Christian M. 7 min read

Sellafield: Britain’s hidden nuclear waste hub

Sellafield in Cumbria is one of the world’s most significant nuclear sites, but very few have even heard about it.

Its eventful history includes nuclear weapon research, narrowly escaping a major meltdown and a surprisingly high number of radioactive leaks and incidents related to its global nuclear waste re-processing (recycling) activities.

Fast-forward to 2024, and Sellafield continues to grapple with its leaky legacy. The decommissioning and remediation works rank amongst the largest in the world and remain a huge burden to British taxpayers.

However, every problem is an opportunity in disguise, and for Sellafield, it’s the development of S-tier nuclear waste management technologies.



What is Sellafield?

Sellafield (formerly known as Windscale) is a large multi-function nuclear site on the coast of Cumbria, England. The site covers an area of 265 hectares and comprises more than 200 nuclear facilities and more than 1,000 buildings. In other words, it’s huge.

Europe’s largest nuclear site has the most diverse range of nuclear facilities worldwide, most of which are being decommissioned. Amongst them are:

The Nuclear Decommissioning Authority (NDA) owns and manages the site through its wholly-owned subsidiary, Sellafield Ltd., which handles all the decommissioning activities.

Sellafield for dummies

If you still have no idea what Sellafield is, see answers to these FAQs to get some clarity before reading on:

What was the Sellafield disaster?

Many nuclear incidents have occurred at the Sellafield site. However, the “Sellafield disaster” typically refers to the Windscale fire on October 10, 1957, at the Windscale Pile No. 1 reactor. A fire broke out in the reactor’s graphite core, which released radioactive iodine-131 and cesium-137 into the atmosphere, resulting in widespread contamination and increased cancer risks in the affected areas.

Is Sellafield still active?

It certainly is. While it no longer reprocesses nuclear waste or generates nuclear power, it hosts some of the world’s most complex nuclear decommissioning operations. It is now a centre of innovation in nuclear waste management technologies.

How hazardous is Sellafield?

Sellafield can be considered highly hazardous due to its large quantities of legacy nuclear waste, decommissioning projects, ageing infrastructure, and associated health risks for nearby populations and workers. Whether the hazard will materialise is another matter altogether!

How much waste is at Sellafield?

Sellafield holds around 85% of the UK’s nuclear waste, estimated at least 4.9M tonnes. This corresponds to about 4.5 million cubic meters, which is “enough to fill Wembley Stadium four times over.” See a more detailed breakdown of radioactive waste at Sellafield here.

What happens to nuclear waste at Sellafield?

Sellafield no longer reprocesses nuclear waste; this is now done within each nuclear power station. Existing nuclear waste at Sellafield comes from legacy activities. See a more detailed breakdown of radioactive waste at Sellafield here.

The history of Sellafield

Here is a summary of the nuclear activities that have taken place at Sellafield since its post-WW2 inception:

1947-1950sEstablishment of SellafieldOriginally part of the British nuclear weapons program; site construction began in 1947. The Windscale Piles, two nuclear reactors, were established as part of the program.
1956Calder Hall Reactor OperationWorld’s first commercial nuclear power station began operation, adjacent to the Windscale Piles. It generated electricity and produced plutonium for weapons.
1957Windscale FireMajor accident in one of the reactors, resulting in significant radioactive release.
1960s-1980sExpansion of Nuclear OperationsCommissioning of Magnox nuclear waste reprocessing plant in 1964. Marks end of focus on nuclear weapon research, instead focusing on the UK's growing amount of nuclear waste from its nuclear power reactors
1990sIntroduction of VitrificationHigh-level waste vitrification process started to immobilise radioactive waste in glass.
1994THORP (Thermal Oxide Reprocessing Plant) OperationalBegan reprocessing spent nuclear fuel from both UK and international reactors using THORP. Several nuclear leaks during this time.
2003Closure of Calder HallEnd of operations for the world’s first commercial nuclear power station.
2005Establishment of Sellafield LtdNew company created to manage and decommission the Sellafield site under the Nuclear Decommissioning Authority.
2010sFocus on DecommissioningIncreased efforts in decommissioning old facilities, including removal and treatment of legacy wastes.
2018THORP ClosureThe THORP reprocessing plant ceased operations, marking the end of large-scale reprocessing at Sellafield
2020sAdvanced Waste Management TechnologiesImplementation of advanced technologies such as robotics and remote handling for waste retrieval.
2022Magnox Reprocessing EndsCompletion of Magnox reprocessing operations, shifting focus to decommissioning and waste management.
OngoingDecommissioning and Environmental RemediationOngoing efforts to decommission legacy facilities and remediate the site for future use.

