At half past four on the afternoon of Thursday 10 October 1957, on the charge hoist in front of Pile No. 1 at Windscale, on the coast of Cumberland, men in full protective clothing pulled the plug out of a charge hole in the front shield. The hole gave on to a group of four fuel channels numbered 21/53. Getting to it had taken longer than it should have, because a thermocouple had been wrongly labelled and the first hole opened was the wrong one. The thermocouple for this group had been climbing fast for an hour and now stood near 450 degrees. Through the hole the uranium in the channels could be seen glowing. The graphite round it, the committee of inquiry recorded sixteen days later, “appeared to have its normal colour”.

The committee, under Sir William Penney, would conclude that the fire had started two days before, on the Tuesday, and that the men running the pile had been reading its temperature all that time from thermocouples fixed in the fuel about sixteen feet from the front face, where the pile ran hottest in ordinary service. The operation in progress was not ordinary service. In it, the committee calculated, the hottest uranium lay “some seven feet nearer the front face of the Pile than the thermocouple positions”. The instruments were in the right place for the reactor’s work and the wrong place for its maintenance, and in five years nobody had moved them.

Who ran it

The piles at Windscale were built to make plutonium for a British bomb. The policy was settled in the middle of the 1940s and carried out, Richard Wakeford wrote in 2007 in the journal he edited, with a speed that was “truly remarkable”. Construction began in September 1947 on the site of a wartime ordnance factory at Sellafield, which was renamed Windscale to keep it distinct from the fuel works at Springfields. Pile No. 1 was running in October 1950 and Pile No. 2 in June 1951. The first plutonium was separated in 1952, and on 3 October 1952 it was exploded off the coast of Australia, five years after the building work started. The Minister of Power, Lord Mills, put the same history to the House of Lords in November 1957 in a sentence: in twelve years, “having started, as has been said, with nothing but grey matter and green fields”, British scientists and engineers had developed a new industry.

From 1954 the piles belonged to the United Kingdom Atomic Energy Authority, under Sir Edwin Plowden, and within it to the Industrial Group, whose headquarters were at Risley in Lancashire and whose first listed responsibility was “the design, building and operation of defence installations”. Its technical direction, the inquiry would find, ran largely by committee, with the research establishment at Harwell, under Sir John Cockcroft, as adviser.

At Windscale the Works General Manager was H. G. Davey, and his charge was not only the two piles and the chemical plants but the new power reactors at Calder Hall, next door, and at Chapelcross in Scotland. His deputy was Tom Tuohy, a chemist from Wallsend, thirty-nine that October, who had come to Windscale in 1949 as a health physics manager. The pile group had a manager, R. Gausden. The operation that went wrong was, by the inquiry’s account, “the responsibility of the Pile Physicist and his two deputies, by virtue of their specialised knowledge”; the control engineers worked on their instructions. The works had a health physics manager, H. Howells, and the Group a medical officer, Dr A. S. McLean. The Group’s director of operations, K. B. Ross, happened to be at Windscale when the fire was found, and the decisions of that night were taken after consultation with him.

The committee that investigated them was appointed by the Authority on 15 October, with the Prime Minister’s approval. Penney was director of the weapons establishment at Aldermaston. With him sat Basil Schonland, deputy director of Harwell; J. M. Kay, professor of nuclear engineering at Imperial College; and Jack Diamond, professor of mechanical engineering at Manchester. David Peirson, the Authority’s secretary, kept the record. They sat at Windscale from 17 to 26 October, heard thirty-seven witnesses, some more than once, and reported on the 26th.

What they were trying to find out

A pile of this kind is a block of graphite with uranium in it. The graphite slows the neutrons so that the chain reaction can go on; the uranium, as it fissions, turns a little of itself into plutonium. Lord Mills explained the rest to the Lords. “In the Windscale pile some of the energy which the neutrons lose as they are slowed down remains stored in the graphite. This stored energy, known as Wigner energy, tends to distort the graphite and is released by a periodic maintenance operation.” Neutrons knock carbon atoms out of their places in the crystal, and at the low temperatures at which the Windscale piles ran the atoms stay out of place and hold the energy. Warm the graphite enough and they go back, giving the energy up as heat, and the heat warms the graphite next to it, which gives up its energy in turn. Let that happen on its own and it can run away. The first time it happened at Windscale, in September 1952, it was not planned. A procedure was drawn up from the study of that accident, and over the four years to the end of 1956 Pile No. 1 was annealed eight times.

