What do we know about Chernobyl?
The 1986 accident at the Chernobyl nuclear power plant in Ukraine (then part of the former Soviet Union) is the only accident in the history of commercial nuclear power to cause fatalities from radiation. Thirty-one people died within a few weeks of the accident from the initial steam explosion, exposure to radiation and thermal burns, and one due to cardiac arrest.
In 2018, the United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR) reported that the accident also was responsible for nearly 20,000 documented cases of thyroid cancer among individuals who were under 18 years of age at the time of the accident in the three affected countries including Belarus, Ukraine, and the Russian Federation. This was due to the high levels of radioactive iodine released from the Chernobyl reactor in the early days after the accident.
Radioactive iodine was deposited in pastures eaten by cows who then concentrated it in their milk which was subsequently ingested by children. This was further exacerbated by a general iodine deficiency in the local diet causing more of the radioactive iodine to be accumulated in the thyroid.