51°23′23″N 30°5′58″E / 51.38972°N 30.09944°E / 51.38972; 30.09944

File:Chernobyl Disaster.jpg
Chernobyl reactor 4 after the disaster, showing the extensive damage to the main reactor hall (image center) and turbine building (image lower left)
File:ChernobylPlant.jpg
The early stages of construction of the sarcophagus.
The Chernobyl Nuclear Power Plant is located near the city of Pripyat in north central Ukraine.

The Chernobyl disaster was a major accident at the Chernobyl Nuclear Power Plant on April 26, 1986 at 01:23 a.m., consisting of an explosion at the plant and subsequent radioactive contamination of the surrounding geographic area. The power plant is located at 51°23′23″N 30°5′58″E / 51.38972°N 30.09944°E / 51.38972; 30.09944, near Pripyat, Ukraine, at the time part of the Soviet Union. It is regarded as the worst accident ever in the history of nuclear power. A plume of radioactive fallout drifted over parts of the western Soviet Union, Eastern and Western Europe, Scandinavia, the UK, Ireland and eastern North America. Large areas of Ukraine, Belarus, and Russia were badly contaminated, resulting in the evacuation and resettlement of over 336,000 people. About 60% of the radioactive fallout landed in Belarus, according to official post-Soviet data.[1]

The accident raised concerns about the safety of the Soviet nuclear power industry, slowing its expansion for a number of years, while forcing the Soviet government to become less secretive. The now-independent countries of Russia, Ukraine, and Belarus have been burdened with the continuing and substantial decontamination and health care costs of the Chernobyl accident. It is difficult to tally accurately the number of deaths caused by the events at Chernobyl, as the Soviet-era cover-up made it difficult to track down victims. Lists were incomplete, and Soviet authorities later forbade doctors to cite "radiation" on death certificates. Most of the expected long-term fatalities, especially those from cancer, have not yet actually occurred, and will be difficult or even impossible to attribute specifically to the accident.

Estimates and figures vary widely. The 2005 report prepared by the Chernobyl Forum, led by the International Atomic Energy Agency (IAEA) and World Health Organization (WHO), attributed 56 direct deaths (47 accident workers, and nine children with thyroid cancer), and estimated that as many as 9,000 people among the approximately 6.6 million most highly exposed, may die from some form of cancer (one of the induced diseases).[2] Nearly 20 years after the disaster, according to the Chernobyl Forum, no evidence of increases in the solid cancers and, possibly more significantly, none of the widely expected increases in leukemia have been found in the population.[3]

The nuclear power plant

Main article: Chernobyl Nuclear Power Plant

The Chernobyl station ( V.I. Lenin Memorial Chernobyl Nuclear Power Station) (51°23′14″N 30°06′41″E / 51.38722°N 30.11139°E / 51.38722; 30.11139) is located near the town of Pripyat, Ukraine, 18 km northwest of the city of Chernobyl, 16 km from the border of Ukraine and Belarus, and about 110 km north of Kiev. The station consisted of four reactors of type RBMK-1000, each capable of producing 1 gigawatt (GW) of electric power (3.2 GW of thermal power), and the four together produced about 10% of Ukraine's electricity at the time of the accident. Construction of the plant began in the 1970s, with reactor no. 1 commissioned in 1977, followed by no. 2 (1978), no. 3 (1981), and no. 4 (1983). Two more reactors, no. 5 and 6, capable of producing 1 GW each, were under construction at the time of the accident.

The accident

On Saturday April 26, 1986 at 1:23:58 a.m. reactor 4 suffered a catastrophic steam explosion that resulted in a fire, a series of additional explosions, and a nuclear meltdown. The accident can be thought of as an extreme version of the SL-1 accident in the United States in 1961 where the core of a reactor was destroyed (killing three men) spreading radioactivity through the inside of the building that SL-1 was in.

Causes

There are two conflicting official theories about the cause of the accident. The first was published in August 1986 and effectively placed the blame solely on the power plant operators. The second theory, proposed by Valeri Legasov and published in 1991, attributed the accident to flaws in the RBMK reactor design, specifically the control rods. Both commissions were heavily lobbied by different groups, including the reactor's designers, power plant personnel, and by the Soviet and Ukrainian governments.

Another important factor contributing to the accident was that the operators were not informed about problems with the reactor. According to one of them, Anatoliy Dyatlov, the designers knew that the reactor was dangerous in some conditions but intentionally concealed this information. Contributing to this was that the plant's management was largely composed of non-RBMK-qualified personnel: the director, V.P. Bryukhanov, had experience and training in a coal-fired power plant. His chief engineer, Nikolai Fomin, also came from a conventional power plant. Dyatlov, deputy chief engineer of reactors 3 and 4, had only "some experience with small nuclear reactors", namely smaller versions of the VVER nuclear reactors that were designed for the Soviet Navy's nuclear submarines.

In particular:

The IAEA's 1986 analysis attributed the main cause of the accident to the operators' actions. But in January 1993, the IAEA issued a revised analysis, attributing the main cause to the reactor's design.

Test plan

During the daytime of April 25, 1986, reactor 4 was scheduled to be shut down for maintenance. It had been decided to use this occasion as an opportunity to test the ability of the reactor's turbine generator to generate sufficient electricity to power the reactor's safety systems (in particular, the water pumps) in the event of a loss of external electric power. This type of reactor requires water to be continuously circulated through the core, as long as the nuclear fuel is present. Chernobyl's reactors have a pair of diesel generators available as standby, but these do not activate instantaneously – the reactor was, therefore, to be used to spin up the turbine, at which point the turbine would be disconnected from the reactor and allowed to spin under its own rotational momentum, and the aim of the test was to determine whether the turbines in the rundown phase could power the pumps while the generators were starting up. The test was successfully carried out previously on another unit (with all safety provisions active) with negative results – the turbines did not generate sufficient power, but additional improvements were made to the turbines, which prompted the need for another test.

