The entry Seven Feet tells how Pile No. 1 at Windscale caught fire during a Wigner release in October 1957 and how the fire was put out. This piece follows the other half of the Penney committee’s terms of reference, “the measures taken to deal with it and its consequences”, out of the works and into the fields.

The vans

The wind on Thursday 10 October was light and, for most of the day, off the land, north-east or north-north-east. In the night it went round to the north-north-west, and through Friday a ten-knot wind blew down the coast; later it backed to the south-west. The committee thought there had very probably been an inversion a few hundred feet up during part of the time the stack was releasing, and that the wind above it might not have been the wind on the ground. “The fall-out pattern as it is now known strongly suggests meteorological conditions of this type.”

At about three on Thursday afternoon, an hour and a half before the glowing channels were seen, a survey van was sent out down-wind along the cinder track towards Seascale. It measured gamma radiation, “because it is so much quicker to make gamma measurements than measurements of air activity”, and so could cover more ground. Its highest reading was four milliroentgens an hour on the Bailey bridge near Sellafield station, most of it from the plume passing overhead. A second van went north of the works at five. The two “maintained continuous patrols throughout the night and the next day”. Some air measurements were made that evening; the highest, on the Calder Farm road at eleven at night, was about the same as inside the Calder works, ten times the level accepted for a lifetime’s breathing.

The health physics manager, H. Howells, had three hazards to think about: gamma radiation to the whole body, inhalation, and ingestion. The committee’s view was that he “correctly decided that irradiation and inhalation were likely to prove well within acceptable limits for the district, and that the main concern should be ingestion”. For a time he planned on the assumption that what was leaving the stack was ordinary fission products, so that the risks would come from iodine and strontium together. By Friday morning the first milk samples had been analysed and so had the first material collected from the air inside the works, and the two agreed: the activity “contained a far greater proportion of iodine activity than would normal fission products”. The explanation followed at once. The filters at the top of the chimney had caught the greater part of the particles. Iodine, which travels as a vapour, had gone through.

A tenth of a microcurie

Iodine-131 has a half-life of eight days. Deposited on grass it is eaten by cows and is in their milk within a day, and in the thyroid of whoever drinks the milk soon after; a young child drinks a great deal of milk for its size and has a very small thyroid, so the dose to the gland is highest there. The teams in the district turned most of their effort to milk. “No established tolerance level existed for radioactive iodine in milk,” the committee recorded. Howells had in mind a paper of 1956 by the Agricultural Research Council, written for the conditions of a nuclear war, which had suggested 0.39 microcuries a litre as the level beyond which milk would be a hazard to infants. The first analyses showed iodine-131 from traces up to 0.48. When the analysis of the Seascale morning milk of Saturday 12 October was finished, at three in the afternoon, it showed 0.8, and Howells advised the Works General Manager, H. G. Davey, that distribution of the milk gathered round the works should stop.

“There followed several hours of consultation by telephone and by meetings between the medical and health physics experts,” the report says, “in order to establish the limit of radio-iodine content beyond which milk should be taken out of distribution. This was calculated, by reference to probable absorption into the thyroid glands of young children, at 0.1 μc per litre, a figure which was subsequently endorsed both by the Authority’s medical consultants and by a meeting specially convened by the Medical Research Council as representing a reasonable assumption.” Lorna Arnold, who later had the papers, set the calculation out. There was medical evidence of thyroid cancers in children after doses of 200 rads and not below; the Authority’s people, led by the Group’s medical officer, Dr A. S. McLean, chose to keep young children’s thyroids below a tenth of that. The constants of 1953 said a microcurie of iodine-131 gave 130 rads to a gram of thyroid. A child was taken to drink a litre of fresh milk a day; with a thyroid of five grams and 45 per cent of the iodine retained, allowing for decay, the concentration in milk that would deliver ten rads was 0.15 microcuries a litre; with a thyroid of a gram and a half and a fifth retained, it was 0.1. The lower figure was the one adopted, “for the whole duration of the milk ban”. Three days later the Authority’s radiological consultants reviewed the sums beside a different set, by Dr Edward Pochin, that assumed half a litre a day, a five-gram thyroid and 45 per cent retained, and gave seven rads on average with twenty in places; they agreed the limit was right for the emergency. On 19 October a committee of the Medical Research Council, taking 250 rads as the cancer dose and two pints a day as the prudent intake, generally confirmed it, and suggested that in future the level should be no more than 0.06. The Council’s published comment, in the White Paper of 8 November, called 0.1 “sufficiently correct for the particular situation”.

