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The Chernobyl disaster, (Template:Lang-uk) Chornobylʹsʹka katastrofa, was a nuclear accident that occurred on 26 April 1986 at the Chernobyl Nuclear Power Plant in the Ukrainian Soviet Socialist Republic (then part of the Soviet Union), now in Ukraine.

The Pripyat Ferris wheel as seen from inside the town's Palace of Culture.

Following the accident, questions arose about the future of the plant and its eventual fate. All work on the unfinished reactors 5 and 6 was halted three years later. However, the trouble at the Chernobyl plant did not end with the disaster in reactor 4. The damaged reactor was sealed off and 200 cubic meters (260 cu yd) of concrete was placed between the disaster site and the operational buildings. The Ukrainian government continued to let the three remaining reactors operate because of an energy shortage in the country.

In 1991, a fire broke out in the turbine building of reactor 2; the authorities subsequently declared the reactor damaged beyond repair and had it taken offline. Reactor 1 was decommissioned in November 1996 as part of a deal between the Ukrainian government and international organizations such as the IAEA to end operations at the plant. On 15 December 2000, then-President Leonid Kuchma personally turned off Reactor 3 in an official ceremony, shutting down the entire site.

Chernobyl today

It has been suggested that this article be merged into Chernobyl Nuclear Power Plant. (Discuss) Proposed since April 2012.

Containment of the reactor

The Chernobyl reactor is now enclosed in a large concrete sarcophagus, which was built quickly to allow continuing operation of the other reactors at the plant.

A New Safe Confinement was to have been built by the end of 2005; however, it has suffered ongoing delays and as of 2010, when construction finally began, is expected to be completed in 2013. The structure is being built adjacent to the existing shelter and will be slid into place on rails. It is to be a metal arch 105 metres (344 ft) high and spanning 257 metres (843 ft), to cover both unit 4 and the hastily built 1986 structure. The Chernobyl Shelter Fund, set up in 1997, has received €810 million from international donors and projects to cover this project and previous work. It and the Nuclear Safety Account, also applied to Chernobyl decommissioning, are managed by the European Bank for Reconstruction and Development (EBRD).

A handful of Ukrainian scientists work inside the sarcophagus, but outsiders are rarely granted access. In 2006 an Australian 60 Minutes team led by reporter Richard Carleton and producer Stephen Rice were allowed to enter the sarcophagus for 15 minutes and film inside the control room.

Radioactive materials and waste management

As of 2006, some fuel remained in the reactors at units 1 through 3, most of it in each unit's cooling pond, as well as some material in a small spent fuel interim storage facility pond (ISF-1).

In 1999 a contract was signed for construction of a radioactive waste management facility to store 25,000 used fuel assemblies from units 1–3 and other operational wastes, as well as material from decommissioning units 1–3 (which will be the first RBMK units decommissioned anywhere). The contract included a processing facility able to cut the RBMK fuel assemblies and to put the material in canisters, which were to be filled with inert gas and welded shut.

The canisters were to be transported to dry storage vaults, where the fuel containers would be enclosed for up to 100 years. This facility, treating 2500 fuel assemblies per year, would be the first of its kind for RBMK fuel. However, after a significant part of the storage structures had been built, technical deficiencies in the concept emerged, and the contract was terminated in 2007. The interim spent fuel storage facility (ISF-2) will now be completed by others by mid-2013.

Another contract has been let for a liquid radioactive waste treatment plant, to handle some 35,000 cubic meters of low- and intermediate-level liquid wastes at the site. This will need to be solidified and eventually buried along with solid wastes on site.

In January 2008, the Ukrainian government announced a 4-stage decommissioning plan that incorporates the above waste activities and progresses towards a cleared site .

Lava-like fuel-containing materials (FCMs)

Main article: corium (nuclear reactor)
The radioactivity levels of different isotopes in the FCM, as back-calculated by Russian workers to April 1986.

According to official estimates, about 95% of the fuel in the reactor at the time of the accident (about 180 metric tons) remains inside the shelter, with a total radioactivity of nearly 18 million curies (670 PBq). The radioactive material consists of core fragments, dust, and lava-like "fuel containing materials" (FCM, also called "corium") that flowed through the wrecked reactor building before hardening into a ceramic form.

Three different lavas are present in the basement of the reactor building: black, brown, and a porous ceramic. They are silicate glasses with inclusions of other materials within them. The porous lava is brown lava that dropped into water and thus cooled rapidly.

Degradation of the lava

It is unclear how long the ceramic form will retard the release of radioactivity. From 1997 to 2002 a series of papers were published that suggested that the self-irradiation of the lava would convert all 1,200 metric tons into a submicrometer and mobile powder within a few weeks. But it has been reported that the degradation of the lava is likely to be a slow and gradual process rather than sudden and rapid. The same paper states that the loss of uranium from the wrecked reactor is only 10 kg (22 lb) per year. This low rate of uranium leaching suggests that the lava is resisting its environment. The paper also states that when the shelter is improved, the leaching rate of the lava will decrease.

