Sellafield: Encyclopedia II - Sellafield - History

Sellafield - History

Sellafield - Windscale

The Sellafield site is built on land that was formerly part of the Windscale nuclear site, which is named after a nearby village. Windscale was owned by the United Kingdom Atomic Energy Authority, but when part of it was transferred to BNFL, the transferred part was renamed as "Sellafield". The remainder of the site remains in the hands of the UKAEA and is still called Windscale.

Two air-cooled, graphite-moderated Windscale reactors constituted the first British weapons grade plutonium 239 production facility, built for the British nuclear weapons program in the late 40s and the 50s.

Windscale was also the site of the prototype British Advanced gas-cooled reactor.

Since its inception Sellafield has also been host to a number of reprocessing facilities, which separate the uranium, plutonium and other fission products from spent nuclear fuel. The uranium can then be used in the manufacture of new nuclear fuel, or in applications where its density is an asset. The plutonium can be used in the manufacture of mixed oxide (MOX) fuel for thermal reactors, or as fuel for fast breeder reactors, such as the Prototype Fast Reactor at Dounreay. In the past there has been some efforts to reuse the other fission products: for example, in the mid to late 50s, Caesium137 was extracted to produce kilocurie radiotherapy sources; however, this is now treated as waste.

Sellafield - The Windscale Piles

Following the decision taken in January 1947 for the UK to have an independent nuclear deterent [2], Sellafield was chosen as the location of the plutonium production plant [3], with the intial fuel load into the Windscale Piles commencing July 1950 [4]. By July of 1952 the separation plant was being used to separate plutonium and uranium from spent fuel.

Unlike the early US reactors at Hanford, which consisted of a graphite core cooled by water, the Windscale Piles consisted of an graphite core cooled by air. Each pile contained almost 2000 tonnes of graphite, and measured over 24 feet high by 50 feet in diameter. Fuel for the reactor consisted of rods of uranium metal, approximately 1 foot long by one inch in diameter, and clad in Aluminum [5].

The Piles themselves are currently being decommissioned.

Sellafield - The B204 reprocessing plant

B204 was built to extract the plutonium from spent fuel as part of the effort to build the UK's atomic weapons [6]. B204 operated from 1951 until 1964, with an annual capacity of 300 tonnes of fuel (or 750 tonnes of low burnup fuel). Following the commissioning of the Magnox reprocessing plant, B204 was itself recycled to become a pre-handling plant to allow oxide fuel to be reprocessed in the new plant, and was closed in 1973.

Sellafield - Calder Hall nuclear power station

Calder Hall was the world's first commercial nuclear power station. First connection to the grid was on 27 August 1956, and the plant was officially opened by Queen Elizabeth II on 17 October 1956 [7]. When the station closed on 31 March 2003, the first reactor had been in use for nearly 47 years [8].

Calder Hall had 4 Magnox reactors capable of generating 50 MWe of power each.

However, in its early life, it was primarily used to produce weapons-grade plutonium, with two fuel loads per year, and electricity production as a secondary purpose [9]. From 1964 it was mainly used on commercial fuel cycles, but it was not until April 1995 that the UK Government announced that all production of plutonium for weapons purposes had ceased [10].

Sellafield - The Windscale fire

In 1957, a fire at one of the twin Windscale reactors caused the world's worst nuclear accident until the Chernobyl accident. An estimated 750 terabecquerels (TBq) (20,000 curies) of radioactive Iodine-131 were released, and milk and other produce from the surrounding farming areas had to be destroyed. For comparison, 250,000 terabecquerels (7 million curies) of Iodine-131 were released by Chernobyl, and only 0.55 terabecquerels (15 curies) of Iodine-131 by Three Mile Island.

Sellafield - Windscale Advanced Gas Cooled Reactor WAGR

The Windscale Advanced Gas Cooled Reactor (WAGR) (http://www.ukaea.org.uk/wagr/history.htm) was a protoype for the UK's second generation of reactors, the Advanced gas-cooled reactor or AGR, which followed on from the Magnox stations. The WAGR golfball is, along with the Pile chimneys, one of the iconic buildings on the Sellafield site. This reactor was shut down in 1981, and is now part of a pilot project to demonstrate techniques for safely decommissioning a nuclear reactor.

Sellafield - Magnox reprocessing plant

In 1964 the B205 Magnox reprocessing plant come on stream to reprocess spent nuclear fuel from the Magnox reactors [11]. The plant uses the "plutonium uranium extraction" Purex method for reprocessing spent fuel, with tributyl phosphate as an extraction agent. The Purex process produces uranium, plutonium and fission products as output streams. Over the 30 years from 1971 to 2001 B205 has reprocessed over 35,000 tonnes of Magnox fuel, with 15,000 tonnes of fuel being regenerated [12]. Magnox fuel is reprocessed, since it corrodes if stored underwater, and routes for dry storage have not yet been proven [13].

