Brief introduction of Chernobyl nuclear power plant
The Chernobyl nuclear power plant (5 1 degree 23 minutes 14 seconds east longitude 30 degrees 6 minutes 4 1 second) is located in Pripyat, Ukraine, northwest of Chernobyl. в, 70 miles north of Kiev (1 100 km). The nuclear power plant consists of four reactors, each of which can generate 1 GW of electric energy (3,200 GW of thermal power). During the nuclear accident, four reactors provided 65,438+00% electricity in Ukraine. The workshop project started in the 1960s, and the 1 reactor was put into operation in 1977, followed by No.2 (1978), No.3 (198 1) and No.4 (1978). At the time of the accident, the other two reactors (No.5 and No.6 reactors, each capable of generating 654.38+0 billion watts of electricity) were still under construction. The four reactors in this plant belong to the same type and are called RBMK- 1000. The official has two contradictory statements about the cause of the accident. The first article, published in August, 1986, effectively blamed the accident on the nuclear power plant operator. The second paper, published in 199 1, holds that the accident was caused by the design defects of pressure tube graphite moderated boiling water reactor (RMBK), especially the design of control rods. The investigation teams of both sides were lobbied by many parties, including reactor designers, Chernobyl nuclear power plant staff and the government. Now some independent experts believe that neither theory is completely correct. Another important factor contributing to the accident was that the staff did not receive reports of reactor problems. According to employee Anatoli Dyatlov, the designer knew that the reactor would be dangerous in some cases, but deliberately concealed it. The reason for this situation is that the factory director widely boasted about the employees without RMBK qualification: the factory director V.P. Bryukhanov, who has training and experience in coal-fired power plants. Nikolai Fomin, his chief engineer, is also from a conventional energy plant. Anatoli Diart, deputy chief engineer of No.3 and No.4 reactors, has only "some experience of small reactors", and the small version of VVER reactor is a nuclear submarine design of the Soviet Navy. ) Specifically, the positive vacancy rate of the reactor is dangerously high. Simply put, this means that if steam bubbles form in the reactor coolant, the nuclear reaction will accelerate, and if there is no other intervention, it will lead to escape reaction. To make matters worse, at low power output, this other factor cannot compensate for the positive vacancy factor, which will make the reactor unstable and dangerous. The danger of the reactor at low power is contrary to expectations, and the staff knows nothing about it. The more important defect of the reactor is the design of control rods. In a nuclear reactor, control rods are inserted into the reactor to slow down the nuclear reaction. However, in the design of RBMK reactor, the control rod part is hollow; When the control scale is inserted, the coolant is offset by the hollow shell of the control rod in the first few seconds. Because the coolant (water) is a neutron absorber, the output power of the reactor actually rises. This situation is also contrary to expectations, and the reactor operators are unaware of it. The operators were careless and violated the regulations, partly because they didn't realize the design defects of the reactor. Some procedural irregularities contributed to the accident. Another reason is the lack of communication between the safety officer and the operator in charge of the experiment that night. It is worth noting that the operator has shut down the safety system of many reactors, which is prohibited by the Technical Guidelines unless the safety system fails. According to the report 1986 released by the government investigation committee in August, the operators removed at least 204 control rods from the reactor core (this type of reactor needs 2 1 1), and there are 7 left. The same guideline (as mentioned above) is to prohibit RBMK- 1000 from operating with less than 30 control rods in the core area.
