It only seems that the world is moving away from the biggest accident of the nuclear age. Time gives a person one more chance to draw the necessary conclusions – the Kyshtym accident in 1957, the accident in Windscale in1957, the accident at the Three Mile Island NPP in1979, the accident at the Chernobyl nuclear power station in 1986, the accident at the Tokaymura nuclear facility in 1999, accident at the Fukushima-1 nuclear power plant in 2011 – this list is incomplete, and most likely, not yet final…
Time is enduring, and still allows humanity to critically review everything related to nuclear energy and the use of peaceful atom.
In 1986, the world community was following with concern the situation in the Soviet Union, where the alarm for the consequences of the nuclear catastrophe grew faster than the radioactivity around the Chernobyl nuclear power plant subsided. The rejection of everything “nuclear” grew, criticism of scientists for their actions both before and after the accident, often had no boundaries.
On April 26, 1986, a chain of events was closed as a result of technical imperfections in the design of the RBMK nuclear reactor and the obvious errors of the Chernobyl technical personnel conducting the experiment to test the strength of the turbogenerator that led to the largest nuclear disaster in the world.
The plant personnel were brought into such a state that the protection system could no longer prevent the accident. Designers did not take into account such a sequence of violation of all possible prohibitions prescribed in the technical characteristics of the reactor installation.
According to eyewitnesses who were outside the fourth block of the Chernobyl nuclear power plant, on April 26, at about 01:24, two explosions were heard sequentially. Its burning debris took off and sparks rained down over the fourth block, forming about 30 burning centers. The primary task was to combat the incipient fire.
The main fires were eliminated by the morning. The accident caused the destruction of the reactor core and part of the building of the fourth power unit of the nuclear power plant. The burning of graphite in the first days after the accident and the residual heat generated high temperatures. Radioactive particles were flown out from the shaft of the reactor, spots of hot graphite masonry were visible from helicopters.
In the first days after the accident, several mega kurie (MKi) radioactive products were released into the air. Immediately measures were taken to localize the accident. The evacuation of the population was carried out systematically, depending on changes in the radiation situation around the station.
The level of radiation in the city of Pripyat had begun to rise by the evening of April 26. The evacuation of the city began in the morning of April 27, which lasted several hours. In total, about 135,000 citizens were evacuated from Pripyat, Chernobyl, and a number of other human settlements. These emergency measures prevented exposure of civilians above acceptable limits.
A group of specialists in military helicopters began throwing the emergency reactor with special compounds from boron, dolomite, sand, clay, lead. About five thousand tons of such material was dumped from April 27 to May 10.
As a result, the reactor shaft was covered with a layer of granular mass, intensively emitting aerosol particles. The release of radioactive elements had begun to decrease significantly by May 6 and had fell to several tens of curies per day by the end of the month.
As a result of the accident, about 50 mega curie (MKi) of radioactive products were thrown out. The implementation of full-scale measures to eliminate the consequences of the Chernobyl accident allowed us to quickly improve the situation at the station and in the territory adjacent to it.
The work, at an accelerated pace, began on the decontamination of the station building, equipment, and the industrial site. Monitoring and diagnostics of the emergency unit state were organized in order to determine the possibility of subsequent operation of the emergency unit, a chemical analysis was carried out of the gases emitted from the mine.
Using sensors lowered from helicopters, temperature and Gamma radiation fields were measured in the space above the shaft of the destroyed reactor. Sensors of various types were installed inside the reactor building – this made it possible to compile a map of the degree of pollution of the premises. The experience of using robotic tools did not give significant results.
The situation had begun to take on a more manageable character and to a large extent stabilized by the end of May. The accident led to the destruction of the northern part of the building. Nevertheless, Chernobyl specialists were able to start work in early July. In the meantime, work had already begun on the isolation of the destroyed structures and the emergency fourth power unit by means of constructing a special sheltering sarcophagus – the Shelter object.
Chernobyl: the report of the Soviet delegation in Vienna
In August 1986, a delegation of Soviet scientists reported internationally on the causes and consequences of the Chernobyl accident, as well as measures to localize the consequences of the disaster. On the one hand, the report is full of quite objective and deserved criticism.
But on the other hand, it is an indicator of the titanic work done by the Soviet liquidators, scientists, specialists from various departmental structures and ordinary citizens of their country. The goal is to do everything possible and impossible as soon as possible in order to eliminate the consequences of a terrible nuclear disaster.
A positive resonance in the report was caused in particular by the fact of an increase in the points of technical and radiation monitoring, which made it possible to monitor the state of the emergency power unit. This made it possible to widely use experimental data for the design and subsequent construction of the Shelter object.
Measurements of the energy of the emissions of nuclear fuel remaining in the building of the emergency unit showed that about 96% of the fuel from its full load was in the reactor shaft and in the rooms surrounding it. The exploration of the rooms under the reactor confirmed the significant placement in them of molten sand discharged to the reactor in May 1986.
This finally confirmed that the temperature in the reactor shaft reached in the first days after the accident more than 2000 degrees. The positive aspect of the report was the professionally designed more than 18 options for the Shelter project. This made it possible to select the final version from all existing ones, implemented in the future, and providing the greatest reliability and safety.
The developed concept of phased protection of the emergency power unit from its periphery to the center allowed builders to carry out work under biological protection of earlier completed structures. In December 1986, seven months after the accident, the Shelter object was commissioned by builders and transferred to the operating organization.
The Shelter construction solved the most important tasks at that time:
- Isolation of the destroyed block, which excluded the active release of radioactive substances into the environment and protected it from penetrating radiation;
- There were excluded conditions for a nuclear chain reaction;
- There were prevented conditions for the formation of explosive nuclear mixtures;
- The necessary temperature conditions are ensured, using ventilation structures;
- Maintenance and long-term observation and research provided;
- Ensuring the protection of operating personnel.
Work on the resumption of operation of 1, 2 and 3 Chernobyl power units was carried out at that time in parallel with the conservation of the destroyed fourth unit. Restoration work began with the deactivation of buildings and structures and the surrounding area. The first and second power units were decontaminated by mid-July 1986. A shift method of operating the station was implemented to ensure their more functional work
By the end of 1986, academician Yevgeny Velikhov, the first president of the USSR Nuclear Society, director of the Kurchatov Institute of Atomic Energy, said that after learning the lessons of the Chernobyl tragedy, the Soviet state had done everything to ensure that the second Chernobyl never happened again. Nevertheless, he did not relieve responsibility, including from the scientific community, which, together with representatives of the authorities, must find keys of understanding with local residents.
They need to be contacted more actively, talked about the rules of conduct with radiation, provided the necessary protective equipment and instruments to measure the level of radiation background. One should resort to completely unnecessary and unjustified secrecy under no circumstances. It not only aggravates the perception of reality, but also does not allow to provide the necessary level of culture, knowledge, which can subsequently become a decisive factor in security.
The conclusion is obvious: the future of nuclear energy in the 21st century will depend on how the social, psychological, moral, human consequences of the Chernobyl disaster are resolved.
