Sunday, August 22, 2010

Chernobyl disaster

LisaMarie: Was it an Accident? humm, I wonder. prolly not.

Chernobyl disaster


The Chernobyl disaster was a nuclear accident that occurred on 26 April 1986, at the Chernobyl Nuclear Power Plant in Ukraine (then in the Ukrainian Soviet Socialist Republic, part of the Soviet Union). It is considered the worst nuclear power plant accident in history and is the only level 7 event on the International Nuclear Event Scale.

The disaster occurred on 26 April 1986, at reactor number four at the Chernobyl plant, near the town of Pripyat in the Ukrainian Soviet Socialist Republic (USSR), during an unusual and (as carried out) unsafe systems test at low power. A sudden rapid growth in power output took place, and when an attempt was made for emergency shutdown, an unexpected and more extreme spike in power output occurred which led to a reactor vessel rupture and a series of explosions. This event exposed the graphite moderator components of the reactor to air and they ignited; the resulting fire sent a plume of radioactive fallout into the atmosphere and over an extensive geographical area, including Pripyat. The plume drifted over large parts of the western Soviet Union, Eastern Europe, Western Europe, and Northern Europe. Large areas in Ukraine, Belarus, and Russia had to be evacuated, with over 336,000 people resettled. According to official post-Soviet data,[1] about 60% of the fallout landed in Belarus.

The accident raised concerns about the safety of the Soviet nuclear power industry as well as nuclear power in general, slowing its expansion for a number of years while forcing the Soviet government to become less secretive about its procedures.[2]

The countries of Russia, Ukraine, and Belarus have been burdened with the continuing and substantial decontamination and health care costs of the Chernobyl accident. A 2006 report prepared by the Chernobyl Forum, led by the World Health Organization (WHO) states, "Among the 134 emergency workers involved in the immediate mitigation of the Chernobyl accident, severely exposed workers and fireman during the first days, 28 persons died in 1986 due to ARS(Acute Radiation Syndrome), and 19 more persons died in 1987-2004 from different causes. Among the general population affected by Chernobyl radioactive fallout, the much lower exposures meant that ARS cases did not occur". It is estimated that there were 4,995 additional deaths, between 1991 -1998, among the approximately 60,000 most highly exposed people.[3][4]

The nearby city of Pripyat was not immediately evacuated after the incident.

Only after radiation levels set off alarms at the Forsmark Nuclear Power Plant in Sweden[42] over one thousand miles from the Chernobyl Plant did the Soviet Union admit that an accident had occurred. Nevertheless, authorities attempted to conceal the scale of the disaster. For example, in evacuating the city of Pripyat, the following warning message was read on local radio: "An accident has occurred at the Chernobyl Nuclear Power Plant. One of the atomic reactors has been damaged. Aid will be given to those affected and a committee of government inquiry has been set up." This message gave the false impression that any damage or radiation was localized.

The government committee was eventually formed as announced to investigate the accident. It was headed by Valeri Legasov who arrived at Chernobyl in the evening of 26 April. By the time Legasov arrived, two people have died and 52 were in the hospital. By the night of 26–27 April — more than 24 hours after the explosion — Legasov's committee had ample evidence showing extremely high levels of radiation and a number of cases of radiation exposure. Based on the evidence at hand, Legasov's committee had to acknowledge the destruction of the reactor and order the evacuation of Pripyat.

The evacuation began at 2 p.m. on 27 April. To speed up the evacuation, the residents were told to bring what was only necessary since the authorities said it would only be temporary and would last approximately three days. As a result, most of the residents left most of their personal belongings which can still be found today at Pripyat. An exclusion zone of 30 km (19 mi) remains in place today

International spread of radioactivity

Four hundred times more radioactive material was released than had been by the atomic bombing of Hiroshima. However, compared to the total amount released by nuclear weapons testing during the 1950s and 1960s, the Chernobyl disaster released 100 to 1000 times less radioactivity.[64] The fallout was detected over all of Europe except for the Iberian Peninsula.[65][66][67]

The initial evidence that a major release of radioactive material was affecting other countries came not from Soviet sources, but from Sweden, where on the morning of 28 April[68] workers at the Forsmark Nuclear Power Plant (approximately 1,100 km (680 mi) from the Chernobyl site) were found to have radioactive particles on their clothes.[69] It was Sweden's search for the source of radioactivity, after they had determined there was no leak at the Swedish plant, that at noon on April 28 led to the first hint of a serious nuclear problem in the western Soviet Union. Hence the evacuation of Pripyat on April 27, 36 hours after the initial explosions, was silently completed before the disaster became known outside the Soviet Union. The rise in radiation levels had at that time already been measured in Finland, but a civil service strike delayed the response and publication.[70]

Contamination from the Chernobyl accident was scattered irregularly depending on weather conditions. Reports from Soviet and Western scientists indicate that Belarus received about 60% of the contamination that fell on the former Soviet Union. However, the 2006 TORCH report stated that half of the volatile particles had landed outside Ukraine, Belarus, and Russia. A large area in Russia south of Bryansk was also contaminated, as were parts of northwestern Ukraine. Studies in surrounding countries indicate that over one million people could have been affected by radiation.[71]

Recently published data from a long-term monitoring program (The Korma-Report)[72] show a decrease in internal radiation exposure of the inhabitants of a region in Belarus close to Gomel. Resettlement may even be possible in prohibited areas provided that people comply with appropriate dietary rules.

