Windscale Fire, United Kingdom (1957)

The Windscale fire remains the UK's worst nuclear accident, severely outranking the Tokaimura incident in long-term contamination scale. On October 10, 1957, an air-cooled plutonium production reactor in Cumberland (now Sellafield) caught fire, releasing 20,000 curies of iodine-131 and polonium-210 across the UK and northern Europe, contaminating an area over 500 kilometers. This single event led to an estimated 240 additional cancer cases, far exceeding the 4 direct deaths from Goiânia, and forced the dumping of 2 million liters of contaminated milk. Unlike the SL-1 explosion which killed three instantly, Windscale's effects unfolded over decades, creating a lasting public health crisis. The release was 10 times more widespread than the average nuclear accident of its era, reshaping British safety regulations and costing over £100 million in cleanup.