These two events are the worst nuclear accidents in the world – 24/7 Wall St.

The risk of a dangerous nuclear accident probably began when the first atomic bomb was assembled in Los Altos, New Mexico in 1945. Since then, there has been a chance of an accident occurring in a reactor or in due to the unexpected explosion of a bomb. The two worst nuclear accidents were Chernobyl in 1986 and the Fukushima Daiichi nuclear power plant in 2011.

To find the world’s worst nuclear accident, 24/7 Wall St. scoured several online sources to list accidents rated Level 4 or higher, according to the International Scale of Nuclear and Radiological Events, or INES. Nuclear accidents are assigned a level ranging from zero to 10 according to a scale developed in 1990 by the International Atomic Energy Agency and the Nuclear Energy Agency of the Organization for Economic Co-operation and Development. Our list does not include military-related accidents and is presented in chronological order.

According to the US Energy Information Association, 31 countries have nuclear reactors that generate 10.3% of the world’s electricity. In the United States, 94 reactors operate in 30 states and produce almost 20% of total annual electricity production. Although nuclear energy does not produce carbon dioxide, it does generate nuclear waste, and this material can remain radioactive and dangerous to people for thousands of years. (These are the oldest nuclear power plants in the United States.)

There have been very few serious nuclear incidents in the United States. Of most concern was the Three Mile Island accident in Pennsylvania in 1979, an incident that strangely followed the release of the nuclear accident film “The China Syndrome” a few weeks earlier. (Here are nuclear mix-ups that almost started World War III.)

Nuclear accidents have occurred for various reasons such as miscalculations involving experiments or tests, human error, or faulty design in some of the facilities. In one case, an old radiotherapy machine stolen by scavengers from a Brazilian hospital was manhandled by numerous people, killing four of them.

The two worst nuclear accidents in history were the Fukushima Daiichi nuclear power plant in Fukushima, Japan in 2011 and Chernobyl in Pripyat, Ukraine in 1986. Both were level 7 incidents.

In Fukushima, the cause of the accident was an earthquake, which triggered a tsunami more than twice as high as the plant was designed for, disabling backup generators and shutting down reactor cooling systems. This led to hydrogen explosions and radiation that contaminated the area around the plant and caused the evacuation of around 500,000 people.

The Chernobyl accident happened when a power surge during a reactor systems test caused an explosion and workers failed to take adequate action. Two died that night and later due to radiation also escaping into the atmosphere over western Soviet Union and Europe. About 220,000 people had to be relocated when the Soviet Union created the Chernobyl Exclusion Zone in the surrounding contaminated area (about 1,500 square miles).

Click here to see the world’s worst nuclear accidents

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