The article "Chernobyl: 20 Years On (Part I)" discussed the Chernobyl accident that happened on 26 April 1986. This article summarizes the consequence of the accident.

After the Chernobyl accident, the initial emergency measures taken at the nuclear station were fire-fighting and to stabilize the reactor. The fire in the plant was put out at 5 a.m. on 26 April 1986 after burning for more than 4 hours. The fire at the reactor core which consisted of a considerable amount of graphite had to be put out quickly so as to minimize the radioactive release. Emergency personnel employed aircraft to drop carbonized boron, dolomite, clay and lead to cover the damaged reactor. Pressurized liquid nitrogen was injected into the reactor base to remove heat from the core. A heat exchange passage was built and the base of the plant was reinforced to sustain the high temperature of the reactor core. To further prevent the leakage of radioactive materials into the atmosphere, a concrete confinement known as 'sarcophagus' was built to cover the remains of the damaged reactor core after half a year later, in November of 1986.

A number of offsite emergency measures were also taken. This included:
- protective measures for the public such as sheltering, evacuation and taking of radioiodine;
- relocation of several tens of thousands of livestocks from the contaminated area; measures to prevent or reduce contamination of drinking water and underground water; food interdiction, in particular milk;
- border control of people and vehicles within a radius of 30 kilometres(km) from the accident site; and
- decontamination of houses, especially the public buildings including schools and kindergartens, within an area of 7,000 sq. km. Those houses that could not be decontaminated were demolished and burnt.

The reactor released radioactive materials continuously in the next ten days after its explosion. The composition of radioactive materials released was complex, but the isotopes of iodine and caesium were of the greatest radiological significance because they accounted for the most radiation dose on the public. The iodine isotopes, with their short radioactive half-lives, had greater radiological impact in the short term whereas the caesium isotopes, with half-lives of the order of tens of years, had a longer-term impact.

Materials released to the atmosphere were widely dispersed and eventually deposited onto the earth's surface. The dispersion of the radioactive particles was related to their size and the prevailing meteorological conditions. Larger particles subsided within 100 kilometres of the reactor but smaller particles could spread farther, and became deposited on the ground mainly by the mechanism of rainfall. Deposition eventually encompassed the whole Northern Hemisphere, though the farther from the reactor, the lower was the level of contamination. The most highly contaminated areas were in Russia, Belarus and Ukraine and practically no pollutant was detected in the Southern Hemisphere. Twenty years have passed. The radiological influence of those radionuclides having short life-span has become negligible. Caesium-137 with a half-life of 30-year, is now the main radionuclide in the contaminated areas that is of concern. Its radiological impact can last for hundreds of years. The radiation caused by the release in the accident affects people's health through direct irradiation, inhalation and ingestion.

The health impact of the Chernobyl accident can be classified into 3 categories:

1. Acute radiation syndrome - some nuclear station workers and people who intervened in the early phase to fight fires, perform rescue and emergency operations suffered from acute radiation syndrome after receiving high radiation dose in the accident, resulting in death and severe health impairment. It should be noted that no member of the public had this kind of health effects;

2. Late health effects - in recent years there was a significant increase of thyroid cancer among the infants and children in the contaminated areas when the accident happened. There were several children deaths and this was attributed to the radioactive fallout. This increase of thyroid cancer is expected to continue for some time in these areas. On the other hand, there is no evidence that the accident has caused any significant increase in other kinds of cancer, leukaemia, congenital abnormalities, abnormal pregnancy symptoms or other radiation-induced diseases to the affected population; and

3. Social/psychological effects - the accident caused a long-term psychological impact on the affected population, with symptoms such as panic, anxious, headache, feeling of helplessness and some irrational emotions. This kind of mental trauma was in the early stage due to their fear of radiation, and worry of life and health but in the later stage, manifested itself as distrust towards public authorities and official experts and the change in the ways of life.

With the exception of the on-site reactor staff and emergency workers exposed to high level of radiation during the time of accident, most recovery operation workers and those living in contaminated territories received relatively low whole-body radiation dose, comparable to background radiation levels accumulated over the 20 year period since the accident, and lower than the average doses received by residents in some parts of the world having high natural background radiation levels.

The vast majority of the five million people residing in the contaminated areas of Russia, Belarus and Ukraine currently receive annual effective dose from the Chernobyl fallout of less than 1 mSv. The exposures are within the recommended dose limit for the general public. However, about 100,000 residents are still receiving higher level of radiation. Remedial measures in these contamination areas and application of some agricultural countermeasures continue.

The total number of actual deaths and expected deaths in the future attributable to Chernobyl is estimated to be about 4,000. This includes some 50 emergency workers who died of acute radiation syndrome and 9 children who died of thyroid cancer, and an estimated total of 3,940 deaths from radiation-induced cancer and leukaemia among about 600,000 people who were exposed to higher radiation dose in the accident. They were the 200,000 emergency workers from 1986-1987, 116,000 evacuees and 270,000 residents of the most contaminated areas.

This estimation of death toll is much fewer than figures quoted in other reports or analyses published before. According to the authoritative analyses quoted in the references, in the years since 1986, thousands of the above-mentioned people, having been exposed to relatively higher radiation dose in the accident, have died of diverse natural causes that are not attributable to radiation. Confusion about the impact of Chernobyl on mortality has arisen. However, expectations of ill health and attribution of health problems to radiation exposure have led local residents to assume much higher Chernobyl-related fatalities than the figure arrived at scientifically.