A nuclear accident is any local or series of accidents that originate from the same cause of nuclear damage. In general, an unexpected situation in a nuclear facility (e.g. a nuclear power plant) that results in the leakage of radioactive material and exposes staff and the public to exposure exceeding or equivalent to the prescribed limits is called a nuclear accident. Obviously, the severity of nuclear accidents can be very wide-ranging, and in order to have a uniform standard of understanding, the international level of safety-important incidents occurring in nuclear facilities is divided into seven levels.
The impact of nuclear leakage on personnel in general is mainly manifested in nuclear radiation, also known as radioactive materials, radioactive materials are an energy emitted in the form of waves or particles, called nuclear radiation, nuclear explosions and nuclear accidents have nuclear radiation. It has three forms of radiation: α, β and γ. Among them: 1) α radiation can be blocked with a piece of paper, but inhalation into the body is very harmful; 2) β radiation is a high-speed electron, and the burn is obvious after the skin is stained; 3) γ radiation is similar to X-rays, can penetrate the human body and buildings, and the harm distance is far. Although there are many radioactive substances in the universe and nature, the harm is often not too great, and only radioactive materials leaked by nuclear explosions or nuclear power plant accidents can cause casualties on a large scale.
While nuclear energy provides energy, the occurrence of catastrophic accidents such as nuclear power plant accidents and leakage of radioactive materials also causes major harm to human beings and even serious disasters. This article will take stock of the world's top ten major nuclear disasters, here are the details:
I. Chernobyl accident (Pripyat, Ukraine)
The Chernobyl nuclear accident was a nuclear reactor accident that occurred at the Chernobyl nuclear power plant in Ukraine in the former Soviet Union. The accident is considered the worst nuclear power accident in history and the first major accident to be rated as a level 7 incident by the International Nuclear Incident Classification Table (the second in the world so far is the Fukushima Daiichi Nuclear Power Plant accident in Fukushima Prefecture, Japan, on March 11, 2011).
At 1:23 a.m. (UTC+3) on 26 April 1986, reactor No. 4 of the Chernobyl nuclear power plant near Pripyat in Ukraine exploded. The ongoing explosions triggered fires and emitted large amounts of high-energy radioactive material into the atmosphere, which covered a large area. According to statistics, the disaster released more than 400 times the radiation dose of the atomic bomb that exploded on Hiroshima during World War II.
Economically, the nuclear catastrophe cost a total of about $200 billion (inflation has been calculated), making it the most expensive catastrophe in recent history. The Chernobyl accident has been called the worst nuclear power accident in history. The city of Pripyat was thus abandoned.
Due to inconsistencies between eyewitness reports and site records, there is some controversy that the actual incident occurred at 1:22:30 local time. According to this theory, the first explosion occurred at about 1:23:47, and the operator ordered an "emergency stop" seven seconds later.
The Chernobyl accident at the time resulted in 31 deaths on the spot, tens of thousands of people fatal or seriously ill due to the long-term effects of radioactive materials, and there are still births of deformed fetuses due to radiation effects. The radioactive dust that was leaked out at that time drifted with the atmosphere to the western part of the former Soviet Union, Eastern Europe, and scandinavia in northern Europe. Among them, Ukraine, Belarus and Russia are the most heavily polluted, and due to the direction of the wind, it is predicted that about 60% of the radioactive material will fall on the land of Belarus. The accident not only raised public concerns about the safety of the Soviet nuclear power plant, but also the belief that the accident indirectly led to the collapse of the Soviet Union.
After the collapse of the Soviet Union, the post-independence countries, including Russia, Belarus and Ukraine, continued to invest every year in the aftermath of the disaster and the health care of their residents. The number of people who died directly or indirectly as a result of accidents is difficult to estimate, especially since the long-term effects of accidents remain unknown to date.
Soon after the accident, 203 people were taken to hospital for treatment, of whom 31 died and 28 died of excessive radiation. Most of those who died were firefighters and ambulance crews. In an effort to control the spread of radioactive soot from nuclear power, authorities immediately sent 135,000 people to evacuate their homes, about 50,000 of whom were residents of the town of Pripyat near Chernobyl. The health unit predicts that the proportion of people who receive cancer from 5–12 Ibeck radiation will increase by 2% over the next 70 years.
According to official 2006 statistics, more than 4,000 people have died so far. But Greenpeace, based on data from the Belarusian National Academy of Sciences, found that in the past 20 years, the total number of victims of the Chernobyl nuclear accident may have reached more than 90,000. Therefore, Greenpeace believes that the official statistics are at least 90,000 fewer than the death toll from the Chernobyl nuclear leak, which is 20 times the official statistics! Of course, there is a lack of theoretical support for Greenpeace's "estimates." The economic loss of Chernobyl is about 18 billion rubles.
As early as 2013, a study in the United States showed that the Chernobyl nuclear accident had a sustained adverse impact on local trees that year. A joint study by the University of South Carolina and other institutions in the United States shows that due to long-term exposure to radiation, many trees in the Chernobyl area have developed very abnormal morphology, mainly because of mutations in the genes of trees. The increasing number of genetic mutations obviously affects the growth, reproduction and survival rate of trees.
