Chernobyl: 33 Years Later

Chernobyl: What do we know now?

Chernobyl. Just the word can evoke a variety of emotions. But it is fear—fear of radiation—€”that is likely one of the most powerful.

The accident at Chernobyl is touted as the worst nuclear power plant accident in world history. In our reading of the authoritative technical reports, we learned that there were several contributing factors to the accident, with the most important factor being Chernobyl's poor design.

On many levels, the Chernobyl reactor design was unlike anything we have in the United States. Most important, there was no containment building. Because of this, when the explosion occurred, 5% of the radioactivity in the reactor core spewed out. Although 5% does not sound like very much, that is a lot of radioactivity. Millions of radioactive atoms blew up into the air and were carried on the wind, contaminating thousands of acres of land in Ukraine and Belarus. If a containment building had been in place, like the thick concrete domes you see for each reactor in the United States and most others in the world, there would have been much, much less (if any) radioactivity released. A good example is the reactor at Three Mile Island, which had a containment building. Even though about one-half of its reactor fuel melted, almost no radioactivity was released.

On the day of the Chernobyl explosion, a test of the unit 4 reactor backup electrical power was being conducted. A series of issues associated with the testing led to hot fuel coming into contact with cooling water, causing the fuel to fragment and to boil the water away. This produced the buildup of steam, the buildup of pressure, and then the resulting explosion.

Among other design factors that also contributed to the magnitude of the Chernobyl accident was a graphite moderated reactor core that stoked the burning of the reactor fuel after the cooling water was lost.

Two people died from the explosion (one immediately at the site and another after reaching the hospital) and a third died shortly thereafter from a heart attack. In fighting the reactor fire, 28 emergency workers died within the weeks that followed, presumably due to exposure to high levels of radiation (acute radiation syndrome). Within 20 years following the accident, 19 others died, although it is not known conclusively if these were due to radiation exposure. Some of the fire fighters who died also had severe thermal burns from putting out related fires.

Because the Russian government tried to keep the accident a secret for as long as it could, no medical prevention (like potassium iodide to prevent radioactive iodine from being taken up in the thyroid gland) was given to the exposed general population living close to the Chernobyl reactor. More than 6,000 thyroid cancers were diagnosed in children and adolescents who drank milk that had high levels of radioactive iodine in the few weeks following the accident.

Epidemiological studies are continuing to determine if other health effects are related to the Chernobyl radiation exposures. There is some indication of increased leukemia and cataract incidence among the emergency-worker population. Otherwise, there is no clearly demonstrated increase in the incidence of cancers or leukemia or any other adverse health effects due to Chernobyl radiation in the exposed populations.

Several studies have reported that the exposed populations had anxiety levels that were twice as high as normal. And we do not know how many people were affected psychologically or died as a result of the evacuation of thousands who lived nearby.

The above information is taken from the following scientific studies/reports. These references also offer you more detailed information on the radiation exposures and health effects, summarized above, along with additional information and facts about the Chernobyl accident.

Socol Y. Reconsidering health consequences of the Chernobyl accident. Dose Response 13(1) [online]; 2015. Available at Accessed 6 May 2019.

United Nations Scientific Committee on the Effects of Atomic Radiation. Report of the United Nations Scientific Committee on the Effects of Atomic Radiation, fifty-ninth session (page 10) [online]. 2012. Available at Accessed 6 May 2019.

World Health Organization. 1986–2016: Chernobyl at 30 [online]. 2016. Available at Accessed 6 May 2019.

World Nuclear Association. Chernobyl accident 1986 [online]. 2018. Available at Accessed 6 May 2019.

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