Chinese name: nuclear power plant mbth: nuclear power plant principle: nuclear fission releases nuclear power generation characteristics: low fuel consumption and other types: gas-cooled reactor nuclear power plant and other disciplines: brief description of electricity, development, characteristics, principle, types, composition, technical requirements, and radioactive effects. A power plant that uses nuclear energy to generate electricity is called a nuclear power plant. In today's world, only the energy generated by fission chain reaction can be used to generate electricity. A nuclear power plant is an electric power facility that uses the thermal energy generated by one or several power reactors to generate electricity or generate electricity and heat. Reactor is the key equipment of nuclear power plant, and the chain reaction of nuclear fission is carried out in the reactor. Systems and facilities that convert nuclear energy released by nuclear fission into heat energy and then into electric energy are usually called nuclear power plants. The reactors commonly used in nuclear power plants in the world are light water reactor, heavy water reactor, improved gas-cooled reactor and fast reactor, but light water reactor is the most widely used. According to the different steam generation processes, light water reactors can be divided into boiling water reactors and pressurized water reactors. Pressurized water reactor (PWR) uses ordinary water as coolant and moderator, which is the most mature and successful power reactor developed from military reactor. Pressurized water reactor nuclear power plant accounts for more than 60% of the total nuclear power capacity in the world. The fuel used in nuclear power plants is uranium. The nuclear fuel made of uranium fission in the equipment of the "reactor" produces a large amount of heat energy, and then the heat energy is taken out by water under high pressure, and steam is generated in the steam generator, which drives the steam turbine to rotate with the generator, continuously generating electricity and transmitting it to all directions through the power grid. Since 1950s, the development of nuclear power plants has been divided into four generations according to the differences in their working principles and safety performance. The development and construction of the first generation of nuclear power plants began in the 1950s. 195 1 year, the United States took the lead in building the world's first experimental nuclear power plant. 1954, the Soviet union also built an experimental nuclear power plant with a power generation capacity of 5000 kilowatts. 1957, a prototype nuclear power plant with a power generation capacity of 90,000 kilowatts was built in the United States. These achievements prove the technical feasibility of using nuclear energy to generate electricity. The above experimental prototype nuclear power unit is called the first generation nuclear power plant. At the end of 1960s, the second generation nuclear power plants built several hundred thousand kilowatts or several million kilowatts of nuclear power plants on the basis of experiments and prototype nuclear power plants, and adopted nuclear reactor technologies such as pressurized water reactor, boiling water reactor, heavy water reactor and graphite water-cooled reactor with different working principles. While further proving the feasibility of nuclear power generation technology, they also proved the economy of nuclear power. Today, most of the more than 400 nuclear power units in commercial operation in the world were built during this period, and they are customarily called the second generation nuclear power plants. In 1990s, in order to eliminate the negative effects of accidents at Three Mile Island in the United States and the Chernobyl nuclear power plant in the former Soviet Union, the world nuclear power industry concentrated on preventing and mitigating serious accidents. The United States and Europe have successively issued User Requirements Document for Advanced Light Water Reactor (URD document) and User Requirements for European Light Water Reactor Nuclear Power Plant (EUR document), which further clarified the requirements for preventing and mitigating serious accidents and improving safety and reliability. Therefore, nuclear power units that meet URD documents or EUR historical documents are generally called the third generation nuclear power units in the world. There are many design schemes for the third generation nuclear power unit, among which the most representative designs are AP 100 of Westinghouse and EPR technology developed by Areva of France. Both of these technologies have high security in theory. These designs are good in theory, but difficult in practice. Because some technologies are not mature enough, the installed capacity of the third generation nuclear power technology is very small in the world. In this respect, China is at the forefront of the world. Zhejiang Sanmen and Shandong Haiyang adopted Westinghouse AP 100 technology. Guangdong Taishan adopts