This report reflected another

This report reflected another view of the main reasons for the accident, presented in Appendix I. According to this account, the operators' actions in turning off the Emergency Core Cooling System, interfering with the settings on the protection equipment, and blocking the level and pressure in the separator drum did not contribute to the original cause of the accident and its magnitude, although they may have been a breach of regulations. ^{Sony VAIO VPCCW21FX/B Battery}

Turning off the emergency system designed to prevent the two turbine generators from stopping was not a violation of regulations.^[23]Human factors contributed to the conditions that led to the disaster. These included operating the reactor at a low power level – less than 700 MW – a level documented in the run-down test program, and operating with a small operational reactivity margin (ORM). ^{Sony VAIO VPCCW21FX/L Battery}

The 1986 assertions of Soviet experts notwithstanding, regulations did not prohibit operating the reactor at this low power level.^[23]:18However, regulations did forbid operating the reactor with a small margin of reactivity. Yet "post-accident studies have shown that the way in which the real role of the ORM is reflected in the Operating Procedures and design documentation for the RBMK-1000 is extremely contradictory, ^{Sony VAIO VPCCW21FX/R Battery}

" and furthermore, "ORM was not treated as an operational safety limit, violation of which could lead to an accident."According to the INSAG-7 Report, the chief reasons for the accident lie in the peculiarities of physics and in the construction of the reactor. There are two such reasons:The reactor had a dangerously large positive void coefficient. The void coefficient is a measurement of how a reactor responds to increased steam formation in the water coolant. ^{Sony VAIO VPCCW21FX/W Battery}

Most other reactor designs have a negative coefficient, i.e. the nuclear reaction rate slows when steam bubbles form in the coolant, since as the vapor phase in the reactor increases, fewer neutrons are slowed down. Faster neutrons are less likely to split uranium atoms, so the reactor produces less power (a negative feed-back). Chernobyl's RBMK reactor, however, used solid graphite as a neutron moderator to slow down the neutrons, ^{Sony VAIO VPCCW26EC Battery}

and the water in it, on the contrary, acts like a harmful neutron absorber. Thus neutrons are slowed down even if steam bubbles form in the water. Furthermore, because steam absorbs neutrons much less readily than water, increasing the intensity of vaporization means that more neutrons are able to split uranium atoms, increasing the reactor's power output. ^{Sony VAIO VPCCW26FX/B Battery}

This makes the RBMK design very unstable at low power levels, and prone to suddenly increasing energy production to a dangerous level. This behavior is counter-intuitive, and this property of the reactor was unknown to the crew.

A more significant flaw was in the design of the control rods that are inserted into the reactor to slow down the reaction. ^{Sony VAIO VPCCW28EC Battery}

In the RBMK reactor design, the lower part of each control rod was made of graphite and was 1.3 meters shorter than necessary, and in the space beneath the rods were hollow channels filled with water. The upper part of the rod, the truly functional part that absorbs the neutrons and thereby halts the reaction, was made of boron carbide. With this design, ^{Sony VAIO VPCCW28FJ/P Battery}

when the rods are inserted into the reactor from the uppermost position, the graphite parts initially displace some water (which absorbs neutrons, as mentioned above), effectively causing less neutrons to be absorbed initially. Thus for the first few seconds of control rod activation, reactor power output is increased, rather than reduced as desired. This behavior is counter-intuitive and was not known to the reactor operators. ^{Sony VAIO VPCCW28FJ/R Battery}

Other deficiencies besides these were noted in the RBMK-1000 reactor design, as were its non-compliance with accepted standards and with the requirements of nuclear reactor safety.