Prior to accident

As conditions to run this test were prepared during the daytime of April 25, and the reactor electricity output had been gradually reduced to 50%, a regional power station unexpectedly went offline. The Kiev grid controller requested that the further reduction of output be postponed, as electricity was needed to satisfy the evening peak demand. The plant director agreed and postponed the test to comply. The ill-advised safety test was then left to be run by the night shift of the plant, a skeleton crew who would be working Reactor 4 that night and the early part of the next morning.[4]

At 11:00pm, April 25, the grid controller allowed the reactor shut-down to continue. The power output of reactor 4 was to be reduced from its nominal 3.2 GW thermal to 0.7–1.0 GW thermal in order to conduct the test at the prescribed lower level of power.[5] However, the new crew were unaware of the prior postponement of the reactor slowdown, and followed the original test protocol, which meant that the power level was decreased too rapidly. In this situation, the reactor produced more of the nuclear poison product xenon-135 (the xenon production rate:xenon loss rate ratio initially goes higher during a reactor power down), which dropped the power output to 30 MW thermal (approximately 5% of what was expected). The operators believed that the rapid fall in output was due to malfunctioning of one of the automatic power regulators, not because of reactor poisoning. In order to increase the reactivity of the underpowered reactor (caused unknowingly by neutron absorption of excess xenon-135), automatic control rods were pulled out of the reactor beyond what is allowed under safety regulations. Despite this breach, the reactor's power only increased to 200MW, still less than a third of the minimum required for the experiment. Despite this, the crew's management chose to continue the experiment. As part of the experiment, at 1:05 a.m. on April 26 the water pumps that were to be driven by the turbine generator were turned on; increasing the water flow beyond what is specified by safety regulations. The water flow increased at 1:19 a.m. – since water also absorbs neutrons, this further increase in the water flow necessitated the removal of the manual control rods, producing a very precarious operating situation where coolant and xenon-135 was substituting some of the role of the control rods of the reactor.

Fatal experiment

The area was evacuated – but according to many people, not quickly enough. This is the now famous Pripyat Ferris wheel as seen from inside the town's Palace of Culture.

At 1:23:04 the experiment began. The unstable state of the reactor was not reflected in any way on the control panel, and it does not appear that anyone in the reactor crew was fully aware of any danger. Electricity to the water pumps was shut off and, as the momentum of the turbine generator drove them, the water flow rate decreased, decreasing the absorption of neutrons by the coolant. The turbine was disconnected from the reactor, increasing the level of steam in the reactor core. As the coolant heated, pockets of steam formed voids in the coolant lines. Due to the RBMK reactor-type's large positive void coefficient, the steam bubbles increased the power of the reactor rapidly, and the reactor operation became progressively less stable and more dangerous. As the reaction continued, the excess xenon-135 was burnt up, increasing the number of neutrons available for fission. The prior removal of manual and automatic control rods had no substitute, leading to a runaway reaction.

At 1:23:40 the operators pressed the AZ-5 ("Rapid Emergency Defense 5") button that ordered a "SCRAM" – a shutdown of the reactor, fully inserting all control rods, including the manual control rods that had been incautiously withdrawn earlier. It is unclear whether it was done as an emergency measure, or simply as a routine method of shutting down the reactor upon the completion of an experiment (the reactor was scheduled to be shut down for routine maintenance). It is usually suggested that the SCRAM was ordered as a response to the unexpected rapid power increase. On the other hand, Anatoly Dyatlov, chief engineer at the nuclear station at the time of the accident, writes in his book:

"Prior to 01:23:40, systems of centralized control … didn't register any parameter changes that could justify the SCRAM. Commission … gathered and analyzed large amount of materials and, as stated in its report, failed to determine the reason why the SCRAM was ordered. There was no need to look for the reason. The reactor was simply being shut down upon the completion of the experiment."[6]

The slow speed of the control rod insertion mechanism (18–20 seconds to complete), and the flawed rod design which initially reduces the amount of coolant present, meant that the SCRAM actually increased the reaction rate. At this point an energy spike occurred and some of the fuel rods began to fracture, placing fragments of the fuel rods in line with the control rod columns. The rods became stuck after being inserted only one-third of the way, and were therefore unable to stop the reaction. At this point nothing could be done to stop the disaster. By 1:23:47 the reactor jumped to around 30 GW, ten times the normal operational output. The fuel rods began to melt and the steam pressure rapidly increased, causing a large steam explosion. Generated steam traveled vertically along the rod channels in the reactor, displacing and destroying the reactor lid, rupturing the coolant tubes and then blowing a hole in the roof.[7] After part of the roof blew off, the inrush of oxygen, combined with the extremely high temperature of the reactor fuel and graphite moderator, sparked a graphite fire. This fire greatly contributed to the spread of radioactive material and the contamination of outlying areas.

Radioactive Release

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 its core. While the general population often perceives plutonium as particularly dangerous, its effects are almost eclipsed by those of its fission products. Particularly dangerous are highly radioactive compounds that accumulate in the food chain, such as some isotopes of iodine and strontium. For more information about the release of radioactivity from power reactors, see fission products, nuclear fuel and nuclear fuel and reactor accidents.

The external gamma dose for a person in the open near the Chernobyl site.

A short report on the release of radioisotopes from the site is on the OSTI web site.[8] A more detailed report can be downloaded from the OECD web site's public library[9] as a 1.85MB PDF file. At different times after the accident, different isotopes were responsible for the majority of the external dose. The dose, which was calculated, is 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 the 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.

