Over the course of nuclear powers existence there have been accidents and tragedies in multiple countries.
Chernobyl, Ukraine 1986.
This is probably one of the most famous and devastating nuclear accidents in history. It was caused by inadequate equipment and poorly trained personnel. 2 plant workers and 28 people died within a few weeks of the explosion. This was a result of the acute radiation poisoning.
Another famous nuclear accident was in Fukushima, Daiichi 2011.
In one day, Fukushima was hit with a massive earthquake and a huge tsunami. Once the earthquake hit, buildings shook, but the nuclear power plant stayed solid. Its safety features shutdown the plant, but then the tsunami hit.
The result was catastrophic. This caused a leak in the power plant, causing it to become unstable. 3 days later an explosion occurred in the power plant.