EPR technology of Areva Company of France, and their completion will become the forerunner of the third generation nuclear power plant in the world. The Fourth Generation Nuclear Power Plant In June 2000, the United States, Britain, Switzerland, South Africa, Japan, France, Canada, Brazil, South Korea, Argentina and other countries interested in developing nuclear energy 10 jointly formed the "Fourth Generation International Nuclear Energy Forum", which was signed in July 2006, with a total of 5438+0. But unfortunately, no fourth-generation nuclear power plant has been built to meet these requirements. The construction of nuclear power plants in China began in the mid-1980s. The first nuclear power station was assembled in Qinshan Nuclear Power Station, and 1985 was started, and 1994 was put into commercial operation with an electric power of 300MW. This is a prototype nuclear power plant designed, built and operated by China. China has become the seventh country in the world to design and build its own nuclear power unit after the United States, Britain, France, the Soviet Union, Canada and Sweden. As of February 20 13, there are 7 nuclear power plants that have been built and put into commercial operation in Chinese mainland, namely, Zhejiang Qinshan Nuclear Power Station Phase I, Phase II and Phase III, Guangdong Daya Bay Nuclear Power Station, Ling 'ao Nuclear Power Station Phase I and Phase II, Jiangsu Tianwan Nuclear Power Station, 15, and 28 are under construction. Characteristics and advantages of nuclear power plants: Compared with traditional thermal power plants, nuclear power plants have obvious advantages: (1) Nuclear power generation does not emit huge pollutants into the atmosphere like fossil fuel power generation, so nuclear power generation will not cause air pollution; (2) Nuclear power generation has no carbon emission and will not aggravate the global greenhouse effect; (3) Uranium fuel used for nuclear power generation has no other uses except power generation; (4) The energy density of nuclear fuel is millions of times higher than that of fossil fuel, so the fuel used in nuclear power plants is small and convenient for transportation and storage. 100000 kw nuclear power plant only needs 30 tons of uranium fuel a year and can be transported by plane in one voyage; (5) In the cost of nuclear power generation, the proportion of fuel is low, so the cost of nuclear power generation is not easily affected by the international economic situation, and the cost of solid power generation is relatively stable. Disadvantages of nuclear power plants also have some obvious disadvantages: (1) Nuclear power plants will produce high-grade and low-grade radioactive waste or used nuclear fuel. Although they are small in size, they must be treated with caution because of their radioactivity; (2) The thermal efficiency of nuclear power plants is low, so they emit more waste heat than ordinary fossil fuel power plants, so the thermal pollution of nuclear power plants to the environment is more serious; (3) The investment cost of nuclear power plants is too high, and the financial risks of power companies are high; (4) Nuclear power is not suitable for full-load operation, nor is it suitable for operation under standard load; (5) The construction of nuclear power plants often leads to political disputes; (6) There are a lot of radioactive materials in the reactors of nuclear power plants. If they are released into the external environment in an accident, it will do harm to ecology and human beings. Principle Nuclear power plants use energy released by nuclear fission reaction and energy conversion to generate electricity. The working principle of PWR nuclear power plant is illustrated (see figure 1). Figure 1 In the PWR, the self-sustaining chain reaction of nuclear fission of nuclear fuel nuclei produces a lot of heat. Coolant (also known as heat carrier) brings the heat in the reactor into the steam generator and transfers it to its working medium-water, and then the coolant is transported back to the reactor by the main circulating pump for recycling, thus forming a loop called the first loop. This process is also an energy conversion process in which nuclear fission energy is converted into heat energy. The working medium on the secondary side outside the U-tube of the steam generator is heated and evaporated to form steam, which enters the steam turbine to expand and do work, and the heat energy released by the enthalpy drop of the steam is converted into mechanical energy for the rotation of the steam turbine rotor. This process is called the energy conversion process from thermal energy to mechanical energy. The steam that does work condenses into condensed water in the condenser and returns to the steam generator to form another circulation loop, which is called the second loop. This process is called the energy conversion process from thermal energy to mechanical energy. The rotating rotor of the steam turbine directly drives the rotor of the generator to rotate, so that the generator generates