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The Windscale fire of 10 October 1957 was the worst nuclear accident in the United Kingdom's history, and one of the worst in the world, ranked in severity at level 5 out of 7 on the International Nuclear Event Scale. The fire was in Unit 1 of the two-pile Windscale site on the north-west coast of England in Cumberland, now Sellafield, Cumbria. The two graphite-moderated reactors, referred to at the time as piles, had been built as part of the British post-war atomic bomb project. Windscale Pile No. 1 was operational in October 1950, followed by Pile No. 2 in June 1951.
The fire burned for three days and released radioactive fallout which spread across the UK and the rest of Europe. The radioactive isotope iodine-131, which may lead to cancer of the thyroid, was of particular concern at the time. It has since come to light that small but significant amounts of the highly dangerous radioactive isotope polonium-210 were also released. It is estimated that the radiation leak may have caused 240 additional cancer cases, with 100 to 240 of these being fatal.
At the time of the incident, no one was evacuated from the surrounding area, but milk from about 500 km2 of the nearby countryside was diluted and destroyed for about a month due to concerns about its radiation exposure. The UK government played down the events at the time, and reports on the fire were subject to heavy censorship, as Prime Minister Harold Macmillan feared the incident would harm British-American nuclear relations.
The event was not an isolated incident; there had been a series of radioactive discharges from the piles in the years leading up to the accident.
In early 1957, there had been a leak of radioactive material in which strontium-90 was released into the environment. Like the later fire, this incident was covered up by the British government. Later studies on the release of radioactive material due to the Windscale fire revealed that much of the contamination had resulted from such radiation leaks before the fire.
A 2010 study of workers involved in the cleanup of the accident found no significant long-term health effects from their involvement.
The December 1938 discovery of nuclear fission by Otto Hahn and Fritz Strassmann following its prediction by Ida Noddack in 1934 -and its explanation and naming by Lise Meitner and Otto Frisch- raised the possibility that an extremely powerful atomic bomb could be created.
During the Second World War, Frisch and Rudolf Peierls at the University of Birmingham calculated the critical mass of a metallic sphere of pure uranium-235, and found that as little as 1 to 10 kilograms might explode with the power of thousands of tons of dynamite.
In response, the British government initiated an atomic-bomb project, codenamed Tube Alloys. The August 1943 Quebec Agreement merged Tube Alloys with the American Manhattan Project. As overall head of the British contribution to the Manhattan Project, James Chadwick forged a close and successful partnership with the Americans, and ensured that British participation was complete and wholehearted.
After the war ended, the Special Relationship between Britain and the United States became very much less special. The British government had assumed that America would continue to share nuclear technology, which it considered a joint discovery, but little information was exchanged immediately after the war. The Atomic Energy Act of 1946 (McMahon Act) officially ended technical cooperation. Its control of restricted data prevented the United States' allies from receiving any information.
The British government saw this as a resurgence of United States isolationism akin to that which had occurred after the First World War. This raised the possibility that Britain might have to fight an aggressor alone. It also feared that Britain might lose its great power status, and therefore its influence in world affairs. The Prime Minister of the United Kingdom, Clement Attlee, set up a cabinet sub-committee, the Gen 75 Committee (known informally as the Atomic Bomb Committee), on 10 August 1945 to examine the feasibility of a renewed nuclear weapons programme.
The Tube Alloys Directorate was transferred from the Department of Scientific and Industrial Research to the Ministry of Supply on 1 November 1945, and Lord Portal was appointed Controller of Production, Atomic Energy (CPAE), with direct access to the Prime Minister. An Atomic Energy Research Establishment (AERE) was established at RAF Harwell, south of Oxford, under the directorship of John Cockcroft. Christopher Hinton agreed to oversee the design, construction and operation of the new nuclear weapons facilities, which included a uranium metal plant at Springfields in Lancashire, and nuclear reactors and plutonium processing facilities at Windscale in Cumbria. He established his headquarters in a former Royal Ordnance Factory at Risley in Lancashire on 4 February 1946.
In July 1946, the Chiefs of Staff Committee recommended that Britain acquire nuclear weapons. They estimated that 200 bombs would be required by 1957. The 8 January 1947 meeting of the Gen 163 Committee, a subcommittee of the Gen 75 Committee, agreed to proceed with the development of atomic bombs, and endorsed Portal's proposal to place Penney, now the Chief Superintendent Armament Research (CSAR) at Fort Halstead in Kent, in charge of the development effort, which was codenamed High Explosive Research. Penney contended that the discriminative test for a first-class power is whether it has made an atomic bomb and we have either got to pass the test or suffer a serious loss of prestige both inside this country and internationally.