Some of the surfaces of the lava flows have started to show new uranium minerals such as Na
4(UO
2)(CO
3)
3 and uranyl carbonate. However, the level of radioactivity is such that during one hundred years the self irradiation of the lava (2 × 10 α decays per gram and 2 to 5 × 10 Gy of β or γ) will fall short of the level of self irradiation required to greatly change the properties of glass (10 α decays per gram and 10 to 10 Gy of β or γ). Also the rate of dissolution of the lava in water is very low (10 g-cm day), suggesting that the lava is unlikely to dissolve in water.

Biological phenomena

Scientists studying the seeds harvested from soybean and flax plants grown inside (five kilometers from the power plant) the exclusion zone found them to be relatively unaffected by radiation. Martin Hajduch from the Institute of Plant Genetics and Biotechnology at the Slovak Academy of Sciences said: "We detected very low radioactivity in the seeds. In the stem or leaves there is radioactivity, but it is somehow blocked and doesn't come to the seeds."

Hajduch and his colleagues in Ukraine conducted a proteomics study of the plants and found that the seeds harvested inside the exclusion zone compared favorably with ones grown in non-contaminated soil outside.

Possible further collapse of the sarcophagus

It has been suggested that this article be merged into Chernobyl Nuclear Power Plant sarcophagus. (Discuss) Proposed since April 2012.
The sarcophagus, the concrete block surrounding reactor #4.

The protective box that was placed over the wrecked reactor was named object "Shelter" by the Soviet government, but the media and the public know it as the "sarcophagus."

The present shelter is constructed over the ruins of the reactor building. The two "Mammoth Beams" that support the roof of the shelter rest partly on the structurally unsound west wall of the reactor building that was damaged by the accident. The western end of the shelter roof is supported by a wall at a point designated axis 50. This wall is reinforced concrete, and was cracked by the accident. In December 2006 the "Designed Stabilisation Steel Structure" (DSSS) was extended until 50% of the roof load (about 400 tons) was transferred from the axis 50 wall to the DSSS.

The DSSS is a yellow steel object that has been placed next to the wrecked reactor; it is 63-meter (207 ft) tall and has a series of cantilevers that extend through the western buttress wall, and is intended to stabilize the sarcophagus. This was done because if the wall of the reactor building or the roof of the shelter were to collapse, then large amounts of radioactive dust and particles would be released directly into the atmosphere, resulting in a large new release of radioactivity into the environment.

A further threat to the shelter is the concrete slab that formed the "Upper Biological Shield" (UBS), situated above the reactor prior to the accident. This concrete slab was thrown upwards by the explosion in the reactor core and now rests at approximately 15° from vertical. The position of the upper bioshield is considered inherently unsafe, as only debris supports it in its nearly upright position. A collapse of the bioshield would further exacerbate the dust conditions in the shelter, possibly spreading some quantity of radioactive materials out of the shelter, and could damage the shelter itself. The UBS is a circle 15 meters in diameter, weighing 1000 tons and consisting of 2000 cubes, each located above a fuel channel. The shield, called Pyatachok ("five kopek coin") before the disaster, was afterwards named Component "E" and nicknamed "Elena"; the twisted fuel bundles still attached to it are called "Elena's hair."

Wildlife status

See also: Radiation hormesis
It has been suggested that this article be merged into Chernobyl Exclusion Zone. (Discuss) Proposed since April 2012.

The Exclusion Zone around the Chernobyl nuclear power station is reportedly a haven for wildlife. As humans were evacuated from the area 25 years ago, existing animal populations multiplied and rare species not seen for centuries have returned or have been reintroduced, for example lynx, wild boar, wolf, Eurasian brown bear, European bison, Przewalski's horse, and eagle owl. Birds even nest inside the cracked concrete sarcophagus shielding in the shattered remains of Reactor 4. The Exclusion Zone is so lush with wildlife and greenery that in 2007 the Ukrainian government designated it a wildlife sanctuary, and at 488.7 km it is one of the largest wildlife sanctuaries in Europe.

According to a 2005 U.N. report, wildlife has returned despite radiation levels that are presently 10 to 100 times higher than normal background radiation. Although they were significantly higher soon after the accident, the levels have fallen because of radioactive decay.

Biologist Anders Møller from the University of Paris Sud in France has been examining the effects of radiation on animals around Chernobyl for two decades. "Areas with higher radiation have fewer animals, survival and reproduction is reduced, sperm are abnormal and have reduced swimming ability. Abnormalities are commonplace and mutations rates are much elevated," Møller said.