event
On April 25th, 1986, No.4 reactor was scheduled to be closed for regular maintenance. It is decided that in this cooperation, in order to test the capability of the reactor turbine generator, sufficient power will be provided to the safety system power supply (especially the water pump) of the reactor in case of power loss. Like Chernobyl, the reactor has a pair of diesel power scales, which can be used as a backup, but can't be started immediately-the reactor will be used to rotate the turbine, and then the turbine will be separated from the reactor and rotated by its own inertia. The goal of the test is to determine whether the turbine can fully supply pump power during the reduction stage when the generator is started. This test has been successfully carried out in other units before (all safety supplies have been started), and the result is failure (that is, the power generated by the steam turbine is not enough to provide power for the pump in the decompression stage), but other improvements indicate that other tests are needed. In order to test in a safer and lower power environment, the energy output of Chernobyl No.4 reactor was reduced from 3.2 GW of normal power to 700 MW. However, due to the delay in the start of the experiment, the reactor controller reduced the energy level too quickly, and the actual power output dropped to only 30 million watts. Therefore, the neutron-attracted fission product xenon-135 has increased (this product is usually consumed in higher power reactors). Although the scale of power reduction is close to the maximum allowed by safety regulations, the managers of the staff team chose not to shut down the reactor and continue the experiment. Later, the experiment decided to "cut corners" and only increased the power output to 200 MW. In order to overcome the neutron absorption of residual xenon-135, the control rods far exceeding the safety regulations were pulled out of the reactor. On the morning of April 26th 1: 05, as part of the experiment, the water pump driven by the turbine generator was started. Because of this action, the flow of water exceeds the safety regulations. The water flow rate increases at 1 h 19 a.m.-Because water will also absorb neutrons, it is necessary to manually remove the control rods to further increase the water flow rate, which will lead to extremely unstable and dangerous operating conditions. In the morning 1: 23: 04, the experiment began. The unstable state of the reactor shows nothing on the control panel, and it seems that all reactor employees are not fully aware of the danger. The power of the water pump is turned off, driven by the inertia of the turbine generator, and the water flow speed is reduced. When the steam turbine is separated from the reactor, the steam level in the reactor core will rise. Because the coolant is heated, separate steam is formed in the coolant pipe. The special design of Chernobyl RBMK graphite mitigation reactor has a high positive vacancy factor, which means that the power of the reactor increases rapidly due to neutron absorption when there is no water. In this case, the operation of the reactor becomes unstable and more dangerous. At 1: 23: 40 in the morning, the operator pressed the AZ-5 ("fast emergency defense 5") button which ordered "emergency shutdown"-all control rods were inserted, including those that were accidentally taken away before. It is not clear whether this is an emergency measure or just a routine method to shut down the reactor when the experiment is completed (the reactor is planned to be shut down for routine maintenance). This usually means that the emergency shutdown command is a response to an unexpected rapid increase in power. On the other hand, Anatoly Diart, the chief engineer who was at the Chernobyl nuclear power plant at the time of the accident, wrote in his book: "Before the centralized control system of 1: 23: 40 ... no parameter changes that could justify the emergency shutdown were recorded. According to this statement, the Committee ... will collect and analyze a lot of materials. In its report, it was not sure why the emergency shutdown was ordered. There's no need to find an excuse. After the experiment was completed, the reactor was simply shut down. " Due to the control rod insertion mechanism (18 completed slowly to 20 seconds), the hollow part of the rod and the coolant temporarily shifted and escaped, resulting in an increase in the reaction rate. The increased energy product leads to the deformation of the control rod pipeline. After the rod is inserted, it gets stuck and can only enter one third of the pipeline, which can't stop the reaction. At 1: 23: 47, the output of the reactor soared to about 30 GW, which was ten times that of normal operation. The fuel rods began to melt, and the steam pressure increased rapidly, which led to the explosion of large steam, which displaced and damaged the top of the reactor, and the coolant pipe burst, blasting a hole in the roof. In order to reduce the cost and its volume is too large, the reactor is built in a single protective layer. This led to radioactive pollutants entering the atmosphere after the main pressure vessel burst due to steam explosion. After a part of the roof was blown up, oxygen flowed in-combined with extremely hot reactor fuel and graphite moderator-causing graphite to catch fire. The fire spread radioactive materials and polluted a larger area. Because the eyewitness reports are inconsistent with the radio records, there are some claims that the actual incident occurred at 1: 22: 30 local time. Finally, the agreed version is as above. According to this theory, the first explosion occurred at about 1: 23: 47, and the operator ordered "emergency stop" after 7 seconds.
What happened afterwards?
