Sellafield is Britain’s nuclear nightmare. It harbours the lethal remains of bomb-making, the accumulated radioactive waste from sixty years of nuclear electricity generation and the world’s largest stockpile of plutonium. There is no other place on earth containing so much radioactive material in so confined an area.

I visited the stones first, before walking the double line of high razor-wire fences that surround the works. I was soon stopped by a squad car of the Civil Nuclear Constabulary, a dedicated armed force protecting nuclear installations. Nobody is taking any chances. The nuclear waste of Sellafield will remain dangerous for far longer than the Grey Croft stones have been here. The open-air ponds of radioactive sludge and corroded nuclear fuel, the tanks of hot liquid waste from nuclear reprocessing, the potentially explosive remains inside the sealed sarcophagus from a fire in 1957: all have radioactive half-lives measured in tens of thousands of years. A terrorist attack, earthquake or cataclysmic accident at Sellafield could make a large area of northern England uninhabitable.

Having satisfied the nuclear police that I posed no threat, I walked down a quiet country lane to Ponsonby Church, part of an estate that William the Conqueror gave to the Ponsonby family over nine hundred years ago. Lambs cavorted round the churchyard in the bright sun, as they must have done every spring, for centuries. But the new landlord here is the Nuclear Decommissioning Authority, and the manor house nearby is occupied by nuclear-waste engineers. Inside the church, a notice warns that if the Sellafield siren blows, nobody should leave. The doors should be shut and news sought by tuning into a radio.

I had travelled here to reacquaint myself with the radiology and psychogeography of Sellafield and its western Cumbrian hinterland. Sellafield and I go back a long way. When I worked as an editor at New Scientist in the early 1980s, it was still known as Windscale, and its leaks, accidents and scandals made regular copy. Since then, the headlines have dried up. You may think that this is because the nuclear beast has been tamed – that new management methods and health and safety rules, brought in to replace Cold War paranoia and hastily invented engineering, might have made Cumbria safe – but Sellafield harbours a toxic legacy of waste that is more dangerous than ever, as many of the buildings, once shiny and new, are now fractured and leaking. Weeds grow from the cracks. Inside, I found that the engineers, in their macho way, are proud that they superintend the two most hazardous industrial buildings in Western Europe; that making the place safe will cost over 70 billion pounds; that it will take a century or more to do. My journey outside the fences, however, revealed a second, equally corrosive legacy – of duplicity, secrecy and plain lies. That legacy may be just as hard to clean.

From its first days, Windscale was steeped in the subterfuge arising from a secret project to rescue Britain from humiliation in the days after the Second World War. British scientists had worked with their American counterparts at Los Alamos in New Mexico to develop the atomic bomb. Then in 1946, wishing to keep the bomb to themselves as the Cold War developed, the US Congress banned American scientists from sharing nuclear secrets with their British colleagues. Outraged, Prime Minister Clement Attlee ordered the banished scientists – headed by Britain’s ‘man behind the mushroom cloud’, the diffident, state-educated mathematics prodigy William Penney – to start from scratch and build a British bomb.

Bankrupt Britain put vast resources into the project. The weapons were assembled at Aldermaston in Berkshire, while a site on the remote Cumbrian coastline was chosen to manufacture the plutonium. Two primitive nuclear reactors, known as the Windscale Piles, were built by the River Calder. Their thick concrete walls contained thousands of tonnes of graphite, honeycombed with horizontal channels to house slugs of uranium metal sheathed in aluminium cans.

Packed together, the uranium emitted sufficient neutrons to start a nuclear chain reaction, turning some of it into plutonium. Meanwhile, the graphite prevented the reactions from running out of control. The uranium slugs were then pushed out of the back of the pile into a giant, open-air pond to cool, before going to the reprocessing plant, where the fuel was dissolved in nitric acid to release the plutonium. The reactions inside the piles created huge amounts of waste heat, which future reactor designs would use to generate electricity. But these piles were intended only to manufacture plutonium. Air pumped through the graphite core took the heat up the two 120-metre chimneys, where filters captured any radioactive particles.

