Fukushima Daiichi
The nuclear power plant in Japan had to be shut down because of the massive earthquake in 2011. The earthquake created a tsunami which also shut down the backup generator, leading to overheating and melting of three nuclear reactors.
Moreover, radiation rose into the air after hydrogen explosions. In 2012, an investigation revealed that the plant’s essential maintenance had been ignored for a long time, concluding that it was a preventable accident.