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Sellafield Nuclear Fuel Plant
Sellafield, Seascale, Cumbria, UK
associated engineer
Ministry of Public Buildings & Works
Allot & Lomax
date  1951, 1964, 1983 - 1994, 1997
UK era  Modern  |  category  Power Generation  |  reference  NY029041
The Sellafield site, formerly known as Windscale, is adjacent to Calder Hall Nuclear Power Station. It was originally set up to produce fuels for use in thermonuclear weapons as part of Britain's effort in the Cold War. The site is now used to reprocess nuclear fuels and deal with nuclear waste. It is also the site of the world's first nuclear accident.
Reprocessing is the name given to the process of chemically separating the constituents of spent nuclear fuel. Spent fuel is retrieved from a nuclear reactor after a certain amount of time inside the core. During this time, the uranium undergoes neutron irradiation and some of its atoms are changed into other elements — such as polonium, plutonium, strontium, caesium, tritium, radioisotopes and other fission products.
Spent reactor fuel is stored in ponds at source until it cools and its radiation levels decrease, then it is transported to Sellafield in secure flasks for reprocessing. After further pond storage on site, the spent fuel is sheared (chopped) and dissolved in nitric acid. This liquid is separated into unused uranium, plutonium and a solution of highly radioactive fission products. The uranium and plutonium are used for new reactor fuel, while the fission products must be treated before safe storage.
The reason for reprocessing spent fuel was to gain usable new reactor fuel — and incidentally weapons grade plutonium-239 — from spent fuels at an advantageous price. However, the cost of raw uranium dropped by almost 80 percent between 1978 and 1999, making the economics less compelling.
The first nuclear fuel reprocessing plant was built at the same time as the Windscale graphite pile reactors (see separate entry), and was designed to extract weapons grade plutonium from spent reactor fuel rods. It operated from 1951 to 1964 then was reconfigured to handle Magnox fuel until its closure in 1973.
Sellafield now has two reprocessing plants — one is for Magnox fuel and the other, called Thorp (Thermal Oxide Reprocessing Plant), is for fuels from Advanced Gas-Cooled Reactors (UK) and Light Water Reactors (worldwide).
The Magnox reprocessing plant has been operational since 1964, and is due to close in 2012. It uses tributyl phosphate to extract plutonium and uranium from the fuel, which cannot be stored underwater for too long as the outer casing of the rods corrodes. Between 1971 and 2001, some 15,000 tonnes of new fuel have been won from 35,000 tonnes of Magnox.
In 1978, it was decided that another nuclear fuel reprocessing plant was required to deal with the increasing quantities of spent fuel from reactors around the world. The £2.7 billion Thorp was completed in 1994 and began operating in 1997, but is due to close in 2010. Allott & Lomax provided the structural engineering for this plant.
Thorp runs at around half capacity most of the time — its original target was to win 7,000 tonnes of new fuel per decade. By 2003 it had recovered 75 tonnes of plutonium and 3,300 tonnes of uranium from reprocessing, making a loss of more than £1 billion in that time.
The plant has a 35m high steel framed building with a 40m stainless steel roof span, and is designed to withstand a 1 in 10,000 year wind. It contains 4,200 tonnes of carbon steel, 600 tonnes of stainless steel, 2,900km of cabling and 320km of pipework.
In April 2005, Thorp operators discovered that a cracked pipe had leaked 83,000 litres of radioactive waste into a stainless steel lined concrete chamber (fortunately built to contain leaks). Sellafield was fined £500,000 for safety breaches, and Thorp did not reopen until January 2007. A breakdown in the underwater lift transferring fuel to Thorp caused the plant to be closed again in January 2008.
Light water reactors increasingly use Mox (mixed oxide) fuel, and a separate plant to reprocess it was completed in 1997 and operation began in 2001. However, it never met its design capacity and fuel had to be sent to France for reprocessing.
Fission products from the reprocessing plants are sent to the Vitrification Plant, which opened in March 1991. The fission solution is concentrated by evaporation and then mixed with 1-2mm diameter glass beads and melted in a furnace. The melted mixture is poured into containers where it cools into solid glass blocks. The containers are sealed and decontaminated before being stored as high level waste in shielded stainless steel tanks. There is storage capacity for 8,000 containers on site.
There have been safety concerns over the storage of fission solution in tanks above ground before evaporation, and breakdowns in two of the three evaporators.
There are three categories of nuclear waste. High level waste is the residue from reprocessing uranium and plutonium, and is sufficiently radioactive to generate heat. Intermediate level waste comprises fuel element cladding, contaminated equipment and effluent/sludge from treatment processes. Solid low level wastes arise where radioactive materials are used — paper towels, protective clothing and laboratory equipment, etc.
Solid low level waste is packaged and buried at the Drigg nuclear landfill site 3km south of Sellafield. Originally, liquid low level waste was discharged into the sea. This was the effluent remaining after radioactive metal residues were removed from the liquid waste by flocculation and precipitation. The Enhanced Actinide Removal Plant (opened 1994) and Solvent Treatment Plant were built to increase the amount of radioactivity removed from the effluent.
In January 2009, a leaking condensate pipe contaminated part of the site with radioactivity, prompting design improvements in the containment of wastes in line with Environment Agency directives.
As mentioned, Sellafield is the site of the world's first nuclear accident. Fire broke out in Windscale Graphite Pile No.1 on the 10th October 1957 after a failed attempt to release stored energy. The temperature inside the reactor core reached 1,300 degrees Celsius. After several days of misadventure, the fire was extinguished but Pile No.1 was ruined. Pile No.2, although undamaged, was judged potentially unsafe and shut down soon after. Pile No.1 was entombed in its concrete bio-shield.
Decommissioning of the various reactors at the Sellafield site is underway. The Nuclear Decommissioning Authority has forecast some £1,175m spending on decommissioning at the site in the 2009-10 financial year.
On 9th November 2009, the government announced their intention to build ten new nuclear power stations. Sellafield was one of the sites selected. However, on 27th November safety concerns were raised about the design of the proposed French and American reactors that might be used. The Health & Safety Executive is investigating.
Architect (Thorp plant): British Nuclear Fuels Ltd
Main contractor (1983 onwards): Sir Robert McAlpine
Boreholes (2009): Hydrock
Research: ECPK
"Going Critical — An Unofficial History of British Nuclear Power"
by Walter C. Patterson, Paladin Books, 1985
"Manufacturing Nuclear Fuel", British Nuclear Fuels Ltd, 2003-04
document in PDF available on www.bnfl.com

Sellafield Nuclear Fuel Plant