The procedure was itself an experiment on the pile, repeated each time with the conditions a little changed. “The general procedure,” Penney’s committee wrote, “has been to shut down the Pile, to arrange the appropriate instrumentation and then to cause the Pile to diverge with no coolant air flow, thus raising the graphite and uranium temperatures. By this means, the graphite is brought up to a temperature at which Wigner release is started.” The hypothesis had two parts. The first was that a short period of nuclear heating, with the fans off and the pile as nearly airtight as it could be made, would carry the graphite past the temperature at which the stored energy let go, and that the release would then spread of its own accord. The second was never written down as a claim, because nobody thought of it as one: that the pile’s instruments, read on the pile roof, would show the operators where the heat was and when they had done enough.

The first claim had been proved often enough to be trusted and seldom enough to be doubted. The procedure had not always worked. In 1956 the attempt made in April “was completely unsuccessful and two others partially successful; that is to say, energy releases were recorded from certain regions of the Pile only, and pockets were left un-annealed.” The interval between releases, set originally at 20,000 megawatt-days of operation, had been raised to 30,000; in September 1957 the Windscale Works Technical Committee considered a paper recommending 50,000 “in view of the increasing difficulties of obtaining a successful release”, and settled, until there was more experience, on 40,000. On that reckoning a release fell due in October 1957. It would be the ninth.

The second claim had never been tested, because the conditions that would test it were the conditions of the release itself. The uranium thermocouples, the committee found, “were installed in all cases in cartridges about 16 feet from the front face of the Pile, where the maximum temperatures occur under normal operating conditions. Since 1954, these thermocouples have been used to control the progress of the nuclear heating for Wigner release.” In a release the control rods crowded the chain reaction into the front and lower part of the pile, and with no air moving the hottest fuel sat where the neutron flux peaked, well in front of the thermocouples. The committee’s estimate was that the true rise in uranium temperature “could be 40% greater than the recorded temperature rise”. No one had made that calculation before October 1957. There was nothing to make it for.

There was, in fact, very little written down at all. “It appears that there is nothing in the nature of a Pile Operating Manual,” the committee reported. “The only written instruction which was produced for our inspection was a minute of 14th November, 1955.” The minute is a hundred words. “Will you please issue the following operating instructions to the operator engaged in controlling the Wigner energy release. If the highest Uranium or Graphite temperature reaches 360 °C, then Mr Fair, Mr Gausden and Mr Robertson are to be informed at once, and the PCE alerted, to be ready to insert plugs and close the chimney base. When the maximum temperature reaches 380 °C, unless further instructions to the contrary have been received, the roof plugs will be inserted and the chimney base closed. At 400 °C all of the dampers in the blower houses are to be opened and at 415 °C, 4 shut down fans are to be started up.” The Pile Manager told the committee there was also a limit of 250 degrees on the fuel in the first stage of a release, “which, it had been laid down, should not be exceeded”. The committee could not find where it had been laid down. “We were obliged to piece together the other details of pile operation from Committee minutes and from traditions which did not seem to have any written authority.”

What they built

Each pile held about 180 tons of uranium metal in more than seventy thousand aluminium-canned elements, lying end to end in 3,440 horizontal channels through nearly 2,000 tons of graphite. The channels ran on an eight-and-a-quarter-inch square lattice. For loading they were grouped in fours behind a single charge hole in the front shield, with a channel of smaller bore in the middle of each group for the isotope cartridges; the pile’s numbers for a group, 20/53 or 21/53, are the row and column of that hole. Fuel went in from a charge hoist that travelled across the front face and was pushed out at the back, when it had done its time, into a duct of water. The piles were cooled by air: fans drew it through the channels and up a chimney 400 feet high. Cockcroft had insisted, on information from the United States and after the chimneys were already going up, that the air be filtered before it left, and the filter galleries built at the top of the stacks were known in the works as Cockcroft’s follies. During the fire, the Nuclear Decommissioning Authority wrote in 2019, they caught an estimated 95 per cent of the radioactive dust.

