At Sellafield, the reprocessing of nuclear fuel in the Thermal Oxide Reprocessing Plant (THORP) came to an end when the last fuel element was sheared in November 2018. This will be followed by the Magnox Reprocessing Plant, which will end operations in 2020. These two landmark developments will transform Sellafield, the UKís largest and most complex nuclear site, from an operational business into an organisation that is wholly focused on decommissioning.
Sellafield, in West Cumbria, was responsible for the production of the nuclear materials for nuclear weapons, including plutonium, tritium, and Highly Enriched Uranium (HEU). Large stocks of military plutonium are held in special vaults at the site, though no plutonium for use in nuclear weapons is currently being produced. In the past plutonium was produced at Sellafield through the reprocessing of spent nuclear fuel from the nuclear reactors at Calder Hall and Chapelcross.
Currently, the main activity at Sellafield is recycling used fuel from nuclear power stations worldwide. The site also houses a series of plants that treat wastes and convert them into forms that can be disposed of safely. In October 1994, Secretary O'Leary signed a memorandum authorizing consideration of shipment of 183,000 gallons of nitric acid containing slightly enriched uranium from the Hanford PUREX plant to the Magnox Fuel Reprocessing Plant at Sellafield.
Also in 1997, Nirex, the radioactive waste management company, abandoned plans to construct a Rock Characterization Facility (RCF) for Intermediate Level Waster (ILW) deep underground near the Sellafield reprocessing complex, after the Environment Secretary rejected an appeal by Nirex against the 1994 refusal by Cumbria County Council to grant planning approval. Nirex had spent an estimated £200 million in preliminary drilling and scientific studies, but the Minister found scientific uncertainties and technical deficiencies in the companyís case. AEA Technology was a member of the consortium that won a £140 million contract to build an ILW encapsulation plant at Sellafield. Low Level Waste (LLW) is stored inside containers, which are then placed inside a concrete vault at Drigg, near Sellafield. The site is also where spent fuel from the UKís nuclear-powered submarine fleet is stored. Construction on a third containment building began in June 2006. The 102 tonne shield door was put in place in February 2010 and filled with shielding concrete (increasing its weight to about 300 tonnes). Roof cladding began in late January 2010, HVAC and services pipe work in late August 2010. The new warehouse will store additional ILW.
The Sellafield site currently houses the vast majority of the UKís nuclear waste, about 65%. It also holds the UKís largest stockpile of plutonium, roughly 100 tonnes. The London-based Royal Society of Science identified three options for the management of the stockpile: immediate disposal as waste, 300-year storage then disposal as waste, or convert it into nuclear fuel. The initial estimate as to the cost of cleaning the entire Sellafield site was £56bn; new estimates up the cost to between £62.7bn and £72bn (as of March 2006).
Windscale Piles 1 & 2
The independent British weapons program began in 1946, with the first priority being to produce plutonium in reactors (known then as atomic piles). The technology of the time meant that the quickest route to an operating reactor was to build reactors that used natural uranium as fuel, graphite as the moderator, and were cooled by air. Accordingly, in 1946 work began at the former Royal Ordnance factory at Sellafield to build two reactors, on a site renamed as Windscale, to produce plutonium for the UK weapons program. Pile No. 1 began operating in October 1950, Pile No. 2 started up 8 months later, and plutonium for the first British bomb was available in March 1952.
Windscale Pile No. 1 caught fire on Thursday 10 October 1957. Fuel melted, the fuel cans burst, uranium ignited and fission products were released into cooling ducts and ejected out of the cooling chimneys. Only after heroic efforts by the operating staff, risking a worse disaster by flooding the reactor with large volumes of water, was the fire put out on Friday 11 October 1957. The main radionuclide of concern in the releases from the fire was iodine-131. Steps were taken to ban milk for 200 square miles around Windscale, limiting the health consequences of the accident. Along with Three Mile Island and Chernobyl, the Windscale fire achieved notoriety as one of the three nuclear disasters which opponents of nuclear power cite as evidence that nuclear power is too risky. While the Windscale fire was a serious nuclear accident, the reactor was not large by modern standards, and the radionuclide releases at Chernobyl were 1,000 times higher. After the fire, both Pile 1 and Pile 2 were taken off-line (1957).