So far so good. Using what they remembered from Los Alamos, Penney’s scientists delivered the first plutonium to Aldermaston in early 1952. Two months later, the first British atomic bomb was detonated on a ship near the Montebello Islands off Western Australia. By then, however, the US had detonated a much bigger and more sophisticated weapon, the hydrogen bomb, whose design employed secrets no British scientists knew.

Penney’s team were given a new job: to make an H-bomb. That proved much harder. But in the aftermath of the Suez Crisis of 1956, the new prime minister, Harold Macmillan, believed such a bomb was essential to rebuilding Britain’s global clout and bolstering relations with the US, especially atomic cooperation. Without such a device, a Cabinet paper in June 1957 argued, Britain would be ‘virtually knocked out as a nuclear power’.

When an H-bomb proved beyond Britain’s best atomic scientists, Macmillan led them to indulge in what Norman Dombey, the researcher who exposed the lie in 1992, would call a ‘thermonuclear bluff’. They hatched a secret plan to test a giant A-bomb, masquerading as an H-bomb. But that required much more plutonium. Windscale went flat out. Corners were cut. Safety was sacrificed. Remembering events much later for a BBC programme, John Dunworth of the nuclear research laboratory at Harwell, one of those who had warned of the dangers at the time, said: ‘They were running much too close to the precipice.’ The scene was set for the world’s first major nuclear accident.

In the summer of 1957, under intense pressure to manufacture more plutonium, operators kept postponing downtime needed to cleanse the piles of Wigner energy in the core. This energy built up as the bombardment of neutrons displaced atoms in the graphite. It could cause a fire unless it was released by operators shutting down the nuclear reactions and then gradually heating the reactor core.

The long-postponed Wigner release finally began on 9 October. Jittery operators, working without a manual and anxious to get the reactor back into production, added too much heat too quickly. One of the fuel cans burst and the uranium inside it released even more heat, igniting a fire that spread through the pile. The uranium was ablaze and before long radioactive smoke had overwhelmed the filter and began pouring out of the chimney.

There was panic. Managers press-ganged off-duty workers who were watching a film at the works cinema in nearby Seascale and gave them scaffolding poles to push jammed fuel cans out of their channels and away from the burning pile. One young scientist, Morlais Harris, told me that he was sent to monitor equipment on top of the reactor, where managers trying to control the fire forgot about him for sixteen hours before bringing him down after the fire was put out. Workers in the know – there was no official information, and many had no idea of the risks – called their families living nearby and told them to flee.

With the fire still spreading, the pile’s managers decided to douse the fire with water. This was do or die. They knew that spraying water onto the burning, molten core risked causing an explosion. ‘Cumberland would have been finished. It would have been like Chernobyl,’ site foreman Cyril McManus told interviewers recently for an oral history of Sellafield. But the water worked. After three days, the fire was out.

The government asked Penney to report on how the fire had happened, but his findings of the chaotic management at Windscale were so damning that Macmillan recalled every copy. The report was only released to the public under the thirty-year rule in January 1988. Instead, Macmillan issued a statement that blamed the fire on an ‘error of judgement’ over the Wigner energy release by an unnamed rogue worker. No mention was made of the underlying cause – government demands for ever more plutonium. ‘He covered it up, plain and simple,’ Macmillan’s grandson and biographer, Lord Stockton, later told the BBC.

In the immediate aftermath of the fire, radiologists monitoring what went up the pile chimney said the main risk to the public was radioactive iodine falling on Cumbrian pastures and getting into milk. Over a couple of weeks, two million litres of milk were collected from farms and poured down drains into the Irish Sea. Managers said this was ‘erring wildly on the cautious side’ against a ‘theoretical’ risk, but they were clearly worried. Secretly, in the weeks afterwards, they sent McManus and others as far away as Devon, collecting samples of soil and vegetation to check the spread of the fallout.

