What happened at the Windscale nuclear site in 1957?

Windscale was Britain’s first nuclear reactor. On 10 October 1957 the reactor developed a problem - its graphite design was accumulating heat. When graphite is exposed to a continuous bombardment by neutrons it suffers dislocations in its crystalline structure, causing a build-up of potential energy.

This energy, if allowed to accumulate, could escape spontaneously in a powerful rush of heat.

How did the Windscale fire start?

The structure had broken down resulting in a fire ripping through the radioactive materials in the core, raising the temperature in excess of 1,300°c.

Following several attempts to cool the reactor using different mediums such as air and 25 tonnes of liquid carbon dioxide to no avail, the decision was made to use water and switch off the air cooling fans.

This, however, had severe implications if it failed; molten metal oxidises when in contact with water, stripping oxygen from the water molecules and leaving free hydrogen, which could explode when mixed with incoming air.

Water was applied for more than 24 hours until the reactor cooled - it was unsalvageable.

What can the industry learn from the Windscale fire?

16 days after the incident the Board of Inquiry met under the chairmanship of Sir William Penney. Its report (the Penney report) was submitted to the Chairman of the United Kingdom Atomic Energy Authority and formed the basis of the Government White Paper submitted to Parliament in November 1957.

Penney reached four conclusions:

• The primary cause of the accident had been the second nuclear heating on 8 October - applied too soon and too rapidly
• Steps taken to deal with the accident, once discovered, were prompt and efficient
• Measures taken to deal with the consequences of the accident were adequate and there had been ‘no immediate damage to health of any of the public or workers at Windscale’ - it was unlikely that any harmful effects would develop
• A more detailed technical assessment was needed

A long salvage operation of the site commenced, lasting more than 50 years. Final completion of the decommissioning is not expected until at least 2037, however some of the site is operational and has been renamed Sellafield.

Changes to legislation were made to ensure the ongoing safety for construction, operation and management of atomic power stations, such as the Atomic Energy Authority Act 1957, 1971, 1986 and 1995, and the Nuclear Installations Act.