Plutonium was not all the piles made. Cartridges of bismuth oxide were irradiated to produce polonium-210, which Aldermaston needed for the initiators of its weapons, and from 1954 cartridges of lithium-magnesium alloy to produce tritium. At the time of the accident Pile No. 1 held natural and slightly enriched uranium “and a considerable variety of isotope cartridges”. The newest mark of lithium-magnesium cartridge, a bare rod of alloy in a single aluminium can, had been loaded in December 1956 and had never been through an anneal in this pile.

Fuel cans failed in ordinary running, and the piles were built to find them. The cooling air carried fission products from a split can past detectors on a scanning gear that could point to the channel, so that the elements could be pushed out before the graphite was contaminated. That gear needed air moving through the pile. A Wigner release needed the air stopped. “In the condition of stagnant air which had necessarily been created within the pile,” the committee found, “there was no means of detecting the smouldering uranium cartridges, which we believe to have been a key event in the development of the accident.” The same stagnant air meant that the one instrument the stack had, the activity meter at the filters, could not see what was happening in the core until the first time the dampers were opened.

The thermocouples were what the operators had. The graphite ones sat four, six and ten feet into the pile; the uranium ones, in the fuel cartridges, sixteen feet in. Their readings were taken on the roof. “The Pile is a very large structure,” the committee noted, “and during a Wigner release operation it is frequently necessary for the people in charge of the release to climb some 70 feet to the roof in order to inspect the thermocouple readings. There is no lift; its absence must have added considerably to the operational difficulties.” The pile was being controlled on temperature, which is to say on the thermocouples.

The second heating

Pile No. 1 was shut down at thirteen minutes past one in the morning of Monday 7 October 1957, and the main blowers were switched off. The thermocouples to be used were checked and the unserviceable ones replaced. The shut-down fans were stopped, the door in the base of the chimney and the inspection holes on the pile roof were opened, so that the chimney would not draw, and at 7:25 that evening the pile was made to diverge. By about one in the morning of Tuesday the 8th the power meter showed 1.8 megawatts. Around midnight two channels had reached the 250-degree limit on the fuel; the rods were run in and by four in the morning the pile was shut down. Most of the graphite temperatures then rose, the stored energy coming out.

At about nine on the Tuesday morning the physicist in charge and the Pile Manager formed the view that the graphite temperatures were tending to fall rather than rise, and that unless more nuclear heat was put in the release would stop. The committee, with the thermocouple records in front of it, read them differently. “Undoubtedly, some of the graphite temperatures were falling and there were some in which no Wigner release was apparent; but a substantial number of the graphite thermocouple readings showed steady increases.” A second heating had been used three times before. In 1954 and 1955 it had not been applied until at least twenty-four hours after the last regional burst of temperature, and after every graphite reading had been seen to fall; in 1956, all but one were falling. This time the physicist “decided to boost the release with more nuclear heating”. The bottom rods were withdrawn and at 11:05 the pile diverged for the second time.

The fuel thermocouples jumped. One rose by 80 degrees to 380 in a quarter of an hour, at a rate that touched 30 degrees a minute, and the committee observed that the normal practice in pile operation was to limit such rises to two degrees a minute. The reading was brought back to 334 degrees in ten minutes by adjusting the rods, and nuclear heating went on at a lower level until five in the afternoon. The committee’s reconstruction of what had happened by then is a chain of inferences from numbers. At the point of peak flux, where a graphite thermocouple nearby read 315 degrees, the uranium could already have been at 340; the sudden heating could have taken it “as much as 450 °C for some minutes”, seven feet in front of the thermocouples that read 380. The older fuel in that region had reached the point at which the cans of that mark cracked at the shoulder as the uranium grew. Rapid heating, the committee reasoned, had pushed the ends off cartridges that were ready to fail; the bared metal began to oxidise, slowly, in air that did not move; and the heat of the oxidation added itself to the heat of the release. “Once the assumption is made that a single uranium cartridge is ignited, there is no difficulty in visualising several probable routes by which final conflagration can be reached.”

