Chernobyl has become more than just the name of the world's biggest ever nuclear disaster. Chernobyl has become a by-word for the dark side of modern life - how technology can fail and how the effects can by terrifying. The agents of disease were tasteless, colourless, odourless, but lethal - invisible assassins created by imperfect technology and human error. 20 years on from the original disaster, Greenpeace has published a report on its effects, which it believes are more extensive than previously thought. Because the disease agents are persistent, the effects of Chernobyl pass down the generations. Chernobyl's contamination is around 100 times the combined contamination of the Hiroshima and Nagasaki bombs. The effects of Hiroshima and Nagasaki are well documented, but the effects of Chernobyl remain speculative. 'The exact number of victims may never be known, but 3 million children require treatment,' said UN secretary-general, Kofi Annan. 'Not until 2016, at the earliest, will be known the full number of those likely to develop serious medical conditions.' Of course, the disaster was not confined to the area evacuated at the time. The clouds of radioactive material were carried by the weather over half the planet, but particularly northern Europe. Caesium-137 is the main radioactive agent from Chernobyl, and it has a half-life of more than 30 years. 'The radiological (and hence health) consequences of this nuclear accident will continue to be experienced for centuries to come,' reads the Greenpeace report. It continues: 'More than half of the Caesium-137 emitted as a result of the explosion was carried in the atmosphere to other European countries. At least 14 other countries in Europe [other than Ukraine, Belarus and Russia] (Austria, Sweden, Finland, Norway, Slovenia, Poland, Romania, Hungary, Switzerland, Czech Republic, Italy, Bulgaria, Republic of Moldova and Greece) were contaminated by radiation levels above the 1 Ci/m squared limit used to define areas as 'contaminated'.' Lower quantities of radiation are found around Europe, stretching to the Mediterranean and Asia. On the area immediately surrounding the Chernobyl site, the report states: 'In Belarus, Russia and the Ukraine alone the incident resulted in an estimated 200,000 additional deaths between 1990 and 2004.' Those who have been the main victims of the incident are: 'liquidators' or clean-up workers, generally drafted in to deal with the disaster; evacuees from the immediate area, 30-km around the site; residents from areas just outside the evacuation zone; and children from all these groups. In the contaminated areas bordering the site, rates of cancer rose by 40 per cent in Belarus as a whole, by more in the areas closest to Chernobyl, by 2.7 times in the contaminated areas of Russia, and by almost three times in the effected parts of Ukraine. For thyroid cancer, a 'trademark' cancer for the Chernobyl disaster, rates are still increasing. In the period 1988 to 1998, rates of thyroid cancer had doubled, but by 1994 had tripled in the Russian contaminated areas. However, the effects are not limited to thyroid cancer. Other diseases of the thyroid have resulted in a diverse collection of endocrine diseases. Rates of Leukaemia, other cancers, respiratory diseases, digestive diseases, blood vascular diseases and immune diseases have all increased by two to four times. As immune responses have been damaged, so-called Chernobyl-AIDS affects many, leaving newly born children with 2.9 times the number of infections experienced by a 'normal' child. Effects of contamination on the reproductive and urogenital systems have increased the incidences of low birth weight and stillbirths across central and northern Europe. In addition, rates of Down's Syndrome and birth defects such as Anencephaly, spina bifida, heart malformations, central nervous system malformations, and cleft palate or cleft lip have all increased across central and northern Europe since the Chernobyl disaster. 'It is reasonable to conclude that the Chernobyl accident has caused, and will continue to cause, a significant amount of morbidity and mortality across Europe, from Scandinavia, through Western Europe, south to where Turkey straddles the border between Europe and Asia, and beyond,' reads the report. 'It will be impossible to back-calculate the exposure to which the populations were exposed [...]. Studies should be carried out to clarify, as far as possible, the extent of morbidity and mortality resulting from the Chernobyl accident.' The remains of the Chernobyl site lie 100 km north of the present-day Ukrainian capital, Kiev, along the Ukraine-Belarus border. The power station had four water-cooled, graphite-moderated reactors. This means that graphite rods were used to keep the fission reaction of uranium-235 under control. During the night of 25/26 April 1986, the plant underwent a test. The management wanted to see whether in the event of power loss, the plant's turbines would be able to take over the running of the coolant pumps. In order to conduct the test, the reactor was powered down to one-quarter of its operating capacity, and the safety systems were deliberately shut down. The test did not go to plan. The power of the plant dropped by far too much - 99 per cent, so in order to make the test work, the power had to be increased slowly. As the power increased, an unexpected power surge occurred. The emergency shut-down failed and the reactor exploded. Precise reasons for the surge and subsequent explosion are not known, but the current thinking places the blame at a crucial design flaw - the graphite rods used to control the reaction. The role of the graphite rods is to moderate and control the fission reaction - when they are lowered into the reactor, the speed of the reaction slows. When the rods are lifted out, the speed of reaction increases. However, researchers believe that if such rods are rapidly inserted into the reactor, the speed of the reaction may actually increase suddenly. Furthermore, graphite, a form of carbon, is combustible. The 1000-ton reactor sealing cap was blown-off, and the graphite ignited, causing a huge fire. The contents of the reactor were thrown into the atmosphere. The fire raged for a further ten days, continuously throwing radioactive material into the atmosphere. By 1989, more than 800,000 people have been involved in clean-up operations around Chernobyl. 300,000 of those people have received radiation doses of 0.5 sieverts (Sv) or more. 0.5 Sv is a dose 500 times higher than the EU's recommended annual maximum dose. Deaths attributed to the disaster, and particularly the subsequent clean-up are extremely difficult to estimate. The then Soviet Union did not provide precise figures, only releasing information on any disaster on 28 April, around three days after the event, and describing it merely as an 'accident'. Once this news was released, researchers in Denmark and Germany were able to piece together what happened through their own research, and deduce that a 'maximum credible accident' had occurred at Chernobyl. Only on 23 May, four weeks after the initial accident, were Iodine tablets distributed. The tablets could have prevented radioactive iodine from entering the thyroid glands of those in the region. Four weeks later, the effect of the iodine tablets on the 130,000 evacuees would have been negligible. Incredibly, the Chernobyl reactor plant was only shut-down in 2000, and although the contaminated area directly around Chernobyl is restricted, a number of people have actually moved back into the area. Some 1500 people have moved back to within 15 km of Chernobyl, 50 to Chernobyl itself or nearby Pripyat, the now ghost-town, originally built to house 45,000 Chernobyl workers and their families.