The Fukushima disaster is considered the world's second-worst nuclear accident, behind Chernobyl.

Only two disasters have ever been designated "level 7" nuclear accidents — the classification used by the International Atomic Energy Agency for major events with widespread health and environmental effects. The 1986 nuclear disaster at the Chernobyl Nuclear Power Plant in Ukraine was one; Fukushima was the other.

The latter released plumes of radioactive material into the air, putting residents at risk of developing some forms of cancer if they stayed in the area.