For Chernobyl, plugging the sources of pollution is a very difficult task, while removing radioactive dust is another very difficult task. In particular, a year after the accident, the first nuclear power plant workers and firefighters killed in the Chernobyl nuclear accident were transferred to a cemetery in Moscow and buried in specially made lead coffins because their remains became a radioactive source large enough to contaminate normal people.
Nuclear dust can be said to be almost pervasive. Nuclear radiation has polluted tens of thousands of square kilometers of fertile land in Ukraine. More than 2.5 million people in Ukraine, including more than 473,000 children, suffer from various diseases as a result of Chernobyl.
Industry experts estimate that it will take at least 800 years if the impact of the catastrophe on the natural environment is completely eliminated, and the ongoing radiation hazard will last for 100,000 years.
Economically, the former Soviet Union lost about 9 billion rubles: of which more than 4 billion rubles were spent on the aftermath and more than 4 billion rubles were lost in agriculture and electricity production. Experts estimate that in addition to the damage to the plants themselves, it would cost billions of dollars to clean up alone, and if all added up, it could amount to tens of billions of dollars.
The area of the Chernobyl nuclear power plant in Ukraine was opened to tourists after the accident (but protective clothing must be worn). Ukraine's Minister of Emergency Situations, Baroga, has announced that from 2011 the Chernobyl nuclear power plant accident area will be open to ordinary tourists, and the Ukrainian Ministry of Emergency Situations plans to organize regular and systematic tourist routes to visit the area. UNDP Administrator Clarke, who supports the tourism initiative of Ukraine's Ministry of Emergency Situations, said a visit to the Chernobyl region would allow people to learn about the tragic history and rediscover the importance of nuclear facility safety.
Ukraine's Minister of Emergency Situations Baroga has noted that the new "bunker" for full coverage of Unit 4 will be fully completed in 2015, which is a 150-meter-long, 260-meter-wide and 105-meter-high arched building used to fully cover Unit 4 together with the temporary protective facility "sarcophagus" previously built. The "bunker" project is supported by donations from the international community, and construction funds are raised by a total of 28 countries of the Group of Eight and the member states of the Council of Europe, of which the construction fund is managed by the European Bank for Reconstruction and Development.
Earlier, Ukraine's First Deputy Prime Minister Kryyev announced that the total cost of the "bunker" project has increased from 505 million euros in 2004 to 870 million euros now due to the sharp increase in security requirements. UNDP Administrator Clark promised that the United Nations will continue to fully support the construction of the project in the future.
2. Fukushima Nuclear Accident (Fukushima Prefecture Industrial Zone, Japan)
The Fukushima Nuclear Power Plant is located at 37 degrees 25 minutes 14 seconds north latitude and 141 degrees 2 minutes east longitude, located in the Fukushima Industrial Zone in Japan. It is currently the largest nuclear power plant in the world, consisting of Fukushima Station 1 and Fukushima Station 2, with a total of 10 units (6 units in 1 station and 4 units in 2 stations), all of which are wastewater dumps. On March 12, 2011, the Atomic Energy Safety and Security Agency of the Ministry of Economy, Trade and Industry of Japan announced that radioactive material from the Fukushima Daiichi Nuclear Power Plant had leaked to the outside world due to the earthquake.
On March 12, 2011, radioactive material from the Fukushima Daiichi Nuclear Power Plant leaked to the outside world due to an earthquake. On April 12, 2011, The Japan Atomic Power Safety and Security Agency designated the Fukushima nuclear accident as the highest level of nuclear accident level 7 and the Chernobyl nuclear accident. Fukushima Prefecture conducted thyroid tests in the wake of the nuclear accident, targeting about 380,000 children in the prefecture. As of February 2018, 159 people have been diagnosed with cancer and 34 are suspected of having cancer. Of the 84 patients in Fukushima Prefecture who were diagnosed with thyroid cancer and underwent surgery, about 80% had a recurrence of cancer and underwent surgery again.
There have also been many accidents before the Fukushima Daiichi and Nikawa nuclear power plant accidents. For example, in 1978, a critical accident occurred at the Fukushima Daiichi Nuclear Power Plant, but the accident was concealed until 2007.
In August 2005, an earthquake in Japan with a magnitude of 7.2 on the Richter scale spilled water from the pools storing nuclear waste at two nuclear power plants in Fukushima Prefecture. In 2006, a radioactive material leak occurred in Unit 6 of the Fukushima Daiichi Nuclear Power Plant.
In 2007, TEPCO admitted that it had tampered with data and concealed safety hazards during a total of 199 regular inspections of its three nuclear power plants since 1977. Among them, the data measured by the main steam pipe flow meter of the reactor of Unit 1 of the Fukushima Daiichi Nuclear Power Plant was tampered with 28 times between 1979 and 1998. The former chairman of Tokyo Electric Power Company resigned as a result.