After the explosion, it did not attract the attention of Soviet officials. The information that nuclear experts and Soviet leaders got in Moscow was only "a fire broke out in the reactor, but it didn't explode", so the official response of the Soviet Union was slow. 48 hours after the accident, some villages near the nuclear power plant began to evacuate, and the government also sent troops to force people to evacuate. At that time, hundreds of times of deadly nuclear radiation was detected in the village near the scene, and the radiation value was still rising. But this still didn't attract attention. Experts would rather believe that it is a machine failure to measure radiation than that there will be such high radiation. However, residents have not been told the whole truth, because officials are worried that this will cause people to panic. Many people have absorbed a lethal amount of radiation before evacuation (if they can evacuate immediately, the number and degree of victims can be greatly reduced). Three days after the accident, the investigation team sent by Moscow arrived at the scene, but they didn't have time to submit the report and the Soviet government didn't know the truth. Finally, nearly a week after the incident, Moscow received news from the Swedish government. At this time, the radiation cloud has drifted to Sweden. The Soviet Union finally realized that things were not as simple as they thought. In the following months, the Soviet government sent countless manpower and material resources to finally put out the fire in the reactor and control the radiation at the same time. However, these people responsible for cleaning up also suffered serious radiation damage; One of the reasons is the technical limitation of the remote control robot. The serious radiation leads to the failure of the electronic circuit of the remote control robot, so the cleaning of many most polluted places still depends on manpower.
Edit the direct impact of this paragraph.
Radioactive dust leaked from the melting of atomic furnaces drifted over Russia, Belarus and Ukraine, as well as parts of Europe, such as Turkey, Greece, Moldova, Romania, Lithuania, Finland, Denmark, Norway, Sweden, Austria, Hungary, Czech Republic, Slovakia, Slovenia, Poland, Switzerland, Germany, Italy, Ireland, France (including Corsica) and Britain. At the earliest time of the accident, some people thought that the Chernobyl nuclear leak came from Sweden rather than Russia. After the accident, the dose map of nuclear radiation in Europe was displayed.
1on April 27th, 986, the staff of Forsmark nuclear power plant in Sweden found abnormal radiation particles stuck on clothes. The power plant is about1100km away from Chernobyl. According to Swedish research, it was found that the radiation did not come from local nuclear power plants, and they suspected that it was a problem with Russian nuclear power plants. At that time, Sweden asked the Soviet Union through diplomatic channels, but it was not confirmed. In addition, the French government claimed that radioactive dust only drifted to the border between Germany and Italy. Because of radioactive dust, Italy stipulates that some crops are forbidden to people, such as mushrooms. In order to avoid causing public fear, the French government did not conduct similar measurements. The Chernobyl disaster not only polluted the surrounding towns and villages, but also was helped by the airflow, so it could spread irregularly. According to the reports of Russian and western scientists, 60% of radioactive dust falling from Russia is in Belarus. According to the report of Torch 2006, half of volatile particles fall outside Ukraine, Belarus and Russia. A large area in southern Bryansk, Russian Federation, and parts of northern Ukraine have been polluted by radioactive materials. Immediately after the accident, 203 people were sent to hospital for treatment, of which 3 1 person died, and 28 of them died of excessive radiation. Not knowing the danger of radiation in the accident, most of the victims were firefighters and paramedics. In order to control the spread of nuclear radiation dust, the authorities immediately sent people to evacuate 65,438+035,000 people from their homes, of whom about 50,000 were residents of the town of Puri Piater near Chernobyl. Health units predict that in the next 70 years, the proportion of people exposed to 5–12 Aybek radiation will increase by 2%. In addition, 10 people have been exposed to radiation and died of cancer. Russian scientists reported that Chernobyl No.4 reactor contained 180 to 190 tons of uranium dioxide and nuclear waste generated by nuclear reaction. They also estimate that about 5%-30% of these substances flow to the outside. However, according to the cleaners who have been to the sarcophagus reactor for subsequent treatment (such as Usatenko and Dr. Kalpan), only about 5%- 10% of the material is left in the reactor. Photos of the reactor show that the reactor is completely empty. Due to the high temperature caused by the fire, many radioactive substances rushed into the upper atmosphere and spread in all directions. In a disaster, the staff responsible for recovery and consolidation are called "cleaners". The cleaner received a high dose of radiation during the cleaning process. According to Russian estimates, within two years after the disaster, about 300,000 to 600,000 cleaners went to the reactor within 30 kilometers to remove radiation pollutants. Soviet Disaster Investigator Medal
In the areas polluted by radiation, there are many children whose radiation dose is as high as 50 Gy. This is because they absorbed locally produced milk contaminated by radiation in the process of drinking milk. Local milk was polluted by iodine-13 1, and the half-life of iodine-13 1 was 8 days. Many studies have found that the proportion of children suffering from thyroid cancer in Belarus, Ukraine and Russia has also increased rapidly. According to the statistics after the atomic bombing in Japan, leukemia in Chernobyl will increase in the next few years. But so far, the increase of leukemia cases is not enough to infer statistically, which is related to radiation leakage. However, it has been proved that the birth rate of deformed babies in Chernobyl has indeed increased. Some surveys show that this is the result of radiation dust after the radiation disaster.