Decades later, it emerged that iodine was not the most dangerous component of the cloud. It also contained polonium, an element so radioactive it glows blue in the dark, and though a handful of scientists were aware of this, it was hushed up. A few specks are enough to kill, as former Russian agent Alexander Litvinenko discovered when someone dropped polonium in his tea in a London hotel in 2006.

Polonium was the essential trigger at the heart of the British bomb, and it was being produced in the Windscale Piles by irradiating bismuth. But this was top secret. The Americans no longer used polonium in their bombs, and revealing that Britain still did would have shown how backward British bomb-makers were. Because of this, its lethal presence in the cloud was never mentioned in any assessments of the radiological hazard from the fire at the time. A few British atomic scientists knew enough of polonium’s presence to mention it fleetingly in a paper presented to a UN technical conference the year after the fire, but the implications were apparently not understood by those conducting risk assessments, and the presence of polonium in the cloud was forgotten for thirty-five years.

Only in 1983 did environmental activist and Newcastle University librarian John Urquhart stumble on the long-forgotten reference and bring his findings to New Scientist. Our scoop was subsequently confirmed by government radiologists, who said they too had been kept in the dark. They calculated the likely death toll from the polonium at about seventy, making it probably the main cause of deaths from the cloud. Nobody has ever assessed the additional risk to workers trying to contain the fire.

Some may argue that the fire was a price worth paying. It forced the closure of the Windscale Piles, but they had by then produced enough plutonium for the successful test of a giant A-bomb masquerading as an H-bomb, which persuaded Congress to rescind the ban on cooperative nuclear research and to allow Eisenhower and Macmillan, by now close friends, to resume what is still known today as the ‘special relationship’ between the two countries. Ever since the signing of the 1958 US-UK Mutual Defence Agreement, British scientists have been able to access US bomb-making expertise and buy American bombs. ‘Our armed forces have never used entirely British-designed weapons,’ Dombey told me. ‘In 1958, we built and tested H-bombs, but they were never put into service. They were too big.’ In truth, the purpose of the bluff was always more diplomatic than technical – to secure Britain’s place on the UN Security Council and in Washington as a nuclear power.

But the fire has scarred Windscale’s reputation ever since. The cover-up – and Macmillan’s decision to blame it on young operators who had risked their lives to prevent much worse – undermined faith in the project and in its management. The narrative of Windscale, and subsequently of Sellafield, as an alien, dangerous and duplicitous presence on the Cumbrian coast was set.

Despite the fire, Windscale remained in business. In 1956, the Queen had opened new, more sophisticated reactors just metres from the piles. The Calder Hall reactors also initially manufactured plutonium for bombs, but their primary purpose was to generate electricity. The cooling gas – now carbon dioxide rather than air – was captured, and its heat was used to drive conventional power-station turbines. The reactors became the prototypes for a fleet of Magnox reactors across Britain. Nuclear energy, Britons were told in the 1960s, would be ‘too cheap to meter’. In 1971, the old quasi-military UK Atomic Energy Authority (UKAEA) was replaced at Windscale by British Nuclear Fuels Limited (BNFL), whose task was to commercialise nuclear power.

It was a brave new world, but the culture of secrecy and cover-ups persisted. It created not just a climate of fear, but also a landscape of secrets. To chart its contours, I recently met Martin Forwood, who runs Cumbrians Opposed to a Radioactive Environment (CORE). Soft-spoken and bearded, Forwood is a former soldier, policeman and government scientist. He took me on his ‘alternative tour’ of Sellafield’s hinterland.

We started on the banks of the River Esk near the hamlet of Newbiggin, about ten kilometres from Sellafield. Forwood got a Geiger counter out of the car and headed for the tidal salt marshes. The counter began to click. There were radioactive particles beneath our feet. The surface mud showed three or four times the natural background level. Then, as he pointed his counter at mud a few inches down on the exposed riverbank, the clicking accelerated to a mad chatter at around thirty times the natural level.