electric energy, which is an energy conversion process from mechanical energy to electric energy. Type I nuclear power plants can be divided into gas-cooled nuclear power plants, improved gas-cooled nuclear power plants, light water nuclear power plants, heavy water nuclear power plants and fast neutron breeder nuclear power plants according to reactor types. (1) gas-cooled reactor nuclear power plant, the reactor uses natural uranium as fuel, graphite as moderator and carbon dioxide or helium as coolant. This kind of reactor is large in size and high in cost, because more fuel is loaded at one time. This kind of reactor has been used in Britain and France. (2) Improved gas-cooled reactor type nuclear power plant, the moderator and coolant used in the reactor are the same as the above-mentioned gas-cooled reactor type, except that the fuel is 2.5% ~ 3% of low enriched uranium, so the fuel for one-time filling is only 1/5 ~ 1/4 (mass) of natural uranium, thus the reactor volume is greatly reduced, the fuel replacement is simpler, and it can be carried out at higher temperature. This type of reactor is used in the United States and Germany. (3) Light water reactor nuclear power plant, the reactor uses 2% ~ 3% low enriched uranium as fuel, and water as moderator and coolant. This reactor is small in size, low in cost and easy to master in technology. More than 85% of nuclear power plants in the world use this type of reactor, and all of them are used in China. Light water reactor nuclear power plant can be divided into boiling water reactor and pressurized water reactor. Boiling water reactor type nuclear power plant, in which water boils directly in the reactor. It has only one loop, and the water is heated in the reactor and turned into steam, which is directly used to drive the steam turbine and drive the generator to generate electricity. Boiling water reactor has few loop equipment, almost no water loss accident, which is more economical than pressurized water reactor and can better meet the needs of external load change. However, the steam with radioactive pollution directly enters the steam turbine unit, which makes the maintenance of the unit difficult and the shutdown time long, thus affecting the effective operation of the nuclear power plant. In addition, the density decreases after water boils, and the moderating effect is weakened, so more nuclear fuel is needed than the pressurized water reactor with the same power, and the core volume and shell diameter are also increased accordingly. Coupled with the change of bubble density in the reactor, it is easy to cause power instability and complicated control. Due to these factors, the number of boiling water reactor nuclear power plants has decreased. Pressurized water reactor nuclear power plant, in which water does not boil in the reactor. It has two loops. The water in the first loop passes through the reactor, bringing the heat in the reactor to the steam generator, and exchanging heat with the water in the second loop passing through the steam generator, so that the water in the second loop is heated into high-pressure steam, which drives the steam turbine to run and drives the generator to generate electricity. China's nuclear power plant construction policy determines that the recent construction of PWR is the main type. Qinshan Nuclear Power Station and Daya Bay Nuclear Power Station have been built, both of which are pressurized water reactors. (4) Heavy water reactor nuclear power plant, in which heavy water (containing deuterium) is used as moderator and coolant, and natural uranium is used as fuel. The fuel cost of this kind of reactor is low, but heavy water is more expensive. Canada has developed this type of reactor. (5) Fast breeder nuclear power plants, reactors do not need moderator. Most of the reactors are fast neutrons, which are easily absorbed by uranium 238 around the reactor, making uranium 238 become fissionable polonium 239. This kind of reactor can increase the initial charge of nuclear fuel polonium 239 by more than 20% in about 10 years, but its initial investment cost is high. The nuclear power plant is composed of nuclear island, conventional island, nuclear power plant supporting facilities and nuclear power plant safety protection measures. Nuclear island is the core part of nuclear power plant, and its main components are a primary loop system consisting of nuclear reactor, pressure vessel (pressure shell), steam generator, main circulating pump, voltage stabilizer and corresponding pipes and valves. Conventional island refers to the secondary loop system composed of steam generator secondary side, steam turbine generator set, condenser, feed water pump and corresponding pipes and valves. Supporting facilities of nuclear power plant refer to some facilities designed to ensure the safety and environmental protection of nuclear power plant, mainly including: (1) nuclear shutdown system of reactor control system, (2) core emergency cooling system; (3) a cold water spray system arranged at the top of the