The actual decommissioning of Pile 1 began in 1981 but in September 1997, the UKAEA awarded its largest decommissioning contract to date. A consortium led by British Nuclear Fuels Limited (BNFL) won the contract to complete the dismantling and removal for treatment and storage the core of Pile 1 at Windscale. The eight-year program of work was valued at £54 million. The removal of reactor fuel and associated equipment was completed in 1983 and all irradiated materials were stored in the IRW storehouse. The four heat exchangers were transported to the LLW repository at Drigg. The Pile, a stack of some 2,000 tonnes of graphite blocks, has been in a state of safe care and maintenance since the October 1957 fire. Its core contains an estimated 15 tonnes of damaged fuel. Due to the high levels of radiation, a remote dismantling machine was installed above the graphite core; the complete systems decommissioning was finished in 1998. The removal of the dismantled core took place in mid-2009 and the spherical containment structure is scheduled to be removed in 2015. Pile Two, which was unaffected by the Fire and which was defuelled at the time, will be put on a care and maintenance regime.
Calder Hall (CH) Magnox reactors
Sellafield is home to the world's first industrial scale nuclear power station, Calder Hall. The four Calder Hall (CH) Magnox reactors, with a total output of 200 MW, entered service between October 1956 and May 1959. Calder Hall was opened by the Queen in October 1956. Its primary function was to manufacture plutonium for nuclear weapons but it was also the first nuclear reactor anywhere in the world to generate commercial electricity. It ceased producing plutonium in April 1995. These carbon-dioxide cooled reactors, identical to the Chapelcross reactors, produced both weapons grade plutonium and electricity. In 1996, the power station was granted a ten-year operating extension by the NII following a Periodic Safety Review.
Calder Hall closed on 31 March 2003. It was initially scheduled for closure between 2006 and 2008. Following an accident at Chapelcross in July 2001, two of the four Calder Hall reactors, similar in design to those at Chapelcross, were shut down to allow defuelling-related tests to be carried out. The remaining two Calder reactors were shut down by the end of 2001. Reactor 1 was returned to power in July 2002. In June 2002, BNFL announced they would close down the Calder Hall Nuclear power plants, and by August 2002, three of the four reactors were closed down. The early closure resulted from the cost of preventing radiation-induced graphite shrinkage in the charge pans used to guide the highly radioactive fuel rods into place. BNFL's announcement followed an economic review of the operation of its whole magnox reactor fleet. The review concluded that continued operation of the larger magnox stations had a sound economic basis but that Calder Hall and Chapelcross, with their relatively low output and high overheads, had become loss making. The reactors are in the process of being defuelled and subsequently decommissioned. The plantís four cooling towers were destroyed in a controlled blast on 29 September 2007.
Thermal Oxide Reprocessing Plant (THORP)
In August 1997, the Nuclear Installations Inspectorate granted British Nuclear Fuels Limited (BNFL) the consent to operate its Thermal Oxide Reprocessing Plant (THORP) at Sellafield. THORP, which has been operating since March 1994, has reprocessed well over 800 tonnes of fuel. THORP recovers usable uranium and plutonium from spent nuclear fuel. The main process areas are the fuel receipt and storage area, the head end plant where the fuel contents are separated out from the cladding, and the chemical plants where the uranium and plutonium are separated out from the waste products. BNFL plans to achieve a throughput of 900 tonnes by THORP's fifth year and reprocess in all 7,000 tonnes of spent fuel in the first ten years, making at least £500 million profit after accounting for all decommissioning and capital costs. THORP is expected to reprocess 14,000 tonnes of spent fuel in its first 20 years of operations and in the order of 100 tonnes of plutonium will be recovered during this time. The exact quantity of plutonium will be dependent on the type of fuel and the level of irradiation in the reactor the fuel originates from. The company has over 15 years' worth of orders, valued at £12 billions, two thirds from overseas as well as the new AGR spent fuel contract.
In April 2005, THORP operators discovered a crack pipe had leaked 83,000 liters of radioactive waste into a stainless steel-lines concrete containment vessel (built for such situations). Sellafield was fined £500,000 for the safety breach and did not reopen until January 2007. A breakdown in the underwater fuel transfer lift caused the plant to close again in January 2008.
MOX Demonstration Facility [MDF]
A data falsification incident at BNFL's MOX Demonstration Facility in 1999 led to an investigation by the Health and Safety Executive and a loss of customer confidence in BNFL. The MDF plant was closed in 1999, when it was discovered that a number of employees had falsified quality control data on fuel consignments. In March 2002, British Nuclear Fuels was granted a license to re-commission a MOX demonstration facility at Sellafield. It will operate as a support facility to the new MOX plant.