Richard Wakeford, writing in 2007, put the matter in one sentence. The health physicists “had little guidance available as to what constituted an acceptable limit” for iodine-131 in milk, “and they derived, essentially from first principles, such a limit” of a tenth of a microcurie a litre “to constrain thyroid doses, particularly to infants and young children.” The Penney committee, for its part, thought it “unsatisfactory that tolerance levels in respect of several of the possible hazards should have had to be worked out in haste after the accident happened”, and recommended that permissible levels for short exposures be laid down in advance for every radioactive substance. Both were right.

Two hundred square miles

The decision was taken at about nine on Saturday night. By arrangements made locally with the Cumberland police and the Milk Marketing Board, the deliveries of twelve milk producers within two miles of Windscale were stopped that night. On Sunday and Monday samples were collected from farms at increasing distances and analysed at Windscale and at Harwell, and “as the analyses were completed, the restriction on distribution had to be extended in successive stages, until by Monday morning it covered a coastal strip approximately thirty miles long, ten miles broad at the southern end and six miles broad in the north. To the south, it included the Barrow Peninsula and the northern boundary was about six miles north of Windscale.” The Authority’s own chronology counts the ban at eighty square miles on the Saturday and two hundred by Tuesday 15 October, when a meeting at Risley of the Authority’s radiological consultants and its senior health and safety staff confirmed both the ban and the limit. Samples were taken round the Lancashire coast, the North Wales coast, the Isle of Man, into Yorkshire and the south of Scotland, “but there was no necessity to extend the boundaries of restriction”. Vegetables, eggs, meat and water were examined and none found harmful.

The farmers kept their milk at home. On Monday the 14th the Evening Star in Washington carried a report from London under the heading “Plant Forces Embargo On Radioactive Milk”: farmers on the coastal strip near the station had kept their milk back while they waited to learn whether it was too radioactive; samples from nearby farms “showed a level of radioactive iodine six times above the normal safety limits”; and McLean, named as the chief medical officer of the Authority’s industrial section, had told them to store it until a decision was made, since it might be used for animal feed or for butter and cheese. The decision was to pour it away. A thyroid survey among the people of the district found the highest activity in any gland, adult or child, to be 0.28 microcuries, in a child, against an accepted continuous level of a tenth for an adult. The strontium results, when they came, showed no hazard, and neither did caesium.

No district warning was given. Two witnesses told the inquiry that high levels of activity had been measured on grass and on clothing in Seascale, and on the clothing of people who had cycled to work along the track from Seascale on Friday morning. Howells was satisfied from the district measurements that no radiation or inhalation hazard existed outside the works, and the committee accepted that a warning “would have caused unnecessary alarm”; what was measured on the clothing was some twenty times below any hazard by the standards the Authority used. Asked in the Commons on 12 November why the public and the schools had not been told, the Prime Minister answered that “at no time did the measured radioactivity in the air or on the ground approach a level at which the public might be at risk”.

In the Lords on 21 November Lord Lawson, who had been a miner, said the restrictions had been extended “until they covered an area of some 200 square miles”, that a great number of farmers had had to destroy their milk, and that he did not know whether any cattle had been destroyed. The Lord President, Viscount Hailsham, answered from the front bench: “No; there was no destruction of cattle.” Later in the debate he explained why. “The danger was from a radioactive iodine in the milk, and it persisted for only twenty-four hours after the last moment at which the cow might have eaten contaminated grass.” Lord Rea, who lived nearby, read the House a letter from an old-age pensioner: “It is a nuisance that I dare not cut a cabbage in my garden”. Lord Mills, the Minister of Power, told the House that the derestriction was proceeding and that the last restrictions would be lifted on Saturday 23 November, six weeks after the first; that the farmers had been paid for their milk in the normal way by the Milk Marketing Board, which the Authority would reimburse; and that under section 5 (3) of the Atomic Energy Authority Act of 1954 the Authority had “an absolute duty” to see that no radiation from its premises hurt anyone or damaged anything, and would consider claims. Between the Seascale morning milk and the last lifting, by a later reckoning, about three million litres were thrown away.

What came out of the chimney

The question of how much had been released, and of what, took half a century to settle, and the answer changed each time somebody was allowed to see another file. The first reports, in 1958 and 1959, put the iodine-131 at about 20,000 curies, which is 740 terabecquerels, and quantified the other fission products; three of them mentioned polonium-210, from the bismuth cartridges that had been in the pile to make initiators for Aldermaston, without putting a figure on it, and the official account of the environmental side, published in 1960 as an appendix to the Medical Research Council’s second report on the hazards of radiation, did not mention the polonium at all, an omission Arnold called incomprehensible. Wakeford, reviewing the record in 2007, noted that the polonium’s release had probably been acknowledged at all only because the Dutch had detected it, and that two unclassified Harwell reports of 1959 and 1961 had discussed it, which made its absence from the official account “even more perplexing”. The security round the weapons materials, he allowed, “would have offered little assistance to any comprehensive ‘external’ investigation”.

