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An official inquiry into a near-catastrophic fire at a nuclear power plant was published 60 years ago today, blaming the accident on a combination of human error, poor management and faulty instruments.

The fire happened a month earlier, on October 10th, at the Windscale site on the Cumbrian coast, the world’s first commercial nuclear power plant to generate electricity on an industrial scale. It remains the worst nuclear accident in British history and was ranked level five in severity out of a possible seven on the International Nuclear Event Scale.

A catastrophic nuclear disaster was only narrowly averted and the government was keen to find out what had gone wrong and take steps to ensure it could never happen again. Published on November 8th, 1957, the preliminary report into the accident set out its main causes.

The inquiry committee established that the fire had broken out at the site’s number one nuclear reactor (at the time called ‘atomic pile’ number one) during a routine maintenance exercise. It involved switching off the reactor’s cooling device to allow graphite to heat up in a controlled situation and release the energy which builds up when graphite is exposed to radiation.

On October 10th the energy had been released much too quickly because the instruments used to monitor the process had not been designed specifically for that purpose and showed incorrect readings. It meant that the fuel got too hot and melted, fuel cans burst, and uranium ignited.

The fire in the reactor at first went unnoticed as a remote scanner had jammed, and it was only after two workers clad in protective clothing made a personal inspection that the full scale of the emergency was realised. Even then, operators were unsure how to react. Their first efforts to blow out the fire by turning cooling fans to full power only fanned the flames.

Next carbon dioxide was tried, but the fire was so hot that it stripped the oxygen out before it could even be applied. By the morning of October 11th, when the fire was at its worst, 11 tons of radioactive uranium were ablaze, with temperatures registered at 1,300°C and the reactor in imminent danger of collapse.

Using water, itself a risky strategy on a white hot fire, also failed and it was only after all air entering the reactor was shut down that the fire began to fade and die. Once it was out, water was passed through the reactor for a full 24 hours until it was completely cold and the immediate crisis had passed.

While the fire was burning, an unspecified amount of radioactive iodine vapour escaped into the atmosphere via a chimney, collecting on the grass in surrounding fields. It was eaten by grazing cows and absorbed into their milk, resulting in all milk from about 500 square kilometres of surrounding countryside being diluted and destroyed for about a month.

The radioactive isotope in the released vapour – iodine 131 – can cause cancer of the thyroid and it has since been estimated that the incident caused up to 240 additional cancer cases in the years that followed.

The official accident report found serious failings in the way the plant was run, some of its equipment and the lack of planning and training for if something should go wrong. It made a series of recommendations, including a speedier assessment of the risks to public health following any future incident.

Prime Minister Harold Macmillan, addressing the House of Commons, announced three new committees would be set up to study the report and advise on lessons to be learned from the fire. But he was keen to stress that the accident had no bearing on Britain’s ongoing policy of developing further nuclear power stations.

The Windscale fire is still one of the ‘big three’ nuclear accidents cited by opponents of nuclear power, the others being Three Mile Island and Chernobyl. In 1971 the management of Windscale was transferred to a new body, British Nuclear Fuels, and the plant was renamed Sellafield. It became the world’s greatest discharger of radioactive waste, most of which went into the Irish Sea, and by 2000, countries including Ireland, Norway and Denmark were all pressing for its closure.

Sellafield is now being decommissioned as part of a programme to close down the UK’s 14 ageing nuclear power stations as they reach the end of their working lives. However, the site still operates as a nuclear fuel reprocessing plant and decommissioning site, employing around 10,000 people. About 1,000 of them are currently on strike in a dispute over pay.

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