The explosion at the Fukushima nuclear power plant is a chemical explosion, an explosion caused by the reaction of hydrogen and air leaked into the reactor plant. The Fukushima nuclear power plant uses MOX fuel, and the shell of the fuel rod is zirconium alloy. Due to the failure of the emergency cooling system due to earthquakes and tsunamis, the cooling level in the reactor was reduced for a time, and the core of the reactor was exposed. Insufficient cooling causes the fuel rod casing to exceed the limit temperature of the zirconium-water reaction, and eventually a zirconium-water reaction occurs to generate a large amount of hydrogen.
It is widely believed in the industry that hydrogen leaks into the plant and is discharged from the gas channel of the pressure relief valve when the pressure in the containment vessel rises. Since the concentration of hydrogen relative to the air in the plant has reached the explosion limit, the explosion occurs after encountering high temperatures or even open flames. The impact of the explosion completely knocked off the roof of the factory building, leaving only the steel skeleton.
Leakage of radioactive materials and leakage of nuclear energy, also known as nuclear meltdown, is a serious sequelae that occurs when a nuclear energy reactor fails. Although the radiation emitted by nuclear energy leakage is far less powerful and influential than nuclear weapons, it can cause almost the same degree of biological casualties.
The Atomic Energy Safety and Security Agency said in a statement at the time that the radiation level in the central control room of Unit 1 of the Fukushima Daiichi Nuclear Power Plant, which was automatically shut down by the earthquake, had reached 1,000 times the normal value.
In order to prevent the pressure inside the vessel where the nuclear reactor was placed from rising, causing the vessel to break due to inability to withstand the pressure, the Atomic Energy Safety and Security Agency had ordered TEPCO to release steam from the reactor vessels of Units 1 and 2 of the Fukushima Daiichi Nuclear Power Plant to the outside.
Tokyo Electric Power Company was preparing to release steam from Unit 1, the first of the three reactors at the Fukushima Daiichi Nuclear Power Plant. Units 2 and 3, if the function of cooling reactors cannot be restored as soon as possible, will take the same measures. Tokyo Electric Power Company has previously pointed out that the steam in the reactor container of Unit 1 of the Fukushima Daiichi Nuclear Power Plant will pass through a huge pool and then be released from the exhaust cylinder. When passing through the water, the radioactive material will be reduced to some extent, and the staff will always be observing the amount of radioactive material at the outlet of the exhaust cylinder. In addition, the Fukushima Daiichi Nuclear Power Plant has lost its cooling function, and Tokyo Electric Power Company has begun to release steam from the reactor vessels of Fukushima Daiichi Nuclear Power Plant Units 1 and 2 when it exploded (15 photos) to reduce the pressure on the vessel and prevent greater damage. The company is also preparing to release steam from two other reactors inside the plant to the outside.
This became the first emergency avoidance measure in Japan to open a valve at a nuclear power plant to release steam outward. Although this initiative may also lead to the leakage of radioactive material into the external environment, it will avoid the failure of the container to cause the nuclear power plant to lose its closed function.
Previously, due to a valve failure, Japanese rescuers were unable to open the exhaust port of reactor No. 2, resulting in extremely high pressure in the reactor and the inability to inject seawater used to cool the reactor. This means that Japan's last resort to cooling the reactors has failed, so that a large amount of nuclear fuel has been exposed to the air for several hours, and the possibility of a nuclear leak is extremely high.
Although rescuers eventually repaired the pressure relief valve, they were unable to fully flood the hot fuel rods with seawater, and as a result, the temperature inside reactor 2 continued to rise until a violent explosion occurred.
Japan could only continue to pour water into the four reactors to cool down, while constantly discharging steam with radioactive contaminants, and hoped that the local wind would always maintain a westerly wind, no east wind and south wind, otherwise the Japanese capital Tokyo and the Korean Peninsula would be polluted. At the same time, it is to wait for the reactor to cool down naturally to a safe state, and then completely seal the nuclear power plant into obsolescence. Radioactive materials detected around the Japan Nuclear Power Plant include iodine-131 and cesium-137. Among them, once iodine 131 is inhaled by the human body, it may cause thyroid disease. The Japanese government has planned to distribute iodine tablets, a drug to protect against iodine-131 radiation, to residents near nuclear power plants. Relevant information shows that cesium-137 can cause damage to the human hematopoietic system and nervous system.
U.S. analysts point out that the current state of Japan's Fukushima nuclear power plant is similar to the nuclear leakage accident that occurred at the Sanridao nuclear power plant in Pennsylvania in the United States in 1979. International nuclear accidents are classified in magnitude zero to 7 according to their severity. The Three Mile Island nuclear accident in the United States was classified as Class 5, when at least 150,000 residents were forced to evacuate due to a failure of the refrigeration system, which led to the leakage of radioactive material.
Yonhap News Agency quoted Japanese media in 2011 as saying that higher radioactive material than usual had been detected in Japan's Kanto region, including Tokyo. Radioactive material detected in Ibaraki Prefecture was 100 times higher than usual, and the radioactive material content in Kana Prefecture was nearly 10 times higher than usual. In addition, high levels of radioactive material have been detected in Chiba Prefecture and Ichihara Prefecture. According to Japan's Kyodo News Agency, measurements from unit 3 of the Fukushima nuclear power plant at the time showed that the level of nuclear radiation was 400 times higher than the legal standard.
