On the 50th anniversary of Britain’s worst nuclear accident, physicists believe that they have a workable plan to dismantle the damaged core of the Windscale Pile 1 reactor.

The dirty relic of an early nuclear age has remained entombed behind its concrete bioshield since fire raged for two days in October 1957, threatening catastrophe and sending a plume of fallout over the North of England, south to London and across the sea to the Netherlands and Scandinavia.

Workers wielded sledgehammers and scaffolding poles at the charge face to dislodge uranium fuel rods and isotope cartridges to isolate the blaze and prevent “thermal runaway”.

The crippled reactor core, a legacy of the postwar Government’s dash to acquire the atomic bomb, has remained untouchable, deemed too volatile for decommissioning, and the object of wild speculation about what lies at its noxious heart. Over the past few weeks a team from the United Kingdom Atomic Energy Authority (UKAEA) has provided the answer.

Video provided by endoscopic probes sent along the narrow fuel channels have enabled physicists to study for the first time what the fire left behind. They reveal a strange, almost lunar landscape of concertinaed fuel boats, some reduced to ash, others with their aluminium fins still intact but jammed into their hiding places by brute force. There is yellow uranium, melted aluminium and a small mountain of irradiated shards and dust.

In the words of one physicist, the core is still home to a whole radio nuclide inventory, primarily caesium137 and cobalt60. But the pictures have reinforced the team’s optimism that the structure is stable enough to tackle head-on without submerging the 50ft core (15m) under water or encasing it inside a giant bubble of inert gas.

It means that the UKAEA can press ahead with plans to begin extracting the 15 tonnes of damaged fuel rods, dismantling the 2,000-tonne graphite core piece-by-piece and return Pile 1 back to a brownfield site. The £500 million project is likely to take until 2020.

The bleak nuclear archaeology that constitutes Britain’s first foray into a nuclear future would still be instantly recognisable to that capable postwar generation. The blower house, which used to pump air into the reactor building, is now an office block but the pile beneath its ugly but instantly familiar 400ft bulbous chimney is unchanged.

The building is still housed in its 1940s utilitarian shell. It is a dark and uncomfortable place. The pile cap, 80ft from the ground, can be reached only by the same rickety staircase that Vic Goodwin, the trainee graduate on the charge face that day, used to check the inspection holes.

The charge face, where the fuel rods were once inserted manually, still has the power to impress with its cathedral-like proportions, an altar to an earlier, more confident nuclear age.

Windscale Pile 1, built in a frenzied three-year period, provided the plutonium that powered Britain’s first A-bomb test, code-named Hurricane, which was detonated in the Monte Bello Islands, northwest of Australia.

At the same time engineers in the Windscale control room began noticing disturbingly abnormal temperature rises in the core, so-called Wigner energy, raising concerns that the fuel and isotope cartridges could burst and lead to “thermal runaway”. Initially, they solved the problem by gently heating the graphite core, a process known as annealing.

In October 1957 engineers shut down the reactor for its ninth annealing process. When the first heating fizzled out, they tried again but the process released so much energy that it began overheating. At about 4.30pm on Thursday, October 10, glowing fuel was noted in about 150 channels. For two days the fire burned inside the reactor core before, at the risk of an explosion, they doused it with water directly from the charge face and shut off the air-cooling system.

The fire was put out, but not before two radioactive plumes escaped through the chimney. The first was blown over South Lancashire and Yorkshire, reaching London and Belgium that Friday evening. It was detected in Frankfurt 24 hours later, and the Netherlands and Scandinavia the next day.

Contemporary newspaper reports of the incident appear, in hindsight, absurdly stiff. The Times reported that, according to Dr A. S. Mclean, chief medical officer, only a few employees had been contaminated and in most cases washing with soap and water was sufficient to cleanse them.

But at the charge face, there had been a very real sense of urgency. Dick Sexton, the pile project leader from the US, said: “They tried really hard to push all the fuel out at one time using sledgehammers and fork-lift trucks. These guys were Cold War warriors. They were thinking that what they were doing was patriotic.”

Windscale Pile 1 remained the benchmark for nuclear near-catastrophe until Chernobyl and Three Mile Island, ushering in a new regulatory era with the birth of the National Radiological Protection Board and other supervisory bodies.

The popular images, derived from the newsreels of the day, are of churns being upended over drains after concern about the presence of iodine131 led to a six-week ban on milk from farms within a 200-mile radius of the reactor. But the fallout contained longer-lasting poisons, which have since been blamed for hundreds of cancers.

Nobody in the UKAEA will celebrate the 50th anniversary, but there is a hope that this symbol of nuclear’s troubled birth will soon disappear from the landscape. There is also fresh optimism that cracking the most toxic problem posed by decommissioning in Britain sends out a powerful message at a time when the Government is due to take the next step over a new generation of nuclear power generators.

Peter Mann, Windscale’s head of site, said: “We see our image as showing the world what can be done with these facilities and that they can be safely decommissioned. Windscale AGR is well under way, and a success, and we are now at a turning point with the piles.”

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