On This Day in 1979: The Three Mile Island Accident

On this day in 1979, a cooling malfunction in Unit 2 at the Three Mile Island plant near Harrisburg, Pennsylvania led to a partial meltdown of the reactor core. A stuck relief valve let coolant escape, instruments told operators the opposite of what was happening, and the crew reduced the flow that would have saved the core. It became the most serious accident in the history of American commercial nuclear power.

The radiation released was small, and follow up studies found no measurable health effect on the surrounding population. The information released was another matter. Official statements over the following days contradicted one another, a precautionary advisory covered pregnant women and small children within five miles, and roughly 140,000 people left the area on their own before anyone was told to go.

Three Mile Island is a communication case study more than a radiological one. When guidance is late or conflicting, families make the call themselves with whatever they have loaded in the car. Deciding in advance who you trust for information, where you would go and what leaves with you is the practical response, and it applies across the whole family of man made disasters. The physics of the worst case is covered in surviving nuclear fallout.