What is an estimated impact of the Chernobyl disaster?

This extract from htp://www.world-nuclear.org/info/inf05.html gives some idea of the radiation effects. I have also included a few sentences on general radiation effect background

The March 1979 accident at Three Mile Island in the US caused some people near the plant to receive very minor doses of radiation, well under the internationally recommended level. Subsequent scientific studies found no evidence of any harm resulting from that exposure. In 1996, some 2,100 lawsuits claiming adverse health effects from the accident were dismissed for lack of evidence. Immediately after the Chernobyl disaster in 1986, much larger doses were experienced. All of the 22 who received more than 6,000 mSv died. Seven of the 23 who received 4,000-6,000 mSv also died, as did one of the 158 receiving 1,000-4,000 mSv. The main casualties were among the firefighters, including those who rapidly put out the initial small fires on the roof of the building. Apart from the residents of nearby Pripyat, who were evacuated within two days, some 24,000 people living within 15 km of the plant received an average of 450 mSv before they were evacuated. In June 1989 a group of experts from the World Health Organisation agreed that an incremental long term dose of 350 mSv should be the criterion for relocating people affected by the 1986 Chernobyl accident. This was considered a "conservative value which ensured that the risk to health from this exposure was very small compared with other risks over a lifetime". (For comparison, background radiation averages about 100-200 mSv over a lifetime in most places.) Over 100,000 people were relocated away from Chernobyl. About 185,000 people received significant radiation exposure, above 20 mSv, between 1986 and 1989. These continue to be monitored. In 1995 the World Health Organisation linked nearly 700 cases of thyroid cancer among children and adolescents to the Chernobyl accident, including 10 which resulted in death. So far no increase in leukaemia is discernable, but this is expected to become evident in the next few years. There has been no increase attributable to Chernobyl in congenital abnorm-alities, adverse pregnancy outcomes or any other radiation-induced disease in the general population either in the contaminated areas or further afield. After the shelter was built over the destroyed reactor at Chernobyl, a team of about 15 engineers and scientists was set up to investigate the situation inside it. Over several years they repeatedly entered the ruin, accumulating doses of up to 15,000 mSv. Daily dose was mostly restricted to 50 mSv, though occasionally it was many times this. None of the men developed any symptoms of radiation sickness, but they must be considered to have a considerably increased cancer risk. Cancer Risks From Radiation Studies of populations exposed to radiation doses in excess of natural background have yielded information on the risk of cancer. The risk associated with large radiation doses is relatively well established. However, the risks associated with doses under about 200 mSv are less obvious because of the large underlying incidence of cancer caused by other factors. Risks for exposures under about 100 mSv are assumed rather than demonstrated. . Epidemiological studies continue on the survivors of the atomic bombing of Hiroshima and Nagasaki, involving some 76,000 people exposed at levels ranging up to more than 5,000 mSv. These have shown that radiation is the likely cause of several hundred deaths from cancer, in addition to the normal incidence found in any population. From this data the ICRP and others estimate the fatal cancer risk as 5% per Sievert exposure for a population of all ages, so that one person in 20 exposed to it could be expected to develop a fatal cancer some years later. In western countries, about a quarter of people die from cancers, with smoking, dietary factors, genetic factors and strong sunlight being among the main causes. Radiation is a weak carcinogen, but undue exposure can certainly increase health risks. In 1990 the US National Cancer Institute (NCI) found no evidence of any increase in cancer mortality among people living near to 62 major nuclear facilities. The NCI study was the broadest of its kind ever conducted and supported similar studies conducted elsewhere in the US as well as in Canada and Europe.

See also University of Michigan Radiation & Health Physics home page and material and the Health Physics Society's Radiation factsheets and position & policy papers. ----
World Nuclear Association, Radiation and Life.
KSU (Sweden) Bakgrund (1990, 91) The consequences of the Chernobyl Accident in the Soviet Union.
NRPB Radiation Protection Bulletin # 167, July 1995, pp 13-16.