The Fukushima nuclear power plant has at least the same level of leakage as the 1979 nuclear leak on three mile island in the United States. However, some experts believe that the Fukushima nuclear accident is more serious than the Three Mile Island incident. The Chernobyl nuclear spill is classified as a grade VII.
The huge leak at the Chernobyl nuclear power plant in 1986 was finally resolved by "mothballing" the reactor. According to the data detected at the time, the Japanese nuclear leak had reached the pollution level of the Chernobyl nuclear power plant.
The Atomic Energy Safety and Security Agency of japan's Ministry of Economy, Trade and Industry has said that the concentration of radioactive iodine in the waters near the drainage of the Fukushima Daiichi nuclear power plant has reached 3,355 times the legal limit at that time, which is the highest relevant value detected by the Japanese side in this water area so far.
The Japan Broadcasting Association Television previously reported that the Atomic Energy Safety and Security Agency of the Ministry of Economy, Trade and Industry of Japan decided to raise the level of nuclear leakage at the Fukushima Daiichi Nuclear Power Plant to level 7. This makes the level of nuclear accidents in Japan the same as those at the Chernobyl nuclear power plant in the Soviet Union.
The 1986 nuclear leak at the Chernobyl nuclear power plant in the Soviet Union was defined as the most serious of class 7. On April 26 of that year, reactor No. 4 of the Chernobyl nuclear power plant in present-day Ukraine exploded, causing a leak of more than 8 tons of intense radiation. The nuclear leakage accident directly polluted more than 60,000 square kilometers of land around the power station and affected more than 3.2 million people by nuclear radiation, causing the largest disaster in the history of the peaceful use of nuclear energy by mankind.
Under international treaties such as general international law and the United Nations Convention on the Law of the Sea, Japan has the obligation to protect and preserve the marine environment and to take all necessary measures to prevent, reduce and control the pollution of the marine environment. In particular, for activities that are likely to have a significant impact on the marine environment, their possible impact should be assessed in advance and their impact observed, measured, estimated and analysed. When it becomes aware that the marine environment is in imminent danger of pollution damage or has already been contaminated, other States and competent international organizations likely to be affected shall be immediately informed.
The United Nations Convention on the Law of the Sea, the Convention on Nuclear Safety and the Convention on Early Notification of a Nuclear Accident are not clearly defined as to whether nuclear waste can be discharged into the sea. However, the transfer of pollution caused by Japan's discharge of nuclear sewage is bound to increase the possibility of causing damage to other countries. For accidents that may cause cross-border impacts, the obligation of the parties concerned to notify is clear in international law, which is the most basic legal and moral requirement for the parties concerned, an objective condition for the outside world to judge whether Japan's response measures and means are reasonable and necessary, and the basis for the relevant countries to take effective countermeasures and avoid the expansion of the impact.
Let's talk about the eye-catching discharge of nuclear sewage in Japan: According to Xinhua News, Tokyo Electric Power has prepared about 1,000 water storage tanks in order to store nuclear wastewater, and 90% of them have been filled. The total capacity of all water storage facilities in Japan at that time was about 1.37 million tons, and the water storage limit is expected to reach by the autumn of 2022.
According to Japan's Yomiuri Shimbun, Japan's Tokyo Electric Power Company is now adding 140 tons of "treated water" per day, and is expected to reach the upper limit of 1.37 million tons of storage tanks by September 2022.
Since 2013, the Japanese government has evaluated five post-treatment wastewater disposal schemes for formation injection, discharge into the ocean, steam release, hydrogen release, and underground burial.
In February 2020, the ALPS Subcommittee on Purified Water Treatment released an evaluation report on the wastewater disposal plan after the Fukushima nuclear accident in Japan, concluding that both discharge into the ocean and steam release are feasible solutions, of which discharge into the ocean is more convenient, and other disposal options are less considered in terms of economy, technological maturity or timing.
The German Marine Scientific Research Institute pointed out that the Coast of Fukushima has the strongest ocean current in the world, and within 57 days from the date of discharge, radioactive materials will spread to most of the Pacific Ocean and 10 years later. Greenpeace nuclear experts point out that carbon-14 contained in Japan's nuclear wastewater is dangerous for thousands of years and can cause genetic damage.
According to media reports, satellite images of the Fukushima nuclear power plant and its surroundings taken by Gaofen-2 on August 29, 2020 show that there are still large open spaces around the nuclear power plant that can be used, and the sewage tanks are also somewhat rusty (satellite source: Gaofen-2).
As can be seen from satellite images, the earliest batch of wastewater tanks have been rusted, and replacement is sooner or later, and this is also a big cost, so the Japanese government discharges nuclear sewage into the ocean not because of insufficient space, but because it is unwilling to bear the cost of maintenance.
