1. What is nuclear energy?

Everything in the world is made up of atoms, and atoms are made up of nuclei and their surrounding electrons. Both the fusion of light nuclei and the division of heavy nuclei can input energy, which is called nuclear fusion energy and nuclear fission energy, or nuclear energy for short.

The nuclear energy mentioned in this book refers to nuclear fission energy. The fuel of the aforementioned nuclear power plant is uranium. Uranium is a heavy metal element, and natural uranium consists of three isotopes:

The content of uranium -235 is 0.7 1%

The content of uranium -238 is 99.28%

The content of uranium -234 is 0.0058%.

Uranium -235 is the only fission nuclide in nature.

When a neutron bombards the uranium -235 nucleus, the nucleus can be split into two lighter nuclei, producing two or three neutron rays at the same time and releasing energy. If the newly generated neutron hits another uranium -235 nucleus, it will trigger a new fission. In the chain reaction, energy will be released continuously.

How much energy is released from uranium -235 fission? Please remember a number,

That is, the energy released by 1 kg uranium -235 is equivalent to the energy released by burning 2700 tons of standard coal.

2. Principle of nuclear reactor

Reactor is the key design of nuclear power plant, and the chain reaction of nuclear fission is among them. There are many kinds of reactors, among which pressurized water reactor is the most widely used one in nuclear power plants.

There must be nuclear fuel in the pressurized water reactor first. The nuclear fuel is to put the sintered uranium dioxide pellets with the size of a little finger into zirconium alloy tubes, and assemble more than 300 zirconium alloy tubes with the pellets to form a fuel assembly. Most components have a bundle of control rods to control the intensity of chain reaction and the start and end of the reaction.

PWR uses water as coolant, flows through the fuel assembly driven by the main pump, absorbs the heat energy generated by nuclear fission, then flows out of the reactor and enters the steam generator, where it transfers the heat to the water on the secondary side, making them turn into steam and send it to power generation, and at the same time, the temperature of the main coolant itself is reduced. The main pump sends the main coolant in the steam generator back to the reactor for heating. This circulating channel of coolant is called primary loop, and the high pressure of primary loop is maintained and regulated by voltage regulator.

3. What is a nuclear power plant?

Coal-fired power stations use coal and oil to generate electricity, hydropower stations use hydropower to generate electricity, and nuclear power stations are new power stations that use the energy contained in atomic nuclei to generate electricity. Nuclear power plants can be roughly divided into two parts: one is a nuclear island that uses nuclear energy to generate steam, including reactor devices and primary loop systems; The other part is a conventional island that uses steam to generate electricity, including a turbine generator system.

The fuel used in nuclear power plants is uranium. Uranium is a heavy metal. Nuclear fuel made of uranium is fissioned in a device called a "reactor" to generate a lot of heat energy, which is carried out by water under high pressure and steam is generated in a steam generator. Steam drives the gas turbine to rotate with the generator, constantly generating electricity and transporting it in all directions through the power grid. This is the working principle of the most common PWR nuclear power plant.

In developed countries, nuclear power has been developed for decades and has become a mature energy source. China's nuclear industry has a history of more than 40 years, and a fairly complete nuclear fuel cycle system has been established, including geological exploration, mining, component processing and post-processing. Many types of nuclear reactors have been built, with many years of experience in safety management and operation, and a team with complete specialties and excellent technology. The construction and operation of nuclear power plants is a complex technology. At present, China has been able to design, build and operate its own nuclear power plants. Qinshan nuclear power station was designed and built by our country.

4. What is a nuclear power plant?

Electricity is produced by power plants. As we know, there are thermal power plants that burn coal or oil, hydropower stations that generate electricity, and some small or experimental power generation devices that use wind energy, solar energy, geothermal energy, tidal energy, wave energy and biogas to generate electricity. Nuclear power plant is a new type of power plant that relies on the energy contained in the nucleus to generate electricity on a large scale.

The fuel used in nuclear power plants is uranium. Uranium is a heavy metal. Nuclear fuel made of uranium is split in a device called a "reactor" to generate a large amount of heat energy, which is then carried by water under high pressure, generated in a steam generator and sent to all directions through the power grid. This is the working principle of the most common PWR nuclear power plant.

5. What is radioactivity

About 100 years ago, scientists found that some substances can emit three kinds of rays: alpha (alpha) ray, beta (beta) ray and gamma (gamma) ray.

Later studies have proved that alpha rays are alpha particles (helium nuclei) and beta rays are beta particles (electron currents), which are collectively called particle radiation. Similarly, there are hit rays, cosmic rays and so on. Gamma rays are electromagnetic waves with short wavelength, which are called electromagnetic radiation. Similarly, there are x-rays and so on.

The * * * characteristics of these rays are: 1, which has a certain ability to penetrate substances; 2, people's five senses can't be perceived, but they can make photographic film sensitive; 3. Visible fluorescence can be emitted when irradiated on some special substances; 4. Ionization will occur when passing through matter.

X-rays have a certain influence on organisms mainly through ionization.

Radiation is not terrible. The food we eat, the house we live in and even our bodies contain substances that can emit radiation. When we wear night-vision goggles, undergo X-ray examination, fly and smoke, we all get a certain dose of radiation. However, too high dose of radiation agent will have harmful effects on health.

Two units of measurement of radioactivity

6. What is a reactor

Nuclear reactor is a device that can maintain and control the chain reaction of nuclear fission, so as to realize the conversion of nuclear energy and thermal energy.

Pressurized water reactor used in nuclear power plant has a thick steel cylindrical shell with several entrances and exits at the waist, which is called pressure vessel. The pressure vessel of 900 MW PWR is12m high, 3.9m in diameter and 0.2m in wall thickness.

Inside the pressure vessel is the reactor core, which consists of fuel assembly and control rod assembly. Water flows between them. Water plays two roles here, one is to slow down the neutron velocity and make it easy to be absorbed by uranium -235 nucleus, and the other is to take away heat. 900 MW PWR is generally equipped with 157 fuel assembly, containing about 80 tons of uranium dioxide.

The top of the pressure vessel is equipped with a control rod drive mechanism, which can realize start-up and shutdown (including emergency shutdown) and adjust power by changing the position of the control rod.

7. What is a nuclear accident?

Generally speaking, an accident at a nuclear facility (such as a nuclear power plant) leads to the leakage of radioactive materials, which causes the staff and the public to be exposed to radiation exceeding or equivalent to the prescribed limit, which is called a nuclear accident. Obviously, the severity of a nuclear accident can be in a wide range. In order to have a unified understanding standard, the events with safety significance in nuclear facilities are divided into seven levels internationally.

As can be seen from the table, only grades 4-7 are called "accidents". Off-site emergency plans need to be implemented for accidents of magnitude 5 or above. There have been three accidents in the world, namely, Chernobyl accident in the Soviet Union, Wintzkell accident in Britain and Three Mile Island accident in the United States.

References:

/bbs/printpage.asp？ BoardID = 32 & ampID=2 133