Last year, Møller and Tim Mousseau published the results of the largest census of animal life in the Chernobyl Exclusion Zone . It revealed, contrary to the Chernobyl Forum's 2005 report, that biodiversity in insects, birds and mammals is declining. Not all species are affected by radiation in the same way according to Møller. Some birds -- including migrant species and long distance dispersers -- are more vulnerable to radiation than others, he said. Martin Hajduch said animal numbers in the exclusion zone are probably higher now than before the accident. But that's because there are no humans there hunting or fishing.

"But if you look at how many species of animals are in the area, I think it would be less," Hajduch said.

Some researchers say that by halting the destruction of habitat, the Chernobyl disaster helped wildlife flourish. Biologist Robert J. Baker of Texas Tech University was one of the first to report that Chernobyl had become a wildlife haven and that many rodents he has studied at Chernobyl since the early 1990s have shown remarkable tolerance for elevated radiation levels.

Møller et al. (2005) suggested that reproductive success and annual survival rates of barn swallows are much lower in the Chernobyl exclusion zone; 28% of barn swallows inhabiting Chernobyl return each year, while at a control area at Kanev 250 km to the southeast, the return rate is around 40%. A later study by Møller et al. (2007) furthermore claimed an elevated frequency of 11 categories of subtle physical abnormalities in barn swallows, such as bent tail feathers, deformed air sacs, deformed beaks, and isolated albinistic feathers.

Smith et al. (2007) have disputed Møller's findings and instead proposed that a lack of human influence in the exclusion zone locally reduced the swallows' insect prey and that radiation levels across the vast majority of the exclusion zone are now too low to have an observable negative effect. But the criticisms raised were responded to in Møller et al. (2008). It is possible that barn swallows are particularly vulnerable to elevated levels of ionizing radiation because they are migratory; they arrive in the exclusion area exhausted and with depleted reserves of radio-protective antioxidants after an arduous journey.

Several research groups have suggested that plants in the area have adapted to cope with the high radiation levels, for example by increasing the activity of DNA cellular repair machinery and by hypermethylation. Given the uncertainties, further research is needed to assess the long-term health effects of elevated ionizing radiation from Chernobyl on flora and fauna.

Grass and forest fires

It has been suggested that this article be merged into Chernobyl Exclusion Zone. (Discuss) Proposed since April 2012.

It is known that fires can make radioactivity mobile again. In particular V.I. Yoschenko et al. reported on the possibility of increased mobility of caesium, strontium, and plutonium due to grass and forest fires. As an experiment, fires were set and the levels of the radioactivity in the air downwind of these fires was measured.

Grass and forest fires have happened inside the contaminated zone, releasing radioactive fallout into the atmosphere. In 1986 a series of fires destroyed 23.36 km (5,772 acres) of forest, and several other fires have since burned within the 30 km (19 mi) zone. A serious fire in early May 1992 affected 5 km (1,240 acres) of land including 2.7 km (670 acres) of forest. This resulted in a great increase in the levels of caesium-137 in airborne dust.

In 2010, a series of wildfires affected contaminated areas, specifically the surroundings of Bryansk and border regions with Belarus and Ukraine. The Russian government claims that there has been no discernible increase in radiation levels, while Greenpeace accuses the government of denial.

