01 Overview
On October 10, 1957, one of the graphite-moderated plutonium production reactors at the Windscale nuclear complex caught fire. The fire burned for three days, releasing significant amounts of iodine-131 across the United Kingdom and reaching continental Europe.
02 Cause
The accident was triggered by a heating operation called "Wigner energy release" to anneal the graphite moderator. The temperature became too high, igniting uranium fuel cartridges. The fire spread through the reactor core, burning for 16 hours before it was discovered.
03 Impact
Radioactive iodine-131 was detected across the UK and northern Europe. About 2 million litres of milk were collected and dumped into the sea over a month. Estimates suggest the fire may have caused hundreds of cancer deaths over subsequent decades.
04 Response
Firefighters attempted carbon dioxide - without success. The reactor was ultimately flooded with water, a desperate measure that risked a steam explosion but succeeded. The damaged reactor was sealed with concrete and has never been dismantled.
05 Legacy
The British government suppressed the accident report, declassified only in 1988. The accident prompted significant reforms in UK nuclear safety. The Windscale site (renamed Sellafield in 1981) is now undergoing a decommissioning project expected to continue until 2120.