In the energy vision of the former Soviet Union, plans were made to save the consumption of organic fuels and establish nuclear industry complexes.
This plan uses three reactor types: the nuclear power plants under construction are based on VVER (Light Water Reactor), RBMK (High Power Pressure Tube Graphite Reactor) and FBR (Fast Breeder Reaction) type reactors . The first two were light water-cooled thermal neutron reactors, which are now the basis of Russian nuclear power plants with an installed capacity of 30 million kilowatts. The third type is a sodium-cooled reactor, which aims to conduct industrial-scale experiments on the technical solutions that have been adopted and the gradual development of a plutonium-based closed-circuit fuel cycle.
In accordance with the main direction of economic and social development of the Soviet Union from 1986 to 1990 and until 2000, it stipulates the rapid development of nuclear power in the European parts of the former Soviet Union and the Ural region. In 1985, the power generation capacity of nuclear power plants was 170 billion kilowatt-hours, and by 2000 it will increase by 5 to 7 times.
Such developments will mean that nuclear power plants will provide the additional capacity needed for parts of Europe's energy system, thus alleviating the need for new thermal power stations burning organic fuels.
A Chernobyl nuclear power plant was built in the Belarusian-Ukrainian forest area in the European part of the former Soviet Union. The surrounding area was originally characterized as a low population density zone, with an average population density of approximately 70 people per square kilometer until the construction of the nuclear power plant began. At the beginning of 1986, the total population in the area within a radius of 30 kilometers from the nuclear power plant was approximately 100,000 people, 49,000 of whom lived in the town of Pripyat, which is located to the west of the safety zone 3 kilometers from the power plant. There are 12,500 people living in the village of Chernobyl in the center of the region, which is located 15 kilometers southeast of the power station.
The first phase of the Chernobyl Nuclear Power Plant (two RBMK-1000 reactor units) was built between 1970 and 1977. The construction of the two nuclear power units in the second phase was completed in It was completed and put into operation in the same factory at the end of 1983.
Author: Duke of York Reply date: 2006-4-27 01:29:56
Let us recall the situation on the day of the accident
1986 On the evening of April 25th and 26th, there were 176 operators on duty, workers from various departments, and maintenance personnel in the first and second phase construction project areas. In addition, there are 268 night shift construction workers and installers on site for the third phase of the construction project.
For maintenance, Unit 4 was scheduled to shut down the reactor on April 25, 1986. At this time, there were 1,659 fuel assemblies in the core with an average burnup of 10.3 MW day/kg. , an additional absorber and an unloaded channel. Most of the fuel assemblies (75%) are fuel rod bundles loaded during the first loading, and their fuel consumption is 12 to 15 MW day/kg.
Before shutting down, some tests must be carried out on the No. 8 turbine generator in a certain prescribed manner, that is, during the shutdown process, the turbine will be used to meet the plant's power demand. The purpose of these tests is to test the possibility of using the kinetic energy of the rotor to maintain the power of the unit itself when the turbine generator cuts off the steam supply during a power outage. This method is actually used in a subsystem of the reactor's rapid emergency core cooling system (ECCS). Such a test should not be prohibited on an operating power station if it is carried out in an appropriate manner and with the necessary additional safety measures.
Similar tests have been carried out at the Chernobyl power station. It was then discovered that during shutdown, the generator's bus voltage dropped long before the rotor kinetic energy was exhausted. In the test planned for April 25, 1986, the experimenters planned to use a special generator magnetic field regulator to solve the above problems. However, the work program for the tests on Turbine Generator No. 8 of the Chernobyl Nuclear Power Plant and the tests to be carried out according to this program were not carefully prepared and the necessary approvals were not obtained.
Author: Duke of York Reply date: 2006-4-27 01:37:22
This bureaucratic bird outline will soon go down in history:) The working outline is of poor quality , the section on safety measures was drafted in a purely formulaic manner (the safety section simply stated that all switching operations during these tests require the permission of the shift supervisor, and that in the event of an emergency the staff will press the station button procedural actions, and the commander-in-chief—an electrical engineer, not a reactor plant expert—should notify the safety personnel on duty before these tests begin). In addition, the outline basically has no provisions for additional safety measures. The outline requires the shutdown of the reactor's emergency core cooling system. This means that during the entire test process, which is about 4 hours, the safety of the reactor is essentially reduced.
In these tests, safety issues were not given the necessary attention, the staff involved were not fully prepared for the tests and were unaware of the possible dangers. In addition, as described below, the staff Violation of the outline requirements laid the foundation for the accident.
