This April 26th marks 40 years since the Chernobyl accident, considered the biggest nuclear energy disaster in history. On the night of April 25 to 26, 1986, a series of explosions ripped off the lid of the containment structure of the plant located in Ukraine and the reactor core partially melted, releasing a large amount of radioactive material into the atmosphere.
International experts estimate that the radioactive cloud that later reached parts of the Soviet Union — regions that are now part of the territories of Belarus, Ukraine and the Russian Federation — affected almost 8.4 million people. Most of this population received relatively low doses of radiation to the entire body, not much higher than doses from natural background radiation.
Although the initial Soviet response was focused on concealing details and risks of the incident from Western powers, as early as April 28 Swedish monitoring stations reported unusually high levels of wind-borne radioactivity — and pressed for an explanation.
Continues after advertising
READ ALSO:
The Soviet government admitted that there had been an accident at Chernobyl, which provoked an international reaction over the dangers posed by radioactive emissions. It was a week before the heat and radioactivity leaking from the reactor could be controlled, and it took months to completely encase the reactor core in concrete and steel – the structure was later deemed unsustainable.
O InfoMoney summarizes details of the accident and its consequences below:
O Local
The Chernobyl Energy Complex was located about 130 km north of Kiev, Ukraine, and about 20 km south of the border with Belarus. It consisted of four nuclear reactors of the RBMK-1000 design, with Units 1 and 2 being built between 1970 and 1977, while Units 3 and 4 of the same design were completed in 1983. Two additional RBMK reactors were under construction at the site at the time of the accident.
Continues after advertising
To the southeast of the plant, an artificial lake measuring around 22 km² was built, located next to the Pripyat River, a tributary of the Dnieper, to provide cooling water for the reactors. About 3 km from the reactor, the city of Pripyat was located, with 45 thousand inhabitants, including workers and their families. The ancient city of Chernobyl, which had a population of 12,500, is about 15 km southeast of the complex. Within a 30 km radius of the plant, the total population was estimated to be between 115,000 and 135,000 at the time of the accident.
What happened before the accident
The Unit 4 reactor would be shut down for routine maintenance on April 25, 1986. It was decided to take advantage of this shutdown to determine whether, in the event of a loss of power to the plant, the slowing turbine could provide sufficient electrical power to operate the emergency equipment and core cooling water circulation pumps. The purpose of this test was to determine whether core cooling could continue to be guaranteed in the event of a power loss.
This type of test had been carried out during a previous period of shutdown, but the results had been inconclusive – so it was decided to repeat it. Unfortunately, this test, considered essentially related to the non-nuclear part of the plant, was carried out without an adequate exchange of information and coordination between the team responsible for the test and the personnel responsible for the operation and safety of the nuclear reactor.
Continues after advertising
The accident
At approximately 01:23 on Saturday, April 26, 1986, two explosions destroyed the core of Unit 4 and the roof of the reactor building. Although it is not known for certain what caused the explosions, it is believed that the first was a hot steam/fuel explosion, and that hydrogen may have played a role in the second.
At the IAEA Post-Accident Assessment Meeting in August 1986, the operators’ responsibility for the accident was highlighted, with little emphasis given to the reactor’s design flaws. Later assessments suggest that the event was due to a combination of the two, with slightly more emphasis on design deficiencies.
The two explosions launched fuel, core components, and structural items, producing a shower of hot, highly radioactive debris, including fuel, core components, structural items, and graphite, into the air and exposed the destroyed core to the atmosphere.
Continues after advertising
The cloud of smoke, radioactive fission products, and debris from the core and building rose to about 1 km in the air. The heaviest debris was deposited close to the site, but lighter components, including fission products and practically the entire noble gas stock, were carried by the wind, predominantly to the northwest of the plant.
Fires broke out in what remained of the Unit 4 building, giving rise to clouds of steam and dust, and pockets of fire also broke out on the adjacent roof of the turbine hall and in various stores of diesel and flammable materials. More than 100 firefighters from the site and those called from Pripyat were needed — it was this group that received the greatest radiation exposure and suffered the greatest personnel losses.
