The Chernobyl disaster occurred on the night of April 25-26, 1986, in the Chernobyl Power Complex in Ukraine. The complex was equipped with four RBMK-1000 reactors, which produced about 10% of Ukraine's electricity. These reactors worked with uranium dioxide (U235) enriched to 2% and were capable of producing 1000 megawatts per day.
The reactor's operation relied on electric pumps connected to the fuel rods through a system of pipes. The pumps circulated water from bottom to top, which was then heated and transformed into steam. This steam was accumulated in the upper part of the reactor in special pressurized tanks, which were then directly connected to the turbines. This cycle then started again, and the power plant generated electricity through the reaction of nuclear fission.
The reactor was stabilized by slowing down the neutrons using a system of control rods made of boron, which absorbed neutrons and therefore slowed down the reaction. However, the reactor had a design flaw and a human factor led to its explosion. The power plant was conducting tests to determine the efficiency of the reactor in conditions of a sudden electrical interruption. This test was postponed for 10 hours and would have been carried out by the night shift workers who were not qualified and not prepared for the test.
At 1:24 am on April 26th, someone decided to interrupt the test by pressing the 'az5' key, thus starting the emergency shutdown of the reactor by entering all the control rods inside the core. This maneuver had the opposite effect and became the detonator of the disaster. The stable conditions of the reactor and the very high temperatures had literally deformed the seats where the control rods slid. The graphite tips, when they began the descent, should have slowed down the reaction due to the impact with the damaged conduits. This generated a reaction so powerful that it broke the control rods, jamming them a third of the way. The core then began to produce 10 times the nominal power of the reactor, creating so much steam that it was unable to discharge it. The fission reactions added up and the pressure completely destroyed the fuel pipes due to the accumulation of vapor and gas inside the core. Due to the lack of adequate control of the nuclear fission process, a violent explosion occurred which blew up the cap of a thousand tons that closed the reactor.
This explosion caused the destruction of the reactor roof and the release of a large quantity of radioactive material into the environment. A few seconds after another explosion much more violent than the first projected throughout the area surrounding what remained of the graphite tips, now radioactive due to the chimney effect, a large amount of heat caused fumes and dust containing fission products and the heavier isotopes to rise into the atmosphere. The more volatile ones, which tend to evolve towards a gaseous state, ended up in the atmosphere.
After the explosion, measures were taken to contain the contamination and mitigate the effects of the accident. These measures included the construction of a temporary reinforced concrete containment structure around the damaged reactor and a new containment structure called 'New Safe' was subsequently built with financing to cover the damaged reactor and allow its long-term safety.
The Chernobyl disaster led to significant environmental and health consequences. The pollution of aquifers of the soil and the atmosphere, especially in the areas close to the power plant. The health consequences were also significant, with the most reported cases of thyroid cancer found in the population caused by radiation. This event changed the perception towards nuclear power.
1. The explosion of reactor 4 in Chernobyl was an unprecedented event, characterized by a powerful blast that shot the thousand-ton cap of the reactor into the air .
2. The explosion was not a nuclear explosion like an atomic bomb, but was caused by a combination of environmental factors and a major design flaw in the reactor .
3. The Chernobyl Power Complex was equipped with four rbmk1000 reactors, which produced about 10% of Ukraine's electricity .
4. Each reactor worked with uranium dioxide u235 enriched to 2% and was capable of producing 1000 electric megawatts per day .
5. The reactors were equipped with control rods made of boron, which could absorb neutrons and slow down the reaction .
6. The power plant was conducting tests to determine the efficiency of the reactor during a sudden electrical interruption .
7. The test was interrupted due to unexpected events, and the night shift workers, who were not qualified or prepared for the test, attempted to restart the test .
8. The reactor was "poisoned" with xenon gas, which absorbs a large quantity of radiation and interferes with the nuclear reaction .
9. Despite safety regulations requiring at least 30 control rods to be inserted precisely to keep the reactor safe, all control rods except six were removed .
10. The rapid drop in power, combined with the unstable conditions of the reactor and the very high temperatures, resulted in the formation of steam bubbles and an increase in pressure .
11. The attempt to interrupt the test by pressing the famous az5 key started the emergency shutdown of the reactor sequence, but this had the opposite effect and became the detonator of the disaster .
12. The stable conditions of the reactor and the very high temperatures deformed the seats where the control rods slid .
13. The reaction was so powerful that it broke the control rods, jamming them a third of the way .
14. The core then began to produce 10 times the nominal power of the reactor, reaching 30 gigawatts of power .
15. The pressure completely destroyed the fuel pipes due to the accumulation of vapor and gas inside the core .
16. A violent explosion occurred which blew up the cap of a thousand tons that closed the reactor .
17. The explosion resulted in the release of a large quantity of radioactive material into the environment .
18. The contamination was contained, and measures were taken to mitigate the effects of the accident .
19. After the explosion, a sarcophagus, a temporary reinforced concrete containment structure, was constructed around the damaged reactor .
20. The explosion led to significant environmental consequences, including the pollution of aquifers and the atmosphere, particularly in the areas close to the power plant .
21. The health consequences of the explosion included confirmed deaths and a significant number of cases of thyroid cancer caused by radiation .
22. The Chernobyl disaster led to a significant change in the perception towards nuclear power .