The buried mud was seriously radioactive. ‘Livestock graze here,’ Forwood said. Fishermen dig for bait; people pick samphire, a local culinary delicacy; and a few metres away the Cumbria Coastal Way offers a shortcut through the mud at low tide. But there were no warning signs. ‘There could be particles of plutonium and americium on my boots,’ he said as we returned to the car. In theory, his boots should probably have gone for burial in the concrete-lined trenches for low-level radioactive waste at Sellafield’s dump at nearby Drigg. ‘But you get similar readings all along the coast here,’ Forwood said. ‘You can’t remove the whole of the Cumbrian shoreline.’

In 2005, Forwood’s CORE colleagues campaigning against Italian nuclear waste coming to Sellafield decided to bake a Cumbrian pizza topped with Esk mud and samphire. They handed it to the economic consul at the Italian embassy in London, with a warning note. He called in the Environment Agency, which took the radioactive pizza to the atomic labs at Harwell in Oxfordshire where it was quarantined for eight years before being interred at Drigg in 2013.

Most of the radioactive particles in the mud come, of course, from Sellafield. They had been discharged down the works’ two-kilometre pipeline into the Irish Sea. Marjorie Higham, a Sellafield scientist in the early days, told the oral-history project that her managers assured her that ‘the plutonium [would] adhere to the mud at the bottom of the sea in perpetuity. But of course it didn’t. It moves around.’ Some of it washes back on the tides that scour the coast. It turns up on beaches and gets trapped in the silt.

Routine discharges down the pipe are legal, but the oral history is full of stories about unwanted and highly radioactive liquids being secretly poured down the pipe. Occasionally the perpetrators get caught. Shortly after midnight in November 1983, half a tonne of reprocessing solvent went into the Irish Sea. This illegal discharge created a radioactive slick that floated ashore. Some Greenpeace activists happened to be diving close to the outlet at the time, devising plans to block it, and they came to the surface with their Geiger counters in overdrive. The discharge, which might otherwise have gone unnoticed, became front-page news and the local beaches were closed for six months. BNFL ended up with a court conviction and a £10,000 fine.

The lower levels of radioactivity that Forwood’s Geiger counter finds in recently deposited surface mud show that the pipeline’s radioactive discharges are generally a lot less than they once were. But the higher levels below the surface reveal that past pollution hasn’t gone away.

How dangerous is this? A cluster of cases of leukaemia among children living around Sellafield in the 1970s and 80s raised alarms that have never subsided. First revealed by a Yorkshire TV documentary in 1983, the cluster was later confirmed by government epidemiologists, who found leukaemia rates fourteen times the national average. Alan Postlethwaite, a local vicar when the scare was at its height, told the Sellafield oral-history project that ‘within quite a short period of time, I conducted funerals of three children who died of leukaemia’. Statisticians had told him to ‘expect one in twenty years, and we’d had three in twelve months . . . That put the frighteners on us.’

BNFL blamed the cluster on outside workers bringing a mystery virus to a previously isolated community. That is plausible, though no virus has ever been identified. A major study funded by BNFL in 2002 found that the children of Sellafield workers who had been exposed to radiation in the plant’s early years were twice as likely as the national average to develop leukaemia.

The cluster seems to have disappeared more recently. But fears run deep. When one couple living in a house overlooking the Esk Estuary tested the contents of their vacuum cleaner, they found plutonium, americium and caesium levels thousands of times higher than natural background levels. And a culture of cover-ups breeds fear and anger, which often gets directed against those who upset the status quo. When the couple brought a case against BNFL for damages, locals stopped visiting the village post office they ran, and someone superglued their front door shut. They sold up and left the area.

Forwood and I stopped at a guest house on a cliff outside Seascale. In the house next door, he told me, two sisters, Jane and Barrie Robinson, ran a bird sanctuary in the garden until a test in 1998 revealed that many of the birds were dangerously radioactive. It turned out the birds often roosted in contaminated buildings at Sellafield and may have fed on insects living around its open-air fuel storage ponds. Soon after, the authorities put 1,500 radioactive bird corpses into lead canisters for burial at Drigg, along with topsoil, garden plants and even the sisters’ garden gnomes.

