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| Fig. 1: The Windscale Piles in Cumbria, New England. (Source: Wikimedia Commons) |
The Windscale Fire of 1957 marked Great Britain's largest nuclear reactor disaster, ranking level 5 classification on the International Nuclear Event Scale. During World War II, the Manhattan Project as a defense against Germany ignited the United Kingdom's involvement in nuclear fission as a military weapon. The Manhattan Project was a collaborative effort from United States, United Kingdom, and Canada. When World War II ended, the United States closed their nuclear weapon program to other countries. In an attempt to maintain their position as a world power, the United Kingdom expedited their research and technology to build their own nuclear weapon project. Thus, in four short years, two Windscale Piles were built in Cumbria, New England. Each pile was housed separately in large, concrete buildings a couple hundred feet apart. Additionally, they were fueled by 180 tons of uranium metal. The reactors manufactured plutonium used for nuclear weapons as well as the polonium and tritium used as fission triggers. The Windscale Piles are pictured in Fig. 1.
On October 7, 1957, a routine heating of Windscale Pile 1 began using the Wigner approach of annealing the reactor core. Next, the power was increased to further raise the temperature. However instead of a gradual release of energy, the high temperature caused a buildup of energy to be stored the core. In hopes of accelerating the Wigner process, the operators increased the power even more. Due to poor placement of reactor 1's thermometers, the operators couldn't get a read of the core's highest temperatures causing operators to be unaware of the dangerously high temperature. This led to the temperature to exceed the maximum of 400°C. On the morning of October 10th, operators noticed the extreme condition and proceeded to venture to the charge face in protective gear to secure the inspection plug. By this point, the operators detected the fuel channels a bright red that soon turned into flames scorching the graphite and the metal aluminum casing around the rods. In attempt to fix the situation, the operators turned the cooling fans to high. Instead of extinguishing the fire, this only fanned the flames. At this point, 21 out of 53 channels were filled with fires. Efforts to discharge the burning cartridges into the water duct were unsuccessful. [1] Operators continued their attempts to diminish the flames with liquid carbon dioxide. Finally, shutdown fans were turned off and water slowly doused away the flames. At around 3:00 P.M., the water was turned off after the fires completely subsided and the reactors were cold. No one in the area despite the release of radioactive contamination. Filters on top of the piles prevented some radiation from escaping.
Shortly following the disaster, an investigation took place over the next ten days. Scientists immediately came up with three possible causes of the fire: the graphite itself, a burst uranium cartridge, a tritium cartridge. Upon further investigation, they concluded that real issue was human error. The operators made a fatal mistake while performing the Wigner Energy method. This process, discovered by Hungarian physicist Eugene Wigner, was a cycle of controlled heating, called annealing cycled, to capture the energy inside the reactor. This controlled heating proved successful and was deemed safe if done correctly. However, the operators that caused the Windscale fire failed to acknowledge that the temperature was dropping as it should. Thus the second heating should not have occurred. Additionally, the operators increased airflow on both October 8th and October 10th in response to the temperature rise. Instead of proceeding to the next phase in the controlled heating, it only fanned the flames. The Wigner Energy method is a process that is taken on a case by case. Furthermore, it is a complicated process that was left in the hands of junior staff who lacked the proper knowledge and training to handle an unforeseen situation such as the overheating that occurred. Additionally, the thermometers were not placed in the accurate place to measure the heat at its highest temperature. Later, researches found out that two thermometers were not even working properly.
© Michelle Ramadan. The author grants permission to copy, distribute and display this work in unaltered form, with attribution to the author, for noncommercial purposes only. All other rights, including commercial rights, are reserved to the author.
[1] C. N. Hill, An Atomic Empire: A Technical History of the Rise and Fall of the British Atomic Energy Programme, (World Scientific, 2013).
