The correct option is A Nuclear accident
Chernobyl
was a nuclear accident in 1986 at the Chernobyl nuclear power station in
Ukraine. It was the worst disaster in the history of nuclear power generation.
This disaster occurred on April 25–26, 1986, when technicians at reactor unit
attempted a poorly designed experiment. A large fireball was triggered due to
several explosions. It blew off the heavy steel and concrete lid of the
reactor. This and the ensuing fire in the graphite reactor core released large
amounts of radioactive material into the atmosphere. Many people died due to
radiations.