After editing this accident
The Chernobyl power plant did not stop running because of the problem of Unit 4, but only closed Unit 4 and separated it from other units with 200 meters of cement. However, due to the lack of energy, the Ukrainian government allowed the other three units to continue to operate. A fire broke out in Unit 199 1, and the Ukrainian government authorities subsequently announced that Unit 2 could not be repaired and had to stop running. 1 996165438+1October, according to the agreement between the Ukrainian government and the International Atomic Energy Agency,1unit stopped running. In June 2000, Ukrainian President Leonid Danilovic Kuchma shut down Unit 3 at an official ceremony. At this point, the entire Chernobyl nuclear power plant stopped generating electricity and never operated again.
Future maintenance requirements
The damaged unit 4 is protected by a sarcophagus cement fence to prevent radiation from spreading, but this is not always safe. The reason is that the sarcophagus built by industrial remote control robot is seriously aging. If the sarcophagus collapses, it may cause the crew to release radioactive dust. The fragility of these sarcophagus may cause their roofs to collapse, even if it is a small earthquake or a strong wind. Therefore, the authorities have formulated several schemes to help the fence. According to official estimates, after the accident, there is still about 95% fuel in the reactor (180 metric tons), and the total radioactivity of this fuel is about180,000 Ci(670 PBq). At present, the residual radioactive substances have hardened into ceramic-like substances. They are mainly in the early stage of the accident, and the core fragments of the reactor can wander around in the reactor, consisting of other dust and lava-like "fuel-containing substances" (FCM). It is uncertain when these ceramic-like substances will delay the release of radioactive materials. According to secret estimates, there are at least 4 tons of radioactive dust in the nuclear power plant. However, the latest estimate has investigated the amount of fuel and kept it in the reactor. Some estimates point out that the total amount of fuel put into fuel reactors is only about 70% of the original fuel. Because of the explosion, the International Atomic Energy Agency lost 5% of the fuel. Moreover, some liquidators estimated that 5 V 10% of the original fuel was only contained in this sarcophagus. As for other aspects, water continues to leak into the reactor. Throughout the reactor building, the flooded environment is spreading radioactive materials. The basement of the reactor building is also slowly filled with substances contaminated by nuclear fuel, and radioactive wastewater is released. Although the hole formed in the roof has been repaired, in this case, the hole can only continue to deteriorate. When the sarcophagus is sealed, heating is easier than cooling, which increases the humidity level in the nuclear power plant. At the same time, it continues to corrode the concrete and steel bars in this sarcophagus in the high humidity of the reactor.
The consequences of further collapse
At present, the roof of the reactor ruins is built by the reactor building. These two so-called "giant beams" not only support the roof of the reactor, but also support the walls of other reactor buildings that rely on this structure. If the walls of the reactor building and the roof of the reactor collapse, an amazing amount of radioactive dust and particles will be released directly into the air, causing radioactive substances to destroy the surrounding environment. A further threat to the reactor is that the position of the sarcophagus itself is very unsafe, because the rubble supports it almost vertically. If the sarcophagus collapses, it will further increase the pressure on the nuclear power plant and spread radioactive materials. This sarcophagus not only covers the damaged reactor, but also contains the residual radioactive materials from the No.4 reactor. When a new sarcophagus design is put forward, the life can only be predicted as 100 years at most. Therefore, the construction of the permanent sarcophagus will undoubtedly be a challenging project for the next few contract engineers.