Liu Xinhua, chief expert of the Nuclear and Radiation Safety Center of the Ministry of Ecology and Environment, believes that the Japanese government should adopt wastewater treatment technologies and devices with high decontamination factors to further purify and treat excess nuclides to reduce the radionuclide content in the treated wastewater as much as possible; study the treatment technology of tritium, and timely disclose the research progress and results, if feasible technology should be used immediately for the treatment of tritium in wastewater.
In summary, although the impact of the Chernobyl accident is very large, if Japan's nuclear sewage is discharged into the sea, it will affect all mankind and the entire earth, and from this level and human survival, the level of the accident should be the highest, and its severity is immeasurable.
Three, three miles of nuclear accident (Pennsylvania, United States)
At 4 a.m. on March 28, 1979, a large amount of radioactive material spilled out of the operating room of the Group 2 reactor of the Three Mile Island Nuclear Power Plant in Pennsylvania, USA. In the Three Mile Island incident, the process took only 120 seconds from the negligence of the staff who initially cleaned the equipment to the complete destruction of the reactor.
After 6 days, the core temperature of the reactor begins to drop and the vapor bubbles disappear – the threat of hydrogen explosions is eliminated. Although the 100 tons of uranium fuel was not melted, 60 percent of the rods were damaged and the reactor eventually collapsed. This accident is the fifth level of nuclear accident. After the accident, the whole Country was shocked, the residents near the nuclear power plant were horrified, and about 200,000 people were evacuated from the area. People in major U.S. cities and residents of areas where nuclear power plants are being built have held rallies and demonstrations demanding that nuclear power plants be halted or shut down. The United States and some Governments in Western Europe have had to reconsider the development of nuclear power programmes.
The major accident of the core losing water and the escape of radioactive materials from the second reactor of the Three Mile Island PWR nuclear power plant in the United States was due to the automatic input of the accident cooling system of the second circuit after the failure of the pump of the second circuit, but because the valve of the accident cooling system was not opened after the workers overhauled a few days ago, the water of the second circuit was still cut off after the system was automatically put in. When the temperature and pressure in the reactor rise under this circumstance, the reactor automatically stops the reactor, and the pressure relief valve also automatically opens to release part of the soda mixture in the reactor core.
At the same time, when the pressure in the reactor drops to normal, the pressure relief valve fails to automatically return to the seat due to the fault, so that the core coolant continues to flow out, and the pressure drops below the normal value, so the emergency core cooling system is automatically put in, but the operator does not determine that the pressure relief valve does not return to the seat, but instead closes the emergency core cooling system and stops injecting water into the core. This series of management and operational errors is intertwined with the failure of the equipment, so that a small failure is greatly expanded in a short period of time, resulting in a serious accident of core melting.
In this accident, the main engineering safety facilities were automatically put in, and because the reactor had several safety barriers (fuel cladding, one-circuit pressure boundary and containment, etc.), there were no casualties, and only 3 people at the accident site were irradiated with a permissible dose of slightly more than half a year.
The average amount of the public within 80 kilometers of a nuclear power plant is less than one percent of the natural background in a year, so the impact of the Three Mile Island accident on the environment is minimal.
Three Mile Island is located 3 miles from the Sasquehana River in Dauphin County, Pennsylvania, United States. Babcock and Wilcox built 900,000 kilometers of nuclear power plants on the island, which began in full operation in 1974 and started Plant 2 in 1978. On March 28, 1979, the cryo-valve of The No. 2 equipment, which had been in operation for four months, failed.
Then-U.S. President Jimmy Carter visited the scene of the accident and announced the decision that "the United States will not build any more nuclear power plants." Due to the aftermath of the accident, Babcock and Wilcox eventually collapsed. In the 21st century, the United States has paid the price of stopping the construction of nuclear power plants. In 2000, California experienced a huge gap in power supply capacity, and New York experienced darkness in 2003 due to a lack of electricity. After that, the U.S. government changed its plans and repaired the nuclear power plant to temporarily alleviate the power shortage. The U.S. government, through President Barack Obama, announced plans to rebuild nuclear power plants. But for the past 31 years, the United States has abandoned nuclear power plant construction.
In 2012, the U.S. Nuclear Regulatory Authority (NRC) approved four new units from two nuclear power plants, all of which were AP1000 produced by Westinghouse, namely vogtle and summer.
Nuclear accident in Goiânia (Goiânia, Brazil)
On September 13, 1987, the Goiânia nuclear accident in Brazil was followed by a garbage dump worker who pried open an abandoned radiotherapy machine and removed a small piece of highly radioactive cesium chloride, and the disaster befell the city, and in the end, 14 people were overlit and 4 people died within 4 weeks. About 112,000 people were monitored and 249 were found contaminated.
The accident left hundreds of homes monitored and 85 found contaminated. The entire decontamination campaign produced 5,000 m3 of radioactive waste, and the social impact was so great that in a remote village in Goiânia, where a waste repository was built, the three-leaf symbol symbolizing radioactivity was made into a village flag.
V. Tokaimura Nuclear Accident (Tokaimura, Japan)
At about 10:35 a.m. on September 30, 1999, the nuclear accident at the Tokaimura Uranium Recovery and Processing Facility in northeastern Tokyo was one of the worst nuclear disasters in Japanese history. The accident resulted in the death of two JCO employees and the exposure of hundreds to nuclear radiation.
