Nuclear power plants provide about 17% of the world's electricity. Some countries or regions rely more on nuclear power than other power generation methods. For example, according to data provided by the International Atomic Energy Agency, in France, about 75% of electricity is produced by nuclear power plants. In the United States, nuclear power plants provide about 15% of electrical energy, but the use of nuclear power by states is not uniform. There are more than 400 nuclear power plants in the world, and more than 100 of them are in the United States. A dome-shaped containment building at the Sheron Harris nuclear power plant in Raleigh, North Carolina. Do you understand how nuclear power plants work and the safety of nuclear energy? In this article, we will introduce you to the workings of nuclear reactors and nuclear power plants, and show you the principles of nuclear fission and the internal conditions of nuclear reactors. Uranium is a fairly common element on Earth that exists in this planet as it Earth formed. Uranium was originally formed in stars. The old stars explode and their dust gathers to form the earth. Uranium-238 (U-238) has a very long half-life (greater than 4.5 billion years), so they are still in large numbers now. Uranium-238 accounts for 99% of all uranium on Earth, and uranium-235 accounts for about 0.7%. Uranium-234 is formed by the decay of uranium-238, which is even rarer. (Uranium-238 can be converted to a stable lead isotope after many stages of alpha and beta decay, and uranium-234 is a ring in this reaction chain.) Uranium-235 has a peculiar property that allows it to be used for nuclear energy. Power generation can also be used to make nuclear bombs. Uranium-235, like uranium-238, decays by radiating alpha rays. Uranium-235 also undergoes spontaneous fission for a small period of time. However, uranium-235 is one of the few substances that can induce fission. If a free neutron strikes the nucleus of uranium-235, its nucleus will immediately absorb this neutron and become unstable and decompose immediately. Please check the Nuclear Radiation Secret for full details. Nuclear fission The animation below demonstrates a neutron that approaches the nucleus of uranium-235 from the top. Once the nucleus captures the neutron, it immediately decomposes into two lighter atoms, releasing two or three new neutrons (the number of neutrons depends on how the uranium-235 atom decomposes). Two new atoms release gamma rays and stabilize to a new state. There are three things that make this fission-inducing process interesting: The probability that a uranium-235 atom captures a neutron that is passing through is very high. In a working nuclear reactor (called a critical state), each neutron released by fission will cause another fission. The process of capturing neutrons and decomposing is very fast, in picoseconds (ie 1x10-12 seconds). When a single atom is decomposed, huge amounts of energy are released in the form of heat and gamma radiation. The two atoms formed by fission are also capable of releasing beta and gamma rays. The reason why a single fission reaction can release energy is because the mass of fission products and neutrons is smaller than the mass of the original uranium-235 atom. Equation E = mc2 determines the ratio of mass difference to energy. The energy of about 200 MeV (million electron volts) is released by decay of uranium-235 atoms (the following formula converts these quantities into our common units, 1eV=1.602x10-12 erg, 1x107 ergs = 1 joule, 1 Joule = 1 watt second, and 1 BTU (heat unit) = 1055 joules). These may not look like a lot, but there are a lot of uranium atoms in a pound of uranium. In fact, a pound of high-enriched uranium is used to power nuclear submarines or nuclear-powered aircraft carriers, which is equivalent to the energy that 3.8 million liters of gasoline can provide. If you consider that a pound of uranium is smaller than a baseball, and 3.8 million liters of gasoline can fill a cube that is 15 meters long (five stories high), you can have the energy of uranium-235. There is a concept. In order for these properties of uranium-235 to be exploited, the uranium sample must be concentrated so that it contains uranium-235 at a concentration of 2-3% or higher. The concentration of 3% is sufficient for nuclear power plants. Uranium in weapons contains 90% or more of uranium-235. The construction of a nuclear reactor inside a nuclear power plant requires a lower concentration of uranium. Usually, uranium is produced into a fuel element having a diameter of about 10 cents and a length of about 2.5 centimeters. The fuel element is mounted into a long fuel rod that is further assembled into a fuel assembly. The fuel assembly is typically immersed in a pressure vessel. The water in the container acts as a cooling element. In order for the reactor to work, the fuel assembly soaked in water must be in a slightly supercritical state. This means that if there is no other equipment, the uranium will eventually overheat and melt. To prevent this from happening, a control rod made of a material that absorbs neutrons is inserted into the fuel assembly through a lifting device. The operator controls the extent of the nuclear reaction by lifting the control rod. When the operator wants the uranium core to generate more heat, the control rod can be raised from the uranium fuel assembly. To reduce heat, lower the control rod to insert into the uranium fuel assembly. In the event of an accident or fuel replacement, the control rod can also be fully inserted into the uranium fuel assembly to shut down the nuclear reactor. The uranium fuel assembly is a heat source that produces extremely high energy. It heats the water and converts it into steam. Steam drives the steam turbine, while the steam turbine drives the generator to generate electricity. In some reactors, the steam produced by the reactor is rotated by a secondary intermediate heat exchange device to heat the water from the other circuit to steam. The benefit of this design is that radioactive water or water vapor does not come into contact with the turbine. Similarly, in some reactors, the cooling fluid in contact with the reactor core is a gas (such as carbon dioxide) or a liquid metal (such as sodium or potassium). This type of reactor allows the core to operate at higher temperatures. If nuclear reactors are removed, nuclear power plants and thermal power plants have very few differences except for the heat source that generates steam. The generator at the Shearon Harris power station supplies electricity to homes and commercial facilities. It generates 870 megawatts of power. A pipe in the power station that transports water vapor that drives the generator to rotate. The pressure vessel of the reactor is typically placed in a concrete lining for radiation protection. This lining is installed in a larger steel closed container. This container has a reactor core and hardware facilities (cranes, etc.) for the staff to maintain the reactor. The purpose of the container is to prevent leakage of radioactive gases or liquids. Finally, this closed container is protected by an external concrete building that is strong enough to withstand the impact of a jet. These secondary containment structures are necessary to prevent leakage of radiation or radioactive steam as in the Sanli Island accident. The nuclear power plant in the former Soviet Union did not have a secondary closed structure, which eventually led to the accident at the Chernobyl nuclear power plant.