The very first nuclear reactor in the world, referred to as Chicago Pile-1 (CP-1), was an astonishing achievement in engineering and physics, orchestrated by the renowned scientist Enrico Fermi, on December 2, 1942. Erected beneath the west stand of a retired football stadium at the University of Chicago, this reactor’s pivotal feature was its manual shutdown mechanism—a man named Norman Hilberry, equipped with an axe. His task was to sever a rope linked to a cadmium rod, nicknamed “zip,” which would halt the nuclear chain reaction if it surpassed safety limits.
Constructed from around 45,000 graphite bricks mixed with uranium, CP-1 was a primitive configuration intended to accomplish the first self-sustaining nuclear chain reaction. The graphite played an essential role as a moderator, slowing down neutrons and increasing the chances of them triggering further fission in uranium atoms.
Even with its location in a heavily populated urban area, no radiation shielding or cooling system was implemented, highlighting the significant risks and uncertainties of this innovative experiment. On the demonstration day, as the neutron count steadily rose, Fermi unexpectedly paused the experiment for lunch. Upon resuming, the reactor achieved criticality with calculated accuracy, heralding a new chapter in nuclear energy.
Legend states that the term “scram” for emergency reactor shutdowns originated from Hilberry’s title as “Safety Control Rod Axe Man,” although this acronym lacks substantiation. Instead, the term likely arose from the idea of quickly vacating the vicinity after activating the shutdown mechanism.
Following the historic achievement of CP-1, it was disassembled and reconfigured with added shielding in a forested area, ultimately leading to the creation of numerous reactors across the globe. Today, the legacy of CP-1 is commemorated by a simple granite plaque at Red Gate Woods. Despite many years of technological advancements, the fundamental safety principle of allowing control rods to descend into position to stop a reaction remains, underscoring the lasting influence of Fermi’s experiment.