Three Mile Island: The Inside Story

The Three Mile Island Unit 2 Nuclear Power Plant 

Figure 2.1.The TMI cooling towers cast noon shadows, April 10, 1979. Learn more

Nuclear power plants in the United States are usually named after the place where they are sited. The Three Mile Island nuclear power plant comprised two complete installations adjoining each other on a like-named island in the Susquehanna River, about ten miles (15 km) south of Harrisburg, the capital of Pennsylvania.

Metropolitan Edison, a subsidiary of General Public Utilities, began construction of TMI-1 at the north end of the island in 1968, and of TMI-2 in 1969, just south of TMI-1. TMI-1 was completed and began generating electricity in 1974, and continues in operation today. It has been a relatively trouble-free facility, setting recent records for time between unscheduled shutdowns.

Figure 2.2. The Three Mile Island nuclear power plants are about 10 miles (15 km) southeast of Harrisburg, and 75 miles (120 km) west of Philadelphia and north of Washington, D.C.

TMI-2, on the contrary, encountered construction delays and then repeated unscheduled shutdowns from the time it began operation in April 1978. The reactor’s operators, struggling with its faulty performance, were led to falsify operational data in order to avoid continual reports to the Nuclear Regulatory Commission and the further interruptions of the reactor’s operation the Commission might have required (ref. 27, pp. 71-73; ref. 28, pp. 373-78).

The accident on March 28, 1979, seemed at its inception just one more glitch in an operation that had yet to become smooth. Partly for that reason, the operators were misled into actions that turned the glitch into a major accident that wrecked the TMI-2 reactor, traumatized the surrounding population, and drew the attention of the entire world.