Nobody could see it. On Wednesday the 9th the fuel readings showed a maximum of 360 degrees, and the graphite, which should by now have been cooling, tended to rise. One graphite thermocouple in particular, in channel 20/53, had read about 255 degrees when the second heating was applied and climbed steadily all day; by ten that night it read 405. At nine the physicist shut the chimney base and the inspection holes so that the chimney draught would pull a little air through the pile, and when that was not enough, at a quarter past ten, he opened the fan dampers for a quarter of an hour. He opened them again at one minute past midnight for ten minutes, at a quarter past two for thirteen, and at ten past five for thirty. Every graphite reading but one came down. In 20/53, “the temperature rise was merely arrested”.

The dampers did two things at once. They cooled the pile, and they blew on the fire. The committee’s account is that the first three openings were too short to set up any steady current of air, so that what was leaving the oxidising fuel never reached the top of the stack; the fourth, at 5:10 on Thursday morning, was long enough. At 5:40 the stack activity meter recorded a sharp rise of six curies. The physicist on duty noted it and took no special action, “because he regarded it as the normal consequence of the first movement of air through the pile and up the stack”. The reading fell away for two and a half hours and then rose steadily. The temperature of the air leaving the pile, which had stood at about 40 degrees until seven on Wednesday morning, was 85 by eight on Thursday.

By noon on Thursday the thermocouple in 20/53 read 428. The dampers were opened at ten past twelve for fifteen minutes and at twenty to two for five, and with the second opening came “the second and very large increase in stack activity”, and a report of high activity on the roof of the meteorological station. A three-hour air sample taken outside the health physics building between eleven and two gave 3,000 beta disintegrations a minute per cubic metre against a normal 200 to 300. That was the first thing anyone saw that said what was happening, and it said a burst cartridge. At 1:45 the shut-down fans were switched on, “as a preliminary move in an attempt either to use the scanning gear to detect any burst cartridges or alternatively to blow the Pile cool”. At 2:30 the turbo-exhauster was started so that the scanning gear could search. The gear was jammed. The Pile Manager said it had jammed at the end of previous releases too, presumably from the heat, though the maintenance section had worked on it the day before and moved it. An air sampler was used instead, and it gave “a large positive reading”. The Pile Manager told Davey there appeared to have been a bad burst, and Davey ordered the channel found and discharged. Since the gear could not find it, the men would have to look.

What it looked like from inside

What they saw at 4:30, through the hole for group 21/53, was uranium at red heat, and the committee’s judgement is that “the accident had happened by this time; what followed were remedial measures”. An attempt was made at once to push the cartridges out of the glowing channels into the water duct behind. They were stuck fast. The main blowers could have brought the temperature down, but with the stack reading what it did, “this would probably have caused a serious neighbourhood hazard”; the shut-down fans were kept running to make the charge hoist workable. The workshops were asked to make graphite plugs to blank off the hot channels. Then more plugs came out of the charge wall, and the hot channels were not a group of four but “a rectangular region of some 40 groups of channels—about 150 channels in all—showing red heat”. The plug-making was abandoned.

From about five in the afternoon there were two lines of attack. Men on the hoist went on all night pushing at the channels in the hot region with steel rods, and when the rods ran out, early on Friday morning, scaffolding poles were fetched from the Calder Hall construction site. Some channels were cleared that way. Tuohy told the inquiry what happened to the rest, by the account of his obituarist fifty years later: “They jammed solid.” The other line was a fire break. At about five it was decided to discharge a complete ring of channels round the hot area, and that was done; a second row was taken out above and to each side, and later, as the fire kept trying to climb, a third row above. At one point the discharging had to stop while the skips in the water duct were moved, to avoid the fuel going critical in the water. Argon was thought of, but the works did not have enough. A tanker of carbon dioxide was brought over from Calder Hall and piped into channel 20/56 at half past four in the morning, “but with no appreciable effect”.

Someone had to see the fire, and the only way to see it was to look down through the inspection holes on the pile roof, seventy feet up, at the back face of the core. Through the east inner hole an observer saw “an obvious glow on the pile rear face” at a quarter to seven in the evening; at half past seven “the flames were much brighter”; at eight “they were yellow” and at half past eight “they were blue”. Tuohy, who had been called from home, went up and looked himself, several times, in protective clothing and breathing apparatus. “I never thought about my own safety,” he said for a television programme in 2007. “I just knew there were things I could do, and I got on and did them.”