Sellafield has a history of showing a cavalier attitude to its neighbours. A scientist at the works, Frank Leslie, turned whistle-blower after the 1957 fire and told the Manchester Guardian about a reckless safety culture in which regular discharges of radioactivity into the air over Cumbria had been hushed up – something BNFL finally admitted in 1986. Similarly in the early days, highly radioactive junk was put into the Drigg trenches as casually as if it were household trash going into a municipal dump.

The safety culture was no better inside the plant. A few weeks after the 1983 beach contamination, it emerged that the plant laundry’s managers had adjusted alarms meant to alert staff to radioactivity on overalls to make sure they ‘did not go off too often’. And then a broken valve in the reprocessing works released a plutonium mist that exposed eleven workers to serious contamination. Around that time, says McManus, workers often accumulated so much radiation in their bodies that they were banned from working in contaminated areas for the rest of their days. He was among those who became, as he puts it, ‘radiation lepers’.

For many years, Sellafield ran a secret programme of autopsies on former workers to check for radioactivity. I stumbled on this one day in 1986, when I was leafing through the journal of the government’s National Radiological Protection Board. The board’s medical researcher Don Popplewell described how the plutonium in the lungs and lymph nodes of Cumbrian corpses were at much higher levels than those in corpses in the rest of the country. The findings were reported without discussing the means employed to get them which were, as Don Popplewell told me, technically illegal. Analysing corpses for ‘scientific’ reasons, rather than to ascertain the cause of death, was common practice at the time. In a handful of former Sellafield workers the plutonium levels were hundreds, and in one case thousands, of times higher than normal. When I called Popplewell he told me that Sellafield’s chief medical officer, Geoffrey Schofield, had analysed more than fifty corpses of former workers and found yet higher levels. All this was done even though, as I wrote in New Scientist, it was ‘strictly illegal to examine autopsy tissue except to ascertain the cause of death’.

My article sank without a trace until twenty years later when, after an unconnected scandal over illegal autopsies on children in Liverpool, lawyers turned it up. They raised a stink and an inquiry was held into the Sellafield autopsies. The government duly issued an apology in 2010, and Schofield was disgraced (they even took his name off the front of a building on a Cumbrian science park), but strangely the staggering contamination of Sellafield workers found by Schofield and Popplewell has been quietly forgotten.

Most people I spoke to during my journeys around Sellafield told me that whatever the worries about historical environmental contamination, the real hazards from the works lie inside the fences, and they are not going away. So I arranged a tour.

The most important buildings on the site are the two vast reprocessing complexes. Reprocessing spent fuel from reactors, mostly from external sources but also its own, has been Sellafield’s raison d’être since it opened. In the old days, it was done to extract the plutonium necessary to make bombs, and more recently the output has been earmarked for the manufacture of new fuel to be put back into reactors. This idea of recycling nuclear fuel, thus optimising energy production, has always been the dream of nuclear engineers.

The spent fuel comes to Sellafield from distant nuclear power stations by train in crash-proof flasks, which are placed into cooling ponds drenched in millions of litres of water taken each day from a lake inside the Lake District National Park. The fuel is then dissolved in nitric acid to separate out the potentially reusable elements. Finally, these valuable products are put into store, while the hot, acidic and extremely radioactive ‘high-level liquid waste’ is collected in giant stainless-steel tanks, each twice the size of a large shipping container, ready to be concentrated in evaporators and then sealed in glass for eventual burial, a process called vitrification.