Sellafield - Thermal Oxide Reprocessing Plant

Between 1977 and 1978 an inquiry was held into an application by BNFL for outline planning permission to build a new plant to reprocess irradiated oxide nuclear fuel from both UK and foreign reactors. The inquiry was to answer three questions: "1. Should oxide fuel from United Kingdom reactors be reprocessed in this country at all; whether at Windscale or elsewhere? 2. If yes, should such reprocessing be carried on at Windscale? 3. If yes, should the reprocessing plant be about double the estimated site required to handle United Kingdom oxide fuels and be used as to the spare capacity, for reprocessing foreign fuels?" [14]. The result of the inquiry was that the new plant, the Thermal Oxide Reprocessing Plant (ThORP) was given the go ahead in 1978, although it did not go into operation until 1994.

Sellafield - The Beach Incident

1983 was the year of the "Beach Discharge Incident" in which high radioactive discharges resulted in the closure of a beach. BNFL recieved a fine of £10,000 for this discharge [15]. 1983 was also the year in which Yorkshire Television produced a documentary "Windscale: The Nuclear Laundry", which claimed that the low levels of radioactivity that are associated with waste streams from nuclear plants such as Sellafield did pose a non-negligible risk [16].

In its early days, Sellafield discharged low-level radioactive waste into the sea, using a flocculation process to remove radioactivity from liquid effluent before dischared. Metals dissolved in acidic effluents produced a metal hydroxide flocculent precipitate following the addition of ammonium hydroxide. The suspension was then transferred to settling tanks where the precipitate would settle out, and the remaining clarified liquor, or supernate, would be discharged to the sea. In 1994 the Enhanced Actinide Removal Plant (EARP) was opened. In EARP the effectiveness of the process is enhanced by the addition of reagents to remove the remaining soluble radioactive species. EARP has recently (2004) been enhanced to further reduce the quantities of Tc-99 released to the environment. [17]

Sellafield - The Vitrification Plant

In 1991 the Windscale Vitrification Plant, which converts high-level radioctive waste into glass, was opened. In this plant, liquid wastes are mixed with glass and melted in a furnace, which when cooled forms a solid block of glass.

The plant has three process lines and is based on the French AVM procedure. Principal item is an inductively heated melting furnace, in which the calcined waste is merged with glass frit (glass beads of 1 to 2 mm in diameter). The melt is placed into waste containers, which are welded shut, their outsides decontaminated and then brought into air-cooled storage facilities. This storage consists of 800 vertical storage tubes, each capable of storing ten containers. The total storage capacity is 8000 containers, and 2280 containers have been stored to 2001.

Sellafield - The Sellafield MOX Plant

Construction of the Sellafield MOX Plant was completed in 1997. Mixed oxide, or MOX fuel, is a blend of plutonium and natural uranium or depleted uranium which behaves similarly (though not identically) to the enriched uranium feed for which most nuclear reactors were designed. MOX fuel is an alternative to Low enriched uranium (LEU) fuel used in the light water reactors which predominate in nuclear power generation. MOX also provides a means of burning weapons-grade plutonium (from military sources) to produce electricity.

Sellafield - 2005 Thorp plant leak

On April 19, 2005 83,000 litres of radioactive waste was discovered to have leaked in the Thorp reprocessing plant from a cracked pipe into a huge stainless steel-lined concrete sump chamber built to contain leaks.

A discrepancy between the amount of material entering and exiting the Thorp processing system had first been noted in August 2004. Documentation of this finding was not passed up to the appropriate administrator.

Other indicators of a problem included a rise in temperature in the sump chamber and findings of radioactive fluid there, but these were ignored. The spill was recognized only after another audit suggested that further material was missing, prompting plant operators, after several days' delay, to train an automated camera on the faulty pipe and to actually measure the volume of liquid in the sump.

Responsible administrators have been disciplined. Some 19 tonnes of uranium and 160 kilograms of plutonium dissolved in nitric acid has been pumped from the sump vessel into a holding tank away from the now-closed Thorp plant. Radiation levels in the building preclude entry of humans and robotic repair of the leak would be prohibitively difficult. Officials are considering bypassing the faulty tank to resume operations.

Adapted from the Wikipedia article "History", under the G.N U Free Docmentation License. Please also see http://en.wikipedia.org/wiki