Water was first considered at about that hour, and it was not an easy thing to consider. Two hazards had to be weighed, the committee recorded: “first the danger of a hydrogen-oxygen explosion which would blow out the filters, second a possible criticality hazard due to the replacement of air by water.” Hot uranium takes the oxygen out of water and leaves hydrogen. And there was a third, which was the thing the whole operation had been for. The management were warned, the report says, “of the danger of releasing high temperature Wigner energy if the graphite temperatures were to rise much higher than 1200 °C. It was thought that this might well ignite the whole pile.” “We were quite honestly frightened of the water,” Tuohy said to the inquiry, as his obituary records it, “because we didn’t know whether there would be an explosion or not.”

By about midnight Davey had decided that if the other measures failed, water would be used. “This was the major decision,” the committee wrote, “and it was supported by the Director of Production and the Deputy Works General Manager.” The fire brigade was told to stand by with every pump it had, and men began rigging hoses to the discharged channels. Shortly after midnight the Chief Constable of Cumberland was warned that there might be an emergency, and at 1:33 the men on the site were told to stay indoors and wear face masks. At 1:38 the graphite in channel 20/53, at the top of the hot area, read 1,000 degrees, and an optical pyrometer put a fuel element at 1,300. Over the next two hours “brute force” cleared almost all the top row of burning elements, “but the fire continued unabated elsewhere”. By 3:44 the hoses could be coupled at fifteen minutes’ notice. At four, through two of the roof holes, there were still blue flames, and the graphite itself appeared to be burning.

At seven on Friday morning it was decided that the water would go in, but not until every man on the site was under cover, and the shift changed at eight, so there was a wait. At 8:55 the water was turned on, through two channels above the top of the fire, at 300 gallons a minute and then 800. “No dramatic change resulted; at 09.56 flames were still feathering out of the back of the pile.” Then, at ten past ten, the shut-down fans were turned off. Without the air the fire had been fed since Thursday afternoon, “the fire immediately began to subside”. At noon two more hoses went in and the flow was raised to a thousand gallons a minute, and it ran at that rate until a quarter to seven on Saturday morning and was tapered off until ten past three that afternoon, when the pile was cold. Tuohy went back up to the roof to be sure. “I went up to check several times until I was satisfied that the fire was out,” he recalled. “I did stand to one side, sort of hopefully, but if you’re staring straight at the core of a shut-down reactor you’re going to get quite a bit of radiation.”

The men were monitored as they came off the hoist. Over the thirteen weeks to 24 October, including the accident, fourteen of those involved exceeded the permitted 3 roentgens; the highest film badge read 4.66. The highest iodine measured in any worker’s thyroid was half a microcurie, against the accepted level of a tenth for continuous exposure. “No worker had to be detained after the accident,” the report says, and the air over the site, which rose on Friday morning to a few peaks of 150 times the lifetime limit near the chemical plants and Calder, was down to twice it by noon and never went back.

What happened

The wind on Thursday had been light and mostly off the land. In the night it went round to the north-west and on Friday blew at ten knots down the coast. A survey van went out at three on Thursday afternoon along the cinder track towards Seascale and found its highest reading, four milliroentgens an hour, on the Bailey bridge by Sellafield station, mostly from the plume overhead. By Friday morning the first milk samples and the first filters from the works had been analysed, and both held far more iodine than fission products should: the filters at the top of the chimney had caught the particles, and iodine, which travels as a vapour, had gone through. Iodine-131 on grass goes into a cow’s milk in a day and into the thyroid of whoever drinks it, and the thyroid of a small child is small. “No established tolerance level existed for radioactive iodine in milk,” the report says. At three on Saturday afternoon the result for the Seascale morning milk came through at 0.8 microcuries a litre, and the health physics manager, Howells, advised Davey that the milk from round the works should stop. Several hours of telephoning and meetings among the medical and health physics people settled a limit of 0.1 microcuries a litre, worked out from the thyroids of young children, and at about nine that night the milk of twelve producers within two miles of Windscale was stopped. By Monday morning the restriction covered a coastal strip thirty miles long, from six miles north of the works to the Barrow peninsula; the Authority’s chronology counts it as two hundred square miles by the Tuesday. The milk was poured away. No one was told to leave. The last restrictions were lifted on 23 November, six weeks after they began, and the farmers were paid. The surveys, the limit and what fifty years of measurement made of the chimney’s output are in The milk.