One hour after the accident, the dose rate of the surrounding γ reached 4 times the normal value, the government evacuated the residents within 350 meters of the factory area, the residents within 10 kilometers of the factory were not allowed to go out, the schools and hospitals were closed, and the harvesting of crops and vegetables was stopped.
Accident: At about 10:35 a.m. on September 30, 1999, at the nuclear fuel processing plant in Tokai village, Naka-gun, Ibaraki Prefecture, Japan, three workers were undergoing a purification step of uranium, and in the process of manufacturing uranyl nitrate, in order to shorten the working time, a worker poured a nitrate solution rich in U-235 (uranium enrichment rate of 18.8%) in a stainless steel drum into the sedimentation tank through a funnel (this operation violated the original use of U3O8 powder into the dissolution tower, And dissolved in nitric acid, and then pumped the material into the storage tower to make the final product uranyl nitrate of the conventional operating procedures), another worker stood next to the sedimentation tank with a hand-held funnel, and the third staff member worked at a desk about a few meters away from the sedimentation tank. According to the calculation, the critical amount of uranium is 2.4kg, and the worker poured 16kg of uranium nitrate solution into the sedimentation tank, which triggered the chain nuclear fission reaction, at that time, in an instant, 3 staff members saw the "blue flash", γ radiation monitoring alarm immediately sounded, and the critical accident occurred. Since the location of the three staff members was 65 cm, 1 m and 2.6 m from the radiation source, they were severely exposed to high doses of neutron and γ rays due to nuclear fission. After the accident, the radiation dose level in the surrounding environment of the plant has risen to 7 to 10 times the usual value.
According to statistics, in this accident, there were about 213 people who were irradiated to varying degrees, of which 2 people were illuminated with doses of 16-23Gy and 6-10Gy, 1 person was 2Gy, 2 people were 10mSv, and the remaining 208 people were about 0-5mSv. Although the three parties to the accident were rescued by medical emergency, one of them died on the 82nd day after the accident, 1 died on the 210th day after the accident, and the other was discharged from the hospital after the accident after the accident because of his good recovery.
From this critical accident at the Donghae Village nuclear fuel processing plant, many defects were found, including emergency handling problems at the time of the accident and rescue and evacuation after the accident. Since the accident unit and the Japanese atomic energy safety management department both believed in advance that there would be no critical accident, they did not formulate a corresponding nuclear accident emergency plan, resulting in a very slow rescue operation after the entire accident, and various command departments were temporarily and hastily established under helpless circumstances.
1) Personnel do not comply with operating procedures
In order to prevent the occurrence of critical accidents and avoid the accumulation of uranium exceeding the critical amount, "critical management" must be strictly implemented. The Tokaimura Nuclear Fuel Processing Plant in Japan had quality control regulations to strictly control the processing or use of uranium. The critical accident occurred because the operator did not strictly abide by the operating procedures, in order to shorten the working time, a large amount of uranium solution exceeding the critical amount of uranium was put into the sedimentation tank. According to the results of the accident investigation, the operators in this accident not only violated the formal operating procedures recognized by the state, but also violated the operating procedures prepared within the unit. Therefore, although there are very well-designed and facilities, there is no guarantee of accidents. It can be seen that it is crucial to further improve and strengthen the safety management mechanism and avoid the recurrence of violations of operating procedures.
2) Lack of protection against neutron radiation
Uranium critical accident will emit neutron radiation, neutron radiation can penetrate the concrete wall, and the accident unit did not consider the monitoring and protection of neutron radiation in advance, the factory is not equipped with the necessary special instruments to monitor neutron radiation, nor is it equipped with protective equipment and supplies to cope with neutron radiation, which undoubtedly brings difficulties to the on-site rescue work, resulting in many rescue personnel having to wait outside the scene and delaying the rescue time. Of course, safe and effective neutron radiation protective clothing, at that time, the world almost did not have.
3) The accident alarm is not standardized
The time when the Donghai Village Fire Brigade received the alarm was 10:43 a.m. on September 30, when the alarm only said that there were emergency patients, please send an ambulance, but did not explain that a nuclear radiation accident had occurred. In the end, the rescue personnel entered the scene of the accident without knowing the truth and without any radiation protection equipment, and suffered different degrees of radiation exposure.
K-431 nuclear submarine accident (former Soviet Union)
In December 1985, the K-431 nuclear submarine leaked on the way back to the base in Vladivostok, the submarine immediately floated to the surface, the leak caused the quality of the coolant in the first circuit to begin to decline, all the personnel diverted water from the submarine's fresh water tank, the reactor was immediately shut down, the leak caused the contaminated water to flow to the sea, radioactive iodine leaks were found in the area around the submarine, and the crew tried to stop the leakage of the cooling system pipes.
At that time, the submarine's crew received emissivity of up to 40 mSv. 10 sailors were killed in the accident and 49 others suffered radiation damage.
