Chernobyl nuclear accident, Soviet Union

Chernobyl radiation, levels of radiation after the desaster

Chernobyl radiation, levels of radiation after the desaster

The Chernobyl accident (Chernobyl) was a nuclear accident, considered the most serious in history. It occurred at the Chernobyl Nuclear Power Plant in Ukraine (then in the Soviet Union ) on Saturday, April 26, 1986. It was the worst nuclear accident in history, followed by the Fukushima disaster, even though both reached the seventh level in the INES scale.

That day, in a sudden increase in power in reactor core number 4 of the plant, it took place an explosion of the hydrogen accumulated within the nucleus by overheating.

Due to the lack of a containment building at the nuclear power plant, a plume of radioactive rain was scattered over several areas of the Soviet Union and the European continent, 60% of which over Belarus. 40% of the whole European territory was polluted with the fuel that dispersed in the atmosphere. Large areas of Ukraine, Belarus, and Russia were severely degraded, leading to the evacuation and resettlement of some 300,000 people living less than 30 miles from the plant.

Spread of Chernobyl’s radiation

After the accident, around 100,000 km² of soil was contaminated with the fallout. Belarus, Ukraine, and Russia were the countries that had the strongest impact. However, some European countries detected lower levels of contamination.

Radioactive fallout from the Chernobyl accident was scattered depending on the weather conditions. Much was deposited in mountainous regions such as the Alps through rainfall.

The Soviet air force purposely seeded rain over the contaminated area to remove radioactive particles from clouds.

According to the Soviet and Western Belarus reports, around 60% of the radioactivity fell on the former Soviet Union. However, the 2006 TORCH report stated that half of the volatile particles had landed outside Ukraine, Belarus, and Russia.

According to surrounding countries, over one million people could have been affected by radiation.

What were the levels of radiation at Chernobyl after the accident?

It is estimated that the radiation levels in the worst-hit areas of the reactor building reached 300Sv/hr. This amount of radiation is enough to cause death in just over a minute.

Before the accident, the reactor of the fourth block contained 180-190 tons of nuclear fuel ( uranium dioxide ). The estimates, which are currently considered the most reliable, were released into the environment from 5 to 30% of this amount. Some researchers dispute this data, citing photographs and eyewitness observations that show that the reactor is practically empty.

However, it should be borne in mind that the volume of 180 tons of uranium dioxide is only an insignificant part of the reactor volume. The reactor was mostly filled with graphite. In addition, some parts of the reactor were melted and moved through the cracks at the bottom of the reactor vessel outside of it.

In addition to fuel, the core at the time of the accident contained fission products and transuranic elements  - various radioactive isotopes accumulated during the nuclear reactor’s operation. They represent the most significant radiation hazard. Most of them remained inside the reactor, but the most volatile substances were released into the atmosphere, including:

  • 100% of the noble gases ( krypton and xenon ) contained in the nuclear reactor;

  • from 50% to 60% radioactive iodine in gas and aerosol forms;

  • up to 60% tellurium and up to 40% cesium in the form of aerosols.

An international team of researchers led by the National Cancer Institute (NCI) found a clear dose-response relationship. The effects of ionizing radiation from I-131 led to an increased risk of health problems like thyroid cancer in the long term.

Chernobyl survivors were worried about how radioactivity could affect the DNA of the new generations. Consequently, some researchers studied the DNA of 130 children born to parents who either lived or worked near the accident, looking at de novo mutations or new mutations in a child’s DNA. They concluded that this mutation rate was not increased in the children born in the years or decades after the explosion.

Radiation exposure from Chernobyl

During the Chernobyl disaster, the amount of radioactive material released was four hundred times higher than at the nuclear bombing of Hiroshima.

Average doses received by different categories of the population



Number, people

Dose ( mSv )




about 100





Residents of "strictly controlled" zones



more than 50

Residents of other contaminated areas




About 1000 people near the reactor at the time of the explosion - that took part in emergency work in the first days after it - received the highest doses of radiation. These doses ranged from 2 to 20 gray (Gy) and were fatal in some cases.

At present, most of the inhabitants of the contaminated zone receive less than one mSv per year above the natural background.

Radioactive doses received by the liquidators

Most of the liquidators who worked in the danger zone in subsequent years and local residents received relatively small doses of radiation to the whole body. For the liquidators, they averaged 100 mSv, although sometimes they exceeded 500. The doses received by residents evacuated from heavily contaminated areas sometimes reached several hundred millisieverts, with an average value estimated at 33 mSv. Doses accumulated over the years after the accident are estimated at 10-50 mSv for most residents of the contaminated area and up to several hundred for some of them.

Some of the liquidators could, in addition to being exposed to external radiation sources, also be exposed to "internal" radiation - from radioactive dust settled in the respiratory organs. The respirators used were not always compelling enough.

For comparison, the general population of some regions of the Earth with an increased natural background (for example, in Brazil, India, Iran, and China ) receives radiation doses equal to approximately 100-200 mSv in 20 years. In addition, the man who received the highest radiation dose was Hisashi Ouchi, being exposed to 20 sieverts in Tokaimura’s accident.

Contaminated food

In the first weeks after the accident, many residents ate food (mainly milk) contaminated with radioactive iodine-131. Iodine accumulated in the thyroid gland, which led to large doses of radiation to this organ. In addition to the dose to the whole body received due to external radiation and radiation of other radionuclides that entered the body.

For residents of Pripyat, these doses have been significantly reduced (estimated by six times) due to the use of iodine-containing preparations. In other areas, such prophylaxis was not carried out. The doses received ranged from 0.03 to several Gy.

Radioactivity detected in Europe.

In the European part of Russia to this day (2009), the levels of radionuclides. In particular marker strontium-90, are higher than background levels but lower than those at which intervention is required to reduce according to NRB-99 /2009.

What is Chernobyl’s radiation today?

Currently, more than 35 years after the accident, the contaminated areas are virtually uninhabited and covered by a thick layer of dust. The dust has a high content of americium and other highly radioactive nuclides.

However, the radiation is decaying—radioactive elements decay. In Chernobyl right now, approximately 10% of the radiation emitted at the time of the accident remains.

Much of the radioactive material released by the Chernobyl power plant has disintegrated and no longer poses a threat. The main danger now comes from an isotope, cesium-137, which persists longer, accumulating in vegetation consumed by cows.

People exposed to radiation can cause health effects such as cancer, cataracts, and digestive conditions. The researchers said the danger could be mitigated by adding a chemical, hexacyanoferrate, to livestock feed. The compound is used to treat poisoning with heavy metals, such as cesium because it binds to them and allows them to pass through the digestive tract without being absorbed.

Publication Date: June 16, 2021
Last Revision: June 16, 2021