The key things to highlight are the irresponsible experiments of the 1940s-50s, the shift away from nuclear weapons and into nuclear waste reprocessing in the 1980s, and finally, the closure of Calder Hall in 2003 and the end of nuclear reprocessing in the 2020s.

Nuclear waste reprocessing at Sellafield

Between 1962 and 2022, Sellafield was one of the world’s leading nuclear waste reprocessing sites.

💡What is nuclear waste reprocessing? It’s synonymous with nuclear waste “recycling”. Spent fuel rods from nuclear power stations are sent to Sellafield, cooled down in pools, broken into little pieces, and dissolved. Any remaining Uranium and Plutonium are rescued and re-concentrated into useful fuel.

Sellafield has had two major reprocessing plants in its history, each for a different type of nuclear reactor technology.

💡Nuclear tech for dummies: MAGNOX is an old technology used in legacy nuclear reactors in the UK. THORP is the name of the nuclear reprocessing plant at Sellafield that recycles spent fuel from nuclear reactors using second-generation AGR and LW technologies. A third-generation nuclear tech will be used in UK reactors under constructions like Sizewell C and other SMRs.

MAGNOX Plant (1962 – 2022)

The Magnox reprocessing unit at Sellafield was designed to handle spent fuel from the country’s fleet of Magnox reactors. Throughout its operational life, the unit processed about 55,000 tonnes of spent fuel.

Magnox fuel rods were first received and stored in cooling ponds at the plant, allowing short-lived radioactive isotopes to decay. Once sufficiently cooled, the fuel rods were sheared into smaller pieces, dissolved in nitric acid, and separated into Uranium, Plutonium and waste solutions:

  • Uranium: Extracted, purified and reused as fuel for other reactors or stored for future use.
  • Plutonium: Extracted, purified and reused in mixed oxide (MOX) fuel, which could be used in certain nuclear reactors.
  • High-Level Waste (HLW): The remaining highly radioactive waste was vitrified (i.e. converted into solid glass and stored in stainless steel canisters for long-term storage until it decays).

The Magnox reprocessing plant ceased operations in 2022, as a result of the technology becoming obsolete in the UK and around the world.

THORP Plant (1994 – 2018)

The Thermal Oxide Reprocessing Plant (THORP) at Sellafield was built to handle the next-gen of spent nuclear fuels, accommodating domestic and international demand.

It was able to reprocess spent oxide fuel rods from advanced gas-cooled reactors (AGRs) and light water reactors (LWRs). It worked similarly to MAGNOX, where spent fuel rods were cooled, sheared, and dissolved, and their constituents were separated into uranium, Plutonium, and waste.

This may sound like the same process as Magnox, but a completely different process called PUREX was required to process these fuel rods.

The THORP plant closed in 2018 because it had completed its reprocessing contracts, reached the end of its operational life, and the economic viability of continuing operations had diminished.

Notable incidents at Sellafield

Unfortunately, many notable radioactive incidents have occurred throughout Sellafield’s history. Here’s a comprehensive list of recorded incidents:

