Chernobyl Nuclear Power Plant Disaster

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The Chernobyl Nuclear Power Plant Disaster

It is a silent enemy, it has no odor, no smell, no shape, yet it is one of man’s deadliest foes. Radiation is not something most people face on a daily basis, but for the town of Prypiat in the Ukraine it is a barren wasteland because of it. The Chernobyl Nuclear Power Plant disaster was the worst nuclear catastrophe to have ever occurred and, is a perfect example of what can happen when the blind and unmasked furry of atomic power is left unharnessed. The Chernobyl Nuclear Power Plant is near the town of Prypiat, Ukraine, 18 km northwest of the city of Chernobyl, 16 km from the border of Ukraine and Belarus, and about 110 km north of Kyiv. The Chernobyl Nuclear Power Plant consisted of four nuclear reactors, each capable of producing 1 gigawatt (GW) of electric power and the four together produced about 10% of the Ukraine's electricity. Construction of the plant began in the late 1970s, with reactor no. 1 commissioned in 1977, followed by no. 2 in 1978, no. 3 in 1981, and no. 4 in 1983. Two more reactors, no. 5 and 6, also capable of producing 1 GW each, were under construction at the time of the disaster. (Marples 27-29) During the daytime of April 25, 1986, reactor 4 was scheduled to be shut down for maintenance as it was near the end of its first fuel cycle. An experiment was scheduled to test a potential safety emergency core cooling feature during the shutdown procedure. Following an emergency shutdown known as a scram, cooling is required to maintain the temperature in the reactor core low enough to avoid fuel damage. The reactor consisted of about 1,600 individual fuel channels and each operational channel required a flow of 28 metric tons of water per hour. There was concern that in case of an external power failure the Chernobyl Power Plant would overload, leading to an automated safety shut down in which case there would be no external power to run the plant's cooling water pumps. Chernobyl's reactors had three backup diesel generators. The generator required 15 seconds to start up but took 60–75 seconds to attain full speed and reach its capacity of 5.5 megawatt (MW) required to run one main cooling water pump. (Marples 26)

Nuclear power reactors require cooling flow to remove decay heat, even when not actively generating power. In the case of an external power failure, the reactor would automatically scram, the control rods would be inserted and this would stop the nuclear fission process. However, in the spent fuel, the fission products themselves are radioactive, and continue to produce heat as they decay. This could amount to 1-2 percent of the normal output of the plant. If not immediately removed by coolant systems, the heat could lead to core damage. (Shcherbak 15-21)

This one-minute power gap was considered unacceptable and it was suggested that the mechanical energy of the steam turbine could be used to generate electricity to run the main cooling water pumps, while it was spinning down. In theory, Analyses indicated that the residual momentum had the potential to provide power for 45 seconds. This would bridge the power gap between the onset of the external power failure and the full availability of electric power from the emergency diesel generators, but this capability needed to be confirmed by test. Previous tests had ended unsuccessfully. An initial test in 1982 showed that the excitation voltage of the turbine-generator was insufficient; it did not maintain the desired magnetic field during the generator spin-down. The system was modified, and in 1984 the test was repeated, but the retest proved unsuccessful. In 1985 the test was attempted a third time, but it also yielded negative results. This test procedure was to be repeated again in 1986. (Parker 10-11)

The test was focused on the switching sequences of the electrical supplies for the reactor. Since the test procedure was to begin when the reactor was...
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