Pile No. 2 was shut down on 18 October. Penney’s committee heard its last witness on the 26th and reported the same day. Its finding on cause was one sentence: “the second nuclear heating was too soon and too rapidly applied.” On the chain from there to the fire it gave the burst fuel cans as “by far the most likely possibility” and a failed lithium-magnesium cartridge as “a second possibility, which we cannot entirely reject”, and it put the start of the fire “in the region of the Pile just below the middle plane and towards the front”. On the men it said that the steps taken once the fire was discovered “were prompt and efficient and displayed considerable devotion to duty on the part of all concerned”, and that “due to the efforts of the Windscale staff, a worse accident was averted”. On the instruments it said this. “A major technical defect contributing to the accident was the inadequacy of instrumentation for the safe and proper operation of a Wigner release. The uranium thermocouples were correctly positioned for normal operations, but not for Wigner releases.” On the organisation it said that responsibility was not clearly defined, that “technical changes made by one team within the Authority have not always been known to others”, that “there is undue reliance on technical direction by committee”, that “changes have been made in operating procedures, with a general tendency to push pile temperatures upwards, without complete realisation of all the technical factors involved”, and that the Windscale organisation “is not strong enough to carry the heavy responsibilities at present laid upon it”, with posts under the general manager unfilled. It recommended, among other things, that Pile No. 2 should not be restarted “until its instrumentation is fully adequate for the safe operation of a Wigner release”.

On 28 October the Authority’s executive recommended that the report be published in full, and sent it to the Prime Minister, who had just come back from three days with President Eisenhower in Washington and a joint declaration that the President “will request the Congress to amend the Atomic Energy Act”, the law that had shut Britain out of American weapons work since 1946. Harold Macmillan told the Commons on 29 October, “I will certainly make a full report to this House”, and that he was “also interested in maintaining, as I am sure is the right hon. Member for Leeds, South, the tremendous, unique reputation of our scientists in this field throughout the world.” On 8 November a White Paper was laid instead, with “a less technical version, prepared by Sir William Penney’s Committee, of their Report”, and a memorandum by the Prime Minister: “It would not be in the national interest to publish the report.” The same memorandum carried the Authority’s account of responsibility, that the accident “was due partly to inadequacies in the instrumentation provided at Windscale for the maintenance operation that was being performed at the time of the accident, and partly to faults of judgment by the operating staff, these faults of judgment being themselves attributable to weaknesses of organisation.” Macmillan’s statement called the release “a routine maintenance operation” and found “no evidence that this accident has done any significant harm to any person, animal or property”. Sir Alexander Fleck, the chairman of Imperial Chemical Industries, was given three committees. Their reports came out between December 1957 and July 1958; on 15 July 1958 it was announced that Pile No. 1 would not be rehabilitated, and on 24 October that Pile No. 2 would not be restarted. The report itself went into the Public Record Office and was opened in January 1988. What was published and what was not, and the thirty years between, are in The White Paper.

After

What had come out of the chimney was argued over for fifty years. The first accounts put the iodine-131 at about 20,000 curies and said little about anything else; the polonium-210 from the bismuth cartridges was mentioned without a figure, and then not mentioned at all; the first full reckoning, at Harwell in 1981, was itself classified. Roger Clarke’s revision in 1990 reckoned about a hundred fatal cancers, most of them from the polonium, and about ninety that would not be fatal. In 2007 John Garland and Wakeford concluded from the original monitoring and the weather of those days that about twice as much had been released as had been thought; the iodine is now put at about 1,800 terabecquerels, which is 49,000 curies. In 2024 a study of everyone born in the affected parts of Cumbria between 1950 and 1958 could find no increase in thyroid cancer at all. The milk ban, Wakeford wrote, “prevented a significant enhancement of the local collective thyroid dose”, and its limit, worked out from first principles on a Saturday, was “a courageous but wise decision”.

Arnold, who had the files, called the operation of the piles “an accident waiting to happen”, and recorded that some senior people in the Authority never accepted the committee’s chain of events and pointed to the lithium-magnesium cartridges; when those were taken out of the closed Pile No. 2 in 1958 some were found badly damaged, and the Fleck committee’s final report found it “necessary to modify the existing design of lithium-magnesium cartridge”. Whether a fuel can or a tritium cartridge went first, the heat that failed it was in a place no thermocouple could see.

