Accident left city uninhabitable and changed the world’s view on nuclear safety
The explosion of the Chernobyl reactor, in Ukraine, turns 40 this Sunday (April 26, 2026). The accident was the most serious in industrial nuclear history and changed the world’s view on nuclear energy safety.
In 1986, one of the reactors at the Chernobyl Nuclear Power Plant, near Pripyat (then the Soviet Union and now Ukraine) exploded and made the entire city uninhabitable. around 150,000 km² around the plant.
Around 200,000 people were relocated, including the 49,360 inhabitants of Pripyat. The exact number of deaths directly linked to the disaster is debated, but it is known that at least (employees who worked on containment and cleanup) died in the first few weeks. also that thousands of other victims have developed cancer and other complications as a result of radiation.
THE ACCIDENT
The accident was a combination of technical and human failures during a safety test of reactor 4’s turbines. The test intended to check whether, during a power outage, it would still be possible to keep the cooling pumps running. Officials reduced reactor power below safe levels and disabled emergency shutdown systems.
The reactor used, of the RBMK type, worked as a graphite block with vertical tubes through which water and uranium, nuclear fuel, circulated. Inside the tubes, uranium underwent nuclear fission, releasing heat and neutrons. The water absorbed the heat and turned into steam, which moved the turbines and generated electricity.
In most reactors, water cools the system and absorbs neutrons, slowing the reaction. In RBMK, when the water turned to vapor, it stopped absorbing neutrons, while the graphite continued to accelerate the reaction. This created an uncontrollable overheating cycle.
To maintain stability, the reactor used graphite-tipped boron control rods. When inserted, they caused an initial spike in energy before reducing. This spike caused the reactor to lose control, resulting in two explosions and a fire that lasted for days, releasing a large amount of radioactive material. After the explosion, the wreckage was covered by a concrete and steel structure called a “sarcophagus” to reduce the dispersion of radioactive particles. Despite the accident, the plant continued operating with other reactors until 2000.
Watch the video that shows the “sarcophagus” (1min3s):
NUCLEAR SAFETY
After the accident, the view on nuclear safety changed globally.
In September 1986, in Vienna, they were signed by more than 60 AEA countries. Both treaties were drafted by the IAEA (International Atomic Energy Agency) as an attempt to prevent further disasters.
For Polina Kolodiazhna, Program Coordinator at and who works directly with nuclear risks, the impact of Chernobyl on Ukrainian society created a new public awareness about the dangers of secrecy, lack of state accountability and technological risk, but which is left aside.
“Unfortunately, many of the lessons of the Chernobyl disaster have been ignored and many are being deliberately forgotten. For the Western nuclear industry, outside the Soviet Union, the claim was that Chernobyl could not happen with their reactors. One of the reasons given was that Western designs, such as the Westinghouse Pressurized Light Water Reactor or the General Electric Boiling Water Reactor, have steel and concrete lined containment, which Chernobyl’s RBMK did not have, and therefore, a massive release of radioactivity would not be possible. The Fukushima Daiichi disaster in 2011 proved them completely wrong Nuclear reactors of all designs are capable of catastrophic failures. […]. Today, the nuclear industry lobby is trying, and succeeding, to reduce and even eliminate safety criteria. For example, the US Nuclear Regulatory Commission (NRC) new reactors of the need for containment and also the inclusion of serious accident analyzes in the project, justifying this measure with the argument that the risk of accidents is so low that it becomes unnecessary”.
Polina says the decision is not scientific, but purely economic. According to the coordinator, the nuclear industry “there is no future if you cannot drastically reduce costs”.
