multidisciplinary art of controlling the atom
• Nuclear engineering is far more than just power plants and atomic weapons
• A Manhattan office name hid the factories that built the bomb
• A submarine engine choice shaped most of the world's nuclear power plants
• How a radical shift in physics created the world's most powerful weapon design
• Why ancient Near Eastern history remains a floating puzzle of contested dates
• How Three Distinct Industrial Towns Amalgamated to Form the Modern City of Cambridge
• An Aztec masterpiece where Mesoamerican artistry meets the European Renaissance
• North America’s greatest earthen city rose opposite St. Louis
• Constantine’s New Rome ruled until Ottoman 1453
• Why did an ancient hero throw a bull's leg at a scorned goddess?
• From professional football pitch to Hollywood screen and back again

More in Historical cities · More in Countries & Cities · Latest · A–Z · All topics