Tezos

Windscale #11

Creator

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Description

Name: Windscale Year of construction: 11.1958 Closing year: 04.1981 Country: UK Coordinate: 54,418050, -3,487962 Blocks: 1 Reactor type: GCR Reactor model: AGR Status: CLOSED Power MW: 36 Operator: UK AEA Provider: UK AEA On October 10, 1957, a major radiation accident occurred at NPS Windscale in the Sellafield nuclear complex in northwest Britain. The accident corresponded to level five on the International Nuclear Event Scale (INES) and was the largest accident in the history of the nuclear power industry in Great Britain. The fire at the installed AGR reactor, an air-cooled graphite reactor, resulted in a significant release of radioactive substances - 550-750 TBq. On October 10, 1957, NPS Windscale, which was producing weapons-grade plutonium, was undergoing a scheduled graphite masonry annealing program. Under the normal program, neutrons bombard graphite and alter its crystalline structure, thereby causing energy to accumulate in the graphite. Annealing consists of restoring the normal structure of the graphite, by shutting down the gas-cooled circuit and consequently increasing the temperature in the reactor. The reactor at NPS Windscale had a number of design features. Because of this, such an annealing had to be performed twice. In the absence of monitoring devices, the personnel did not pay attention to the situation getting out of control. Overheating of the reactor caused the metallic uranium fuel to react with the air and burn. At 11:00 am an air sampler detected a 10 times increase in radioactivity at a distance of 800 meters from the reactor. Analysis of the air near the reactor confirmed the accident. At 16:30 a.m. a visual inspection revealed that the temperature of some of the fuel assemblies increased to 1,400 degrees Celsius. As a result the fuel assemblies bloated and it became impossible to take them out of the reactor. Work was begun to unload the maximum number of fuel elements. Nevertheless, by the evening of October 10 the fire consumed 150 channels of fuel assemblies with a total mass of 8 tons of uranium. During the night of October 10-11, unsuccessful attempts were made to extinguish the fire using carbon dioxide. At 8:55 on October 11 the reactor was flooded with water with the risk of a possible explosion, which nevertheless did not happen. At 3:20 on 12 October the reactor was put into a cold state. The accident resulted in the release of radioactive elements, primarily Iodine-131 - 740 TBq and Cesium-137 - 30 TBq. The workers involved in elimination of the accident did not receive doses exceeding 10 times the annual norm of irradiation. For 6 weeks milk sales from nearby farms at a distance of up to 30 kilometers from the nuclear power plant were stopped. Britain's National Commission on Radiological Protection found that about 30 cancer deaths may have been caused by the Windscale accident. Other estimates increase the number of cancer deaths from the incident to as many as 200. Modern reactors at NPS stopped using metallic nuclear fuel because the metal has a lower melting point. The Windscale accident was considered the most serious before the accident at America's Three Mile Island Nuclear Power Plant.