Two plants do all this. Both have been hit by repeated shutdowns and backlogs. The Magnox Reprocessing Plant takes spent fuel from the country’s ageing Magnox reactors, which are now mostly closed, and spent Magnox fuel needs to be reprocessed within a year. If it is left too long in cooling ponds, the fuel rods corrode, releasing radioactive material into the water. This has happened in the past, most dramatically during the coal miners’ strikes of the early 1970s, when nuclear power stations were run as hard as possible to keep the lights on, and Sellafield was overwhelmed with spent fuel. It happened again during a six-week strike at Sellafield itself in 1977, which shut down all reprocessing. The resulting mess of unprocessed spent fuel is a continuing problem that will require a multi-billion-dollar clean-up operation to solve.

A second plant, the Thermal Oxide Reprocessing Plant (THORP), handles so-called oxide fuels from Britain’s later generation of advanced gas-cooled reactors (AGRs) and the pressurised water reactors more common worldwide. THORP was Sellafield’s great hope in the days of BNFL, from the 1970s to the 1990s. The company wanted Sellafield to become the world centre for reprocessing. It would take spent fuel from around the world and convert it into new fuel, generating huge revenues for the government.

But from the day it opened in 1994, THORP’s commercial rationale has evaporated. Enthusiasm for nuclear power has waned and with it demand for the new fuel. What’s more, unlike spent Magnox fuel, the modern feedstock for THORP can be stored for decades without deteriorating, so the plant’s value as a waste-disposal facility has been minimal. Since it opened for business in 1994, the intended big moneymaker has become what Harold Bolter, BNFL’s PR man during the inquiry and company secretary when it was being built, later called ‘a huge financial drain on the nation’.

The plant has continued to work, though never reliably. Constant stops and starts have created backlogs of spent fuel in the cooling ponds, while delays in investing in the evaporation and vitrification plant have led to a build-up of high-level liquid waste. According to Gordon Thompson of the Institute for Resource and Security Studies in the US, the tanks of waste contain many times more radioactive caesium than was released across Europe during the Chernobyl disaster in Ukraine in 1986. A worst-case accident at Sellafield could release 90 per cent of it, he says.

The prospects of such a disaster may be remote, but it could happen swiftly if the tanks were breached by an act of terrorism or an earthquake, or if the cooling coils failed. According to a Royal Commission report on Britain’s nuclear industry as long ago as 1976, a cooling failure would ‘cause the solution to boil dry and the heat generated would then disseminate volatile materials to the atmosphere and cause widespread contamination’. If that happened, says Thompson, ‘a large area of land could be rendered unusable for a period of decades. Neighbouring countries could be significantly affected.’ He estimates there would be three thousand cancer deaths.

Such an event has long been of concern to nuclear regulators. In 2001, the Health and Safety Executive ordered Sellafield to cut stocks of the liquid waste from 1,575 cubic metres to no more than 200 cubic metres by 2015, either by speeding up evaporation and vitrification or by halting reprocessing. But in January of this year, as the target date arrived and the last-reported stockpile still stood at 900 cubic metres, the HSE’s successor, the Office for Nuclear Regulation, abandoned the target.

It is hard to see a case for such lenience. Post-9/11, the possibility of a terrorist attack on Sellafield must have increased, and a reassessment of seismic risks, made after the earthquake that wrecked Japan’s Fukushima Daiichi Nuclear Power Plant, resulted in the government extending the zone around Sellafield covered by evacuation plans from two to six kilometres earlier this year.

But the new regulator has decided that operational convenience takes priority. The target became a problem for Sellafield’s managers because of continuing gridlock in handling the liquid waste: a new £640 million evaporator promised for completion in 2010 is still more than a year off, and the plant that encapsulates the liquid into glass has suffered a series of shutdowns. Rather than halting reprocessing, the regulator has decided to let the radioactive build-up continue.

This is typical. Sellafield has a lamentable history of management failures that create backlogs of waste and allows them to accumulate in unsafe conditions. The ‘legacy problem’, as managers call it, became so great that in 2005 the government replaced the bankrupt ‘commercial’ BNFL with the Nuclear Decommissioning Authority (NDA), whose top priority is to work out how to shut Sellafield down and make the site safe for future generations – something even optimists believe will take upwards of a century.