Accident: In December 1985, the K-431 nuclear submarine (Type 675 Echo-II class) was on its way back to the base in Vladivostok (Vladivostok), and the Type 675 Echo-II submarine immediately surfaced due to a leak in a circuit. The leak caused the coolant quality in the first circuit to drop, and the entire crew began to divert water from the submarine's fresh water tank. The reactor shuts down immediately. The leak causes contaminated water to flow into the sea, so the radiation level cannot be determined. In the area around the submarine, a leak of radioactive iodine was soon discovered. The crew tried to stop the leaks from the cooling system piping, but how long it would take to shut down the coolant supply was unknown. As the coolant was lost, the temperature of the reactor rose, and the alarm went off. The coolant supply was immediately switched on again, but it was too late.
The resupply of coolant caused the fuel collection to burst due to excessive temperatures, and the water flowed in and came into contact with the uranium fuel. Heavily polluted water was discharged to the Amur, causing the treatment equipment to collapse. At the base, the radioactivity of the contaminated coolant was measured at 0.3 curie/l, totaling 74 megabex, 2000 curiae. The submarine's crew received radiation of up to 40 mSv (4 roentgen).
Maintenance and repair of nuclear submarines in the former Soviet Union was usually carried out in different naval shipyards. This system was defined in the initial phase of the construction of nuclear submarines and was fully rolled out during the Cold War. During this period, almost 25 nuclear submarine models were introduced and developed. The lack of standardization has led to problems in the planning phase, at the level of capacity of the entire crew and in the inefficient use of spare parts. In particular, the quality and safety of the equipment are compromised, which is one of the most important factors why the high probability of accidents in the nuclear submarines of the former Soviet Union compared with American submarines.
VII. Gacca Level Nuclear Accident (Gaca, Nevada, U.S.)
The Gacca Level Nuclear Accident of December 18, 1970. During the Barnabelli nuclear experiment, a 10,000-ton equivalent nuclear device exploded in the Gaka Flat Land in Nevada, USA, and after the experiment, the plug that closed the surface shaft failed, causing radioactive debris to leak into the air. Six staff members at the scene were exposed to nuclear radiation.
Officials at the Nevada test site acknowledge that in the more than 20 years since the United States halted surface nuclear testing and switched to underground nuclear testing, 475 underground nuclear explosions were carried out at the site, including 62 accidents of varying degrees. According to the U.S. Department of Energy's accident classification, 53 were classified as radiation "leaks or leaks" and 7 were classified as "severe radiation leaks." One of the most serious was the 10,000-ton nuclear bomb code-named "Bainbarry" that exploded on December 18, 1970. The bomb was housed in a shaft 900 feet deep and 86 inches in diameter, and after the explosion, the equivalent of 3 million curiae of radioactive material was ejected into the atmosphere at an altitude of 8,000 feet in 24 hours, and its radioactive dust drifted all the way to North Dakota.
VIII. Thule Nuclear Accident (Tulle Air Force Base, United States)
In 1968, the B-52 crash at Tulle Air Force Base in the United States was a plane crash that occurred on January 21, 1968, in which a U.S. Air Force B-52 bomber crashed. It is worth mentioning that this B-52 bomber carried 4 hydrogen bombs, carried out the "Chrome Dome" mission during the Cold War, and when flying over Baffin Bay in the Arctic Ocean, the crew was forced to abandon the aircraft before landing due to a fire in the cabin. Six crew members managed to escape, but 1 died while trying to skydive because they did not have a catapult seat.
The plane then crashed into The Polaris Bay in Greenland, causing four hydrogen warheads to rupture and spread, creating widespread radioactive contamination.
The United States and Denmark launched a centralized clean-up and recovery effort, but one of the warheads was not found. As a result, the U.S. Strategic Air Force's "Chrome Dome" mission was immediately terminated, which undoubtedly highlighted the security and political risks of this mission. Subsequently, a series of security measures were strengthened and more stable conventional explosives were developed on nuclear weapons.
In 1995, reports revealed that the Danish Government intended to remain silent about the nuclear weapons accident in Greenland, arguing that it violated Denmark's 1957 nuclear-weapon-free regional policy. Workers involved in the clean-up have been seeking compensation for radiation-related illnesses. In March 2009, Time magazine argued that the accident was one of the world's worst nuclear accidents.
IX. Palimares Hydrogen Bomb Accident (Palomares, Spain)
On January 17, 1966, an American B-52 bomber over the southern coast of Spain collided with a KC-135 air tanker while flying. The accident damaged both aircraft and killed seven pilots, and more seriously, four thermonuclear bombs mounted by the B-52 bombers went out of control, one of which sank into the Mediterranean Sea not far from the coastline, but three others crashed into Palimares.
Although the three crashed hydrogen bombs did not explode in fusion, the physical collision caused two of them to have a conventional non-nuclear explosion, leaving radioactive plutonium dust to fill the village.
