In March of 1979, an accident at the Three Mile Island Nuclear Power Plant near Harrisburg, Pennsylvania touched off a wave of fear and distrust that swept the country. What began as a simple equipment malfunction was followed by other malfunctions and several layers of human error, quickly turning the situation into the worst nuclear accident in U.S. history. Although a complete meltdown of the reactor core was averted, for many the dream of cheap, clean, safe power was permanently damaged.

Nuclear power plants have at least five basic requirements. They need radioactive fuel, such as uranium, to provide the energy for the plant; control rods to control the speed of the nuclear reaction in the fuel; a coolant, usually water, to remove heat from the reactor and carry it to where it can be used to make steam, thus preventing the reactor from overheating; a turbine, driven by steam, to drive an electrical generator; and, a containment structure to prevent the escape of radioactive materials during normal operation or when an accident occurs.

In addition, nuclear power plants, including the Three Mile Island facility, rely on a complex system of automated pumps, valves, and gauges, and on the expertise of plant operators to interpret and manage the functioning of the various parts of the system. At the time it was built, Three Mile Island was considered a state-of-the-art facility. As one plant operator described it, even backup systems had backups. Unfortunately, as the events of March 28, 1979 proved, seemingly fail-safe systems sometimes fail, and without sufficient preparation, workers may be unable to appropriately respond to such events.

In the aftermath of the Three Mile Island accident, government agencies, including the Nuclear Regulatory Commission, took steps to avoid similar incidents in the future. These steps included more rigorous training for plant workers and stricter requirements for equipment and safety features.