Fukushima Daiichi, Japan (2011)

Fukushima Daiichi, Japan, ranks #2 because a magnitude-9.0 earthquake and 14-meter tsunami knocked out backup cooling at three reactors, triggering triple meltdowns and hydrogen explosions that released cesium and iodine into the Pacific. The evacuation of over 154,000 residents—15 times more than Three Mile Island's minimal displacement—underscores its human impact. Cleanup is projected to take 40 years and cost over $200 billion, making it the most expensive nuclear cleanup in history. Its meltdown severity approaches Chernobyl's level of damage, but the lower total radioactive release places it firmly behind the 1986 disaster.