Nuclear reactor

The nuclear reactor didn't arrive in a flash of genius on December 2, 1942. It crystallized from a cascade of discoveries that made its emergence inevitable—each one opening a door that couldn't be closed.

The story begins with James Chadwick's 1932 discovery of the neutron at Cambridge's Cavendish Laboratory. Unlike protons, neutrons carried no electrical charge, meaning they could slip past electromagnetic barriers surrounding atomic nuclei. Within seven months, Hungarian physicist Leo Szilard, walking through London after reading H.G. Wells' The World Set Free, conceived of the chain reaction: if an element's atoms, when struck by neutrons, would release more neutrons, you'd have self-sustaining energy release. Szilard filed a patent in June 1934.

For six years, his chain reaction remained theoretical. Then, in December 1938, German chemists Otto Hahn and Fritz Strassmann found barium when bombarding uranium with neutrons. The nucleus had split. Lise Meitner and Otto Frisch provided the explanation: nuclear fission. When Eugene Wigner told Szilard about fission in January 1939, Szilard immediately understood: fission fragments would shed excess neutrons. Uranium could sustain his chain reaction.

By 1942, the Manhattan Project had begun. Arthur Compton and Enrico Fermi made a fateful decision: build the reactor under the abandoned west stands of Stagg Field at the University of Chicago, in a squash court 30 feet by 60 feet. Crews purified 771,000 pounds of graphite and arranged it with 80,590 pounds of uranium oxide and 12,400 pounds of uranium metal—roughly $1 million in materials. The structure rose 20 feet tall across 57 layers.

On December 2, 1942, 49 scientists gathered. At 3:53 PM, after operators slowly withdrew the cadmium control rods for 28 minutes, the clicks became a steady roar: the first self-sustaining nuclear chain reaction. Within months, larger reactors at Hanford produced plutonium-239 for the Trinity test. The USS Nautilus put to sea in 1955 using reactor propulsion. Today, 85% of the world's nuclear electricity comes from pressurized water reactors descended from submarine designs.