A crude pile of black bricks
Beneath the ivy-covered stone stands of the University of Chicago's Stagg Field, in a disused squash court, a team of 49 scientists assembled what Enrico Fermi called "a crude pile of black bricks and wooden timbers". This was Chicago Pile-1 (CP-1), the world's first artificial nuclear reactor. Construction began on November 16, 1942, and crews worked around the clock for two weeks.
The final structure was a flattened ellipsoid, 6 meters tall and 7.5 meters wide, composed of 57 layers of material. It contained 360 metric tons (771,000 pounds) of machined graphite blocks that was a neutron moderator. Embedded within the graphite were 5.4 metric tons (12,400 pounds) of pure uranium metal and 45 metric tons (80,590 pounds) of uranium oxide, which was the nuclear fuel. The entire assembly was built inside a wooden frame, without any radiation shielding or specialized cooling system. Control of the reaction depended on several cadmium-coated rods, which absorb neutrons. One was electrically operated, another was an emergency rod tied to a rope that could be cut with an ax, and the final rod was withdrawn by hand by physicist George Weil. A "suicide squad" of scientists stood on a platform above the pile with buckets of cadmium nitrate solution, ready to douse the reactor if all other control methods failed.