The Windscale Fire: Britain's worst nuclear disaster in history
In October 1957, a fire began in a plutonium-producing reactor in Cumbria. This would become known as the Windscale Fire, a Level Five nuclear accident.
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In 1957, the UK suffered the worst nuclear disaster in its history. How it happened is a complicated story.
The Windscale Piles
At the start of the 1950s, the UK built two nuclear reactors, then referred to as ‘piles’, at the Windscale nuclear site in Cumbria. These reactors were not built to produce energy. Instead, their mission was to produce plutonium for nuclear weapons, allowing the UK to take part in the Cold War arms race.
However, some factors complicated the process of constructing and designing the reactors. Firstly, the Windscale project was planned and executed at a fast speed – perhaps too fast.
For example, the reactor’s chimneys were already partly constructed when Sir John Cockcroft, director of an atomic energy regulator, insisted that filters be added to them to sift out radioactive particles in the case of an accident. As it was too late to add them within the chimneys, the filters were added on top of them. At the time, these additions were derisively referred to as ‘Cockcroft’s Follies’.
Another issue was that the technology was so new and not perfectly understood by the scientists creating the reactors.
The graphite components of the Windscale Piles, and the low temperatures at which they were operated, caused a build-up of something called Wigner energy, which could cause a fire in the reactor if it accumulated for too long.
The Windscale scientists were unaware that this would occur. When they noticed the problem, the only available solution was to intentionally heat the piles on a regular basis to help release the energy. This process, called ‘annealing’, seemed to work – at least for some time.
There were also other problems with the design and components of the piles. Their interiors had been modified to create tritium for hydrogen bombs – a change that went beyond original specifications.
How fire broke out
In October 1957, a fire broke out in Windscale’s Pile 1 while it was being annealed.
When the annealing process was initiated on 7th October, the pile failed to get warm enough. So, the process was tried again the next day. This time, the pile was sufficiently hot. Strangely, it stayed hot afterwards.
Temperatures within the reactor rose and rose. On 10th October, the site operators finally realised what was happening. The interior of the pile glowed with heat - the uranium fuel inside the reactor had caught on fire.
The exact reason why the uranium caught fire is still somewhat debated. The problems discussed likely played a role. However, reports in recent years have concluded that the fire was ultimately caused by the Windscale project’s emphasis on speed and outputs over safety and care.
Containment efforts
The reactor’s operators made several different efforts to fight the fire. First, they attempted to knock the burning uranium out using metal poles. Then they blew carbon dioxide gas into the reactor. Neither strategy had an effect.
On 11th October, water also failed to quench the fire. Finally, the airflow to the reactor was closed off and the fire died out.
The disaster would later be rated Level Five on the seven-point International Nuclear Event Scale – the same level as the USA’s Three Mile Island disaster. Fortunately, Cockcroft’s Follies, the filters on the chimneys, had prevented the impacts from being even worse by keeping radioactive particles from the air.
The disaster’s effects
The most prominent impact of the fire at the time, and the only one the government acknowledged, was the contamination of milk.
After the radioactive iodine-131 particles were released into the air, they dropped onto the grass and were eaten by cows. The milk produced from these cows would then contain radioactive iodine – enough to raise the risks of thyroid cancer for people, especially children, who consumed it. Therefore, sales of milk from within about 200 square miles of the Windscale plant were banned for a month.
Other than implementing this ban, the government insisted there was little to worry about. In fact, radioactive particles had spread across the country and eastward over Europe.
It was not until the late 1980s that relevant documents were declassified. In 1990, the director of the UK’s National Radiological Protection Board estimated that the fire had likely caused about 100 deaths from cancer, in addition to countless non-fatal cancers.
How the site is being contained today
For decades, Pile 1 remained sealed away. In recent years, a very slow process of decommissioning has begun. This is not limited to clean-up of the fire’s effects as spent fuel from before the fire also needs to be treated and stored.
In 2021, the government announced that it had finally demolished Pile 1’s famous chimneys, having removed the filters eight years before.
Through the years since the fire, the Windscale site, renamed in the 1980s as Sellafield, has continued to host nuclear activities, including energy generation and waste management. Although it has never experienced another Level Five nuclear incident again, it has experienced other safety problems, including Level Three and Four incidents. Currently, the target date for completing all decommissioning activities at Sellafield is set for 2140.
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