On March 28, 1979, a series of events took place at the nuclear reactor at Three Mile Island, Unit 2 (TMI-2), near Harrisburg, Pennsylvania, that resulted in an accident in which a significant fraction of the nuclear reactor core melted and a small amount of radioactivity was released to the environment. After more than twenty years of government-stimulated development of the nuclear power industry and in the context of increasing public objections, that accident became the focus for an intensely polarized debate about the wisdom of further construction of nuclear reactors. The accident at the Three Mile Island nuclear power station has taken on a key historical role in discussions concerning science, technology, and ethics.

Reactor Design

Understanding the accident requires a general understanding of the way the TMI-2 reactor worked. TMI-2 was a pressurized water reactor. A simple diagram of the system is shown in Figure 1.

The fission...