At l o'clock on April 25, the staff began to reduce the reactor power (until this time, the unit had been operating under rated parameters), and at 13:05 the reactor power was 1,600 MW (thermal) The No. 7 turbine generator was removed. The power required by the unit itself (four main circulation pumps, two feed water pumps, and other equipment) is switched to the No. 8 turbine generator bus.
At 14:00, in accordance with the requirements of the test program, the reactor emergency core cooling system was disconnected from the forced circulation circuit (MFCC). However, requests from the control room delayed the unit's demobilization from operation. Therefore, in violation of operating procedures, the unit continued to operate after the emergency cooling system was disconnected.
The power reduction started again at 23:10. In the test outline, while the generator idles and supplies the power required by the unit, it should be completed at a reactor power of 700 to 1000 megawatts (heat). However, when part of the automatic adjustment system was cut off (as it was supposed to do under low-power operating procedures), the operator was not able to eliminate the imbalance caused by the automatic adjustment rod's measuring part quickly enough. As a result, power dropped below 30 MW(thermal).
On April 26 at 1:00, the operators succeeded in stabilizing the power at 200 MW (thermal). At the same time, because reactor "poisoning" continues, further power increases are limited by the small available excess reactivity. Therefore, the power at that time was actually lower than the level required by regulations.
The Three Mile Island accident in the United States in 1979 attracted worldwide attention. At that time, Uncle Sam activated the emergency core cooling system at the most critical moment to avoid causing a catastrophe, and this time the power plant was shut down. It's incredible for the staff to protect themselves. As you can see below: It was a series of reckless behaviors that did not respect science and a simple and rough work attitude that led to irreparable disasters. ． ． ． ． ．
Despite the emergence of many bad signs, the people in charge decided to continue these experiments. At 1:30 and 1:70, a backup main circulation pump was put in from each side to work together with the 6 pumps that were already running. So when the experiment was completed, there were still four pumps running on the MFCC system to safely cool the core.
Because the reactor power and the resulting water resistance of the core and MFCC system are significantly lower than expected, and because all eight main circulation pumps are in operation, the coolant passing through the core The flow rate is as high as 56,000 to 58,000 cubic meters/hour, and the flow rate of individual single pumps can reach 8,000 cubic meters/hour. This violates operating procedures. This mode of operation is prohibited because of the risk of damage to the pump and the formation of cavitations in the main coolant lines, which can cause mechanical vibrations. The backup main circulation pump was put into operation and caused an increase in flow through the reactor core, which caused a decrease in steam volume, a decrease in steam pressure in the steam drum steam-water separator, and caused changes in other reactor parameters. The operators attempted to maintain the system's key parameters, however, they were not entirely successful in doing so.
At this stage, they saw that the steam pressure in the drum steam-water separator dropped by about 0.5 to 0.6 MPa, and the water level was lower than the emergency mark. In this case, in order to avoid a shutdown, the operator disables the accident protection system related to these parameters.
At the same time, reactivity slowly and continuously decreases. At l:23:30, the operator saw from the output of the rapid reactivity calculation program that the excess reactivity had now reached a level that required immediate shutdown. However, the staff did not shut down the reactor based on this, but began to conduct various experiments.
At 1:23:4, the accident regulating valve of the No. 8 turbine generator unit was closed. The reactor continues to operate at approximately 200 MW(thermal) power. The accident protection systems related to the closing of the emergency regulating valves of both turbine-generator units (Turbine-generator unit 7 was shut down on April 25) were disengaged to make it possible to redo the test if the first test failed. The experiment. This represents a further violation of the experimental program, which does not provide for the removal of the reactor accident protection system when shutting down the two turbine generator units.
The reactor power began to slowly increase shortly after the experiment began.
At 1:23:40, the flight crew leader issued an order to press the AZ-5 button. This will insert all control rods and shutdown rods into the core. A few seconds after the rods fell, some vibrations were felt, and the operator saw that the absorber rods were not fully inserted into their stop position at the bottom of the core. Then he cut off the power supply to the servo drive mechanism of the rod control system so that the absorbing rod would fall into the core under its own weight. ． ． ． ． ．
After four fatal mistakes, the situation was completely irreversible. Unit 4 collapsed tragically!
According to the information provided by witnesses outside Unit 4, two explosions occurred one after another at 1:24. Flaming clumps and sparks rushed into the sky above the reactor, some of which landed on the roof of the turbine building and started catching fire.
In the design of the reactor, its various physical characteristics are taken into consideration, and protective measures are provided to prevent accidents. This includes technical protective measures, as well as technical protection measures for the implementation of nuclear power plant processes. various directives and strict rules.
In the process of preparing and conducting experiments on the turbine generator, the turbine had to meet the power needs of the unit during idle operation, but the operator cut off various important protection systems, violating stipulates the most important operating procedures for the safety management of technical processes.
