Three Mile Island

At four in the morning on March twenty-eighth, nineteen seventy-nine, a pump failed in the secondary cooling loop of Unit Two at the Three Mile Island nuclear power plant on the Susquehanna River, twelve miles southeast of Harrisburg. The failure triggered an automatic shutdown of the reactor. What followed over the next several days was the most serious accident in the history of commercial nuclear power in the United States, and one of the most consequential industrial crises of the twentieth century, not primarily because of the physical damage it caused, but because of what it revealed about the gap between institutional confidence and operational reality.

Operators, facing confusing instrument readings and contradictory alarm signals, made decisions that allowed the reactor core to partially melt. The control room did not have a clear picture of what was happening inside the reactor vessel for most of the first day. The Nuclear Regulatory Commission, which was informed within hours, struggled to communicate clearly with state and federal officials.

Pennsylvania's Governor Richard Thornburgh, working with incomplete information from the NRC, advised pregnant women and preschool children within five miles of the plant to leave, and on March thirtieth widened that advisory to twenty miles. Roughly one hundred forty thousand people in the region left voluntarily. The partial meltdown released small amounts of radioactive gases into the atmosphere.

The long-term health consequences to the surrounding population remain scientifically debated; multiple epidemiological studies have reached different conclusions, and the public record acknowledges the uncertainty. What is not disputed is the effect on American nuclear energy policy. No new nuclear power plant was ordered in the United States after nineteen seventy-eight, and the Three Mile Island accident reinforced that halt.

A nuclear energy expansion that the industry had projected would supply much of America's electricity by two thousand was never built. The cooling towers at Three Mile Island, those hyperbolic concrete silhouettes beside the Susquehanna, became the most recognized symbols of nuclear anxiety in the Western world. Unit One continued operating until September twenty, twenty-nineteen, when it was shut down for economic reasons.

Unit Two has remained in monitored storage.