On 30 September, 1999, workers at a nuclear plant in Tokaimura, Japan poured the wrong solution into a precipitation tank, achieving criticality and causing a frightening blue flash
Two workers received massive doses of radiation, and later died.
Today, Japan's nuclear power plants (situated on highly earthquake prone land) produce more electricity than goes through the entire electricity grid in Australia - and yet this remains their worst accident related to nuclear power.
Many more people die mining and producing coal, falling off roofs when installing solar energy panels, or servicing wind turbines - which is why nuclear energy is pretty much the safest energy source on the planet.
On this subject, here is the story of the greenie who finally got a clue.