In Western Europe, precautionary measures taken in response to the radiation included seemingly arbitrary regulations banning the importation of certain foods but not others. In France some officials stated that the Chernobyl accident had no adverse effects.[citation needed]. Official figures in southern Bavaria in Germany indicated that some wild plant species contained substantial levels of caesium, which were believed to have been passed onto them by wild boars, a significant number of which had already contained radioactive particles above the allowed level, consuming them.[73]

Health of plant workers and local people

In the aftermath of the accident, 237 people suffered from acute radiation sickness, of whom 31 died within the first three months.[76][77] Most of these were fire and rescue workers trying to bring the accident under control, who were not fully aware of how dangerous exposure to the radiation in the smoke was. Whereas, the World Health Organization's report 2006 Report of the Chernobyl Forum Expert Group from the 237 emergency workers who were diagnosed with ARS, ARS was identified as the cause of death for 28 of these people within the first few months after the disaster. There were no further deaths identified in the general population affected by the disaster as being caused by ARS. Of the 72,000 Russian Emergency Workers being studied, 216 non cancer deaths are attributed to the disaster, between 1991 and 1998. The latency period for solid cancers caused by excess radiation exposure is 10 or more years, thus at the time of the WHO report being undertaken the rates of solid cancer deaths were no greater than the general population.Some 135,000 people were evacuated from the area, including 50,000 from Pripyat.

Rivers, lakes and reservoirs

Earth Observing-1 image of the reactor and surrounding area in April 2009The Chernobyl nuclear power plant is located next to the Pripyat River, which feeds into the Dnipro River reservoir system, one of the largest surface water systems in Europe. The radioactive contamination of aquatic systems therefore became a major issue in the immediate aftermath of the accident.[78] In the most affected areas of Ukraine, levels of radioactivity (particularly radioiodine: I-131, radiocaesium: Cs-137 and radiostrontium: Sr-90) in drinking water caused concern during the weeks and months after the accident. After this initial period, however, radioactivity in rivers and reservoirs was generally below guideline limits for safe drinking water.[78]

Bio-accumulation of radioactivity in fish[79] resulted in concentrations (both in western Europe and in the former Soviet Union) that in many cases were significantly above guideline maximum levels for consumption.[78] Guideline maximum levels for radiocaesium in fish vary from country to country but are approximately 1,000 Bq/kg in the European Union.[80] In the Kiev Reservoir in Ukraine, concentrations in fish were several thousand Bq/kg during the years after the accident.[79] In small "closed" lakes in Belarus and the Bryansk region of Russia, concentrations in a number of fish species varied from 0.1 to 60 kBq/kg during the period 1990–92.[81] The contamination of fish caused short-term concern in parts of the UK and Germany and in the long term (years rather than months) in the affected areas of Ukraine, Belarus, and Russia as well as in parts of Scandinavia.[78]


Map of radiation levels in 1996 around Chernobyl.Groundwater was not badly affected by the Chernobyl accident since radionuclides with short half-lives decayed away long before they could affect groundwater supplies, and longer-lived radionuclides such as radiocaesium and radiostrontium were adsorbed to surface soils before they could transfer to groundwater.[82] However, significant transfers of radionuclides to groundwater have occurred from waste disposal sites in the 30 km (19 mi) exclusion zone around Chernobyl. Although there is a potential for transfer of radionuclides from these disposal sites off-site (i.e. out of the 30 km (19 mi) exclusion zone), the IAEA Chernobyl Report[82] argues that this is not significant in comparison to current levels of washout of surface-deposited radioactivity.

Flora and fauna

After the disaster, four square kilometers of pine forest in the immediate vicinity of the reactor turned reddish-brown and died, earning the name of the "Red Forest".[83] Some animals in the worst-hit areas also died or stopped reproducing. Most domestic animals were evacuated from the exclusion zone, but horses left on an island in the Pripyat River 6 km (4 mi) from the power plant died when their thyroid glands were destroyed by radiation doses of 150–200 Sv.[84] Some cattle on the same island died and those that survived were stunted because of thyroid damage. The next generation appeared to be normal.[84]

A robot sent into the reactor itself has returned with samples of black, melanin-rich radiotrophic fungi that are growing on the reactor's walls.[85]