Nuclear power provides about 20% of the electricity generated in the United States. We’ve had only one serious commercial nuclear power plant scare; on 28 March 1979, the Three Mile Island (TMI) Unit 2 reactor core partially melted down.
A blockbuster disaster movie, The China Syndrome, had been released less than two weeks earlier. Starring Jack Lemmon, Jane Fonda and Michael Douglas, the film focuses on a news crew that discovers safety coverups at a nuclear power plant and was based on events at a Chicago facility.
Film critic Roger Ebert described the movie as “scary as hell.” For many Americans, it must have felt like a foreshadowing of TMI. Public opinion polls revealed an opinion shift.
In July 1977, 69% of those polled supported additional nuclear power plant development. The summer of 1979 that support had dropped to 46%. In addition, more Americans (from 40% to 66%) wanted to restrict existing nuclear plant operations until stricter safety regulations could be implemented.
Built in 1974, the TMI nuclear power plant was situated on a Susquehanna River island near the Pennsylvania state capital, Harrisburg. Its second reactor came online in 1978. The cause of the 1979 disaster: a combination of human and mechanical error led to a cooling system failure.
Left alone, these safety devices would have prevented the development of a larger crisis. However, human operators in the control room misread confusing and contradictory readings and shut off the emergency water system… By early morning, the core had heated to over 4,000 degrees, just 1,000 degrees short of meltdown. In the meltdown scenario, the core melts, and deadly radiation drifts across the countryside, fatally sickening a potentially great number of people… More than half the core was destroyed or molten, but it had not broken its protective shell, and no radiation was escaping.
Human-centered design engineer Don Norman explains (0:0:54) how investigating the TMI accident started him on a journey to fashion a new field of study and practice:
If you were to design a control room to make errors, to cause errors, you couldn’t have done a better job… we know a lot about psychology and we know a lot about engineering, you’ve got to take the two and put them together.
The TMI accident occurred almost seven years before the Chernobyl reactor had an uncontrolled nuclear chain reaction (Ukraine/USSR, 26 April 1986) and 22 years before the Fukushima plant suffered catastrophic failure due to a tsunami (Japan, 11 March 2011).
Compared to each of those, TMI merely hinted at harm. Only a small amount of radiation escaped but that news created panic:
Governor Thornburgh advised “pregnant women and pre-school age children to leave the area within a five-mile radius of the Three Mile Island facility until further notice.” This led to the panic the governor had hoped to avoid; within days, more than 100,000 people had fled surrounding towns.
Conversely, the explosion at Chernobyl led to thousands of deaths and an unknown number of birth defects as well as a thyroid cancer epidemic. The Chernobyl accident also had human error as a component.
At Fukushima, the nuclear reactors survived the Great East Japan Earthquake (magnitude 9.0) but did not survive effects of the resulting tsunami. Unlike Chernobyl, neither employees nor the general public showed signs of acute disease or died after the event.
No discernible increased incidence of radiation-related health effects are expected among exposed members of the public or their descendants… any increased incidence of cancer in [a group of 160 employees] is expected to be indiscernible because of the difficulty of confirming such a small incidence against the normal statistical fluctuations in cancer incidence.
Most of the nuclear plants operating today were designed to last 25 to 40 years and, with an average age of 35 years, a quarter of them in developed countries will likely be shut down by 2025… The U.S. has  nuclear reactors in operation, but only one new reactor has started up in the last 20 years.