Both views were heavily lobbied by different groups, including the reactor's designers, power plant personnel, and the Soviet and Ukrainian governments. ^{Sony VAIO VPCCW28FJ/W Battery}

According to the IAEA's 1986 analysis, the main cause of the accident was the operators' actions. But according to the IAEA's 1993 revised analysis the main cause was the reactor's design.^[74] One reason there were such contradictory viewpoints and so much debate about the causes of the Chernobyl accident was that the primary data covering the disaster, as registered by the instruments and sensors, were not completely published in the official sources. ^{Sony VAIO VPCCW29FJ/W Battery}

Once again, the human factor had to be considered as a major element in causing the accident. INSAG notes that both the operating regulations and staff handled the disabling of the reactor protection easily enough: witness the length of time for which the ECCS was out of service while the reactor was operated at half power. INSAG's view is that it was the operating crew's deviation from the test program that was mostly to blame. ^{Sony VAIO VPCCW2AFJ Battery}

"Most reprehensibly, unapproved changes in the test procedure were deliberately made on the spot, although the plant was known to be in a very different condition from that intended for the test."^[23]:24

As in the previously released report INSAG-1, close attention is paid in report INSAG-7 to the inadequate (at the moment of the accident) "culture of safety" at all levels. ^{Sony VAIO VPCCW2AHJ Battery}

Deficiency in the safety culture was inherent not only at the operational stage but also, and to no lesser extent, during activities at other stages in the lifetime of nuclear power plants (including design, engineering, construction, manufacture and regulation). The poor quality of operating procedures and instructions, and their conflicting character, put a heavy burden on the operating crew, including the Chief Engineer. ^{Sony VAIO VPCCW2S1E Battery}

"The accident can be said to have flowed from a deficient safety culture, not only at the Chernobyl plant, but throughout the Soviet design, operating and regulatory organizations for nuclear power that existed at that time."Four hundred times more radioactive material was released than had been by the atomic bombing of Hiroshima. The disaster released 1/100 to 1/1000 of the total amount of radioactivity released by nuclear weapons testing during the 1950s and 1960s.^{Sony VAIO VPCCW2S1E/B Battery}

Approximately 100,000 km² of land was significantly contaminated with fallout, the worst hit regions being inBelarus, Ukraine and Russia^[83] Slighter levels of contamination were detected over all of Europe except for the Iberian Peninsula.

The initial evidence that a major release of radioactive material was affecting other countries came not from Soviet sources, ^{Sony VAIO VPCCW2S1E/L Battery}

but from Sweden, where on the morning of 28 April^[86] 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.^[87]

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 28 April led to the first hint of a serious nuclear problem in the western Soviet Union. ^{Sony VAIO VPCCW2S1E/P Battery}

Hence the evacuation of Pripyat on 27 April 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.

Contamination from the Chernobyl accident was scattered irregularly depending on weather conditions, ^{Sony VAIO VPCCW2S1E/R Battery}

much of it deposited on mountainous regions such as theAlps, Wales and the Scottish Highlands, where adibatic cooling caused rainfall. The resulting patches of contamination could be highly localised, and water-flows across the ground contributed further to large variations in radioactivity over small areas. Sweden and Norway also received heavy fallout when the contaminated air collided with a cold front, bringing rain. ^{Sony VAIO VPCCW2S1E/W Battery}

Rain was purposely seeded over 10,000 km² of the Belorussian SSR by the Soviet air force to remove radioactive particles from clouds heading toward highly populated areas. Heavy, black-coloured rain fell on the city of Gomel.^[91] Reports from Soviet and Western scientists indicate that Belarus received about 60% of the contamination that fell on the former Soviet Union. ^{Sony VAIO VPCCW2S5C CN1 Battery}

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. ^{Sony VAIO VPCF112FX/B Battery}

Recently published data from a long-term monitoring program (The Korma Report)^[93] shows 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. ^{Sony VAIO VPCF115FG/B Battery}

In France some officials stated that the Chernobyl accident had no adverse effects.^[94] 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. ^{Sony VAIO VPCF116FGBI Battery}

Like many other releases of radioactivity into the environment, the Chernobyl release was controlled by the physical and chemical properties of the radioactive elements in the core. While the general population often perceives plutonium as a particularly dangerous nuclear fuel, its effects are almost eclipsed by those of its fission products. ^{Sony VAIO VPCF117FJ/W Battery}

Particularly dangerous are highly radioactive compounds that accumulate in the food chain, such as some isotopes of iodine and strontium.Two reports on the release of radioisotopes from the site were made available, one by the OSTI and a more detailed report by the OECD, both in 1998.At different times after the accident, differentisotopes were responsible for the majority of the external dose. ^{Sony VAIO VPCF117HG/BI Battery}

The dose that was calculated is that received from external gamma irradiation for a person standing in the open. The dose to a person in a shelter or the internal dose is harder to estimate.