Through their participation in the wartime Tube Alloys and Manhattan Project, British scientists had considerable knowledge of the production of fissile materials. The Americans had created two kinds, uranium-235 and plutonium, and had pursued three different methods of uranium enrichment. An early decision had to be made as to whether High Explosive Research should concentrate on uranium-235 or plutonium. While everyone would have liked to pursue every avenue, like the Americans had, it was doubtful whether the cash-strapped post-war British economy could afford the money or the skilled manpower that this would require.
More information: BBC
The scientists who had remained in Britain favoured uranium-235, but those who had been working in America were strongly in favour of plutonium. They estimated that a uranium-235 bomb would require ten times the fissile material as one using plutonium to produce half the TNT equivalent. Estimates of the cost of nuclear reactors varied, but it was reckoned that a uranium enrichment plant would cost ten times as much to produce the same number of atomic bombs as a reactor. The decision was therefore taken in favour of plutonium.
The reactors were built in a short time near the village of Seascale, Cumberland. They were known as Windscale Pile 1 and Pile 2, housed in large concrete buildings a few hundred feet apart.
On 7 October 1957, Pile 1 reached the 40,000 MWh mark, and it was time for the 9th Wigner release. This had been carried out eight times in the past, and it was known that the cycle would cause the entire reactor core to heat up evenly. During this attempt the temperatures anomalously began falling across the reactor core, except in channel 20/53, whose temperature was rising. Concluding that 20/53 was releasing energy but none of the others were, on the morning of 8 October the decision was made to try a second Wigner release. This attempt caused the temperature of the entire reactor to rise, indicating a successful release.
Early in the morning of 10 October it was suspected that something unusual was going on. The temperature in the core was supposed to gradually fall as Wigner energy release ended, but the monitoring equipment showed something more ambiguous, and one thermocouple indicated that core temperature was instead rising. As this process continued, the temperature continued to rise and eventually reached 400 °C.
In an effort to cool the pile, the cooling fans were sped up and airflow was increased. Radiation detectors in the chimney then indicated a release, and it was assumed that a cartridge had burst. This was not a fatal problem, and had happened in the past. However, unknown to the operators, the cartridge had not just burst, but caught fire, and this was the source of the anomalous heating in channel 20/53, not a Wigner release.
Speeding up the fans increased the airflow in the channel, fanning the flames. The fire spread to surrounding fuel channels, and soon the radioactivity in the chimney was rapidly increasing.
A foreman, arriving for work, noticed smoke coming out of the chimney. The core temperature continued to rise, and the operators began to suspect the core was on fire.
Operators were unsure what to do about the fire. First, they tried to blow the flames out by running the fans at maximum speed, but this fed the flames.
Next, the operators tried to extinguish the fire using carbon dioxide.
At 01:30 hours on Friday 11 October, when the fire was at its worst, eleven tons of uranium were ablaze. The magnesium in the cartridges was now ablaze, with one thermocouple registering 3,100 °C, and the biological shield around the stricken reactor was now in severe danger of collapse.
Water was kept flowing through the pile for a further 24 hours until it was completely cold. After the water hoses were turned off, the now contaminated water spilled out onto the forecourt.
There was a release into the atmosphere of radioactive material that spread across the UK and Europe. The fire released an estimated 740 terabecquerels of iodine-131, as well as 22 TBq of caesium-137 and 12,000 TBq of xenon-133, among other radionuclides. The UK government under Harold Macmillan ordered original reports into the fire to be heavily censored and information about the incident to be kept largely secret, and it later came to light that small but significant amounts of the highly dangerous radioactive isotope polonium-210 were released during the fire.
The original report into the incident, the Penney Report, was ordered to be heavily censored by prime minister Harold Macmillan. Macmillan feared that the news of the incident would shake public confidence in nuclear power and damage British-American nuclear relations. As a result, information about the release of radioactive fallout was kept hidden by the government. It was not until 1988 that Penney's report was released in full.
More information: International Atomic Energy Agency
our feet in horror at the danger of nuclear power.
Nuclear power is not infinitely dangerous.
It's just dangerous, much as coal mines,
petrol repositories, fossil-fuel burning a
nd wind turbines are dangerous.
David J. C. MacKay
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