Two sizes of particles were released: small particles of 0.3 to 1.5 micrometers (aerodynamic diameter) and large of 10 micrometers. The large particles contained about 80% to 90% of the released nonvolatile radioisotopes (95Zr, 95Nb, 140La, 144Ce and the transuranic elements (neptunium, plutonium and the minor actinides) embedded in a uranium oxide matrix.

The contributions by the various isotopes to the dose (in air) in the contaminated area soon after the accident. This image was drawn using data from the OECD report, the Korean table of the isotopes and the second edition of 'The radiochemical manual'.

Immediate crisis management

The scale of the tragedy was exacerbated because plant workers and local administrators lacked preparation and proper equipment, which led to severe misassessments of the situation. The radiation levels in the worst-hit areas of the reactor building have been estimated to be 5.6 röntgen per second (R/s), which is equivalent to 20,000 röntgen per hour (R/h). A lethal dose is around 500 röntgen over 5 hours, so in some areas, unprotected workers received fatal doses within several minutes. However, at the time of the disaster, the plant's staff didn't know about the true radiation levels: A dosimeter capable of measuring up to 1,000 R/s was inaccessible due to the explosion, and another one broke when turned on. All remaining dosimeters had limits of 0.001 R/s and therefore read "off scale". Thus, the reactor crew could ascertain only that the radiation levels were somewhere above 0.001 R/s (3.6 R/h), while the true levels were 5,600 times higher in some areas.

Because of the fallacious low readings, the reactor crew chief Alexander Akimov assumed that the reactor was intact. The evidence of pieces of graphite and reactor fuel lying around the building was ignored, and the readings of another dosimeter brought in by 4:30 a.m. were dismissed under the assumption that the new dosimeter must have been defective. Akimov stayed with his crew in the reactor building until morning, trying to pump water into the reactor. None of them wore any protective gear. Most of them, including Akimov, died from radiation exposure within three weeks.

Shortly after the accident, firefighters arrived to try to extinguish the fires. The first one to the scene was a Chernobyl Power Station firefighter brigade under the command of Lieutenant Vladimir Pravik, who died on May 9, 1986. They were not told how dangerously radioactive the smoke and the debris were, and may not even have known the accident was anything more than a regular electrical fire: "We didn't know it was the reactor. No one had told us."[10] The fires on the roof of the station and the area around the building containing Reactor No. 4 were extinguished by 5 a.m., but many firefighters received high doses of radiation. The fire inside Reactor No. 4 continued to burn until the fire was extinguished by helicopters dropping materials like sand, lead, clay and boron onto the burning reactor.

The explosion and fire threw into the air not just the particles of the nuclear fuel but also far more dangerous radioactive elements like caesium-137, iodine-131, strontium-90 and other radionuclides. The residents of the surrounding area observed the radioactive cloud on the night of the explosion.

The government committee formed to investigate the accident, led by Valeri Legasov, arrived at Chernobyl in the evening of April 26. By that time two people were dead and 52 were hospitalized. During the night of April 26–April 27 – more than 24 hours after the explosion – the committee, faced with ample evidence of extremely high levels of radiation and a number of cases of radiation exposure, had to acknowledge the destruction of the reactor and order the evacuation of the nearby city of Pripyat. The evacuation began at 14:00, April 27. In order to reduce baggage, the residents were told that the evacuation would be temporary, lasting approximately three days. As a result, Pripyat still contains personal belongings that can never be moved due to radiation. From eyewitness accounts of the firefighters involved before they died (as reported on the BBC television series Witness), one described his experience of the radiation as "tasting like metal", and feeling a sensation similar to that of pins and needles all over his face.

The water that had hurriedly been pumped into the reactor building in a futile attempt to extinguish the fire had run down to the space underneath the reactor floor. Thus the smoldering fuel and other material on the reactor floor was starting to burn its way through this floor, melting the concrete and changing it to lava. This was made worse by materials being dropped from helicopters, which simply acted as a furnace to increase the temperatures further. If this material had come into contact with the water, it would have generated a thermal explosion, which would have arguably been worse than the initial reactor explosion itself. By many estimates, that would have rendered land in a radius of hundreds of miles from the plant radioactive.[11]

In order to prevent this, soldiers and workers (called "liquidators") were sent in as cleanup staff by the Soviet government. Two of these were sent in wet suits to open the sluice gates to vent the radioactive water, and thus prevent a thermal explosion.[12] They are thought to be engineers Alexei Ananenko (who knew where the valves were) and Valeri Bezpalov, accompanied by a third man, Boris Baranov, who provided them with light from a lamp, though this lamp failed, leaving them to find the valves by feeling their way along a pipe.[13]

The worst of the radioactive debris was collected inside what was left of the reactor. The reactor itself was covered with bags containing sand, lead and boric acid thrown off helicopters (some 5,000 tons during the week following the accident). By December 1986 a large concrete sarcophagus had been erected, to seal off the reactor and its contents.[14]

Many of the vehicles used by the "liquidators" remain scattered around the Chernobyl area to this day.[15]

The effects of the disaster

Main article: Chernobyl disaster effects

Immediate results

File:Evstafiev-chernobyl tragedy monument.jpg
A monument to the victims of the Chernobyl disaster at Moscow's Mitino cemetery, where some of the firefighters who battled the flames and later died of radiation exposure are buried. Photo by Mikhail Evstafiev

The nuclear meltdown produced a radioactive cloud which spread all over Europe.[16][17][18] The initial evidence that a major exhaust of radioactive material was affecting other countries came not from Soviet sources, but from Sweden, where on April 27 workers at the Forsmark Nuclear Power Plant (approximately 1100 km from the Chernobyl site) were found to have radioactive particles on their clothes. It was Sweden's search for the source of radioactivity, after they had determined there was no leak at the Swedish plant, which led to the first hint of a serious nuclear problem in the western Soviet Union. The rise of radiation levels had at time already been measured in Finland but it had not been published.

