Windscale fire happened in 1957.

i see holly i see holly

Gordon R. Thompson has written:

'Evidence to the Windscale Inquiry on the safety assessment of nuclear fuel reprocessing, storage and ancillary activities' -- subject(s): British Nuclear Fuels, British Nuclear Fuels. Windscale and Calder Works

It is the only case where a reactor has been completely disrupted so that the fuel was ejected or melted, with massive release of radioactivity. It was much much worse than Three Mile Island, or the Windscale reactor fire in the UK.

I don't know that there is a technical definition of a nuclear disaster. There are two accidents that are commonly referred to as disasters. One is the well known Chernobyl disaster, and the other is the Kyshtym disaster, both of which were in the former USSR. The Windscale fire, Three Mile Island Accident, and other problems are referred to as accidents.

There is an International Nuclear Event Scale, which rates events on a scale of 1 (least important) to 7 (most important). On this scale, the Chernobyl Disaster is rated at a 7, and the Kyshtym Disaster is rated at 6. Three Mile Island Accident is rated at 5, as is the Windscale Fire, and two other accidents.

There is a link below to an article on the International Nuclear Event Scale.