R NMAH | Three Mile Island: The Inside Story
Smithsonian - National Museum of American History, Behring Center
Three Mile Island
Unit 2 nuclear power plant
Three Mile Island: The Inside Story 
The Accident at Three Mile Island
Click to enlarge imageThe cover of the report of the investigative commission appointed by President Jimmy Carter immediately following the accident. The wrecked reactor is inside a steel pressure vessel inside the cylindrical, domed concrete building in the foreground.

America’s worst accident at a civilian nuclear power plant occurred on March 28, 1979. Unbeknown to anyone, half the fuel melted in one of two nuclear reactors on Three Mile Island near Harrisburg, Pa. Large quantities of radioactivity leaked from the reactor, but most of it was contained. In all probability, no one received a harmful amount of radiation. The enormous damage to the reactor was revealed only years later when TV cameras and a specially developed ultrasonic, sonar-like imaging system looked inside the reactor vessel.

In recognition of the 25th anniversary of this event, the National Museum of American History devoted its History-in-the-News display case during spring 2004, to the accident in Unit 2 of the Three Mile Island nuclear power station (TMI-2). That exhibit featured the 1983 computer-controlled ultrasonic survey. It included the sonar probe and a precise topographic scale model of the upper third of the reactor’s destroyed core that was prepared to present in visual form the numerical sonar data.

Half of topographic scale model
Click to enlarge imageHalf of topographic scale model of the upper third of the TMI-2 reactor’s destroyed core, constructed on the basis of data gathered and analyzed in 1983 by the Idaho National Engineering and Environmental Laboratory’s sonar survey team.

This Web site has been created in order to provide more information about the Three Mile Island nuclear power plant; about the course of the accident there; about the steps—extending over almost 15 years—through which the nature and extent of the damage were gradually revealed; and, especially, about the sonar survey, and the topographic maps and models that were prepared with the survey data, providing a full and detailed picture of the first and most astonishing discovery: a cavernous void in the core of the reactor, where once there had been a dense forest of fuel rods.

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