Contamination from the Chernobyl accident was not evenly spread across the surrounding countryside, but 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 TORCH 2006 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.

In Western Europe, measures were taken including seemingly arbitrary regulations pertaining to the legality of importation of certain foods but not others. In France some officials stated that the Chernobyl accident had no adverse effects – this was ridiculed as pretending that the radioactive cloud had stopped at the German and Italian borders.

Soviet badge awarded to liquidators.

Two hundred people were hospitalized immediately, of whom 31 died (28 of them died from acute radiation exposure) [citation needed]. Most of these were fire and rescue workers trying to bring the accident under control, who were not fully aware of how dangerous the radiation exposure (from the smoke) was (for a discussion of the more important isotopes in fallout see fission products). 135,000 people were evacuated from the area, including 50,000 from Pripyat. Health officials from the Nuclear Energy Agency have predicted that over the next 70 years there will be a 0.01% increase in cancer rates above the base rate in much of the population that was exposed to the 5–12 (depending on source) EBq of radioactive contamination released from the reactor. So far three people have died of thyroid cancer as a result of the accident.[19]

Soviet scientists reported that reactor 4 contained about 180–190 tonnes of uranium dioxide fuel and fission products. Estimates of the amount of this material that escaped range from 5 to 30%, but some liquidators who have actually been inside the sarcophagus and the reactor shell itself – e.g. Mr. Usatenko and Dr. Karpan [citation needed] – state that not more than 5–10% of the fuel remains inside; indeed, photographs of the reactor shell show that it is completely empty. Because of the intense heat of the fire, much of the ejected fuel was lofted high into the atmosphere, with no containment building to stop it, where it spread.[citation needed]

The "liquidators" received high doses of radiation. According to Soviet estimates, between 300,000 and 600,000 liquidators were involved in the cleanup of the 30-km evacuation zone around the reactor, but many of them entered the zone two years after the accident.[20]

Long-term health effects

Map showing caesium-137 contamination in Belarus, Russia, and Ukraine. In curies per square kilometer (1 curie is 37 gigabecquerels).

Right after the accident, the main health concern involved radioactive iodine, with a half-life of eight days. Today, there is concern about contamination of the soil with strontium-90 and caesium-137, which have half-lives of about 30 years. The highest levels of caesium-137 are found in the surface layers of the soil where they are absorbed by plants, insects and mushrooms, entering the local food supply. However, in 2006, hedgehogs from the area, an insectivorous species seem to have absorbed little if any radioactive material, whilst rodents are strongly radiating (20 millisieverts per day), although seem to suffer no ill effects.

Some persons in the contaminated areas were exposed to large thyroid doses of up to 50 grays (Gy) because of an intake of radioactive iodine-131, a relatively short-lived isotope with a half-life of eight days, but which concentrates in the thyroid gland. This would have been absorbed from contaminated milk produced locally, particularly in children. By 2002, more than 4000 thyroid cancer cases had been diagnosed in this group, and it is most likely that a large fraction of these thyroid cancers is attributable to radioiodine intake. [1]

Apart from the dramatic increase in thyroid cancer incidence among those exposed at a young age, there is no clearly demonstrated increase in the incidence of solid cancers or leukaemia due to radiation in the most affected populations. There was, however, an increase in psychological problems among the affected population, compounded by insufficient communication about radiation effects and by the social disruption and economic depression that followed the break-up of the Soviet Union. [2]

Soviet authorities started evacuating people from the area around the Chernobyl reactor 36 hours after the accident.[21][22] By May 1986, about a month later, all those living within a 30-kilometre (18 mile) radius of the plant – about 116,000 people – had been relocated. This region is often referred to as the Zone of alienation. However, radiation affected the area in a much wider scale than this 30 km radius.

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A monument to victims of Chernobyl disaster in Luhansk, Ukraine

The issue of long-term effects of Chernobyl disaster on civilians is controversial. Over 300,000 people were resettled because of the accident; millions lived and continue to live in the contaminated area. On the other hand, most of those affected received relatively low doses of radiation, there is little evidence of increased mortality – cancers or birth defects among them – and, when such evidence is present, existence of a causal link to radioactive contamination is uncertain. However, in 2000 the United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR) stated: "Apart from the substantial increase in thyroid cancer after childhood exposure observed in Belarus, in the Russian Federation and in Ukraine, there is no evidence of a major public health impact related to ionizing radiation 14 years after the Chernobyl accident. No increases in overall cancer incidence or mortality that could be associated with radiation exposure have been observed."[23]

Aside from obstacles posed by Soviet policies during and after the catastrophe, scientific studies may still be limited by a lack of democratic transparency. In Belarus, Yuri Bandazhevsky, a scientist who questioned the official estimates of Chernobyl's consequences and the relevance of the official maximum limit of 1000 Bq/kg, has allegedly been a victim of political repression. He was imprisoned from 2001 to 2005 on a bribery conviction, after his 1999 publication of reports critical of the official research being conducted into the Chernobyl incident.

Farming

Cows

Jiří Hála's textbook (Radioactivity, Ionizing Radiation and Nuclear Energy, ISBN 80-7302-053-X) explains how cattle only pass a minority of the strontium, cesium, plutonium and americium they ingest to the humans who consume milk and meat. For instance, for milk if the cow has a daily intake of 1000 Bq of the following isotopes then the milk will have the following activities. The meat and milk of cows was identified as a radioactive byproduct because of the extremely high amount of radioactive material that it contained.

Soil

Jiří Hála's text book states that soils vary greatly in their ability to bind radioisotopes, the clay particles and humic acids can alter the distribution of the isotopes between the soil water and the soil. The distribution coefficient Kd is the ratio of the soil's radioactivity (Bq g-1) to that of the soil water (Bq ml-1). If the radioactivity is tightly bonded to by the minerals in the soil then less radioactivity can be absorbed by crops and grass growing on the soil.

