The Chernobyl nuclear power plant accident occurred on April 26, 1986. It was the largest nuclear energy disaster in history. The explosion took place in the fourth block of the Chernobyl power plant, located only 120 km from the capital of Ukraine – Kiev, close to the border with Belarus.
Chernobyl power plant was at that time one of the largest in the world. It was dedicated to a strategic military program for the Soviet army. The actual crash happened due to a coincidence of several factors. Beside the fact that the reactor did not have an updated security system, it had a low level of automation. On the fatal night of April 26, there was an experiment going on, which should have tested the inertial range of the turbo-generator unit. Overheating fuel caused the destruction of the generator’s surface.
At 1:24 AM local time, 40-60 seconds after commencing the experiment, two large explosions took place. According to some accident investigators, taking off all the absorbing sticks from the active zone of the reactor, together with the reactor’s growing power capacity, the crash was unavoidable. It was recorded that safety systems were shut off or even out of service at the time of the initial explosion and the explosion of steam and hydrogen blew the 1200 ton cover of the reactor and destroyed the roof. After a few seconds there came the second explosion. According to several independent studies, while the first explosion was normal – chemical, the second explosion with the burning of the prompt neutrons, it had characteristics of a nuclear explosion with a yield of 0.3 kilotons (equal to around 300 tons of TNT). According to witnesses the first explosion was followed by a red blaze and the second explosion had a light-blue blaze, after which a mushroom cloud rose above the reactor.
The nuclear disaster was also a coincidence and the reactor should have been shut down before the experiment could begin. However, this was postponed by nine hours because of the forthcoming May 1 celebrations and the electricity needed to fulfill the production plan. This delay meant that the experiment had to be managed by a different shift than the one which prepared it. The night shift conducting the experiment comprised fewer experienced operators.
After The Disaster
Radioactivity started to radiate out of the destroyed and burning fourth reactor of Chernobyl power plant, which contaminated both the near and far environment. The investigation of Chernobyl disaster was officially closed with a result that the personnel of the power plant did not follow the necessary safety regulations. Lenin Nuclear Power Plant was just the beginning of an aftermath that re-wrote not just the safety rules in nuclear energy, but also the history of mankind. Radioactivity started to radiate out of the destroyed and burning fourth reactor of Chernobyl power plant, which contaminated both the near and far environment.
The first step in liquidation of the nuclear accident at Chernobyl was extinguishing the burning reactor hall and the roof of turbo-generator’s hall. Special power plant fire department, together with firemen from the nearby town of Chernobyl, extinguished the fire within three hours after the explosion. Yet, in the heart of the reactor, graphite was still burning…
Firemen who worked at the accident did not know the cause of the fire and thus they just poured water at the ruins of the reactor. This worsened the situation and several smaller explosions followed, together with a severe radioactive contamination. To prevent radioactivity from further spreading into the environment, the reactor was filled with five thousand tons of boron, dolomite, sand, clay and lead compound - thrown from a helicopter flying above the reactor. These loose materials extinguished the burning graphite and absorbed radioactive aerosols. Two weeks after the breakdown, Soviet official bodies decided to conserve the whole crashed block of the power plant into a special sarcophagus – concrete body with its own cooling system.
The explosion at Chernobyl brought up radioactive substances to the altitude of 1.5 kilometer in the air. In this elevation, wind from the southeast took the radioactive cloud to as far as Scandinavia. The cloud flew over Scandinavia and then turned back to Ukraine again. During the day of the accident, the direction of the wind changed to westward. The second contaminated cloud thus flew via Poland to Czechoslovakia and further to Austria. There, it bounced back from the Alps and flew back to Poland. As far as we know today, there is no place in the world where the radioactive clouds from Chernobyl were not present. Contaminated clouds flew all around the world.
The most affected territories were Ukraine and Belarus, which decided to evacuate parts of their countries forever because of the contamination of the environment. In the process of contamination, a large role was played by radioactive iodide. This element has a short disintegration half-time and relatively soon after the accident naturally decomposed to harmless substances. Today, the radioactive pollution is made up mostly by substances such as strontium and cesium – these have a 30-year disintegration half-time. Thus, they will continue to pollute the close environment for several decades. Isotope of plutonium and americium will be present at the respective territory probably for several thousand years. However, they have a negligible radiation affect for the human body.