The operator's main purpose is to complete the experiment as quickly as possible. Lack of adequate preparation, failure to follow procedures when conducting experiments, failure to comply with the requirements of the inherently unreliable Bird Program itself, and careless operation of the reactor unit prove that the operators did not have specialized knowledge about the reactor process and did not understand the reactor Potentially dangerous.
The designers of the reactor facility did not provide safety protection systems capable of preventing an accident such as that of Unit 4 (i.e., the removal of technical protection systems and several consecutive violations of operating procedures) because they It is considered highly unlikely that such a combination of events would occur.
Initially, it was believed that the main cause of the accident should be a combination of extremely unlikely events in which the operators of the unit violated operating instructions and procedures. At that time, the operator caused the reactor to enter an uncontrollable state. In this state, the positive reactivity coefficient of the cavitation could cause the reactor power to increase suddenly. Such accidents are considered catastrophic.
But seven years after the incident, the Russian newspaper "Izvestia" published an article on April 17, 1993, exposing the deeper reasons for the Chernobyl nuclear accident.
In fact, half a year before the Chernobyl explosion, an expert from the Kursk Nuclear Power Plant wrote to the State Nuclear Energy Supervision Commission, warning that this type of high-power pipeline reactor (ie, RBMK reactor ) danger, but the competent "central" leadership did not take this warning seriously.
After the accident, on May 1, 1986, the leader of the nuclear power plant safety supervision team proposed an opinion to the director of the Institute of Atomic Energy: "The accident was not caused by the operator's violation of regulations, but because of defects in the structure of the reaction zone. defects, as well as misunderstandings of neutron physical processes in the reaction zone.
" On May 9, 1986, he wrote the same letter to the national leaders.
On July 2 and 17, 1986, an interdepartmental science and technology meeting was held under the chairmanship of a certain academician to discuss Structural defects in the reactor.
Nevertheless, they attributed the cause of the accident to an operational error, and this became the official position of the Soviet government internationally, first and foremost with the International Atomic Energy Agency. .
After reporting to the International Atomic Energy Agency, it approved the report of the Institute of Atomic Energy, which stated: "The accident was mainly caused by violations by the crew operators, but the reactor and safety core rods were also exposed. structural defects. "However, the latter sentence was deleted from the reports submitted by the former Soviet Union to the expert meetings held by the International Atomic Energy Agency in 1986 and 1987.
They had to do this. Because of the design of high-power pipeline reactors The person is an academician himself, who is unwilling to do anything detrimental to himself.
An article on May 17, 1989 talked about the unfinished RBMK-1000 mentioned by the acting director of the National Invention Appraisal Laboratory. The reason for being able to register. It was the academician and others who submitted the application materials at that time: "The first batch of application materials submitted in 1967 was a page and a half of typed paper, without formulas and drawings. I returned the materials to the applicant and asked them to make supplements. ”
On October 6, 1967, they handed over the revised application materials, but before the review was made, an academician declared in the "Pravda" on November 10, 1967: "The Soviet Union Scientists have solved the problem of improving the safety of nuclear power plants. "Subsequently, this kind of reactor was used without recognition, and accidents often occurred.
Chernobyl Nuclear Power Plant*** had 104 accidents, of which only 35 were accidents. Due to improper operation.
I am not going to discuss the defects of the technical structure here. From the problems exposed above, it can be seen that there are problems in the science and technology management system of the former Soviet Union. Chernobyl The reasons for the occurrence of nuclear accidents may be found in undemocratic and unscientific decision-making of scientific and technological projects, inadequate supervision and control mechanisms, etc. ． Sweeping across the border area of ??the Three Kingdoms
The hell fire began to burn the entire factory area, and the first three units were in danger of exploding at any time in the rain of molten graphite flowing all over the sky. The most touching and tragic stage of the entire incident began. ．．．．． Fire. Due to a rupture of some oil pipes, a cable short circuit and strong heat radiation from the reactor, a fire broke out above the No. 7 turbine generator of the steam turbine building, the destroyed reactor hall and part of the building connected to the hall
1. At 0:30, the on-duty fire brigade of the nuclear power plant rushed to the scene of the accident from Pripyat and Chernobyl.
Because the fire on the roof of the steam turbine factory directly threatened the adjacent Unit 3 and the fire was intense. It became increasingly fierce and urgent measures were taken to put out the fire in this important area. At the same time, fire extinguishers and indoor fixed fire hydrants were used to put out the fire on the roof of the steam turbine factory. The fire on the top of the reactor building was basically extinguished at 2:30 a.m. By 5 a.m., the fire was extinguished.
Because some of the melted fuel may have reached a critical mass and a self-sustaining chain reaction occurred. This potential danger requires preventive measures. In addition, the destroyed reactor has been emitting a large amount of radioactivity into the surrounding environment.