Sellafield MOX Plant
The MOX Plant at Sellafield is valued by BNFL at a cost of around £460 million. Its purpose is to manufacture a mixed oxide fuel for use in nuclear power stations. The fuel would be made from uranium and plutonium material separated from spent fuel, which is reprocessed mainly at the THORP plant at Sellafield.
With the end of the Cold War, there are now stockpiles of surplus ex-military plutonium from decommissioned warheads. A study by the US National Academy of Sciences identified two possible ways of reducing the amount of surplus plutonium taken from nuclear weapons in the US and former Soviet Union. One is to convert the plutonium into glass and then bury it deep underground. The other is to convert it into fuel for power reactors. When plutonium dioxide is mixed with uranium dioxide to form a mixed oxide (MOX) fuel, it can be burnt in the conventional nuclear power reactors. A demonstration MOX manufacturing facility at Sellafield began operating in October 1993. The construction of the Sellafield MOX Plant began in April 1994, and was projected to cost some £300 million. With a 120-ton production capacity, it was expected to commence operations in 1998. The Sellafield MOX Plant was designed to fabricate new fuel with depleted, natural, or recycled uranium and plutonium, which is recovered from used nuclear fuel when it is reprocessed in THORP.
Before the plant could start operations, it needed to pass a test of justification required by European law: the benefits of a practice involving ionizing radiation need to outweigh any environmental or other detriments. BNFL applied to the Environment Agency in November 1996 for approval to operate the plant. The Environment Agency, after two rounds of public consultations, concluded its consideration in October 1998. The issue was referred to the Secretary of State for the Environment, Transport, and the Regions and the Minister of Agriculture, Fisheries, and Food in November 1998 because of their statutory responsibility to consider requests that had been made to them to decide the application themselves. The Government's provisional view, in a consultation paper published in June 1999, was that full operation of BNFL's MOX Plant would be justified, but a final decision would depend on the outcome of further consultation on the economic assessment of the practice and on the market for MOX fuel. BNFL submitted a revised economic case in 2001. Ministerial responsibilities changed during this period.
In 1999, the Food Safety Act established the Food Standards Agency and amended the Radioactive Substances Act 1993. In addition, in June 2001, the Department for the Environment, Transport, and the Regions (DETR) was reorganized with responsibility for environmental protection passing to the new Department for Environment, Food, and Rural Affairs (DEFRA). As a result, justification decisions that would have been taken jointly by the Secretary of State for the Environment, Transport and the Regions and the Minister of Agriculture are now taken jointly by the Secretary of State for Environment, Food and Rural Affairs and the Secretary of State for Health.
The Arthur D Little Ltd (ADL) report, published for consultation 27 July 2001, said that the MOX plant, if allowed to go into operation, would give a financial benefit with a "net present value" of over £200m to the UK over its lifetime. The first stage of active plutonium commissioning of the plant commenced on 21 December 2001. The process involves introducing plutonium bearing material in order to start testing the plant and equipment as a precursor to MOX fuel manufacture. The Magnox reprocessing plant has been operational in various forms since 1964 and is due to close in 2012.
Sellafield Ltd. High Alcohol Liquor Evaporation and Storage (HALES)
Sellafield Ltd. currently operates three HAL evaporators, A, B, and C. HAL evaporator D was under construction as of 2010 and is scheduled to come online in 2014. The evaporators take the radioactive waste materials from the THORP and Magnox reprocessing plants and condition the waste into a form suitable for vitrification.
Sellafield Ltd. Vitrification Plant
In 1991, the Windscale Vitrification Plant (WVP) was opened. In this plant, liquid fissile wastes are mixed with sugar and glass, and are then melted in a furnace. When cooled, the material forms a solid block of black, radioactive glass.
The plant has three process lines based on the French Atelier de Vitrification Marcoule (AVM) procedure. The principal item is an inductively heated melting furnace, in which the calcinated waste is merged with glass beads of 1 to 2 mm in diameter. The melt is poured into waste containers, which are welded shut, their outsides decontaminated, and then brought into air-cooled storage facilities. The storage warehouse consists of 800 vertical storage tubes, each capable of storing ten containers. The total storage capacity is 8000 containers, and as of 2010, 5000 containers have been stored. By volume, the vitrified material makes up just 10% of the total nuclear waste in the UK but 95% of the total radioactivity of the wastes produced. Vitrified material is safe to store for medium-to-long periods of time, but there is no cost-effective way to reclaim the fissile material.
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