Tuohy was made general manager of Windscale in 1958, ran the Authority’s production group through the 1960s, was the first managing director of British Nuclear Fuels in 1971, and retired early in 1974. He died in Australia on 12 March 2008, aged ninety. The chimneys stood for another sixty years, the one over Pile No. 2 shortened and capped in the 1990s, the one over Pile No. 1 taken down from the top from December 2018, its diffuser and filter galleries cut into blocks and lowered by a crane 162 metres high. Inside Pile No. 1, the Nuclear Decommissioning Authority wrote in October 2025, “some fuel remains trapped in fire-damaged channels, inaccessible using original discharge equipment”.

What it taught

A thermocouple measures the temperature of the place it is in. The ones at Windscale were in the right place for a running reactor, and had been chosen for it; a Wigner release moved the reactor’s hottest point seven feet towards the front, and for five years the readings taken on the roof described a point the operation had left behind. The committee’s arithmetic was that the real rise could be forty per cent more than the recorded rise. The operators on 8 October held the pile to a reading of 380 degrees and were, by that arithmetic, somewhere near 450. Nobody had done that sum, because the thermocouples had been “used to control the progress of the nuclear heating” since 1954.

Repetition is not a procedure. The ninth release was run from a hundred-word minute of 1955, a limit of 250 degrees that nobody could find in writing, and “traditions which did not seem to have any written authority”. Between the first release and the ninth the interval had doubled, from 20,000 megawatt-days to 40,000, because the releases were getting harder to achieve; the operating temperatures had crept up; a new kind of cartridge had gone in. An operation that has succeeded eight times under changing conditions has not been tested eight times. It has been tested once, each time.

Design the test for its own failure, not the plant’s. The pile had good instruments for the hazards of running: a scanning gear to find a burst can, a chimney meter to catch what the filters missed, blowers to cool anything. The release switched all three off, because it needed still air. Nobody then asked what would find a smouldering cartridge in a pile with no air moving through it, and the committee’s answer was that nothing could. The Soviet commission that re-examined Chernobyl in 1991 found a test whose authors did not know how the reactor behaved in the state the test created; Windscale is the same finding in a smaller pile, thirty years earlier.

The readings and the judgement. At nine on 8 October the physicist in charge looked at the graphite temperatures, saw them falling, and heated the pile again. The committee looked at the same records, with the fire known and time to study the curves, and saw a substantial number rising. Lord Mills’s sentence, that every man did his duty “with the instruments and the information with which he was provided”, is the fair one, and it cuts both ways: the judgement was wrong, and the instruments had made a right one very hard. A pile seventy feet high with no lift and its readings on the roof is an instrument too.

The dampers. Every opening of the dampers cooled the graphite and fed the fire, and the chart could show only the cooling. The chimney meter’s six curies at 5:40 on Thursday morning was the first true reading of the pile’s state in three days, and it was read as the normal effect of the first air through the stack. When an instrument finally speaks, the hardest thing is to hear a new message in it rather than the old one.

What was published taught the wrong lesson. The committee wrote that the instruments were wrong for the job, the manual did not exist, the organisation was too thin and the temperatures had been pushed up without anyone taking in all the factors. The public account said the accident happened during “a routine maintenance operation”, and the Authority’s memorandum laid it “partly to faults of judgment by the operating staff”. The report that would have told other reactor operators where to put their thermocouples went into a file for thirty years, in a month when Britain’s case for a share of American weapons work rested on the “unique reputation of our scientists”. The record of Chernobyl ran the same way, operators first and design later, and so, in a smaller key, did Three Mile Island. A lesson locked up is not a lesson.

The one number that was worked out in time. The limit of a tenth of a microcurie a litre was set on a Saturday night from first principles, by people who had, the committee said, no established tolerance level to work from, and it was the one thing in the whole affair that was decided before the harm it addressed had happened. The committee called it unsatisfactory that such levels “should have had to be worked out in haste after the accident happened”. It was. It also held, and sixty years of measurement have not faulted it. The plant had every instrument for the fire except the one that would have seen it, and no rule for the milk except the one its people made that night; the second was the better preparation, because it was made by people who knew what they did not know.

