Table of Contents
What were the Windscale Piles?
The Windscale Piles were located near to Seascale in Cumbria, UK (now part of the Sellafield site). They were constructed as part of Britain’s post-war efforts for the production of the atomic bomb.
The two graphite “piles” were built between 1947 and 1951, with the intention of producing nuclear energy and plutonium-239 to use within atomic weaponry; the piles commenced operations from 1950 and 1951 respectively.
How did the Windscale Pile reactors work?
The choice of fuel, moderator and coolant were constrained by the knowledge and technology available to the UK at the time. Therefore, the piles were designed around using natural uranium metal as their fuel, because the UK was not yet able to carry out enrichment.
Fuel
Fuel
Moderator
Moderator
Coolant
Coolant
How was coolant air filtered?
The Windscale Piles operated using an air-cooled system, with coolant air pulled through the 120 m tall chimneys via convection. In this process, hot air rises up through the pile chimney and escapes, due to its lower density. This creates a lower pressure zone at the bottom of the chimney, thereby sucking cooler surrounding in. This convection current was enhanced via use of blowers: forced convection.
This use of an air-based cooling system resulted in a design that is efficient for smaller facilities but unfortunately increases the likelihood of releasing contaminated air into the atmosphere. To stop this risk, a respected scientist, named Sir John Cockroft, insisted filters were installed on top of the piles. Named after the scientist himself, “Cockroft’s follies” potentially saved countless people from absorbing dangerous radiation. We’ll mention this in more detail a little later on!
The Windscale Fire
Windscale Pile 1
Due to the pressures of the Cold War, in the early 1950s Britain’s government was heavily focused on ensuring the country was able to manufacture their own nuclear weaponry and keep up with countries around the world that could already manufacture their own nuclear weapons.
To prevent a build-up of Wigner energy within the graphite and therefore minimise the risk of spontaneous energy release and ignition, the cores of the two Pile Reactors were regularly heated during shutdown – a process known as annealing. During October 1957, following the ninth annealing of Pile 1, there was concern regarding higher than expected temperatures: the temperature of one of the fuel cartridge’s remained elevated and did not drop. This fuel rod continued to burn for three days and, overtime, set other fuel rods alight.
Operators and volunteers in protective suits made many brave attempts to control and extinguish the fire. These included running the blowers at maximum speed, using scaffolding poles to push fuel rods out of the reactor into a cooling pond (to create a fire break around the burning cartridges), pumping carbon dioxide into the reactor and dousing the fire with water. Finally, after 3 days of burning, operators decided to turn off air flow to the burning uranium fuel rods; this starved the fire of oxygen, and the fire was extinguished.
What were the underlying causes?
From the beginning, there was heavy pressure from the government towards having an operating nuclear reactor over the safe construction and operation of the piles; this can be referred to as “production imperative”. One example of this is pile operatives cutting components to the size needed during the construction phase to ensure there were no delays – an action that would never be allowed in construction of a nuclear reactor nowadays.
“Production imperative” becomes more evident during the operation of Windscale; due to the immense pressure from the government the piles were producing plutonium above a level of which they were designed to operate at.
Too little, too late however, as the fire had released a radioactive cloud into the eastern winds which spread the radioactive debris across the UK and Europe. Fortunately, Sir John Cockroft and his insistence on his “follies” prevented the Windscale incident from being dramatically worse and saved a considerable part of the Lake District and Cumbria! Regardless of this, the Windscale event was categorised as a level 5 (out of 7) on the International Nuclear Event Scale (INES) and still to this date it remains Britain’s worst nuclear event in history.
The uncontrollable radioactive debris had a huge impact on local agriculture, the government demanded that all local milk (produced within 300 square miles of the incident) was disposed of for the subsequent month.
Windscale Pile 2
Pile 2 remained undamaged by the fire, but was shut down soon afterwards. It has since been decommissioned.
The Nuclear Installations Act
Windscale is still the UK’s worst nuclear accident, at INES Level 5. This is due to the establishment of the UK’s independent nuclear regulator following the incident: the Nuclear Installations Inspectorate (NII) was initially formed under the Nuclear Installations Act 1959. By 1965, the Nuclear Installations Act 1965 (NIA 65) established the current licensing regime for nuclear licensed sites.
The NII has developed over the years, becoming the Office for Nuclear Regulation (ONR) in 2014, under the Energy Act 2013.
Throughout its history, the UK’s independent nuclear regulator has sought to ensure that nuclear facilities, including power stations, are operated safely throughout their lifecycle – including construction, operation and decommissioning. This includes consideration that any nuclear facility is safe for both people and for the environment.
Explore Further
Choose from the articles below to continue learning about nuclear.
Institute of Nuclear Power Operators – What does INPO stand for?
Interim Storage – How is Spent Nuclear Fuel Stored?
How Different Energy Sources Power Modern Life
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Below you can find references to the information and images used on this page.
Content References
- Nuclear Development in the United Kingdom, World Nuclear Association
- Safety of Nuclear Power Reactors, World Nuclear Association
- Windscale fire – Wikipedia
- BBC – Cumbria – Places – The Windscale Fire
- Sixty-two years on – Cleaning up our nuclear past: faster, safer and sooner
- When Windscale burned – Nuclear Engineering International
- Windscale fire | Nuclear Disaster, Cumbrian Village | Britannica