On my tour of the works, my NDA hosts were keen to show me their highest-profile decommission to date. I watched as robots scooped up the last remains from the floor of the prototype Windscale AGR reactor, leaving behind its iconic golf-ball exterior. Much of the waste has gone into 120 concrete boxes, each two metres high, stacked in a store close by. The boxes are so safe that I took up their offer to go and touch them. This technical success has proved expensive, however. The dismantling of the Windscale AGR reactor, which was intended to take six years, ended up taking twenty years and costing £111 million.

Altogether, Sellafield has 240 radioactive buildings awaiting decommissioning. The most obvious is the pile that caught fire almost sixty years ago. Every day, Sellafield’s 10,000 workers still pass the remains – nobody has yet dared breach the seal. Inside, the graphite core still contains the Wigner energy that operators were trying to remove on the fateful day of the fire. Disturbing the remains could cause the core and the estimated fifteen tonnes of buckled uranium fuel to catch fire again, or even explode.

The pile will wait its turn. There are four other buildings that the NDA says have higher priority. Each will take billions of pounds to make safe. They contain fuel and waste that should have been made safe decades ago, but were instead abandoned. They are the dark hearts of Sellafield, the radioactive reminders of past follies.

The structure known as B29 was one of Windscale’s first. The hundred-metre-long open-air pond sits like an outsize swimming pool between the remains of the two Windscale piles. It received the cans of spent fuel as they were pushed from the backs of the piles, prior to reprocessing. After the 1957 fire, it was retired, but it was resurrected as an emergency store for spent fuel during the miners’ strikes of the early 1970s, when Sellafield’s reprocessing line couldn’t keep up. Stuck there too long, the skips of fuel began to corrode and the pond and its contents were abandoned again. The fuel remains and the corrosion has created 300 cubic metres of radioactive sludge that coats the bottom of the pond.

Close by is B41. This giant silo, constructed in 1950, houses six hoppers, each twenty-one metres high, which received the aluminium cans cut from pile fuel after it left B29. Later, it took cladding that sheathed spent Magnox fuel. Once full, it was closed in 1965. Plans for emptying it in the 1990s came to nothing. As the cans and cladding corrode, they generate hydrogen that could catch fire; argon gas is constantly pumped in to stifle any conflagration.

B30 opened in 1959. It is another giant pond, 150 metres long, and like its older brother B29 it is open to the elements. Until 1985, it received spent Magnox fuel awaiting reprocessing. As with B29, it still contains fuel that stayed too long and has corroded. The 1,500 cubic metres of sludge and corroded fuel in the pond contain up to 1.3 tonnes of plutonium. Sellafield managers don’t show B30 to visitors, but pictures leaked in 2014 revealed weeds growing round the tank and radioactive algae on the water. B30 is known to workers as ‘dirty 30’, because since the 1980s it has been Sellafield’s biggest source of contamination. They can only work in some areas for two or three minutes at a time. Safety experts call it Western Europe’s most hazardous industrial building.

The second most dangerous industrial building in Western Europe is B38, just next door. After B41 was filled, its four concrete silos took cladding from Magnox reactors. Some of the waste has since liquefied and sludge has seeped through cracks in the floor, forming a radioactive plume spreading through the soil beneath. As with B41, there is a risk of explosion from the hydrogen being generated in the silos, which are constantly ventilated.

The first steps towards emptying these monstrous ponds and silos have finally been taken, though all is not going well. This spring, the NDA postponed the expected completion dates for emptying B29 and B41 by five years, to 2030 and 2029 respectively, and the schedules may well slip further. ‘We have to do a lot of Research and Development just to characterise the inventory before we can work out how to retrieve the materials,’ Paul Howarth, the managing director of the UK National Nuclear Laboratory told me as we toured the site.

Sellafield’s baleful inventory also includes the world’s largest stockpile of non-military plutonium – over 120 tonnes of the stuff, with around four tonnes added from reprocessing each year. That is more than the US and Russian civilian stockpiles put together, and enough to make 20,000 Nagasaki-size bombs. A quarter of it is owned by foreign countries, mostly Japan and Germany, that sent spent fuel to the UK for reprocessing, but few are interested in taking it back.