Edit this eternal nightmare
Blocking pollution sources is an arduous task, and removing nuclear radiation dust is another arduous task. A year later, the first batch of nuclear power plant workers and firefighters killed in the Chernobyl nuclear accident were transferred to a cemetery in Moscow and buried in special lead coffins! Because their remains have become radioactive sources that can pollute normal people. Nuclear dust is almost everywhere. Nuclear radiation has polluted tens of millions of square kilometers of fertile farmland in Ukraine. As a result of the Chernobyl accident, more than 2.5 million people in Ukraine suffered from various diseases, including more than 473,000 children. According to experts' estimation, it will take at least 800 years to completely eliminate the impact of this catastrophe on the natural environment, and the continuous nuclear radiation risk will last for 654.38 million+years. Economically, the former Soviet Union lost about 9 billion rubles: more than 4 billion rubles in the aftermath, and more than 4 billion rubles in agriculture and electricity production. Experts estimate that it will cost billions of dollars to clean up only one item except the loss of the nuclear power plant itself. If all of them are added up, it may reach tens of billions of dollars. The accident area of Chernobyl nuclear power plant in Ukraine will be open to tourists (but protective clothing must be worn). According to a report by RIA Novosti on February 12, Ukrainian Minister of Emergency Situations Baloga announced on February 12 that the accident area of Chernobyl nuclear power plant will be open to ordinary tourists from 20 1 1 day, and the Ukrainian Ministry of Emergency Situations plans to organize a visit to this area. Ukrainian Emergency Minister Baloga announced that the direction of Chernobyl is limited to extreme tourism, not mass tourism, and it is only open to foreign tourists organized by several private companies. Baloga believes that the territory of Chernobyl should be open to ordinary tourists. The Ministry of Emergency Situations of Ukraine is doing a lot of work and plans to report the results before the end of this year, so that this visit will become a regular and systematic form of tourism in June 5438+next year 10. Clark, Administrator of the United Nations Development Programme, supports the tourism initiative of the Ministry of Emergency Situations of Ukraine. She said that visiting Chernobyl can help people understand the tragic history and re-recognize the importance of nuclear facility safety. Although this is a very sad history, this tourist attraction also has certain economic potential. The accident at the Chernobyl nuclear power plant occurred in the territory of the Ukrainian Soviet Republic on April 26th 1986. The fourth generator set of the power plant exploded, all the nuclear reactors were destroyed, and a large number of radioactive materials leaked, which became the biggest accident since the nuclear power era. The radiation hazard is serious, resulting in the death of 3 1 person in the first three months after the accident, followed by the death of 60,000-80,000 people in 15 years.134,000 people suffered from radiation diseases of different degrees, and more than10/50,000 people within 30 kilometers of Fiona Fang were forced to evacuate. In order to eliminate the consequences of the accident, a lot of manpower and material resources were consumed. Ukraine and the international community have been working hard to eliminate radiation hazards and ensure the ecological safety of the accident area. Ukrainian Minister of Emergency Situations Baloga pointed out that the new "bunker" for completely covering Unit 4 will be completed in 20 15. It is an arch-shaped building with a length of150m, a width of 260m and a height of105m, which is used to completely cover Unit 4 and the temporary protective facility "sarcophagus" previously built. The "bunker" project was supported by donations from the international community. Construction funds were raised by the G8 and 28 Council of Europe member countries and managed by the European Bank for Reconstruction and Development. After 10 years of selection and demonstration, the project is now stepping up construction. It should effectively protect the surrounding environment of the accident area and ensure that some faulty and unreliable structures can be installed and removed. It is believed that this comprehensive protection facility can be completed and used in 20 15. Earlier, Ukrainian First Deputy Prime Minister Klyuyev announced that the total cost of the "bunker" project had increased from 505 million euros in 2004 to 870 million euros now due to the sharp increase in security requirements. Clark, Administrator of the United Nations Development Programme, promised that the United Nations will continue to fully support the construction of the project in the future, and the Ukrainian government should also continue its dialogue with international partners.
Edit this paragraph. The accident area is open.