Environmental impacts

Impact on aquatic systems

Pripyat-Dnieper River-Reservoir system showing Chernobyl and Kiev with the Kiev Reservoir in between.

Rivers, lakes and reservoirs

The Chernobyl nuclear power plant lies next to the river Pripyat which feeds into the Dnieper 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.[24] 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.[24]

Bio-accumulation of radioactivity (particularly radiocaesium) in fish[25] 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.[24] Guideline maximum levels for radiocaesium in fish vary from country to country but are approximately 1000 Bq/kg or 1 kBq/kg in the European Union.[26] In the Kiev Reservoir in Ukraine, activity concentrations in fish were several thousand Bq/kg during the years after the accident.[25] In small "closed" lakes in Belarus and the Bryansk region of Russia, activity concentrations in a number of fish species varied from 0.1 to 60 kBq/kg during the period 1990-92.[27] The contamination of fish caused concern in the short term (months) for parts of the UK and Germany and in the long term (years-decades) in the Chernobyl affected areas of Ukraine, Belarus and Russia as well as in parts of Scandinavia.[24]

Groundwaters

Groundwaters were not badly affected by the Chernobyl accident since radionuclides with short half-lives decayed away a long time before they could affect groundwater supplies, and longer-lived radionuclides such as radiocaesium and radiostrontium were absorbed to surface soils before they could transfer to groundwaters.[28] Significant transfers of radionuclides to groundwaters have occurred from waste disposal sites in the 30 km exclusion zone around Chernobyl. Although there is a potential for off-site (i.e. out of the 30-km exclusion zone) transfer of radionuclides from these disposal sites, the IAEA Chernobyl Report[28] argues that this will not be significant in comparison to current levels of wash out of surface deposited radioactivity.

Marine systems

The nearest seas to Chernobyl are the Black Sea (approx. dist. 520 km) and the Baltic Sea (approx. dist. 750 km). The large distances from the reactor, and the huge dilution of deposited radioactivity in marine systems meant that concentrations of radioactivity were relatively low in comparison with freshwater systems.[28] The maximum radioactive fallout onto the Baltic Sea occurred in the northern Gulf of Bothnia and Gulf of Finland where 137Cs activity concentrations of up to 0.93 Bq/litre were observed.[29] By 1988-89, 137Cs activity concentrations were much more uniform being in the range 0.1-0.2 Bq/l.[29][30] Sr-90 only increased by 20% above pre-accident levels in this area.[29] In the Black Sea, radiocaesium activity concentrations were up to 0.2 Bq/l.[31] Inputs of radioactivity from rivers (primarily from the Danube and Dnieper rivers) to the Black Sea were much less significant than direct atmospheric fallout to the sea surface.[24]

Accumulation of radionuclides in animals and plants in marine systems is generally lower than in freshwater because of the much higher concentration of other elements in saline waters. Radiocaesium activity concentrations in fish in the Black and Baltic seas were less than 100 Bq/kg,[28] significantly lower than those typically observed in contaminated freshwater systems.

Food restrictions

An abandoned village near Pripyat, close to Chernobyl

In April 1986 several European countries, excluding France, had enforced food restrictions, most notably on mushrooms and milk. Twenty years after the catastrophe, restriction orders remain in place in the production, transportation and consumption of food contaminated by Chernobyl fallout, in particular caesium-137, in order to prevent them from entering the human food chain. In parts of Sweden and Finland, restrictions are in place on stock animals, including reindeer, in natural and near-natural environments. "In certain regions of Germany, Austria, Italy, Sweden, Finland, Lithuania and Poland, wild game, including boar and deer, wild mushrooms, berries and carnivore fish from lakes reach levels of several thousand Bq per kg of caesium-137", while "in Germany, caesium-137 levels in wild boar muscle reached 40,000 Bq/kg. The average level is 6800 Bq/kg, more than ten times the EU limit of 600 Bq/kg", according to the TORCH 2006 report. The European Commission has stated that "The restrictions on certain foodstuffs from certain Member States must therefore continue to be maintained for many years to come".[17]

In the United Kingdom, under powers in the 1985 Food and Environment Protection Act (FEPA), Emergency Orders have been used since 1986 to impose restrictions on the movement and sale of sheep exceeding the limit of 1000 Bq/kg. This safety limit was introduced in the UK in 1986 based on advice from the European Commission's Article 31 group of experts. However, the area covered by these restrictions has decreased by 95% since 1986: while it covered at first almost 9000 farms and over 4 million sheep, as of 2006 it covers 374 farms covering 750 km² and 200,000 sheep. Only limited areas of Cumbria, South Western Scotland and Northern Wales are still covered by restrictions.[32]

In Norway and Sweden the Sami people were affected by contaminated food. Their reindeer had been contaminated by eating lichens, which extract radioactive particles from the atmosphere along with their nutrients.[33]

Fauna and vegetation

After the disaster, four square kilometres of pine forest in the immediate vicinity of the reactor went ginger brown and died, earning the name of the "Red Forest", according to the BBC.[34] 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 from the power plant died when their thyroid glands were destroyed by radiation doses of 150-200 Sv.[35] Some cattle on the same island died and those that survived were stunted because of thyroid damage. The next generation appeared to be normal.[35]

In the years since the disaster, the exclusion zone abandoned by humans has become a haven for wildlife, with nature reserves declared (Belarus) or proposed (Ukraine) for the area. Many species of wild animals and birds, which were never seen in the area prior to the disaster, are now plentiful, due to the absence of humans in the area.[34]

Chernobyl after the disaster

File:Chernobyl2006.jpg
The completed (but crumbling) sarcophagus surrounding Chernobyl reactor 4, viewed from the northwest.