October 10, 1957Windscale FireA fire in one of the two Windscale Piles (a graphite-moderated reactor) led to the release of radioactive contamination. It was the worst nuclear accident in UK history, resulting in significant releases of radioactive iodine and contamination of the surrounding area.
February 1973Leak from Magnox reprocessing plantA discharge of around 45 gallons of radioactive waste into the Irish Sea due to a failure in a pipeline. The leak went undetected for several days.
1983Alpha activity found in pipelineHigh levels of alpha-emitting radionuclides were discovered in a pipeline discharging into the sea, indicating a significant leak.
1986Cesium contamination in milkElevated levels of cesium-137 were detected in local milk, leading to temporary restrictions on milk distribution. This was linked to routine discharges from the site.
1992Plutonium found in a worker's homeA significant contamination event where plutonium was found in a worker's home, highlighting issues with contamination control and monitoring.
March 2005Thorp LeakA major incident in the Thorp reprocessing plant where approximately 83,000 liters of highly radioactive liquor leaked from a ruptured pipe into a containment cell. The leak went undetected for at least 9 months and resulted in a significant release of radioactivity.
January 2009Loss of containment at Magnox plantA small amount of plutonium-contaminated material was released inside the plant, resulting in a shutdown for decontamination.
January 2014Elevated radiation levelsElevated levels of radiation were detected at the perimeter of the site, causing part of the facility to be temporarily closed. The source of the radiation was not immediately clear, but it highlighted concerns about monitoring and containment.
February 2014Ventilation system leakA small leak was detected in the site's ventilation system, leading to a temporary shutdown of the affected area.
November 2016Leak in the reprocessing plantA leak was discovered in a pipe within the reprocessing plant, leading to a minor release of radioactive material. The incident was contained, but it raised concerns about aging infrastructure.
Source Wikipedia

Unfortunately, radioactive leaks have occurred even into the late 2010s, away from media scrutiny. Much of this was due to nuclear waste reprocessing activities, highlighting the environmental and health risks of waste management.

This excludes a series of cybersecurity incidents over the last couple of years that highlight Sellafield’s continued environmental and health risks.

Sellafield in 2024

Despite its shady past, Sellafield’s activities have shifted dramatically over the past twenty years from nuclear power and waste reprocessing to managing the millions of tonnes of radioactive waste left by these historical activities and developing the latest technology.

This closure involves decommissioning ageing sites, managing nuclear waste, and developing technologies to ease these tasks and monitor environmental effects.

Let’s focus on the two activities that impact its role in the nuclear waste management industry:

Sellafield: Nuclear site decommissioning

Sellafield hosts one of the world’s largest and most complex nuclear site decommissioning projects.

This involves safely dismantling legacy nuclear facilities, such as old reactors and supporting structures. These are all contaminated with radioactive material and wastes that need careful management.

It’s a very specialised job that must completely avoid the release of significant radioactivity to the surrounding area, so it is extremely resource-intensive and time-consuming. Some structures, like Calder Hall, must take hundreds of years to decommission.

Here’s a summary of the decommissioning projects currently taking place at Sellafield:

ProjectKey ActivitiesTimeline
Fuel Storage PondRemove sludge and prepare for drainingOngoing
Fuel Cladding SiloStart waste removalBegan August 2023
Magnox Storage PondRemove fuel and sludgeOngoing
Swarf Storage SiloStart removing wasteStarted June 2022, ongoing for 20 years
Pile No.1 ChimneyContinue demolitionOngoing
Calder HallRemove fuel and buildings, maintain siteUntil 2032, final demolition by 2114

Decommissioning results in millions of tonnes of radioactive waste of different grades, most of which are managed on-site at Sellafield or at the nearby Drigg site, which handles low-level radioactive waste.

In 2023, Sellafield Ltd (the government-owned decommissioning subsidiary) spent £2.5bn on its decommissioning activities, which were funded principally by the UK government with taxpayers’ support.

This cost represents a mere 0.2% of the UK’s total public spending for that year, yet was equivalent to the entire expenditure of the Culture, Media, and Sport government department.

The total decommissioning cost of the entire site throughout the 100+ years timeline is currently expected to be at least £84 bn!

Sellafield: Nuclear waste management

Sellafield holds around 85% of the UK’s nuclear waste, estimated at least 4.9M tonnes. This corresponds to about 4.5 million cubic meters, which is “enough to fill Wembley Stadium four times over.”

Interestingly, most of this waste was generated from the initial nuclear research from the 1940s to about the 1980s, including the decommissioning of operational sites during this time of hurried nuclear research. For context, this was the Cold War where accelerating nuclear research was seen as a matter of survival.