Accident: On January 17, 1966, the U.S. Air Force conducted flight practice in Western Europe, and one of the "B-52" strategic bombers carrying four hydrogen bombs patrolled the sky day and night, and the KC-135 transport aircraft carried out aerial refueling. At 10:10 a.m. on the same day, the two aircraft were connected over Spain for aerial refueling. At that time, the two planes were 50 meters apart and were flying over Palomares in Spain, flying at an altitude of 9300 meters and flying at a speed of 600 kilometers per hour. Suddenly, the two planes collided, and one of the eight jet engines on the "B-52" exploded and caught fire, and flames and smoke enveloped the wings.
The pilot decisively threw off the spare fuel tank and continued to fly. At 10:22, when the plane was 1.6 kilometers away from Palomares, the pilots saw that the fire accident could not be ruled out and quickly took emergency measures, that is, to drop the hydrogen bomb. Only a few seconds later, the fuel tank exploded and the cockpit caught fire. If the pilot had not decisively dropped the hydrogen bomb at that time, the consequences would have been unimaginable. The pilot forcibly jumped out of the burning cockpit with a parachute, and debris from the plane's explosion was scattered around 39 square kilometers of Palomares.
Shortly after the plane crash, the parachute pilot was rescued by the fishing boat Manueto, which was fishing nearby. Three hydrogen bombs were found on land near Palomares, and it is worth mentioning that the B-52 bombers were 1250 times more powerful than the atomic bomb that bombed Hiroshima. If a hydrogen bomb explodes, it will destroy all life within 15 kilometers of the center of the explosion in an instant. Fortunately, none of the three hydrogen bombs found on land exploded.
The U.S. military set up a temporary military command at that time, because there was still a hydrogen bomb that had not been found. U.S. Air Force reconnaissance planes took pictures of the entire area 12 miles long and 8 miles wide and made a certain proportion of aerial photographs, and the entire area on the map was divided into many small pieces, each with an area of 1,000 square feet, so that when searching block by piece, each small piece of aircraft fragment was found.
Because all kinds of computers are put into operation. Based on the location of the three hydrogen bombs that have been found, people have calculated their flight trajectories and aerodynamic trajectories in the air to determine the exact collision point. From this point of speculation, the hypothetical trajectory and aerodynamic trajectory of the hydrogen bomb that has not yet been found are made. It is thought that the hydrogen bomb could either land deep inland or fall into the sea a few miles offshore, but it depends on whether the parachute is open, how open it is open and whether it has been burned.
According to calculations, the lost hydrogen bomb most likely landed in a circular area more than two miles in diameter, which was scattered with many small plots of arable land, and a hill was honeycomb-dotted with abandoned tunnels and vents. The authorities organized more than 300 people to start slowly traversing the area hand in hand, planting small red flags outside every suspicious depression, pit, mine and tunnel, and there were about 400 such places. Helicopters then brought in ordnance experts who climbed into every old mine tunnel and cratern with lighting equipment. The search line advanced from north to south, and it took 7 hours to complete the area. Then, a second search began, the second more detailed than the last, but still to no avail.
At 9:20 a.m. on March 15, 1966, Alvin began to dive into another blue world, approaching the shelf slope at 11:50 a.m. It searched deep along the slope and found strange fragments of 2.5 meters in length at a depth of more than 700 meters. The crew was suddenly alert, carefully observed and searched. A few minutes later, under the intense searchlight, closer and closer to the debris, they finally saw clearly: a 6-meter-wide parachute covered the slope of the seabed. The crew was thrilled, because it was the hydrogen bomb parachute they were looking for! They continued to work underwater for 80 minutes, taking underwater photographs of the parachute to determine whether it was connected to a hydrogen bomb and asking the surface ship to indicate its exact location. The Alvin then turned off its glare and engines and slowly maneuvered around the target, waiting for the Aruminna to take over. It took 1 hour for the Aruminna to dive to the bottom of the sea and work underwater for 3 hours to find out that the parachute was still connected to the hydrogen bomb and to determine the precise location of the parachute.
On April 2, divers wrapped the hydrogen bomb around metal straps and tied steel cables to them. At 8:45, 22 hours and 23 minutes on the 79th day after the accident, the hydrogen bomb was pulled onto the ship and returned to the hands of the Americans. A battle that mobilized more than 3,000 people and did everything in its power for nearly three months, using the most sophisticated and bizarre equipment, finally achieved unprecedented success.
10. Tomsk nuclear accident (Tomsk, Siberia, former Soviet Union)
Tomsk-7 nuclear explosion of 6 April 1993: This occurred during the reprocessing of spent reactor fuel at the siberian Chemical Enterprises Company near the city of Siberian Tomsk. The explosion caused the Tomsk-7 recovery facility to release a cloud of radioactive gases.
Because the accident was a nuclear accident, it caused pollution to the environment and can be classified as radioactive pollution.
Although this accident was not related to the safety of the radiation source, it was identified as a typical case of arbitrary tampering with security rules. The accident damaged reprocessing equipment and buildings, resulting in the release of radionuclides, including plutonium-239. Part of the site and complex of the facility, as well as a large area of the surrounding countryside, including the village of Grugivka and part of the arterial road connecting Samus and Tomsk, is contaminated with radionuclides. Although the level of pollution is low, decontamination of buildings and roads is laborious.