Following the accident, questions arose on the future of the plant and its eventual fate. All work on the unfinished reactors 5 and 6 were immediately halted. However, the trouble at the Chernobyl plant did not end with the disaster in reactor 4. The damaged reactor was sealed off and 200 meters 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. A fire broke out in reactor 2 in 1991; 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 December 15, 2000, then-President Leonid Kuchma personally turned off Reactor 3 in an official ceremony, effectively shutting down the entire plant. This transformed the Chernobyl plant from energy producer to energy consumer.

The need for future repairs

The sarcophagus is not an effective permanent enclosure for the destroyed reactor. Its hasty construction, in many cases conducted remotely with industrial robots, is aging badly. If it collapses another cloud of radioactive dust could be released. The sarcophagus is so badly damaged that a small earthquake or severe wind could cause the roof to collapse. A number of plans have been discussed for building a more permanent enclosure.

The radioactivity levels of different isotopes in the FCM, this has been back calculated by Russian workers to April 1986

According to official estimates, about 95% of the fuel (about 180 tonnes) in the reactor at the time of the accident 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) that flowed through the wrecked reactor building before hardening into a ceramic form.

It is unclear how long the ceramic form will retard the release of radioactivity. By conservative estimates, there is at least four tons of radioactive dust inside the shelter. However, more recent estimates have strongly questioned the previously held assumptions regarding the quantity of fuel remaining in the reactor. Some estimates now place the total quantity of fuel in the reactor at only about 70% of the original fuel load, however the IAEA maintains that less than 5% of the fuel was lost due to the explosion. Moreover, some liquidators estimate that only 5–10% of the original fuel load remains inside the sarcophagus.

File:Pictureofchernobyllavaflow.jpg
A photograph of one of the lava-flows formed by corium Fuel containing mass in the basement of the Chernobyl plant. 1 is the lava flow, 2 is concrete, 3 is a steam pipe and 4 is some electrical equipment

Water continues to leak into the shelter, spreading radioactive materials throughout the wrecked reactor building and potentially into the surrounding groundwater. The basement of the reactor building is slowly filling with water that is contaminated with nuclear fuel and is considered high-level radioactive waste. Though repairs were undertaken to fix some of the most gaping holes that had formed in the roof, it is by no means watertight, and will only continue to deteriorate.

The sarcophagus, while not airtight, heats up much more readily than it cools down. This is contributing to rising humidity levels inside the shelter. The high humidity inside the shelter continues to erode the concrete and steel of the sarcophagus.

Further, dust is becoming an increasing problem within the shelter. Radioactive particles of varying size, most of similar consistency to ash makes up a large portion of the debris inside the shelter. Convection currents compounded with increasing intrusion of outside airflow are increasingly stirring up and suspending the particles in the air inside the shelter. The installation of air filtration systems in 2001 has reduced the problem, but not eliminated it.

Some signs of a criticality were observed in June 24 1990–July 1 1990 inside room 304/3;[36] to avoid any further nuclear fission reaction, a neutron poison was added to this room.

Consequences of further collapse

The present shelter is constructed atop the ruins of the reactor building. The two "Mammoth Beams" that support the roof of the shelter are resting upon the structurally unsound west wall of the reactor building that was damaged by the accident. If the wall of the reactor building and subsequently 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 radiation into the environment.

A further threat to the shelter is the concrete slab that formed the "Upper Biological Shield" (UBS), and rested atop 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, in that only debris is supporting it in a nearly upright position. The collapse of the bioshield would further exacerbate the dust conditions in the shelter, would probably spread some quantity of radioactive materials out of the shelter, and could damage the shelter itself.

The sarcophagus was never designed to last for the 100 years needed to contain the radioactivity found within the remains of reactor 4. While present designs for a new shelter anticipate a lifetime of up to 100 years, that time is minuscule compared to the lifetime of the radioactive materials within the reactor. The construction and maintenance of a permanent sarcophagus that can completely contain the remains of reactor 4 will present a continuing task to engineers for many generations to come.

Grass and forest fires

It is known that fires can make the radioactivity mobile again.[37][38][39][40]

It has been reported by V.I. Yoschenko et. al., Journal of Environmental Radioactivity, 2006, 86, 143-163 that grass and forest fires can make the caesium, strontium, and plutonium become mobile in the air again. As an experiment, fires were set and the levels of radioactivity in the air down wind of these fires were measured.

File:Chernobylgrassfire2.png
The rate of delivery of radioactivity which has been made mobile by a grass fire. The distance unit is meters

The Chernobyl Fund and the Shelter Implementation Plan

File:New-Safe-Confinement.jpg
A conceptual rendering of the New Safe Confinement to replace the aging sarcophagus.

The Chernobyl Shelter Fund was established in 1997 at the Denver G7 summit to fund the Shelter Implementation Fund. The Shelter Implementation Plan (SIP) calls for transforming the site into an ecologically safe condition through stabilization of the sarcophagus, followed by construction of a New Safe Confinement (NSC). The original cost estimate for the SIP was US$768 million. The SIP is being managed by a consortium of Bechtel, Battelle, and Electricité de France, and conceptual design for the NSC consists of a movable arch, constructed away from the shelter to avoid high radiation, to be slid over the sarcophagus. The NSC is expected to be completed in early 2008, and will be the largest movable structure ever built.

Dimensions:

Controversy over human health effects

The majority of premature deaths caused by Chernobyl are expected to be the result of cancers and other diseases induced by radiation in the decades after the event. This will be the result of a large population (some studies have considered the entire population of Europe) exposed to relatively low doses of radiation increasing the risk of cancer across that population. It will be impossible to attribute specific deaths to Chernobyl, and many estimates indicate that the rate of excess deaths will be so small as to be statistically undetectable, even if the ultimate number of extra premature deaths is large. Furthermore, interpretations of the current health state of exposed populations vary. Therefore, estimates of the ultimate human impact of the disaster have relied on numerical models of the effects of radiation on health. Furthermore, the effects of low-level radiation on human health are not well understood, and so the models used, notably the linear no threshold model, are open to question.