About 200 to 300 tons of water per hour was injected into the intact half of the reactor using the auxiliary feedwater pumps, but this was stopped after half a day due to the danger of it flowing out and flooding units 1 and 2.
Continues after advertising
A few weeks after the accident, crews completely covered the damaged unit with a temporary concrete structure, called a “sarcophagus,” to limit further release of radioactive material. The Soviet government also cut down and buried about a square mile of pine forest near the plant to reduce radioactive contamination at the site and surrounding area.
It is estimated that, from the second to the tenth day after the accident, around 5,000 tons of boron, dolomite, sand, clay and lead were dropped onto the burning core by helicopter in an attempt to extinguish the fire and limit the release of radioactive particles.
Number of victims
Severe radiation effects from the Chernobyl accident killed 28 of the site’s 600 workers in the first four months after the event. Another 106 workers received doses high enough to cause acute radiation sickness. Two workers died within hours of the reactor explosion from non-radiological causes.
About 200,000 cleaning workers in 1986 and 1987 received doses of between 1 and 100 rem (in the US, the average annual radiation dose for a citizen is about 0.6 rem). Cleanup activities at Chernobyl eventually required around 600,000 workers, although only a small fraction of these workers were exposed to high levels of radiation.
No one outside the site suffered acute radiation effects, although a significant but uncertain fraction of thyroid cancer cases diagnosed since the accident in patients who were children at the time are likely due to ingestion of radioactive iodine. Additionally, large areas of Belarus, Ukraine, Russia and beyond have been contaminated to varying degrees.
Many children and teenagers in the region in 1986 drank milk contaminated with radioactive iodine, which delivered substantial doses to their thyroid glands. About 6,000 cases of thyroid cancer have been detected among these children — 15 children and adolescents in the three most affected countries died from thyroid cancer by 2005. Available evidence shows no effect on the number of adverse pregnancy outcomes, birth complications, stillbirths, or the overall health of children among families living in the most contaminated areas.
Consequences
The city of the plant’s operators, Pripyat, with around 45,000 inhabitants, was evacuated on April 27. As of May 14, approximately 116,000 people living within a 30-kilometer radius had been evacuated and subsequently relocated. About 1,000 of these people returned informally to live within the contaminated zone. Most evacuees received radiation doses of less than 50 millisievert (mSv), or effective dose, although some received 100 mSv or more.
In the years following the accident, an additional 220,000 people were relocated to less contaminated areas and the initial 30 km (2,800 km) radius exclusion zone.2) was modified and extended to cover 4,300 square kilometers.
In 1989, the World Health Organization (WHO) first raised concerns that local medical scientists had incorrectly attributed various biological and health effects to radiation exposure. The Soviet government asked the International Atomic Energy Agency (IAEA) to coordinate an international expert assessment of the radiological, environmental and health consequences of accidents in selected cities in the most contaminated areas of Belarus, Russia and Ukraine.
Between March 1990 and June 1991, a total of 50 field missions were conducted by 200 experts from 25 countries (including the USSR), seven organizations and 11 laboratories3. In the absence of data prior to 1986, a control population was compared with those exposed to radiation. Significant health disorders were evident in both the control and exposed groups, but at that time, none were related to radiation.
Chernobyl today
Pripyat remains a ghost town and the Ukrainian military limits access to the Chernobyl Exclusion Zone, a 1,100-square-mile “dead zone” centered on the reactor, but much of the area has been looted in the past. Amid the crumbling Soviet architecture, trees broke through the asphalt and plants took over many structures.
Although radiation levels remain dangerously high in many areas, the absence of humans has made the Exclusion Zone a de facto nature reserve. Ironically, the region’s post-apocalyptic atmosphere has attracted tourists, with this year’s grim anniversary and the 2011 Fukushima accident in Japan sparking even more interest in the place.
In 2011, Chernobyl was officially declared a tourist attraction, with many visitors – this number peaked at around 100,000 in 2019, but tourism has been suspended since the Russian invasion in February 2022.
