CHERNOBYL

On April 26, 1986, at 1:23 a.m., an accident occurred during a test of a turbine generator on the Unit 4 reactor at the Chernobyl nuclear power station in the Ukraine. The accident resulted from the improper withdrawal of control rods and the inactivation of important safety systems—in violation of the operating rules—which caused the reactor to overheat, explode, and catch fire. Because the facility lacked an adequate containment structure, the damage to the reactor core and control building allowed large quantities of radiation and millions of curies of krypton-85, xenon-133, iodine-131, tellurium-132, strontium-89, strontium-90, plutonium-240, and other radionuclides from the rector core to be released during the ensuing ten days, necessitating the evacuation of tens of thousands of people and farm animals from the surrounding area and resulting in radiation sickness and burns in more than two hundred emergency personnel and firefighters, thirty-one of whom were injured fatally.

The heaviest contamination occurred in the vicinity of the reactor itself and, to a lesser extent, in neighboring countries of eastern Europe. Those living in the vicinity of the reactor were given potassium iodide preparations to inhibit the thyroidal uptake of radioactive iodine, but infants in a number of areas elsewhere in eastern Europe are estimated to have received sizeable radiation doses to the thyroid gland, largely through ingestion of radioiodine via cow's milk, and the incidence of thyroid cancer in such persons has since risen dramatically in Belarus and in Ukraine. In areas outside Belarus, Russia, and Ukraine, organs other than the thyroid typically received only a small fraction of the radiation dose normally accumulated each year from natural background radiation. For example, the highest average effective dose in such areas during the first year was received in Bulgaria, where it is estimated to have approximated slightly less than one-third of the average annual effective dose received from natural sources. Because of the small magnitude of the average dose to a given individual, the ultimate health impacts of the accident cannot be predicted with certainty. However, nonthreshold risk models for the carcinogenic effects of radiation imply that the collective dose to the population of the northern hemisphere may cause up to thirty thousand additional cancer deaths during the next seventy years.

The accident, by far the worst nuclear reactor accident to date, highlighted flaws in the design, as well as the operation, of the Chernobyl reactor. The reactor's lack of adequate containment and its positive void coefficient, which made the reactor potentially unstable at low-risk power levels, prompted the International Atomic Energy Agency subsequently to recommend the decommissioning of all Chernobyl-type reactors, a recommendation yet to be fully implemented throughout eastern Europe. In spite of the fact that the accident also prompted reassessment and upgrading of the safety of nuclear power systems everywhere, nuclear power has fallen into disfavor in most countries because of the magnitude of the disaster. To many experts, nevertheless, nuclear power still compares favorably with other sources of energy in its impact on human health and the environment, and it is expected to continue to play a role in helping to meet the world's rapidly growing demands for energy.

Arthur C. Upton

(see also: Nuclear Power; Nuclear Waste; Radiation, Ionizing; Three Mile Island )

Bibliography

Eisenbud, M., and Gesell, T. (1999). Environmental Radioactivity: From Natural, Industrial, and Military Sources, 4th edition. San Diego, CA: Academic Press.

Heidenreich, W. F.; Kenigsberg, J.; Jacob, P.; Buglova, E.; Goulko, G.; Paretzke, H. G.; Demidchik, E. P.; and Golovneva, A. (1999). "Time Trends of Thyroid Cancer Incidence in Belarus After the Chernobyl Accident." Radiation Research 181:617–625.

Krewitt, W.; Hurley, F.; Trukenmuller, A.; and Friedrich, R. (1998). "Health Risks of Energy Systems." Risk Analysis 18:377–385.

Rhodes, R., and Beller, D. (2000). "The Need for Nuclear Power." Foreign Affairs 79:30–44.

Chernobyl , Ukr. Chornobyl, abandoned city, N Ukraine, near the Belarus border, on the Pripyat River. Ten miles (16 km) to the north, in the town of Pripyat, is the Chernobyl nuclear power station, site of the worst nuclear reactor disaster in history. On Apr. 25, 1986, during an unauthorized test of one of the plant's four reactors, engineers initiated an uncontrolled chain reaction in the core of the reactor after disabling emergency backup systems. On Apr. 26, an explosion ripped the top off the containment building, expelling radioactive material into the atmosphere; more was released in the subsequent fire. Only after Swedish instruments detected fallout from the explosion did Soviet authorities admit that an accident had occurred. The reactor core was sealed off by air-dropping a cement mixture, but not before eight tons of radioactive material had escaped.

