Nuclear power plants use the energy released by nuclear fission reactions to produce electricity through energy conversion.
The energy required to produce nuclear power comes from the fission energy released by the fission reaction of fissile materials (nuclear fuel) in the nuclear reactor. Fission reaction refers to the process in which heavy elements such as uranium 235, plutonium 239 and uranium 233 split into two fragments under the action of neutrons, simultaneously releasing neutrons and a large amount of energy.
In the reaction, the nucleus of a fissile substance absorbs a neutron and then fission releases two or three neutrons. If these neutrons are removed and consumed, at least one neutron can cause the fission of another atomic nucleus, allowing the fission to proceed on its own. This reaction is called a fission chain reaction. The realizationOn of a chain reaction is the prerequisite for the production of nuclear energy.
Advantages
The world has relatively abundant nuclear resources. Nuclear fuels include uranium, thorium, deuterium, lithium, boron, etc. World uranium reserves are approximately 4.17 million tonnes. Nuclear fuel resources available for development on earth can provide more than 100,000 times the energy of fossil fuels. As a cost-effective measure to alleviate the global energy crisis, the application of nuclear energy has many advantages:
First, nuclear fuel has many advantages, such as small size and high energy, and nuclear energy accounts for millions. times greater than chemical energy; the energy released by 1,000 grams of uranium is equivalent to the energy released by 2,400 tons of standard coal; alarge 1 million kilowatt coal-fired power plant requires 3 to 4 million tons of raw coal each year, and 2,760 trains are needed to transport this coal, equivalent to 8 trains per day, and 40 million tons of ash will be transported.
The second is less pollution. Thermal power plants continuously emit harmful substances such as sulfur dioxide and nitrogen oxides into the atmosphere. At the same time, small amounts of radioactive substances such as uranium, titanium and radium present in coal also fall into the surroundings of the thermal power plant. smoke and dust, polluting the environment. Nuclear power plants have erected layers of barriers and emit practically no polluting substances for the environment. Even the radioactive pollution is much less than that of coal-fired power plants.
The third is reinforced securityrcee. Since the construction of the first nuclear power plant, more than 400 nuclear power plants have been put into operation around the world, and they have been basically safe and normal for more than 30 years. Although there were accidents at the Three Mile Island Pressurized Water Reactor Nuclear Power Plant in the United States in 1979 and the Chernobyl Graphite Boiling Water Reactor Nuclear Power Plant accident in the Soviet Union in 1986, both accidents were caused by human factors. As pressurized water reactors continue to improve, nuclear power plants will likely become safer.
Extended information
Implement the principle of defense in depth
In other words, security defense is divided into three levels when designing:
Firstly, improve reliability and minimize accidents through design overhead, quality managementlity, training of operating personnel and other measures.
Second, put in place a safety system to avoid damage to the reactor core in the event of an accident.
Third, in the event of an accident with a very low probability of damage to the reactor core, the safety system will attempt to limit the release of radioactive materials into the environment.
Reference accident (DBA)
Method used to design safety installations for nuclear power plant projects with some hypothetical accidents. Different types of nuclear power plants have different DBAs. Light water reactor DBAs include: loss of coolant accidents, rod ejection accidents, steam line rupture accidents, etc. The most serious of these are water loss accidents. A double mainline rupture is assumed in a pressurized water reactor, also appThe maximum credible accident.
Baidu Encyclopedia - Nuclear Power Generation
How does geothermal energy produce electricity?
The classification of generators includes:
Generators are divided into: direct current generators and alternators; AC generators are divided into: synchronous generators and asynchronous generators (rarely adopted); can also be divided into single-phase generator and three-phase generator.
There are many types of generators. In principle, they are divided into synchronous generators, asynchronous generators, single-phase generators and three-phase generators.
In terms of production methods, they are divided into steam turbine generators, hydraulic generators, diesel generators, gasoline generators, etc. In terms of energy, it is divided into thermal generators, hydraulic generators, etc.
Detailed information:
1. Operating characteristics:
The performance of synchronous generators is mainly characterized by no-load characteristics and on-load operating characteristics. These features provide an important basis for users to choose generators.
2. No-load characteristics:
When the generator is not connected to a load, the armature current is zero, which is called no-load operation. At this time, the three-phase winding of the motor stator only has the no-load electromotive force E0 (three-phase symmetry) induced by the excitation current If, and its size increases with the increase of If. However, due to the saturation phenomenon in the core of the motor magnetic circuit, the two are not proportional. The curve reflecting the relationship between the electromotor forceno-load rice E0 and the excitation current If is called no-load characteristic of the synchronous generator.
3. Armature Reaction:
When the generator is connected to a symmetrical load, the three-phase current in the armature winding will produce another rotating magnetic field, called the armature. reaction magnetic field. Its speed is exactly equal to the speed of the rotor and the two rotate synchronously.
The armature reaction magnetic field and the excitation magnetic field of the synchronous generator rotor can be approximately considered to be distributed according to the sinusoidal law. The spatial phase difference between them depends on the temporal phase difference between the no-load electromotive force E0 and the armature current I. The armature reaction magnetic field is also related to the charge state.
When the generator load is inductive, the armature reaction magnetic field acts as a demagneteur, which will cause the generator voltage to decrease; when the load is capacitive, the armature reaction magnetic field acts as; a magnetizer. This will increase the output voltage of the generator.
Baidu Encyclopedia - Generator
Geothermal Power Generation
Geothermal power generation actually uses steam energy to produce electricity. Dig a well to find a natural stream of hot water shooting upwards. As the water comes from a depth of 1 to 4 kilometers underground, it is under high pressure. Bottom diameter of an eyeA 25 cm well can produce 200,000 to 800,000 kilograms of geothermal water and steam per hour. Depending on water temperature, the steam produced by 5 to 10 wells can enable a power generation device to produce 55 megawatts of electricity.
There are two types of electricity production devices:steam turbine power generation and binary power generation devices. To supply steam to a turbogenerator, extracted geothermal water (under pressure) is released to the surface of a container called a flash tank, and some of the water (about 35%, depending on its temperature) flashes (mush) in the form of steam. , it enters the turbomachine and drives a generator. The turbine exhaust gases are cooled using a conventional cooling tower. The water remaining in the flash reservoir after the boiling phase is injected underground at the edge of the thermal reservoir, where it helps maintain pressure in the thermal reservoir and completes the convective hydrothermal system.
In a binary power plant, instead of turning hot water into steam, it is sent to a heat exchanger to heat the working fluid, which is usually an organic compound.e such as isobutane or isopentane. The working fluid is gasified and the gasified steam is used to drive the turbomachine and then the generator. After leaving the turbine, the working fluid condenses into a liquid and returns to the heat exchanger to be vaporized again. Geothermal fluids are returned to the ground via injection wells, much like what happens in turbogenerators. Since the working fluid used in a binary geothermal power generation device evaporates at a lower temperature than water, its power generation efficiency is higher than that of a turbogenerator.
Each of these two types of electricity production devices has its own advantages. Turbogenerators are inexpensive to manufacture and operate, but to operate at high efficiency they require water temperatures above 180 to 200°C. Production devicesBinary electricity generation binaries are more expensive to manufacture and operate, but they can produce electricity using water at 100°C or less. Most geothermal power generation devices currently in operation around the world are steam turbine types, but binary power generation devices are becoming increasingly popular.