On the night of 25 to 26 April 1986, reactor No. 4 of the Chernobyl nuclear power plant, located in Ukraine on the right bank of Pripyat, 12 km from the town of Chernobyl, near Kiev, exploded, causing the worst nuclear accident in the history of atomic energy worldwide.
The reactor in question was a 1000 RBMK (high-power reactor pressure tubes) used in industrial operation in December 1983. By this time the Kurchatov Institute researchers (main research and development of the nuclear industry for the Soviet Union) were observed that physical RBMK 1000 launches second-generation RBMK and 1500 were accompanied by demonstrations abnormal reactivity during descent control rods in the heart of the reactor.
Moreover, the two accidents of RBMK reactors prior to the disaster of 1986 (No. 1 reactor of Leningrad NPP in 1975 and the No. 1 reactor of the Chernobyl plant in 1982) found significant flaws in the characteristics operating RBMK reactors. Some experts believe the accident at the center of Leningrad in 1975 as the precursor of the Chernobyl disaster.
On 25 April 1986 in Chernobyl was scheduled to perform tests of a security systems of the reactor No. 4 and then to shut down reactor to carry out regular maintenance . During testing, the electric current had to be cut in the center, and security systems of the reactor had to be powered by mechanical energy generated by the rotational inertia of the turbine generators. It should be noted that the test program in the No. 4 reactor of the Chernobyl plant had not been coordinated with the scientific director and designer of the reactor. Furthermore, by performing the experiment, the plant staff has violated a series of safety rules.
All these causes have led to 1:24, April 26, 1986, an uncontrolled runaway reactor power, which caused an explosion and destruction of much of the reactor facilities. Following the accident, radioactive material with a volume of hundreds of millions of curies were released into the atmosphere.
The explosion destroyed the roof of the reactor building. The walls were damaged by the explosion in a space portion formed on the north side of the reactor. The upper floors of the shelf vent, adjacent to the reactor, also collapsed. The roof of the engine room, where were the turbo-alternators, collapsed and burned in places, 8 140 tons of nuclear fuel ended up in the air. Column of steam and smoke rising from the rubble rejected tens of thousands of curies per hour in the atmosphere.
Radioactive discharges resulted from destruction during the crash barriers and safety systems to protect the environment of radionuclides contained in spent fuel. They lasted 10 days, from April 26 to May 6, then dropped their intensity several thousand times and continued to decline thereafter.
Despite the importance of the disaster, the possibility of serious consequences radioactive near the center, and evidence of cross-border transportation of radioactive materials on the territories of the countries of Western Europe, the Soviet government hid for several days the accident to its people and the world community. Moreover, from the first days after the accident, steps were taken to classify information on actual and forecast the consequences of the disaster.
Following the accident, a territory of nearly 160,000 square kilometers was contaminated by radiation. The northern Ukraine, Belarus and western regions of Russia have been affected.
The disaster killed 31 people on site, and 600 liquidators involved in extinguishing the fire and clearing rubble have received high doses of radiation.
1 March 2011, the Russian State Register of medical dosimetry were over 194,000 liquidators of the accident in the Chernobyl nuclear power plant, of which over 134,000 have received high doses of external irradiation with known dates input and output in the area of hazardous work related to radiation.
24 hours after the accident, the ad hoc government commission declared the evacuation of residents of neighboring communities of the Central. In total, by the end of 1986, 116,000 people were evacuated from 188 localities, including the city of Pripyat.
In mid-May 1986, the Government Commission decided a long-term storage of reactor No. 4 in order to prevent releases of radionuclides into the atmosphere and reduce the impact of penetrating radiation on the site of the nuclear .
The Soviet Ministry of Medium Machine building was commissioned for the work containment of the fourth reactor of the Chernobyl nuclear power plant and related facilities. The structure covering the ruins of the reactor building is now known worldwide as the Sarcophagus. November 30, 1986, he was officially put into operation.
In autumn 1993, the No. 2 reactor of the plant has been arrested following a fire.
On the night of 29 to 30 November 1996, the No. 1 reactor of the plant has been put out of operation in accordance with the Memorandum signed in 1995 between Ukraine and the G7 states.
December 6, 2000, due to the malfunction of the safety system, the third and last reactor was shut down.
In March 2000, the Ukrainian government ordered the closure of the Chernobyl nuclear power plant which ceased operations on 15 December 2000, 1:17 p.m..
The Ukrainian parliament has endorsed a program of decommissioning operations of the Chernobyl plant which provides the total dismantling by 2065. The first step that runs from 2010 to 2013 will be marked by the withdrawal of nuclear fuel to be stored in long-term deposits. Between 2013 and 2022, the reactor facilities will be conservation.
The experts will spend the period between 2022 and 2045 to expect the decline in radioactivity in the reactors. Between 2045 and 2065, facilities will be dismantled and the site of the plant will be decontaminated. According to forecasts, the implementation of the program will transform the area into a Sarcophagus ecologically clean site.
In recent years, efforts have often been undertaken to understand why the Chernobyl accident and its causes. However, to date, no final and confirmed by testing of the disaster has not been developed.
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