Types of nuclear waste at Sellafield

All nuclear waste, including that at Sellafield, is categorised according to its levels of radioactivity and its state, either liquid or solid. Each is processed, packaged, and stored differently to ensure it can be managed safely and efficiently:

Waste TypeDescription
Low-level waste (LLW)Typically compacted, placed in large metal containers, and placed inside concrete-lined vaults.
Intermediate-level waste (ILC)Stored in 500L stainless steel drums and encapsulated in a cement-based structure before being stored in the vaults.
High-level radioactive fluids (HLW)Vitrified into glass and poured into stainless steel canisters that are welded to ensure there are no spills.

At Sellafield, these wastes exist in different proportions:

Radioactive waste typeProportionAmount
Low-level waste (LLW)94%4.2M cubic meters
Intermediate-level waste (ILW)
6%290k cubic meters
High-level waste (HLW)0.1%1,100 cubic meters

Source: UK Radioactive Waste Inventory 2022

Here is how different sites manage and temporarily store radioactive waste:

Storage SiteType of WasteAmount
Magnox Swarf Storage SiloWaste from Magnox reactor fuel cladding1,000s of cubic meters
Magnox Storage PondSpent fuel and sludge from Magnox reactors100s of tonnes
Fuel Storage PondFuel and sludge from early reactorsLarge quantities
Fuel Cladding SiloCladding from Windscale Piles1,000s of cubic meters
Vitrification PlantHigh-level waste in glass form1,000s of canisters
Spent Fuel PondsSpent nuclear fuel1,000s of tonnes
Encapsulation PlantsSolidified intermediate and high-level waste100s of tonnes
Low-Level Waste RepositoryLow-level waste like contaminated materials100,000s of cubic meters
Dry Storage FacilitiesSpent nuclear fuel in dry casks1,000s of tonnes

The main reason so much radioactive waste is stored at Sellafield is that the UK does not have a long-term facility for storing highly radioactive waste. A Geological Disposal Facility (GDF) to provide a permanent solution remains in the planning stage.

It would be easy to blame the UK government for this lack of action. Still, the fact is that the vast majority of nuclear nations are in the same position, with Finland’s Onkolo repository being the sole to be under construction.

Research and development

One advantage of having this scale and complexity of decommissioning as one of Western Europe’s most radioactive sites is that Sellafield now excels as a centre for innovation in nuclear site decommissioning and waste management technologies.

The site is a hub for developing and testing new techniques and approaches for handling radioactive waste, decontamination techniques, vitrification technologies and environmental monitoring:

  • Advanced robotic systems and remote handling technologies to safely retrieve and process waste from highly contaminated areas.
  • Research into new decontamination techniques to clean radioactive surfaces and equipment
  • Continued development of vitrification and encapsulation technologies.
  • Continuous research into better methods for monitoring the environment around Sellafield


Sellafield is one of Britain’s skeletons in the closet. Its long list of nuclear incidents is extensive, yet very few know of its existence. Ask your colleagues, friends, or family members next to you, and chances are they’re more likely to know who scored England’s 1966 World Cup-winning goals than know anything about Sellafield.

After all, there’s nothing sexy about hosting the most radioactive place in Western Europe, costing British taxpayers billions of pounds every year. On the bright side, Sellafield is quietly becoming a centre of innovation in nuclear decommissioning and waste management.

Let’s hope this will keep any future leaks at a minimum!

Sellafield – FAQs

Our business waste experts answer commonly asked questions on Sellafield’s nuclear waste management:

Is Sellafield the largest nuclear site in Europe?

Yes, Sellafield is the largest nuclear site in Europe in terms of site area, facility complexity and amount of nuclear waste in storage.

Where is Sellafield?

The Sellafield site lies in Cumbria, England. It borders the Irish Sea to the west and the Lake District to the north and east and Lancashire to the south.

Is radioactive waste the same as hazardous waste?

No, radioactive waste is not the same as hazardous waste. They are regulated separately due to their distinct properties and risks. Hazardous waste includes a variety of dangerous materials like chemicals and biological waste, but different waste regulations govern both.

What other industries produce radioactive waste?

Besides the nuclear power industry, other industries also generate radioactive waste. Examples include hospital waste from the healthcare sector, university research, heavy industry, mining, and oil & gas waste.

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