The 18 Worst Nuclear Accidents in World History

The partial meltdown at Three Mile Island Unit 2 is the most serious nuclear accident in U.S. history. The accident began with a series of failures in the non-nuclear secondary system. This was followed by a relief valve in the primary system that got stuck in the open position, allowing nuclear-reactor coolant to escape. The accident was compounded by the inability of plant operators to identify the problem and by an operator mistakenly overriding the automatic emergency cooling system. Eventually operators got the reactor under control.

In a twist of art imitating life, the film “The China Syndrome,” about an accident at a mythical nuclear plant in California, was released several weeks before the accident at TMI took place.

There have been two Level-4 events at the Saint-Laurent nuclear power plant in Saint-Laurent-des-Eaux, in central France, the most serious nuclear accidents in French history. On the night of Oct.17, 1969, the core of the nuclear reactor partially melted during refueling as a result of equipment failure and operator error. The power unit was restored almost exactly a year later. In 1980, an accident caused two fuel rods to melt, damaging the reactor.

A small atomic research reactor in Argentina operating on highly enriched uranium fuel was rocked by an energy surge on Sept. 23, 1983, and the reactor operator died from radiation exposure. The small reactor, in a suburb of Buenos Aires, went through the process of fission reaction that occurs at the start of a nuclear explosion. Only a minor explosion occurred. According to the International Atomic Energy Agency, Argentina told the agency that no radiation was released from the facility.

The Chernobyl accident is one of the world’s worst nuclear disasters and one of two Level-7 accidents on the list. The incident occurred on April 26, 1986, when a power surge during a reactor systems test produced an explosion and fire that destroyed one of the units. Workers did not take adequate safety precautions or alert operators to the electrical test’s risks. Radiation escaped into the atmosphere over western Soviet Union and Europe.

Two plant workers died the night of the accident, and another 28 people perished within a few weeks because of acute radiation syndrome. Because of the incident, about 220,000 people had to be relocated from their homes as the Soviet Union created the Chernobyl Exclusion Zone in the surrounding contaminated area (about 1,500 sq. miles including the area in Belarus).

One of the world’s worst nuclear-contamination incidents was the result of a fatal mishandling of contaminated material in Goiania, Brazil, southwest of the capital of Brasilia. A radiotherapy institute in the city had relocated, leaving behind a teletherapy unit that still contained cesium chloride. Scavengers found the unit, carted it away in a wheelbarrow and sold it to a junkyard. The owner showed the glowing blue material inside the unit to family and friends, exposing them to radiation. After they left the premises, they irradiated others all over the city. In total, 245 people were exposed to radiation and four died.