In the early days of the accident, an attempt was made to use an emergency auxiliary water pump to supply water to the core space to lower the reactor pit. This attempt failed to reduce the temperature in the room and prevent the graphite masonry from catching fire.
I then had to choose one of two decisions: one is to cover the reactor body with heat absorber and filter material to prevent the accident. The second is to allow the burning process of the pile body to end on its own.
The first option was adopted because the second option had the potential to contaminate large areas with radioactivity and endanger the health of residents in large cities.
And all actions will be carried out with difficulty in a harsh environment with a lethal dose of tens of thousands times. Therefore, for the damage control personnel who are ready to go, regardless of the success or failure of the operation, they will definitely die!
A team of experts began using military helicopters to drop a mixture of boron, dolomite, sand, clay, and lead to cover the destroyed reactor. From April 27 to May 10, approximately 5,000 tons of materials were put in, mainly from April 28 to May 2. As a result, the reactor is covered by a layer of loose material that strongly absorbs aerosol particles. By May 6 radioactive emissions were no longer a major problem and had fallen to a few hundred curies per day and night, and by the end of the month to a few tens of curies per day and night.
The problem of lowering fuel temperature is also solved. In order to lower the temperature and reduce the oxygen concentration, the compressor station uses a blower to send nitrogen to the space under the reactor pit.
By May 6 the temperature in the reactor pit stopped rising and began to fall with constant air convection through the core to the atmosphere.
Due to concerns about the extremely unlikely possibility of damage to the lower part of the reactor building structure (although it was possible in the first days of the accident), double insurance measures were taken and it was decided to build an artificial structure below the factory building foundation. Heat exhaust channel. The method adopted was to set up a flat plate heat exchanger on a concrete slab, and by the end of June the planned work had been completed.
Although the experimenters showed incredible blindness in the series of perverse behaviors that led to the accident, the decisions taken by the heroic damage control personnel were basically correct. He regained the honor he had paid for with his life.
Since the end of May, the situation has been generally stable. The destroyed part of the reactor building is in a stable condition. After the decay of short-lived isotopes, the radiation situation improves. The amount of radioactivity entering the atmosphere from the unit depends primarily on the amount of aerosols carried away by the wind. The amount of radioactive emissions does not exceed a few tens of curies per day and night. The temperature state in the reactor pit chamber has stabilized. The maximum temperature in various parts of the reactor is several hundred degrees Celsius, and decreases steadily at a rate of about 0.5 degrees Celsius every day and night. The bottom concrete slab of the reactor chamber is intact, and most (~96%) of the fuel is confined within the reactor and within the compartments of the steam-water lines and lower water pipes. In order to eliminate the consequences of the nuclear power plant accident and decontaminate the plant area, the former Soviet government also adopted a series of pollution removal measures in a 30-kilometer area, and carried out long-term buried structure construction for Unit 4.
During the accident, radioactive materials spread over the factory area and fell on the roof of the steam turbine building and Unit 3, as well as on the metal supports of the pipelines.
Due to the fall of radioactive aerosols and radioactive dust, the entire factory area, as well as the walls and roofs of buildings, were also seriously contaminated. The contamination in the factory area is extremely uneven.
In order to reduce the spread of radioactive dust from the factory area, the roof and road shoulders of the steam turbine factory were treated with solutions of different polymers. These measures facilitate fixation of the soil surface and prevent dust from rising.
After the accident, people also made estimates of the main characteristics and possible ecological consequences of atmospheric and ground radioactive pollution.
From the first few days of the accident, monitoring of the radioisotope content in bottom sediments of water bodies within and beyond 30 kilometers was organized.
In the cooling pools of the Chernobyl Nuclear Power Plant, significant radiation effects on its ecosystem can be observed.
Within a 30-kilometer area around the Chernobyl power station, quite high radiation levels were observed in individual sections contaminated by radioactive fallout. This can significantly change the status of radiation-sensitive crops in these sectors. However, the radiation levels in areas 30 kilometers away did not seem to have any obvious impact on plant and animal groups at that time.
Based on the analysis of environmental radioactive contamination in the 30 kilometers surrounding the Chernobyl nuclear power plant, the actual and expected radiation doses to residents of cities, towns, villages and other residential areas were evaluated.
Based on these evaluations, the decision was taken to evacuate Pripyat and some other residents. The evacuated population totaled 135,000 people.
These and other measures will result in residents being exposed to exposures that do not exceed prescribed limits. At the same time, the radiation effects on residents over recent decades were also estimated.
The short-term impact has been eliminated, but the long-term consequences will have to be borne by history. ． ． ． ． ．