The Worst Nuclear Disasters. The Chernoby l Nuclear disaster is widely considered to have been the worst power plant accident in history, and is one of only two classified as a level 7 event on the International Nuclear Event Scale (the other being the Fukushima, Daiichi disaster in 2011). “The Worst Nuclear Disaster in U.S. History” For twelve years, things ran smoothly, but on July 1, high levels of radiation leaked from the Sodium Reactor Experiment (SRE). As fears of a meltdown at the earthquake and tsunami-damaged Fukushima nuclear plant persist, TIME takes a look at some of the more frightening nuclear … The nuclear disaster was caused by a botched experiment on a reactor in Unit 4, and it was intensified … 4 reactor suffered a catastrophic meltdown. Workers initiated a contamination cleanup and started and stopped the reactor for two weeks. During what should have been a routine safety test, Chernobyl’s No. This press release — issued five weeks after the end of the United States' worst nuclear reactor meltdown — was the public's first notification that something unusual had happened up on "The Hill." Nuclear disaster at Three Mile Island At 4 a.m. on March 28, 1979, the worst accident in the history of the U.S. nuclear power industry begins when … The worst nuclear disaster to affect the entire planet happened on April 26, 1986, at the Chernobyl nuclear facility near Pripyat in the Soviet Union. Note that the Chernobyl disaster may have scored an 8 or 9, if the scale continued. In the early morning hours of April 26, 1968, a power plant in Chernobyl, Ukraine, exploded and ignited one the of the worst nuclear accidents of all time. On March 28, 1979, almost a decade before the Chernobyl nuclear disaster, a nuclear reactor at Three Mile Island experienced a partial meltdown. Twenty years ago on Dec. 15, 2000 - 14 years after the world’s worst industrial disaster - the Chernobyl nuclear power plant in the Ukraine was permanently shut down. A nuclear reactor located at a power plant in Chernobyl experienced a steam explosion and fire that caused a meltdown, releasing massive quantities of radioactive material. The world's worst nuclear accident has been the 1986 Chernobyl disaster in the Soviet Union, one of two accidents that has been rated as a level 7 (the highest) event on the International Nuclear Event Scale. Considered history’s worst nuclear accident, the Chernobyl disaster killed 31 people directly, including 28 workers and firefighters who died of acute radiation poisoning during the cleanup.