Twenty firefighters died immediately from overexposure to radioactivity, while hundreds suffered from severe radiation sickness. Pripyat, Chernobyl, and nearby towns were evacuated. People who lived near the plant in Ukraine and Belarus at the time have seen a greatly increased incidence of thyroid cancer, and genetic mutations have been discovered in children later born to exposed parents. Nearly all thyroid cancer cases, however, were successfully treated. Ukraine has estimated that some 4,400 people died as a result of the accident and during its cleanup, but a 2005 report prepared by several UN agencies and regional governments indicated that some 50 deaths were directly attributable to radiation from the disaster and an estimated 4,000 deaths might ultimately result from it, mainly due to higher cancer rates. That prediction was challenged the following year by a Greenpeace report that said more than 90,000 deaths might result, roughly half of which would be due to conditions other than cancer. The agricultural economies of E and N Europe were temporarily devastated, as farm products were contaminated by fallout. One Chernobyl reactor remained in operation until Dec., 2000, when the complex was shut down.

Bibliography: See S. Alexievich, Voices from Chernobyl (2005).

Chernobyl A Ukrainian town near Kiev, which was the site of the world's worst peacetime nuclear disaster. On 26 April 1986, inadequately prepared tests in block 4 of the graphite-moderated nuclear power station led to the outbreak of fire in the reactor. The fire was not completely put out for weeks. The rogue generator itself was buried in concrete, while other parts of the nuclear power station continued to function. The catastrophe resulted in thirty-one immediate deaths. One year into Gorbachev's leadership, the disaster was dealt with in the usual Soviet manner, and thus epitomized how entrenched old traditions were, and just how far reform would have to go to effect real change. The catastrophe was long denied, with traditional May Day parades in Kiev and elsewhere suggesting business as usual. The accident itself was met with typical bureaucratic incompetence, whilst provisions to prevent contamination were virtually non-existent. Once Western scientists had produced inescapable evidence of the disaster, it was admitted. An evacuation of around 135,000 people living in a radius of 30 km took place. Altogether an estimated 600,000 people have suffered from the effects of the radiation, while agricultural produce in large parts of Finland, Scandinavia, Poland, and Romania, and to a lesser extent Germany and Britain, was also contaminated.

Chernobyl A nuclear power-station near Kiev in Ukraine, the site in 1986 of the worst nuclear accident in the world to date. 31 people died trying to fight subsequent fires, and many more received radiation burns or suffered from associated diseases. The accident was the result of unauthorized experiments by the operators of one of the four reactors, in which safety systems were deliberately circumvented in order to learn more about the plant's operation. Fallout from the explosions, containing the radioactive isotope caesium-137, affected large areas of Europe. In particular, livestock in high-rainfall areas received unacceptable doses of radiation. In the mid-1990s large areas of land in Ukraine, Belarus, and south-west Russia were still contaminated and high levels of cancer (especially leukaemia in children) were reported. The Ukrainian government announced plans to replace the power-station with a gas-fired one by 2000.

Chernobyl (Chornobyl) City on the River Pripyat River, n central Ukraine. It is 20km (12mi) from the Chernobyl power plant. On April 26, 1986, an explosion in one of the plant's reactors released eight tonnes of radioactive material into the atmosphere. Within the first few hours, 31 people died. Fallout spread across e and n Europe, contaminating agricultural produce. The long-term effects of contamination are inconclusive, but 25,000 local inhabitants have died prematurely. Two of the three remaining reactors were reworking by the end of 1986. In 1991 Ukraine pledged to shut down the plant, but energy needs dictated its continued output. With aid from the West, the plant finally closed in December 2000.

Chernobyl a town near Kiev in Ukraine where, in April 1986, an accident at a nuclear power station resulted in a serious escape of radioactive material, and the subsequent contamination of Ukraine, Belarus, and other parts of Europe. (See also cultural Chernobyl.)

Chernobyl packet A badly formed PACKET of data which causes a network to malfunction badly. Usually such packets are caused by a hardware error. See also BROADCAST STORM and NETWORK MELTDOWN. The term is derived from the Russian nuclear accident at Chernobyl.

Chernobyl, Ukraine Derived from the Russian chernobyl′nik ‘wormwood’, an aromatic plant of the composite family, Artemisia absinthium, abundant here.

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