See also

External links

References

  1. Information Notice No. 93-71
  2. IAEA's Power Reactor Information System polled in May 2008 reports shut down for units 1, 2, 3 and 4 respectively at 1996/11/30, 1991/10/11, 2000/12/15 and 1986/04/26.
  3. "Shelter" object description
  4. "Inside Chernobyl". 60 Minutes Australia, Nine Network Australia. 16 April 2006.
  5. "Chernobyl Accident". World Nuclear Association. May 2008. Retrieved 18 June 2008.
  6. V. Baryakhtar, V. Gonchar, A. Zhidkov and V. Zhidkov, Radiation damages and self-spluttering of high radioactive dielectrics: Spontaneous emission of submicrometre dust particles, Condensed Matter Physics, 2002, 5(3{31}), 449–471.
  7. ^ Borovoi, A. A. (2006). "Nuclear fuel in the shelter". Atomic Energy. 100 (4): 249–256. doi:10.1007/s10512-006-0079-3.
  8. See BBC documentary
  9. Nuclear Engineering International, July 2007, page 12.
  10. "Chernobyl Glossary". Angelfire.com. Retrieved 2010-03-22.
  11. Decade of disaster - Google Books. Books.google.com. 2000. ISBN 9780252068201. Retrieved 2010-03-22.
  12. "Chernobyl Tour | Radiation Protection | US EPA". Epa.gov. 2006-06-28. Retrieved 2010-03-22.
  13. ^ BBC, 20 April 2006, Wildlife defies Chernobyl radiation
  14. ^ Mycio, Mary (2005-09-09). Wormwood Forest: A Natural History of Chernobyl. Joseph Henry Press. ISBN 0309094305. Retrieved 2009-09-25.
  15. ^ Washington Post, 7 June 2007, Chernobyl Area Becomes Wildlife Haven
  16. Mother Nature Network, 7 May 2009, Scientists disagree over radiation effects
  17. ^ Baker, Robert J. and Chesser, Roland K. "The Chernobyl Nuclear Disaster And Subsequent Creation of a Wildlife Preserve". Environmental Toxicology and Chemistry, Vol.19, No.5, pp.1231-1232, 2000. Retrieved 2010-08-14. {{cite web}}: Italic or bold markup not allowed in: |publisher= (help)CS1 maint: multiple names: authors list (link)
  18. ^ Ravilious, Kate (2009-06-29). "Despite Mutations, Chernobyl Wildlife Is Thriving". National Geographic Magazine. ISSN 0027-9358. Retrieved 2009-09-23.
  19. Møller, A. P. (2005). "Condition, reproduction and survival of barn swallows from Chernobyl". Journal of Animal Ecology. 74 (6): 1102–1111. doi:10.1111/j.1365-2656.2005.01009.x. {{cite journal}}: Unknown parameter |coauthors= ignored (|author= suggested) (help)
  20. Møller, A.P. (2007). "Elevated frequency of abnormalities in barn swallows from Chernobyl". Biology Letters. 3 (4): 414–417. doi:10.1098/rsbl.2007.0136. PMC 1994720. PMID 17439847. Retrieved 2009-09-23. {{cite journal}}: Unknown parameter |coauthors= ignored (|author= suggested) (help)
  21. Smith, J.T. (2008-02-23). "Is Chernobyl radiation really causing negative individual and population-level effects on barn swallows?". Biology Letters. 4 (1): 63–64. doi:10.1098/rsbl.2007.0430. PMC 2412919. PMID 18042513. Retrieved 2009-09-23.
  22. Møller, A. P. (2008). "Anecdotes and empirical research in Chernobyl". Biology Letters. 4 (1): 65. doi:10.1098/rsbl.2007.0528. {{cite journal}}: Unknown parameter |coauthors= ignored (|author= suggested) (help)
  23. Danchenko, Maksym (2009-06-05). "Proteomic Analysis of Mature Soybean Seeds from the Chernobyl Area Suggests Plant Adaptation to the Contaminated Environment". Journal of Proteome Research. 8 (6): 2915–2922. doi:10.1021/pr900034u. PMID 19320472. {{cite journal}}: Unknown parameter |coauthors= ignored (|author= suggested) (help)
  24. ^ Kovalchuk, Igor (2004-05-01). "Molecular Aspects of Plant Adaptation to Life in the Chernobyl Zone". Plant Physiol. 135 (1): 357–363. doi:10.1104/pp.104.040477. PMC 429389. PMID 15133154. Retrieved 2009-09-24. {{cite journal}}: Unknown parameter |coauthors= ignored (|author= suggested) (help) Cite error: The named reference "Kovalchuk1" was defined multiple times with different content (see the help page).
  25. Boubriak, I. I. (2008-01-01). "Adaptation and Impairment of DNA Repair Function in Pollen of Betula verrucosa and Seeds of Oenothera biennis from Differently Radionuclide-contaminated Sites of Chernobyl". Ann Bot. 101 (2): 267–276. doi:10.1093/aob/mcm276. PMC 2711018. PMID 17981881. Retrieved 2009-09-24. {{cite journal}}: Unknown parameter |coauthors= ignored (|author= suggested) (help)
  26. ^ Dusha-Gudym, Sergei I. (August 1992). "Forest Fires on the Areas Contaminated by Radionuclides from the Chernobyl Nuclear Power Plant Accident". IFFN. Global Fire Monitoring Center (GFMC). pp. No. 7, p. 4–6. Retrieved 2008-06-18.
  27. Template:PDFlink
  28. Davidenko, Eduard P. (January 1994). "News from the Forest Fire Situation in the Radioactively Contaminated Regions". {{cite web}}: Unknown parameter |coauthors= ignored (|author= suggested) (help)
  29. Antonov, Mikhail (2002-09-18). "Radioactive fires threaten Russia and Europe". Pravda.ru. {{cite web}}: Unknown parameter |coauthors= ignored (|author= suggested) (help)
  30. Yoschenko et al., Journal of Environmental Radioactivity, 2006, 86, 143–163.
  31. Template:PDFlink
  32. Template:PDFlink
  33. Allard, Gillian. "Fire prevention in radiation contaminated forests". Forestry Department, FAO. Retrieved 2008-06-18.
  34. ^ Deutsche Welle (August 11, 2010). "Russian fires hit Chernobyl-affected areas, threatening recontamination".
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