From a technical point of view, nuclear waste is mainly divided into three categories: high radioactivity, medium radioactivity and low radioactivity. High-level radioactive nuclear waste mainly includes spent fuel generated after nuclear fuel power generation and its disposal. Low-level radioactive nuclear waste generally includes contaminated equipment, testing equipment, hydration system during operation, exchange resin, waste water and gloves and other labor protection articles, accounting for 99% of all nuclear waste. Low and medium level radioactive nuclear waste is less harmful; High-level radioactive nuclear waste contains a variety of high-level radioactive elements that are extremely harmful to human body. For example, only 10 mg of plutonium can kill people, and the half-life of these highly radioactive elements ranges from tens of thousands of years to100000 years. Therefore, various nuclear waste treatment methods are different.
The unique nature of nuclear waste makes it very troublesome to handle:
① Radioactivity: The radioactivity of nuclear waste cannot be eliminated by general physical, chemical and biological methods, but can only be reduced by the decay of radionuclides themselves.
② Radiation hazard: When the radiation emitted by nuclear waste passes through substances, it will be ionized and excited, causing radiation damage to living things.
(3) Thermal energy release: Radionuclides in nuclear waste release energy through decay. When the content of radionuclides is high, the released heat energy will make the temperature of nuclear waste rise continuously, even make the solution boil and the solid melt by itself.
2. World problems
In the past decades, how to deal with nuclear waste has always been an unsolved problem facing the nuclear industry. For example, the United States has studied this issue for 20 years and spent tens of billions of dollars. 1987, the United States first proposed a plan to store nuclear waste in the address structure deep in the Sierra Nevada, but so far, the implementation of this plan has not made any progress. For the high-level radioactive nuclear waste known as the "Millennium evil spirit", the academic circles believe that the most appropriate disposal method is geological burial. However, due to its special construction requirements and complex technology, so far, there is no permanent waste disposal repository in the world.
3. Relevant cases
United States: March 22nd, 20 13, radioactive and toxic wastes leaked from at least six underground storage tanks containing nuclear waste in the nuclear restricted area of hanford, Washington, USA. 177 storage tanks in this site contain 200 million liters of radioactive nuclear waste. These storage tanks have been used for more than 20 years, and many of them have been leaked before. It is estimated that * * * leaked 3.78 million liters of radioactive liquid. The US government now needs to spend $2 billion a year to clean up the site, which accounts for 1/3 of the total US nuclear clean-up budget. A new nuclear waste treatment plant will be built in this site, with an estimated cost of more than 654.38+0.23 billion US dollars, and it will not be put into use until at least 2065.438+09.
Former Soviet Union: During the Cold War of last century, the former Soviet Union directly discharged the high-level radioactive waste produced by nuclear weapons factories into nearby rivers and lakes due to cost and other factors, which caused serious ecological disasters. Gala Su Hu, located next to the famous atomic energy city of Chelyabinsk, used to be a paradise for wild animals, but now it has become a backwater due to nuclear waste pollution. According to the prediction of Russian environmental experts, the ecological environment of the lake will not be restored in the next100000 years.
1. If you wander around the solar system or fall to the sun after being sent into space, it will be difficult for nuclear waste to damage the environment on earth. However, how to send nuclear waste into space is still a difficult problem. Because, using rockets to carry in this way sometimes encounters launch failure.
2. Deep well drilling Deep well drilling needs to wrap the used nuclear fuel rods in a sealed steel structure and then bury them several miles underground. Its advantage is that it can drill holes near the nuclear reactor and shorten the transportation distance of high-level nuclear waste before treatment.
3. Most areas of the ocean are stored under the sea floor-the sea floor is made of thick clay, which is most suitable for absorbing radioactive decay products. But the storage under the sea floor needs to be drilled underwater, which is a lesson from the oil spill in the Gulf of Mexico. It seems that this scheme will take a long time to be tested before it can be put into practice. In addition, the practice of dealing with nuclear waste in the ocean requires the revision of international agreements.
4. Burying nuclear waste in subduction zone (subduction refers to the process that one plate is forced to descend below another plate) can make spent nuclear fuel rods move along the "conveyor belt" of the earth's tectonic plates and finally enter the mantle layer. However, burying in flooded areas also violates some international treaties.
The temperature of frozen nuclear waste is generally high. Put the tungsten wire ball on a relatively stable ice sheet. The tungsten ball will move down with the melting of the surrounding ice, and the melted ice on it will solidify again. However, the ice sheet will move, causing radioactive materials to float in the ocean like icebergs.
6. It is necessary to consider how to prevent nuclear waste from polluting the surrounding soil and water when it is sealed in synthetic rocks and buried underground. Synthetic rocks can absorb specific wastes from clean water reactors and plutonium nuclear fission. They are a kind of ceramic products, which can seal nuclear waste into crystal lattice to simulate ores with relatively stable geological structure.
7. Once hydraulic cages are used to infiltrate groundwater, underground nuclear waste storage facilities will become particularly dangerous. If a water cage similar to a three-dimensional deep ditch is built around nuclear waste, groundwater will not penetrate radioactive materials. The future nuclear waste treatment device should be leak-proof, and the role of hydraulic cage is to prevent groundwater pollution.
In the past 30 years, China's nuclear industry system has accumulated tens of thousands of cubic meters of low-level radioactive solid waste, and now it will produce about 150 tons of high-level radioactive waste every year. In addition, experts speculate that the pressure of nuclear waste storage space in China will appear around 2030, when the annual high-level nuclear waste generated by nuclear power plants alone will reach 3,200 tons.
