History of Nuclear Power: Chicago Pile-1 to Small Modular Reactors

A Squash Court Beneath Stagg Field Changed History

On December 2, 1942, beneath the west stands of the University of Chicago's Stagg Field stadium — in a repurposed squash court — Enrico Fermi and a team of 49 scientists achieved the world's first self-sustained nuclear chain reaction. Chicago Pile-1 (CP-1) consisted of 385 tons of graphite, 46 tons of uranium oxide, and 6 tons of metallic uranium arranged in a lattice 20 feet wide and 20 feet tall. At 3:25 PM, Fermi ordered the control rod pulled out far enough to allow the reaction to proceed. The power output was 0.5 watts — barely enough to light a small indicator bulb. Physicist Arthur Compton made a coded phone call to James Conant at Harvard: "The Italian navigator has just landed in the New World. The natives were very friendly." The atomic age had begun.

From CP-1 to Electricity: The First Reactors

CP-1 was a proof of concept, not a power source. The Manhattan Project used its principles to build production reactors at Hanford, Washington, breeding plutonium for atomic weapons. The transition from weapons production to electricity generation required nearly a decade after the war's end.

• Experimental Breeder Reactor I (EBR-I): On December 20, 1951, at the National Reactor Testing Station in Idaho, EBR-I became the first reactor to generate usable electricity — enough to power four 200-watt light bulbs. The facility still stands as a National Historic Landmark.
• USS Nautilus (SSN-571): The world's first nuclear-powered submarine, launched January 21, 1954, powered by a Westinghouse S2W reactor. Nautilus demonstrated that naval nuclear propulsion was operationally viable and traveled more than 62,500 nautical miles on its first uranium fuel load — impossible for a diesel submarine.
• Shippingport Atomic Power Station: Opened December 2, 1958 (exactly 16 years after CP-1), in Beaver County, Pennsylvania. The first full-scale civilian nuclear power plant in the United States, it produced 60 megawatts of electricity. President Eisenhower's "Atoms for Peace" program had promised that nuclear energy would be "too cheap to meter." That prediction proved wrong.

The Nuclear Expansion Era: 1960–1979

Commercial nuclear power expanded rapidly through the 1960s and 1970s as utilities ordered reactors in large numbers, anticipating continued growth in electricity demand and low uranium fuel costs relative to oil and coal.

Three Mile Island and Chernobyl: Turning Points

Two accidents reshaped public attitudes toward nuclear power more than any technical argument could.

At Three Mile Island Unit 2 in Pennsylvania, a combination of equipment failure and operator error on March 28, 1979, caused a partial core meltdown. Approximately 50% of the reactor core melted. A small amount of radioactive gas was released. No fatalities were directly caused by radiation, and epidemiological studies found no statistically significant increase in cancer rates in surrounding communities. The accident's lasting damage was psychological and regulatory: no new nuclear power plant construction orders were placed in the United States in the following 30 years.

The Chernobyl disaster of April 26, 1986, was categorically different. A poorly designed safety test at Reactor No. 4 of the Chernobyl Nuclear Power Plant in Soviet Ukraine caused an explosion and fire that ejected the reactor's 1,000-ton graphite moderator and burned for 10 days. The United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR) attributed 31 direct deaths to the accident; the long-term cancer mortality estimate ranges from 4,000 (UNSCEAR) to 60,000 (independent researchers), depending on methodology. An 18-mile exclusion zone around the plant remains in place as of 2024.

• Chernobyl resulted from design flaws unique to the Soviet RBMK reactor — a positive void coefficient meant the reactor became more reactive as it lost cooling water, opposite to Western light-water reactor behavior.
• The accident directly caused the cancellation of nuclear plant construction across Western Europe and accelerated the decline of Soviet nuclear exports.
• Sweden, which had no connection to the accident, detected Chernobyl radiation on workers' clothing at the Forsmark Nuclear Power Plant on April 28 — two days after the explosion — prompting the Soviet Union to officially acknowledge the accident it had initially attempted to conceal.

Fukushima and the Current Landscape

The March 11, 2011 earthquake and tsunami at Japan's Fukushima Daiichi plant caused three reactor core meltdowns and the release of radioactive cesium and iodine — the second worst nuclear accident in history by radioactive material released. The Japanese government evacuated 154,000 people. Germany announced the permanent shutdown of all its nuclear plants by 2022 in response. Japan shut down all 54 of its reactors for safety reviews; by 2023, only 10 had restarted.

Nuclear power's share of global electricity generation fell from 17.5% in 1996 to approximately 9.2% in 2022. The economic challenge is acute: new large reactors in Western countries — Finland's Olkiluoto-3, the United Kingdom's Hinkley Point C, Georgia's Vogtle Units 3 and 4 — have run 4–12 years over schedule and billions over budget.

Small Modular Reactors: The Next Chapter

Small Modular Reactors (SMRs) — designs producing 50–300 megawatts, compared to 1,000–1,600 MW for conventional large reactors — are positioned as the solution to nuclear's construction cost and schedule problems. Factory manufacturing of standardized modules, passive safety systems that require no active cooling in loss-of-power scenarios, and smaller footprints enabling installation at industrial sites and remote communities are the key claimed advantages.

• As of 2024, over 80 SMR designs are in development globally. NuScale Power received the first U.S. NRC design approval for an SMR in 2022.
• China's HTR-PM high-temperature gas-cooled reactor demonstration plant achieved grid connection in December 2021 — the first Generation IV reactor to produce commercial electricity.
• The United States Congress passed the ADVANCE Act in July 2024, streamlining NRC licensing processes for advanced reactor designs — the most significant nuclear regulatory reform in decades.