Three Mile Island: The Night the Reactor Cracked

At four in the morning on March twenty-eighth, nineteen seventy-nine, a feedwater pump at Unit Two of the Three Mile Island nuclear plant failed. A relief valve opened automatically and then stuck open, draining coolant from the reactor core. Operators, reading instruments that did not tell them the full picture, took actions that made the situation worse. Within two hours, the top portion of the reactor core was exposed and beginning to melt.

Three Mile Island sits on an island in the Susquehanna River, visible from the highway bridge south of Harrisburg. The cooling towers you can see from the road are the most recognizable industrial shapes in central Pennsylvania.

In the days after the pump failure, the Nuclear Regulatory Commission and the governor's office issued conflicting guidance. On March thirtieth, Governor Richard Thornburgh recommended voluntary evacuation for pregnant women and young children within five miles of the plant. No mandatory evacuation was ordered. In the absence of clear direction, roughly one hundred thousand people within a twelve-mile radius left on their own.

No direct deaths were attributed to the accident. The official position of the Nuclear Regulatory Commission is that the radiation released, primarily radioactive krypton gas, was not sufficient to produce measurable health effects in the surrounding population. Independent epidemiological studies conducted in the years following have produced contested results, with some researchers finding elevated cancer rates in downwind communities. This is a genuine scientific dispute, not a resolved question, and the full public health record remains debated.

What is not disputed is the accident's effect on the American nuclear industry. No new nuclear power plant received a construction permit in the United States for more than thirty years after March nineteen seventy-nine. The fear, amplified by conflicting information during the crisis, outlasted the engineering problems the accident had actually revealed.

Unit One of Three Mile Island announced a restart agreement with Microsoft in twenty twenty-four, with operations planned to resume around twenty twenty-eight, which needed electricity for its data centers. It is the first United States nuclear plant to restart after a closure. The cooling towers are still the most recognizable shapes on the Susquehanna.