containment; (4) Volume control system, which mainly regulates boron content and volume change of main cooling water; (5) Chemical control system, which is mainly used to control the oxygen content and pH value of primary cooling water and inhibit the corrosion of related equipment and materials; (6) Other systems, such as waste heat output system, cooling liquid purification system and three wastes (waste gas, waste liquid and waste residue) treatment system. Nuclear power plant safety protection measures are used to ensure the safety and environmental protection of nuclear power plants and prevent radioactive substances from escaping. The nuclear power plant has set up three strict and reliable barriers to nuclear fuel and related components. As the first barrier, the core is used as a fuel cladding, which is made of zirconium alloy tube or stainless steel tube, and the nuclear fuel core is sealed in the cladding. Its second barrier is the pressure shell, which is the pressure boundary of the reactor coolant and consists of the primary circuit and the reactor pressure vessel. The shell is made of thick alloy steel plate (usually a pressurized water reactor with a power of 300,000 kilowatts, and the wall thickness of the pressure shell is160mm; ; 900,000 kW PWR, the pressure shell wall thickness is more than 200mm), its function is that if the fuel cladding seal is broken and radioactive material leaks into the water, it will still be protected by the pressure shell in the sealed primary circuit. The third barrier is containment, or reactor building. It is a prestressed reinforced concrete building with a spherical top and a wall thickness of about 1m, and is lined with 6 ~ 7 mm thick steel plates. The primary circuit equipment is installed in the containment with good sealing performance. Even in the case of serious accidents such as primary pipeline damage or earthquake, it can ensure that radioactive substances will not leak out and prevent the surrounding environment of nuclear power plant from being polluted by nuclear radiation. Technical Requirements The development of nuclear power in the world and the public's requirements for the technical performance of the new generation of nuclear power have the following aspects. (1) Pursuing Better Safety The probability of core melting accident and a large amount of radioactive release in nuclear power plants is reduced from and to and respectively, from the inherent safety concept of nuclear power units to the natural safety concept including the whole nuclear fuel cycle system. (2) Continuously improve the economy of nuclear power. To develop nuclear energy on a large scale, we must improve economic competitiveness, that is, we need more economical nuclear energy technology, lower construction cost and lower power generation cost. (3) To meet the sustainable development of environment and ecology, the inherent advantage of nuclear energy is that it does not emit wastes such as sulfur dioxide and greenhouse gas carbon dioxide that pollute the environment, and it has advantages that conventional energy sources do not have. However, long-lived radionuclides will be produced and accumulated continuously, and they will be burned to meet the requirements of environmental and ecological sustainable development. (4) In order to meet the requirements of sustainable development of resource utilization, nuclear reactor power generation technology can only utilize about 65,438+0% of the energy contained in natural uranium resources. The development of new nuclear power technology adopts a closed fuel cycle to realize the diffusion of fissile materials and make limited nuclear energy develop into large-scale nuclear energy. (5) To meet the requirements of nuclear non-proliferation, the most important thing is to strictly control the production of separated polonium and study new fuel cycle technology. Implement the integration of nuclear power plant and post-treatment, and adopt high-temperature metallurgical post-treatment process. What the public is most worried about is the impact of radioactivity on the radioactivity of nuclear power plants. In fact, people unconsciously receive background radiation from natural radioactivity and various artificial radioactivity all the time in their lives. According to French data, the annual dose of radioactive radiation to human body is about 1.3mSv, including: (1) cosmic rays, 0.4 ~ 1 msv, depending on altitude. (2) Earth radiation, 0.3 ~ 1.3 msv, which depends on the nature of soil. (3) human body, about 0.25mSv; (4) radiotherapy, about 0.5mSv; (5) television, about 0. 1mSv. (6) Luminous dial, about 0.02 msv(7) oil-fired power station, about 0.02 msv(8) coal-fired power station, about 1mSv. (9) Nuclear power plant, about 0.0 1mSv. In addition, diet, smoking and flying will all affect people's exposure to radiation. Judging from the above data, the radiation of nuclear power plants to residents is completely inadequate, which is much smaller than that of coal-fired power plants, because coal contains radium and has strong radiation.