Given these factors, several different studies of Chernobyl's health effects have come up with substantially different conclusions and are the subject of considerable scientific and political controversy. The following section presents some of the major studies on this topic.

The Chernobyl Forum report

In September 2005, a draft summary report by the Chernobyl Forum, comprising a number of UN agencies including the International Atomic Energy Agency (IAEA), the World Health Organization (WHO), the United Nations Development Programme (UNDP), other UN bodies and the Governments of Belarus, the Russian Federation and Ukraine, put the total predicted number of deaths due to the accident at 4000.[2] This death toll predicted by the WHO included the 47 workers who died of acute radiation syndrome as a direct result of radiation from the disaster and nine children who died from thyroid cancer, in the estimated 4000 excess cancer deaths expected among the 600,000 with the highest levels of exposure.[41] The full version of the WHO health effects report adopted by the UN, published in April 2006, included the prediction of 5000 additional fatalities from significantly contaminated areas in Belarus, Russia and Ukraine and predicted that, in total, 9000 will die from cancer among the 6.8 million most-exposed Soviet citizens.[42] This report is not free of controversy, and has been accused of trying to minimize the consequences of the accident.[43]

The TORCH report

Main article: TORCH report

File:Radioactive fallout caesium137 after Chernobyl.jpg
Map of radioactive fallout caesium-137 after Chernobyl catastrophe. In kilobecquerels per square meter (kBq/m²). Copyright J.Smith and N.A. Beresford, "Chernobyl: Catastrophe and Consequences" (Praxis, Chichester, 2005). See also an animated map of radioactive fallout caesium-137, produced by the French Institut de radioprotection et de sûreté nucléaire

In 2006 German Green Party Member of the European Parliament) Rebecca Harms, commissioned two UK scientists for an alternate report (TORCH ,The Other Report on Chernobyl) in response to the UN report. The report included areas not covered by the Chernobyl forum report, and also lower radiation doses. It predicted about 30,000 to 60,000 excess cancer deaths and warned that predictions of excess cancer deaths strongly depend on the risk factor used, and urged more research stating that large uncertainties made it difficult to properly assess the full scale of the disaster.

Greenpeace

Greenpeace claimed contradictions in the Chernobyl Forum reports, quoting a 1998 WHO study referenced in the 2005 report, which projected 212 dead from 72,000 liquidators.[44] In its report, Greenpeace suggested there will be 270,000 cases of cancer attributable to Chernobyl fallout, and that 93,000 of these will probably be fatal, but state in their report that "The most recently published figures indicate that in Belarus, Russia and Ukraine alone the accident could have resulted in an estimated 200,000 additional deaths in the period between 1990 and 2004." Blake Lee-Harwood, campaigns director at Greenpeace, believes that cancer was likely to be the cause of less than half of the final fatalities and that "intestinal problems, heart and circulation problems, respiratory problems, endocrine problems, and particularly effects on the immune system," will also cause fatalities. However, concern has been expressed about the methods used in compiling the Greenpeace report.[45][43]

The April 2006 IPPNW report

According to an April 2006 report by the German affiliate of the International Physicians for Prevention of Nuclear Warfare (IPPNW), entitled "Health Effects of Chernobyl", more than 10,000 people are today affected by thyroid cancer and 50,000 cases are expected. The report projected tens of thousands dead among the liquidators. In Europe, it alleges that 10,000 deformities have been observed in newborns because of Chernobyl's radioactive discharge, with 5000 deaths among newborn children. They also claimed that several hundreds of thousands of the people who worked on the site after the accident are now sick because of radiation, and tens of thousands are dead.[46]

Other studies and claims

French legal action

File:Cartcriirad.gif
Map of radioactive contamination in France following the catastrophe, in May 1986. Bcq by square meters. Corsica and South-East of France were some of the most affected regions.

Since March 2001 400 lawsuits have been filed in France against "X" by the French Association of Thyroid-affected People, including 200 in April 2006. These persons are affected by thyroid cancer or goitres, and have filed lawsuits alleging that the French government, at the time led by Prime Minister Jacques Chirac, had not adequately informed the population of the risks linked to the Chernobyl radioactive fallout. The complaint contrasts the health protection measures put in place in nearby countries (warning against consumption of green vegetables or milk by children and pregnant women) with the relatively high contamination suffered by the east of France and Corsica. Although the 2006 study by the French Institute of Radioprotection and Nuclear Safety said that no clear link could be found between Chernobyl and the increase of thyroid cancers in France, it also stated that papillary thyroid cancer had tripled in the following years.[57]

Comparison with other disasters

The Chernobyl disaster caused a few tens of immediate deaths due to radiation poisoning; thousands of premature deaths are predicted over the coming decades. Since it is often not possible to prove the origin of the cancer which causes a person's death, it is difficult to estimate Chernobyl's long-term death toll.

Other man-made disasters with very high death tolls include:

Comparisons with other various incidents concerning radioactivity are at Chernobyl compared to other radioactivity releases

Chernobyl in the popular consciousness

Main article: Chernobyl in the popular consciousness

The Chernobyl accident attracted a great deal of interest. Because of the distrust that many people had in the Soviet authorities (people both within and outside the USSR) a great deal of debate about the situation at the site occurred in the first world during the early days of the event. Due to defective intelligence based upon photographs taken from space, it was thought that unit number three had also suffered a dire accident.

In general the public knew little about radioactivity and radiation and as a result their degree of fear was increased. It was the case that many professionals (such as the spokesman from the UK NRPB) were mistrusted by journalists, who in turn encouraged the public to mistrust them.