At present, China has built two low-level radioactive waste repositories and plans to build two more, but there is no high-level radioactive waste repository. Two low-level and medium-level radioactive nuclear waste repositories have been built, which are located in Yumen, Gansu Province and Belon near Daya Bay, Guangdong Province.
Low-level radioactive waste treatment: Peron disposal site, etc.
Beilong disposal site covers an area of nearly 2 1 hectare, with a designed total disposal capacity of 80,000 cubic meters, 5 kilometers away from Daya Bay Nuclear Power Station and 4 kilometers away from Ling 'ao Nuclear Power Station. Low-and medium-level solid waste generated by nuclear power plants in Guangdong and its neighboring areas will be sent here for permanent disposal. From the exploration site selection in 199 1 year to the first temporary storage of spent nuclear guide tubes in Daya Bay Nuclear Power Station in 2006 1 year, * * * used1year.
As a relatively simple civil nuclear treatment facility, the Bellon disposal site has 70 disposal units, covering an area of about 6.5438+300,000 square meters, and can dispose of 80,000 cubic meters of low-level radioactive waste. Each disposal unit is a 17m× 17m× 7m cubic shielding box made of reinforced concrete. When the treatment unit is full of waste bags, cement slurry will fill the gaps between waste bags to fix the waste bags and play a role in enhancing shielding. Then cover the treatment unit with reinforced concrete. Even if there is an earthquake, it is a complete cement block and will not break easily.
Northwest treatment plant is located below the surface, with a distance of 10-20m. The Belon garbage disposal site is built on the surface of the earth, forming a square box fence. After burying the soil in this closed place, a mountain bag will be formed, on which vegetation will be planted for greening. Tens of square kilometers of safety barriers should be set up near these two low-level radioactive disposal sites.
Generally, low-level radioactive disposal sites need 300-500 years of isolation from the outside world.
High-level radioactive waste treatment: "Beishan No.1" deep in Gobi
Both the Belon disposal site and the northwest disposal site can only collect and store the "soft waste" generated by nuclear power plants.
In the first half of 2005, the Commission of Science, Technology and Industry for National Defense specially held a seminar on high-level radioactive waste disposal, and began to plan for medium and long-term nuclear waste disposal. It is finally determined that China will build a permanent repository for high-level radioactive waste, with a design life of 10000, and the capacity should be able to store the nuclear waste generated in China from 100 to 200, and it will be permanently sealed after it is filled. In other words, it will be at least 100 years before the second permanent high-level radioactive repository will appear in Chinese mainland. According to China's nuclear power development plan, China will determine the site of permanent high-level nuclear waste repository from 20 15 to 2020.
In order to avoid adverse effects on the environment, high-level radioactive nuclear waste must go through a strict treatment process. These nuclear wastes are first made into vitrified solids, then put into metal cans that can shield radiation, and finally put into a repository located at 500- 1000 meters underground. Because the half-life of nuclear waste ranges from tens of thousands of years to 65438+ ten thousand years, it is necessary to ensure that the geological conditions can ensure the safety of the repository at least 65438+ ten thousand years when selecting the repository.
Beishan, Dunhuang, Gansu, is the first underground nuclear waste repository in Chinese mainland. It has been rumored for a long time, and its code name is "Beishan No.1". But its exact name is "Geological Disposal Repository of Gansu Beishan High Level Radioactive Waste". Located about 25 kilometers southeast of Dunhuang Mogao Grottoes, it is a Gobi desert with an area equivalent to Hainan Province. The land is vast and sparsely populated, with a population of less than1.2000. It can be said that apart from the gravel and the yellow camel grass, it is so lonely that there is no response. The economic development of Beishan is relatively backward, and there are no mineral resources around it. The construction of nuclear waste repository has little impact on economic development. The climatic conditions here are also ideal. The annual rainfall is only 70 mm, but the evaporation is 3000 mm, so the groundwater level is very low, which reduces the risk of radioactive elements diffusing with groundwater. Beishan also has convenient traffic conditions, and the library site is only 70 to 80 kilometers away from the railway. In addition, the geological conditions in Beishan are very superior. Located in the stable area of crustal movement, there is a complete granite body at the location of the reservoir site, and granite is the best' protective suit' to deal with radiation. Experts from the International Atomic Energy Agency said after their investigation in Beishan that Beishan is one of the most ideal nuclear waste storage sites in the world.
The construction of high-level radioactive waste disposal site is imminent.
Because before the nuclear waste repository is completed, all high-level nuclear waste can only be temporarily stored in the boron pool of nuclear power plants. If the nuclear waste repository can't be built in time, China's nuclear industry will face the situation that there is nowhere to store nuclear waste.
In this regard, the United States has learned a painful lesson. The United States originally planned to build a repository of high-level radioactive nuclear waste in 1998, but due to the high technical difficulty, although the US government invested a lot of money and manpower in research, it finally had to extend the completion time to 20 10. As a result, more than 40 nuclear power plants in the United States are all pools for storing nuclear waste, which has caused huge economic losses and led the owners of nuclear power plants to sue the US Department of Energy.
China's high-level radioactive waste repository is planned to be completed in 2030-2040, which can be said to be quite urgent. At the same time, the repository of high-level radioactive nuclear waste is a costly project. Take the United States as an example, its budget for the Yucca Mountain nuclear waste repository project is 96.2 billion US dollars. According to the scale of China's nuclear power in the future, China's high-level radioactive waste repository will cost tens of billions of RMB, which has enough capacity to accommodate all the high-level radioactive waste generated by China's nuclear industry in the future. Our repository keeps nuclear waste in the deep underground forever.