The Windscale Piles were two air-cooled graphite-moderated nuclear reactors on the Windscale nuclear site in Cumberland (now known as Sellafield site, Cumbria) on the north-west coast of England. The two reactors, referred to at the time as "piles", were built as part of the British post-war atomic bomb project and produced weapons-grade plutonium for use in nuclear weapons.
Windscale Pile No. 1 became operational in October 1950 followed by Pile No. 2 in June 1951.Force V: The history of Britain's airborne deterrent, by Andrew Brookes. Jane's Publishing Co Ltd; First Edition 1 Jan. 1982, , p.9. They were intended to last five years, but operated for seven until shut down following the Windscale fire on 10 October 1957. Nuclear decommissioning operations commenced in the 1980s and are estimated to last beyond 2040. Visible changes have been seen as the chimneys were slowly dismantled from top-down; Pile 2's chimney being reduced to the height of adjacent buildings in the early 2000s. However, the demolition of pile 1 chimney has taken much longer as it was significantly contaminated after the 1957 fire. The reactor cores still remain to be dismantled.
Background The 1938 discovery of nuclear fission by Otto Hahn and Fritz Strassmann, and its explanation 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 might explode with the power of thousands of tons of dynamite.
In response, the British government initiated an atomic bomb project, code-named Tube Alloys. The August 1943 Quebec Agreement merged Tube Alloys with the American Manhattan Project. As overall head of the British Mission, James Chadwick forged a close and successful partnership with Brigadier General Leslie R. Groves, the director of the Manhattan Project, and ensured that the British contribution to the Manhattan Project 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 trusted that America would continue to share nuclear technology, which it considered a joint discovery, but little information was exchanged immediately after the war, and 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 further research and development 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 on 29 October 1945 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 (ROF) 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 William Penney, 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."
Design and location
Product 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 to produce the former. British scientists had been most heavily involved with the electromagnetic isotope separation process, but it was recognised that it might be uneconomical in peacetime. They also knew a great deal about the gaseous diffusion process through work done not just in the United States, but in Britain as well, where ICI had designed a gaseous diffusion production plant, and a pilot plant to produce membranes for it was under construction. Least was known about the production of plutonium in nuclear reactors, or "piles" as they were often known at the time; only Chadwick had been permitted to visit the Manhattan Project's reactors.
An early decision had to be taken 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. The scientists who had remained in Britain favoured uranium-235, which could be enriched with gaseous diffusion, and a final electromagnetic step. However, those who had been working at the Los Alamos Laboratory 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 were about half that of a gaseous diffusion plant. Thus, a gaseous diffusion plant would cost ten times as much to produce the same number of atomic bombs each year. The decision was therefore taken in favour of plutonium. Part of the deficit of technical knowledge was addressed by the Montreal Laboratory in Canada, where the ZEEP reactor went critical on 5 September 1945, and the Americans had supplied some irradiated fuel rods for experiments with plutonium separation there.
Moderator The British scientists were aware that the choices they made at this point might influence British reactor design for many years to come. In designing a reactor, there are three key choices to be made: that of the fuel, the moderator, and the coolant. The first choice, that of fuel, was a Hobson's choice: the only fuel available was natural uranium, since there were no enrichment plants to produce uranium-235, and no reactors to produce plutonium or uranium-233. This restricted the choice of moderators to heavy water and graphite. Although ZEEP had used heavy water, this was not available in the UK. The choice therefore narrowed to graphite. The first nuclear reactor in the UK, a small 100 kW research reactor known as GLEEP, went critical at Harwell on 15 August 1947.
This was fine for some experimental work, but the production of radioactive isotopes required a more powerful 6,000 kW reactor with a higher neutron flux. For this, British scientists and engineers at the Montreal Laboratory designed the British Experimental Pile Zero (BEPO). Risley handled the engineering and construction. Hinton designated James Kendall as the engineer in charge of reactor design, both BEPO and the production reactors. His team worked closely with the scientists at Harwell, in particular J. V. Dunworth, F. W. Fenning and C. A. Rennie. For an experimental reactor like BEPO, air cooling was the obvious choice. The resulting reactor was thus quite similar to the Manhattan Project's X-10 Graphite Reactor in both design and purpose. BEPO went critical on 5 July 1948.
Much was learned from the design and construction of BEPO, which ran continuously until it was decommissioned in December 1968. When it came to the design of the much larger production reactors, the initial assumption was that they would differ from BEPO in that they would be water cooled. It was known that this was the approach that the Americans had taken at the Hanford Site, although only Portal was allowed to visit it, and not being a scientist, had not brought back much useful information.
It was estimated that a water-cooled reactor the size of the B Reactor at Hanford required about of water per day, and it had to be exceptionally pure lest it corrode the tubes holding the uranium fuel rods. Because water absorbed neutrons, a loss of cooling water would not only mean a rise in temperature, but would also trigger an increase in the number of neutrons in the reactor, creating more fissions and increasing the temperature further, possibly resulting in a nuclear meltdown and the release of radioactive fission products. Groves confided to the British in 1946 that he "would not be surprised to be called to the telephone any morning to hear the news that one of the piles had gone up."
Location To minimise this risk, the Americans had established strict siting criteria. The reactors were to be located from any town with a population of over 50,000, from one of over 10,000, and from one of over 1,000, and were to be built 5miles apart. Groves also had a four-lane highway built in order to evacuate the Hanford area in an emergency. If such criteria were applied in the UK, all of England and Wales would have been ruled out, leaving only the north and west of Scotland.
The possibility of building reactors in Canada was suggested by Chadwick and Cockcroft, and strongly supported by the Field Marshal Lord Wilson, the Chief of the British Joint Staff Mission, and the Americans, but was rejected by the British government. Canada was outside the sterling area and construction costs could only be met by further borrowing from Canada. Under the circumstances, the reactors would be owned and controlled by the Canadian government, and this the British government could not accept.
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A consulting engineer firm was brought in to advise on possible locations. Two were suggested: Harlech in Wales and Arisaig in Scotland. Hinton opposed Harlech on the basis of its historic associations, and because too many people lived nearby. That left Arisaig, and the remoteness of the site foreshadowed difficulties with communications and finding skilled labour. At this point, Risley began reconsidering the technology of an air-cooled reactor. R. G. Newell, who had been the wartime head of the engineering section at the Montreal Laboratory, proposed in a 1946 paper that the reactor be encased in a pressure vessel. This would make it safer, and it would allow more heat to be obtained from a given core size.