It was noted in Chernobyl ten years on that different governments tried to set contamination level limits which were stricter than the next country. In the dash to be seen to be protecting the public from radioactive food, it was often the case that the risk caused by the modification of the nations' diet was greater and un-noticed.

References

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  2. ^ a b "IAEA Report". In Focus: Chernobyl. Retrieved 2006-03-29. Cite error: The named reference "iaea" was defined multiple times with different content (see the help page).
  3. ^ a b BBC "Horizon" programme 13 July 2006
  4. ^ BBC (British Broadcasting Corporation) Documentary entitled "Days That Shook The World"
  5. ^ Template:Ru icon The official program of the test.
  6. ^ Template:Ru icon Anatoly Dyatlov, Chernobyl. How did it happen? Chapter 4.
  7. ^ Template:Ru icon Фатахов Алексей Чернобыль как это было - 2
  8. ^ Chernobyl source term, atmospheric dispersion, and dose estimation, EnergyCitationsDatabase, November 1, 1989
  9. ^ OECD Papers Volume 3 Issue 1, OECD, 2003
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  12. ^ BBC.co.uk – The Chernobyl nightmare revisited
  13. ^ The Worst Accident in the World: Chernobyl: The End of the Nuclear Dream, 1986, p178, by Nigel Hawkes et al., IBSN0330297430
  14. ^ The Social Impact of the Chernobyl Disaster, 1988, p166, by David R. Marples ISBN 0-333-48198-4
  15. ^ "Chernobyl's silent graveyards". BBC News. BBC. 2006-04-20. ((cite news)): Check date values in: |date= (help)
  16. ^ Template:Fr "Tchernobyl, 20 ans après". RFI. 2006-04-24. Retrieved 2006-04-24. ((cite news)): Check date values in: |date= (help)
  17. ^ a b "TORCH report executive summary" (PDF). European Greens and UK scientists Ian Fairlie PhD and David Sumner. April 2006. Retrieved 2006-04-21. (page 3)
  18. ^ Template:Fr "Les leçons de Tchernobyl". IRSN. Retrieved 2006-12-16.
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  20. ^ Chapter IV: Dose estimates, Nuclear Energy Agency, 2002
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  22. ^ Chernobyl.info – Management of the disaster (humanitarian aspects)
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  26. ^ EURATOM Council Regulations No. 3958/87, No. 994/89, No. 2218/89, No. 770/90
  27. ^ Fleishman, D.G., et al., Cs-137 in fish of some lakes and rivers of the Bryansk region and North-West Russia in 1990-1992. Journal of Environmental Radioactivity, 1994. 24: p. 145-158
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  30. ^ Carlson, L. and E. Holm, Radioactivity in Fucus vesiculosus L. from the Baltic Sea following the Chernobyl accident. Journal of Environmental Radioactivity, 1992. 15: p. 231-248
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  36. ^ Russian Research Centre Kurchatov Institute
  37. ^ http://www.maik.ru/abstract/radchem/4/radchem0102_abstract.pdf
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  39. ^ Eduard P. Davidenko, Johann Georg Goldammer (January 1994). "News from the Forest Fire Situation in the Radioactively Contaminated Regions".
  40. ^ Mikhail Antonov, Maria Gousseva (2002-09-18). "Radioactive fires threaten Russia and Europe". Pravda.ru.
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  43. ^ a b "Spiegel, The Chernobyl body count controversy". In Focus: Chernobyl. Retrieved 2006-08-25. Cite error: The named reference "spiegel" was defined multiple times with different content (see the help page).
  44. ^ WHO Chernobyl report 2006 pdf
  45. ^ Wall Street Journal, 27 April 2006
  46. ^ "20 years after Chernobyl – The ongoing health effects". IPPNW. April , 2006. Retrieved 2006-04-24. ((cite web)): Check date values in: |date= (help)
  47. ^ Cite error: The named reference RFI 24 was invoked but never defined (see the help page).
  48. ^ Chernobyl 'caused Sweden cancers', BBC News, November 20, 2004
  49. ^ Increase of regional total cancer incidence in north Sweden due to the Chernobyl accident?
  50. ^ Template:Fr "Selon un rapport indépendant, les chiffres de l'ONU sur les victimes de Tchernobyl ont été sous-estimés (According to an independent report, UN numbers on Chernobyl's victims has been underestimated)". Le Monde. 2006-04-06. ((cite news)): Check date values in: |date= (help)
  51. ^ Scherb, Hagen. "Congenital Malformation and Stillbirth in Germany and Europe Before and After the Chernobyl Nuclear Power Plant Accident" (PDF). ((cite web)): Unknown parameter |coauthors= ignored (|author= suggested) (help)
  52. ^ Eds Busby, C C and Yablokov, A V (2006): Chernobyl: 20 Years On. Green Audit Press, Aberystwyth, UK. ISBN 1-897761-25-2
  53. ^ Abstract of April 2006 IARC report 'Estimates of the cancer burden in Europe from radioactive fallout from the Chernobyl accident'
  54. ^ IARC Press release on the report 'Estimates of the cancer burden in Europe from radioactive fallout from the Chernobyl accident'
  55. ^ Briefing document: Cancer burden in Europe following Chernobyl
  56. ^ Allison, Wade (24 November 2006). "How dangerous is ionising radiation?".
  57. ^ Template:Fr icon "Nouvelles plaintes de malades français après Tchernobyl". RFI. 2006-04-26. Retrieved 2006-04-26. ((cite news)): Check date values in: |date= (help) (includes Audio files, with an interview with Chantal Loire, president of the French Association of Thyroid-Affected People, as well as interviews with member of the CRIIRAD

See also

General information

Event and technical analysis

Witness accounts (before and after)

Books

Websites and other

Photography/videography/infography

Charitable and voluntary organizations concerned with the effects

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