Windscale (Sellafield) Plutonium Reactor

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Windscale (Sellafield) plutonium reactor

The Windscale nuclear reactor was built in the 1940s near Sellafield, a remote farm area of northern England, to supply nuclear power to the region. This early reactor was designed with a large graphite block in which cans containing the uranium fuel were embedded. The graphite served to slow down fast-moving neutrons produced during nuclear fission , allowing the reactor to operate more efficiently.

Graphite behaves in a somewhat unusual way when bombarded with neutrons. Water, its modern counterpart, becomes warmer inside the reactor and circulates to transfer heat away from the core. Graphite, on the other hand, increases in volume and begins to store energy. At some point above 572°F (300°C), it may then suddenly release that stored energy in the form of heat.

A safety system that allowed this stored energy to be released slowly was installed in the Windscale reactor. On October 7, 1957, however, a routine procedure designed to release energy stored in the graphite cube failed, and a huge amount of heat was released in a short period of time. The graphite moderator caught fire, uranium metal melted, and radioactive gases were released to the atmosphere . The fire burned for two days before it was finally extinguished with water.

Fortunately, the area around Windscale is sparsely populated, and no immediate deaths resulted from the accident. However, quantities of radiation exceeding safe levels were observed shortly after the accident in Norway, Denmark, and other countries east of the British islands. British authorities estimate that 30 or more cancer deaths since 1957 can be attributed to radioactivity released during the accident. In addition, milk from cows contaminated with radioactive iodine-131 had to be destroyed. The British government eventually decided to close down and seal off the damaged nuclear reactor.

Four decades after the accident, Sellafield is still in the news. In 1991, the Radioactive Waste Management Advisory Committee recommended that Sellafield be chosen as the site for burying Britain's high-, low-, and intermediate-level radioactive wastes. A complex network of tunnels 2,500 ft (800 m) below ground level would be ready to accept wastes by the year 2005, according to the committee's plan.

Although some environmental groups object to the plan, many citizens do not seem to be concerned. In spite of the high levels of radiation buried in the old plant, Sellafield has become one of the most popular vacation spots for Britons.

See also High-level radioactive waste; Liquid metal fast breeder reactor; Low-level radioactive waste; Radiation exposure; Radiation sickness

[David E. Newton ]



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