The release of radioisotopes from the nuclear fuel was largely controlled by their boiling points, and the majority of the radioactivity present in the core was retained in the reactor. ^{Sony VAIO VPCF118FJ/W Battery}

All of the noble gases, including krypton and xenon, contained within the reactor were released immediately into the atmosphere by the first steam explosion.55% of the radioactive iodine in the reactor, containing about 1760 PBq or 400 kg of I-131, was released, as a mixture of vapor, solid particles, and organic iodine compounds.Caesium (85 PBq Cs-137^[98]) and tellurium were released in aerosol form. ^{Sony VAIO VPCF119FC Battery}

An early estimate for fuel material released to the environment was 3 ± 1.5%; this was later revised to 3.5 ± 0.5%. This corresponds to the atmospheric emission of 6 t of fragmented fuel.Total atmospheric release is estimated at 5200 PBq.Two sizes of particles were released: small particles of 0.3 to 1.5 micrometers (aerodynamic diameter) and large particles of 10 micrometers. ^{Sony VAIO VPCF119FC/BI Battery}

The large particles contained about 80% to 90% of the released nonvolatile radioisotopes zirconium-95, niobium-95, lanthanum-140, cerium-144 and the transuranic elements, including neptunium, plutonium and the minor actinides, embedded in a uranium oxide matrix.

In the aftermath of the accident, 237 people suffered from acute radiation sickness (ARS), of whom 31 died within the first three months. ^{Sony VAIO VPCF119FJ/BI Battery}

Most of the victims were fire and rescue workers trying to bring the accident under control, who were not fully aware of how dangerous the exposure to radiation in the smoke was. Whereas, in the World Health Organization's 2006 report of the Chernobyl Forum expert group on 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. ^{Sony VAIO VPCF11AFJ Battery}

No further ARS-related deaths were identified in the general population affected by the disaster. Of the 72,000 Russian Emergency Workers being studied, 216 non-cancer deaths are attributed to the disaster, between 1991 and 1998.Of all 66,000 Belarusian emergency workers, by the mid-1990s only 150 (roughly 0.2%) were reported by their government as having died. ^{Sony VAIO VPCF11AGJ Battery}

In contrast, 5,722 casualties were reported among Ukrainian clean-up workers up to the year 1995, by the National Committee for Radiation Protection of the Ukrainian Population.

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. ^{Sony VAIO VPCF11AHJ Battery}

Some 135,000 people were evacuated from the area, including 50,000 from Pripyat.

The 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, which at the time supplied water to Kiev's 2.4 million residents, and was still in spring flood when the accident occurred. ^{Sony VAIO VPCF11JFX/B Battery}

The radioactive contamination of aquatic systems therefore became a major problem in the immediate aftermath of the accident.^[102] In the most affected areas of Ukraine, levels of radioactivity (particularly from radionuclides ¹³¹I, ¹³⁷Cs and ⁹⁰Sr) in drinking water caused concern during the weeks and months after the accident,^[102] though officially it was stated that all contaminants had settled to the bottom "in an insoluble phase" and would not dissolve for 800–1,000 years. ^{Sony VAIO VPCF11M1E Battery}

Guidelines for levels of radioiodine in drinking water were temporarily raised to 3,700 Bq/L, allowing most water to be reported as safe,^[102] and a year after the accident it was announced that even the water of the Chernobyl plant's cooling pond was within acceptable norms. Despite this, two months after the disaster the Kiev water supply was abruptly switched from the Dnieper to the Desna River. ^{Sony VAIO VPCF11M1E/H Battery}

