Subsequent key developments have included the building of Calder Hall nuclear power station - the world's first nuclear power station to export electricity on a commercial scale to a public grid, the Magnox fuel reprocessing plant, the prototype Advanced Gas-cooled Reactor (AGR) and the Thermal Oxide Reprocessing Plant (THORP).

Decommissioning projects include the Windscale Piles,[4] Calder Hall nuclear power station, and a number of historic reprocessing facilities and waste stores.

They were built in this location to be remote from large centres of population because of the hazardous nature of the process, and to reduce the risk of World War II enemy air attack.

After the War, the Sellafield site was briefly in the ownership of Courtaulds for development as a rayon factory, but was re-acquired by the Ministry of Supply for the production of plutonium for nuclear weapons.

At this time the site was being expanded across the River Calder where four Magnox reactors were being built to create the world's first commercial-scale nuclear power station.

The UK retained low and intermediate level waste resulting from that reprocessing, and in substitution shipped out a radiologically equivalent amount of its own HLW.

[49] The first generation reprocessing plant was built to extract the plutonium from spent fuel to provide fissile material for the UK's atomic weapons programme, and for exchange with the United States through the US-UK Mutual Defence Agreement.

Normal operating procedures and overall design of the silo allowed for hydrogen gas to be safely vented before it could accumulate, and the heat can be removed through re-circulation of the water.

[70][note 1] The Calder Hall design was codenamed PIPPA (Pressurised Pile Producing Power and Plutonium) by the UKAEA to denote the plant's dual commercial and military role.

[74] In its early life Calder Hall primarily produced weapons-grade plutonium, with two fuel loads per year; electricity production was a secondary purpose.

[citation needed] Between 1977 and 1978 an inquiry, chaired by Mr Justice Parker, was held into an application by BNFL for outline planning permission to build a new plant to reprocess irradiated oxide nuclear fuel from both UK and foreign reactors.

Production eventually restarted at the plant in early 2008, but almost immediately had to be put on hold again, as an underwater lift that takes the fuel for reprocessing needed to be repaired.

[110] However, despite a large refurbishment in 1995, and the transfer of creative control to the Science Museum in 2002,[111][112] its popularity deteriorated, prompting the change from a tourist attraction to a conference facility in 2008.

[119] Because it is almost uniquely produced by nuclear fuel reprocessing, technetium-99 is an important element as part of the OSPAR Convention since it provides a good tracer for discharges into the sea.

[citation needed] In itself, the technetium discharges do not represent a significant radiological hazard,[120] and in 2000, a study noted "...that in the most recently reported dose estimates for the most exposed Sellafield group of seafood consumers (FSA/SEPA 2000), the contributions from technetium-99 and actinide nuclides from Sellafield (<100 μSv) was less than that from 210Po attributable to discharges from the Whitehaven phosphate fertiliser plant and probably less than the dose from naturally occurring background levels of 210Po.

"[121] Because of the need to comply with the OSPAR Convention, British Nuclear Group commissioned a new process in which technetium-99 was removed from the waste stream and vitrified in glass blocks in the new Vitrification Plant on site.

The UK government downplayed the events for some time and the original reports on the fire were subject to heavy censorship, as Prime Minister Harold Macmillan feared the incident would harm British-American nuclear relations.

[139] In 2014 photographs of the storage ponds were leaked to the media, showing they were in poor condition with cracked concrete, vegetation growing amongst machinery and seagulls bathing in the pools.

[142] A Nuclear Installations Inspectorate (NII) investigation concluded four of the five work-shifts were involved in the falsification, though only one worker admitted to falsifying data, and that "the level of control and supervision ... had been virtually non-existent.".

[146][147] On 17 February 2005, the UK Atomic Energy Authority reported that 29.6 kilograms (65 lb) of plutonium was unaccounted for in auditing records at the Sellafield nuclear fuel reprocessing plant.

[148][149] In 2000, wires on six robotic arms that moved vitrified glass blocks were deliberately cut by staff, putting the vitrification plant out of operation for three days.

[153] At the same time The Observer revealed that official documents showed that during the 1960s volunteer workers at Sellafield had participated in secret Cold War experiments to assess the biological effect of exposure to radioactive substances, such as from ingesting caesium-134.

[155] In December 2023, it emerged that Sellafield was the victim to cyber hacking by groups closely linked to Russia and China[157] It was first reported by UK newspaper The Guardian, it is unknown if the malware has yet been eradicated.

[158] In 1983, the Medical Officer of West Cumbria, is said by Paul Foot to have announced that cancer fatality rates were lower around the nuclear plant than elsewhere in Great Britain.

This claim, according to a book written by Stephanie Cooke, was challenged by Professor Eric Wright, an expert on blood disorders at the University of Dundee, who said that even microscopic amounts of plutonium might cause cancer.

In the analysis of childhood leukaemia/NHL in Cumbria, excluding Seascale, they noted that if both parents were born outside the Cumbrian area (incomers), there was a significantly higher rate of leukaemia/NHL in their children.

[166] Potassium iodate tablets were distributed to every household in Ireland in the wake of 9/11 in case of a terror attack on reprocessing plants and nuclear power stations in Britain.

[173] In February 2009, NuGeneration (NuGen), a consortium of GDF Suez, Iberdrola and Scottish and Southern Energy (SSE), announced plans to build a new nuclear power station of up to 3.6 GW capacity adjacent to Sellafield.

[175] In June 2011, the government confirmed the suitability of the site, and hoped an electricity generating company would choose to build a power station near Sellafield at Moorside by 2025.

[184] All three of these documentaries include interviews with key plant workers and Tom Tuohy, the deputy general manager of Windscale at the time of the accident and the man who risked his life to extinguish the flames.