Arthur Chamberlain of Harwell, who had worked on the original assessment, made the first thorough reckoning of every nuclide in 1981, polonium and tritium included. He had used classified papers, so his report was classified too, until 1983. The National Radiological Protection Board’s first assessment of the harm, by Malcolm Crick and Gordon Linsley in 1982, did not know of it and left the polonium out; a letter in the New Scientist pointed this out, and their addendum of 1983 and paper of 1984 put it in, with the finding that although thyroid cancer from the iodine remained the greatest risk, the predicted health effects of the polonium “came in a close second”. Roger Clarke, with updated risk coefficients in 1990, estimated that the accident “had caused, or would cause” about a hundred fatal cancers, fewer than ten of them thyroid cancers from the iodine and about seventy, mostly of the lung, from the polonium, and about ninety non-fatal cancers, some fifty-five of the thyroid. In 2007 John Garland, Chamberlain’s long-time colleague, and Wakeford went back to the original documents and had the Meteorological Office run the weather of October 1957 through its dispersion model, and concluded that about twice as much had been released as had been thought. “The reassessments showed that there was roughly twice the amount than was initially assessed,” Garland told the Register that October, which reported the estimate of cancers as more than 240. The iodine is now put at about 1,800 terabecquerels, which is 49,000 curies.

The accident is rated 5 on the seven-point International Nuclear Event Scale. The iodine, Wakeford observed, was a thousandth of what Chernobyl released thirty years later; the accident “can hardly be considered as trivial”, and “could have been a lot worse”. In 2024 a study led by Richard McNally, with Wakeford among the authors, followed everyone born between 1950 and 1958 in the parts of Cumbria that the milk ban had covered, where the measured thyroid doses to children had been mostly tens of milligray with one of 160, and found no rate of thyroid cancer that differed from the rest of the county: in the two most contaminated areas combined the ratio was 0.68, and in the most contaminated of all there was no case. The ban, Wakeford had written, “prevented a significant enhancement of the local collective thyroid dose and limited individual thyroid doses. A milk ban based on these ad hoc calculations was a courageous but wise decision.” It is the one part of the affair that was decided, from first principles and in time, by people who knew exactly what they did not know.

Sources

• William Penney and others, Report on the accident at Windscale No. 1 Pile on 10 October 1957, 26 October 1957, reproduced in the Journal of Radiological Protection 37, 2017, chapters VI and VII and recommendation (d): the wind, the vans, the three hazards, the iodine, the 0.39 and the 0.8, the limit of 0.1, the twelve producers, the strip, the thyroid survey, the witnesses from Seascale and the committee’s view of the warning. iopscience.iop.org
• Lorna Arnold, Windscale 1957: Anatomy of a Nuclear Accident, Macmillan, 1992, Appendix I (the chronology: 80 and 200 square miles, the meetings of 15 and 19 October) and Appendix VIII, “Calculations of Emergency Levels for Iodine-131”, for the eight derivations of the limit from 1956 to 1975, the Pochin and Medical Research Council figures and “sufficiently correct for the particular situation”. link.springer.com
• Atomic Energy Establishment, Windscale (Accident), House of Commons, 12 November 1957, column 780, for the Prime Minister on the public and the schools. api.parliament.uk
• Windscale Atomic Plant Accident, House of Lords, 21 November 1957, columns 448 to 476: Lord Lawson’s “some 200 square miles”, Viscount Hailsham on the cattle and the iodine, Lord Rea’s pensioner, and Lord Mills on the derestriction, the Milk Marketing Board and the Act of 1954. columns 448 to 457, columns 459 to 476
• “Plant Forces Embargo On Radioactive Milk”, Evening Star, Washington, 14 October 1957, page 17, datelined London. loc.gov
• Richard Wakeford, “The Windscale reactor accident—50 years on”, Journal of Radiological Protection 27, 2007, pages 211 to 215: the history of the release estimates, the polonium, Chamberlain, Crick and Linsley, Urquhart, Clarke’s figures, Garland, the Level 5 rating, the thousandth of Chernobyl, the derivation of the limit and “courageous but wise”. Arnold’s “incomprehensible” is quoted as Wakeford quotes it. iopscience.iop.org
• Richard J. Q. McNally and others, “Thyroid cancer incidence in cohorts exposed in childhood to 131I released during the Windscale nuclear reactor accident at Sellafield, England, in 1957”, Radiation and Environmental Biophysics 63, 2024, pages 491 to 503: the 1,800 terabecquerels, the three million litres, the measured thyroid doses, the rate ratio of 0.68 and the finding. link.springer.com
• Lucy Sherriff, “Windscale fallout underestimated”, The Register, 8 October 2007, for Garland’s “roughly twice” and the figure of more than 240 cancers; Garland and Wakeford’s paper in Atmospheric Environment 41, 2007, is behind a paywall and was not read. theregister.com