Meanwhile, massive silt traps were constructed, along with an enormous 30m-deep underground barrier to prevent groundwater from the destroyed reactor entering the Pripyat River.^[101]:65–7

Bio-accumulation of radioactivity in fish^[103] 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.^{[102] Sony VAIO VPCF11MFX/B Battery}

Guideline maximum levels for radiocaesium in fish vary from country to country but are approximately 1,000 Bq/kg in the European Union.^[104] In the Kiev Reservoir in Ukraine, concentrations in fish were several thousand Bq/kg during the years after the accident.In small "closed" lakes in Belarus and the Bryansk region of Russia, concentrations in a number of fish species varied from 100 to 60,000 Bq/kg during the period 1990–92.^{[105] Sony VAIO VPCF11S1E Battery}

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.

Groundwater was not badly affected by the Chernobyl accident since radionuclides with short half-lives decayed away long before they could affect groundwater supplies, <sup>Sony VAIO VPCF11S1E/B Battery

Sony VAIO VPCF11Z1E Battery</sup>

and longer-lived radionuclides such as radiocaesium and radiostrontium were adsorbed to surface soils before they could transfer to groundwater.^[106] 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), ^{Sony VAIO VPCF11Z1E/BI Battery}

the IAEA Chernobyl Report^[106] argues that this is not significant in comparison to current levels of washout of surface-deposited radioactivity.

After the disaster, four square kilometers of pine forest directly downwind of the reactor turned reddish-brown and died, earning the name of the "Red Forest".^[107] Some animals in the worst-hit areas also died or stopped reproducing. ^{Sony VAIO VPCF11ZHJ Battery}

Most domestic animals were removed 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.^[108] Some cattle on the same island died and those that survived were stunted because of thyroid damage. The next generation appeared to be normal.^{[108] Sony VAIO VPCF127HGBI Battery}

A robot sent into the reactor itself has returned with samples of black, melanin-rich radiotrophic fungithat are growing on the reactor's walls.Of the 440,350 wild boar killed in the 2010 hunting season in Germany, over 1,000 were found to be contaminated with levels of radiation above the permitted limit of 600 bequerels, due to residual radioactivity from Chernobyl. ^{Sony VAIO VPCF137HG/BI Battery}

Germany has "banned wild game meat because of contamination linked to radioactive mushrooms".^[111]

The Norwegian Agricultural Authority reported that in 2009 a total of 18,000 livestock in Norway needed to be given uncontaminated feed for a period of time before slaughter in order to ensure that their meat was safe for human consumption. ^{Sony VAIO VPCS111FM/S Battery}

This was due to residual radioactivity from Chernobyl in the plants they graze on in the wild during the summer. The after-effects of Chernobyl were expected to be seen for a further 100 years, although the severity of the effects would decline over that period.^[112] In Britain and Norway, as of 2011, "slaughter restrictions remain for sheep raised on pasture contaminated by radiation fallout".Sony VAIO VGN-SR41M/P Battery

The Chernobyl Forum first met on 3 February 2003 for a three day meeting. It consisted of the International Atomic Energy Agency (IAEA), other United Nations organizations (FAO, UN-OCHA, UNDP, UNEP, UNSCEAR, WHO, and the World Bank), and the governments of Belarus, Russia, and Ukraine. A second meeting was held on 10–11 March 2004, and a third on 18–20 April 2005. Sony VAIO VGN-SR41M/S Battery

The aim of the Forum was to "scientifically clarify the radiological environmental and health consequences of the Chernobyl accident, to provide advice on and to contribute to a scientifically sound remediation and health care programmes, and to consider the necessity of, and opportunities for continued research/learning lessons." Sony VAIO VGN-SR49VN/H Battery

A report was published by Chernobyl Forum in 2005 which revealed thyroid cancer among children to be one of the main health impacts from the Chornobyl accident. In that publication more than 4000 cases were reported, and that there was no evidence of an increase in solid cancers or leukemia. It said that there was an increase in psychological problems among the affected population. Sony VAIO VGN-SR51B/P Battery