Sources

• William Penney, Basil F. J. Schonland, J. M. Kay, Jack Diamond and David E. H. Peirson, Report on the accident at Windscale No. 1 Pile on 10 October 1957, the report of the Committee of Inquiry to the Chairman of the United Kingdom Atomic Energy Authority, 26 October 1957, reproduced from The National Archives file AB 86/25 as a memorandum in the Journal of Radiological Protection 37, 2017, pages 780 to 796, Crown copyright under the Open Government Licence v3.0 and CC BY 3.0. The whole chronology of 7 to 12 October, the thermocouple positions and the seven feet, the minute of 1955, the measures taken, the doses, the milk, the conclusions and recommendations, the witness list, and Appendix B, the figure. iopscience.iop.org
• Atomic Energy Establishment, Windscale (Accident), House of Commons, 29 October 1957, columns 32 to 36 (Macmillan’s first answers, “I will certainly make a full report”, “unique reputation”), and 8 November 1957, columns 465 to 468 (the statement on the White Paper, “routine maintenance operation”, “no evidence that this accident has done any significant harm”, the Fleck committees). 29 October, 8 November
• Atomic Energy Establishment, Windscale (Accident), House of Commons, 28 November 1957, columns 1273 to 1274, for the Works General Manager’s responsibility and the Director of Production at Windscale. api.parliament.uk
• Windscale Atomic Plant Accident, House of Lords, 21 November 1957, columns 448 to 476. Lord Lawson’s quotations of the Prime Minister’s memorandum and the Authority’s statement in the White Paper (Cmnd. 302); Lord Mills’s account of the piles, Wigner energy, the chimneys, “grey matter and green fields”, “every man did his utmost”, and the lifting of the last restrictions on 23 November. columns 448 to 457, columns 459 to 476
• Atomic Energy Office, Accident at Windscale No. 1 Pile on 10th October, 1957, Cmnd. 302, HMSO, 8 November 1957. Not reached; its memorandum and annexes are quoted here as Hansard quotes them.
• Lorna Arnold, Windscale 1957: Anatomy of a Nuclear Accident, Macmillan, 1992 (second edition 1995), the appendices: I, the chronology of October 1957 to October 1958 (the 200 square miles, the Authority’s recommendation of 28 October to publish in full, the dates of the Fleck reports and of the announcements of 15 July and 24 October 1958); II, the Industrial Group’s responsibilities; III, the minute of 14 November 1955; IV, the table of Wigner releases; V and VI, the fuel and lithium-magnesium cartridges and the Fleck committee’s findings on them. The main text, which reproduces the Penney report as an appendix, was not reached. link.springer.com
• Richard Wakeford, “The Windscale reactor accident—50 years on”, Journal of Radiological Protection 27, 2007, pages 211 to 215. The construction and the dates, the piles’ dimensions, the isotope cartridges and the enriched fuel, Cockcroft’s follies, the Wigner physics, the publication of a summary only, the history of the release estimates from 1958 to 2007, Clarke’s figures of 1990, the milk limit and “courageous but wise”; Arnold’s “an accident waiting to happen” is quoted as Wakeford quotes it. iopscience.iop.org
• Richard J. Q. McNally, Richard Wakeford 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 and the finding of no detectable increase. link.springer.com
• David Lowry, “Tom Tuohy”, obituary, The Guardian, 7 May 2008. Tuohy’s life and career, and his words to the inquiry and to a television documentary of 2007, which are quoted here at second hand from the obituary. theguardian.com
• Dwight D. Eisenhower and Harold Macmillan, Declaration of Common Purpose, Washington, 25 October 1957, with the note on the meetings of 23 to 25 October. presidency.ucsb.edu
• Ian Curwen, “Sixty-two years on”, Nuclear Decommissioning Authority, 10 October 2019 (the chimneys, the filters, the demolition from December 2018), and Eleanor Thursby and Billy Simpson, “Windscale: from nuclear pioneer to decommissioning landmark”, 14 October 2025 (the 95 per cent, the crane, the fuel still in the fire-damaged channels). 2019, 2025
• The National Archives, catalogue entries for series AB 86, the Windscale Accident Inquiry, and for CAB 128/31/78, the Cabinet conclusions of 6 November 1957 with “Atomic Energy: accident at Windscale Plant” as item 4. AB 86, CAB 128/31/78