The working structure of nuclear power plant and its working principle

First, atoms and nuclear energy

Nuclear energy is the energy produced by the recombination and arrangement of atomic particles, also known as atomic energy. Nuclear energy is essentially a transfer of mass and energy... The main characteristic of nuclear energy is: high concentration of energy. The energy produced by the entire fission of 1t of uranium-235 is about equal to the energy released when 2.4 million tons of standard coal is burned.

Second, the working principle of nuclear power plants

Nuclear power plants currently in commercial operation use nuclear fission reactions to generate electricity.

Nuclear power plants are generally divided into two parts: nuclear islands that use nuclear fission to produce steam (including reactor units and primary circuit systems) and conventional islands that use steam to generate electricity (including turbo-generator systems). The fuel used in nuclear power plants is usually radioactive heavy metals: uranium and plutonium.

Now the most common civil nuclear power plants are mostly pressurized water reactor nuclear power plant, its working principle is: the nuclear fuel made of uranium in the reactor fission and release a lot of heat; Circulating cooling water at high pressure takes the heat out and generates steam inside the steam generator, which spins the generator and generates electricity.

3. Working equipment of nuclear power plant

The main pump: If the coolant in the reactor is compared to human blood, the main pump is the heart. Its function is to send coolant into the reactor and then through the steam generator to ensure that the heat generated by the fission reaction is transferred in time.

Pressurizer: Also known as pressure balancer, is used to control the pressure changes of the reactor system equipment. In normal operation, it plays the role of maintaining pressure; Provides overpressure protection in the event of an accident. The pressurizer is equipped with a heater and spray system, when the pressure in the reactor is too high, spray cold water to reduce the pressure; When the pressure in the reactor is too low, the heater is automatically energized to heat the water to increase the pressure.

Steam generator: Its role is to pass the heat of the coolant through the reactor to the secondary circuit water, and make it into steam, and then into the cylinder of the turbine generator for work.

Containment: Containment is used to control and limit the spread of radioactive materials from the reactor to protect the public from radioactive materials. In the rare event of a loss of water in the primary reactor, the containment vessel is the last barrier to prevent the release of fission products into the surrounding area. The containment is generally a thick-walled prestressed concrete vessel lined with steel plates.

Steam turbine: The steam turbine generator used in nuclear power plant is much the same as that used in conventional thermal power station in structure, but the difference is that because the steam pressure and temperature are lower, the turbine volume of the same power unit is larger than that of conventional thermal power station.

Emergency cooling system: In order to cope with the extreme water loss accident caused by the rupture of the primary main pipeline of the nuclear power plant, modern nuclear power plants have emergency cooling systems. It consists of an injection system and a containment spray system. Once the signal of an extreme water loss accident is received, the safety injection system injects high-pressure boron-containing water into the reactor, and the spray system sprays water and chemicals into the containment vessel. It can mitigate the consequences of accidents and limit the spread of accidents.

Nuclear reactors

The interior of a nuclear power plant is usually composed of a primary circuit system and a secondary circuit system. The reactor is the core of a nuclear power plant. The thermal energy released during reactor operation is carried out by the coolant in the primary system to produce steam. Therefore, the entire primary system is called the "nuclear steam supply system", which is equivalent to the boiler system of a thermal power plant. To ensure safety, the entire primary circuit system is housed in a closed building called a containment, so that safety will not be affected during normal operation or in the event of an accident. The second circuit system of generating power by steam driven turbine generator set is basically the same as that of steam turbine generator system in thermal power plant.

First, the concept of hot reactor

After the neutron into the original nucleus of uranium-235, the nucleus becomes unstable and will split into two new nuclei of smaller mass, which is the nuclear fission reaction, and the energy released is called fission energy; As well as producing a huge amount of energy, it also emits two or three neutrons and other rays. These neutrons then penetrate into other uranium-235 nuclei, causing new nuclear fission, which in turn produces new neutrons and fission energy, and so on, forming a chain reaction. Reactors built using the principle of nuclear reaction need to slow down the neutrons released during fission, and then cause new nuclear fission, because the speed of the neutron and the thermal motion of the molecule reach a balance state, this neutron is called thermal neutron. A reactor in which the fission is mainly caused by thermal neutrons is called a thermal neutron reactor (referred to as a hot reactor). Thermal reactor, which uses a moderator to slow down fast neutrons.