The original purpose of separating the plutonium was to make fuel for a future generation of reactors, and many believe that project should be revived. The government’s chief scientist for energy David MacKay says that it contains enough energy to run the country’s electricity grid for five hundred years, but efforts to build two plutonium-burning plants – a fast-breeder reactor at Dounreay in Scotland and a mixed-oxide fuel plant at Sellafield – were both abandoned after the expenditure of more than a billion pounds. The asset has become a liability.

It is safe, if kept secure. But managers at Sellafield are reluctant even to identify the building containing the stuff, which costs around £100 million a year to protect. Most of the plutonium is in the form of plutonium dioxide powder that could be made into a crude nuclear bomb. In 2007, the Royal Society said the stockpile ‘poses a severe security risk’, and ‘undermines the UK’s credibility in non-proliferation debates’.

Whatever happens to the plutonium, the rest of Sellafield’s lethal legacy has to be kept safe. Terrorism is one threat, but so are the societies of the future – people whose cultures and technical skills could be as far removed from ours as the Neolithic people who built the Grey Croft stone circle. And safety, almost everyone agrees, ultimately means burial deep underground.

A couple of kilometres from Sellafield’s back fence, within metres of the Lake District National Park, lies the burial site the authorities keep coming back to. In the 1990s, Longlands Farm was proposed as the entry point for a test repository that might one day extend underground for up to twenty square kilometres. After a damning planning inspectors’ report warned that the rocks could transmit radioactive leaks into water supplies, however, the government threw the plan out. But a decade on, new ministers revived it, only for the Cumbrian County Council to vote against it four years ago.

Eddie Martin, county leader at the time of the vote, thinks the government could be about to resurrect it once more. He now runs the Cumbria Trust, which is dedicated to preventing that from happening. When I met him at his home outside Maryport, he said: ‘They want the disposal facility here not because the geology is favourable – it isn’t, as the old miners know, it is riddled with faults and fissures that make it unsuitable – but because they think we won’t object.’

Maybe policymakers in faraway London are right to think that. Western Cumbria is trapped by Sellafield. The complex provides most of the area’s jobs, spends most of the money, and has its tentacles in all kinds of local activities. Even the current local MP Jamie Reed – who was returned in May with a 2,564 vote majority – is a former PR man at Sellafield. He is supported by GMB, the largest blue-collar union at the site. Sellafield’s relatively high wages and environmental stigma repel other potential industrial employers, and school-leavers can either work at Sellafield or take low-paid work in tourism or farming. This summer, locals were being asked to comment on plans for a giant conventional nuclear power plant right over the fence from Sellafield. With many jobs on offer, they may be tempted. Construction could be under way by 2018.

Back in 1946, the government stipulated that, for safety reasons, Sellafield’s plutonium factory should be at least fifty miles from any large town. ‘Sellafield has stored the country’s nuclear waste and operated some of its most dangerous plants for almost seventy years,’ Eddie Martin tells me. ‘For what we have done for the country, the streets should be paved with gold. Instead, we have been largely ignored. Our infrastructure is poor. Too many children live in poverty. And in the back of our mind, we know that if there is an accident the whole area could become uninhabitable.’

Continued political chaos doesn’t help. In 2008, most of Sellafield’s activities were privatised. The aim, said then energy minister Mike O’Brien, was to ‘get to grips with the legacy after decades of inaction’. But as costs ballooned, O’Brien’s successors decided to renationalise it in early 2015. Whoever is in charge, the bills keep going up, from half a billion pounds in 1980 to 79 billion pounds today. Unlike other nations that rely on nuclear power, Britain never established a special fund to pay for eventual decommissioning. As former energy minister Chris Huhne put it four years ago: ‘When waste started piling up, we effectively crossed our fingers and hoped that it would all go away.’

Photograph courtesy of the author, Sellafield, 2015