Today’s nuclear power is produced from the fission process with 415 reactors operating in the world, mainly cooled by water.
Tianwan Nuclear Power Plant in Jiangsu, China. Image: Xinhua
“Nuclear energy is one of the safest, cleanest, least environmentally burdensome and cheapest energy sources available if we consider the entire life cycle of a nuclear power plant,” Rafael Mariano Grossi, IAEA Director General, said during the 54th annual conference of the World Economic Forum taking place in Davos, Switzerland, January 2024.
These benefits are increasingly recognized by environmental activists and world leaders. At the COP28 conference in Dubai, leaders from 22 countries signed a declaration to triple global nuclear energy capacity by 2050 to meet climate goals and energy needs.
“After 28 years of neglect, nuclear is finally getting attention at the world’s most important conference on climate change, almost too late. As someone who once opposed nuclear energy but later changed his mind, I think, I’m very happy to see how much attitudes towards nuclear energy have changed,” said Zion Lights, former British spokesman for the environmental protection movement Extinction Rebellion.
How is nuclear power produced?
Nuclear energy is a form of energy released from the nucleus – the core of atoms, made of protons and neutrons. This energy source can be created in two ways: fission (the nucleus splits into parts), and fusion or fusion (the nucleus fuses together).
Today, the nuclear energy that the world exploits to produce electricity is generated from the fission process. Meanwhile, the technology to produce electricity from the fusion process is still in the research and development (R&D) stage.
Nuclear fission is a reaction in which the nucleus of an atom splits into two or more smaller nuclei, releasing energy. For example, upon collision with a neutron, the nucleus of a uranium-235 atom will split into two smaller nuclei, perhaps a barium nucleus, a krypton nucleus, and 2 or 3 neutrons. These additional neutrons will collide with surrounding uranium-235 atoms, causing them to split and continue to create more neutrons, leading to a chain reaction in a split second.
Each time a reaction occurs, energy is released in the form of heat and radiation. Heat can be converted into electricity in a nuclear power plant. Inside a nuclear power plant, reactors and equipment contain and control chain reactions. The heat generated from the reaction heats the reactor’s coolant, usually water, creating steam. The steam is then directed to rotating turbines, activating generators to produce electricity.
Outstanding reactor technologies in the world
According to statistics from the International Atomic Energy Agency (IAEA), as of November 13, 2024, the world has 440 nuclear reactors, of which 415 are in operation, distributed in 30 countries. family. The United States is the largest contributor with 94 reactors and a total electrical capacity of 96.95 GW. Followed by France (56 reactors, total capacity 61.37 GW), China (56 reactors, total capacity 54.15 GW), Russia (36 reactors, total capacity 26.8 GW) and South Korea (26 furnace, total capacity 25.82 GW).
Nuclear reactors come in many different shapes and sizes, most large enough to power major cities. Small reactor models are being developed to complement them.
In addition to a few reactors that use gas or metal for cooling, there are about 400 reactors in the world, with capacities ranging from 30 – 1660 MW, cooled by water. Current water-cooled reactors are divided into three main types: pressurized water reactors (PWR), boiling water reactors (BWR), pressurized heavy water reactors (PWHR).
The Watts Bar nuclear power plant in Tennessee, USA, uses a pressurized water reactor (PWR). Image: Energyeducation
Pressurized water reactor (PWR) accounting for nearly 70% of global reactors, according to the World Nuclear Association (WNA). There are about 300 reactors operating to produce electricity with a total capacity of 300 GW. Countries that commonly use PWR are the US, France, Japan, Russia, China, and Korea.
PWR uses regular water as a coolant and also as a moderator (a substance in the core that helps slow down the neutrons released from fission reactions so they create more fission reactions). This design has a main cooling circuit running through the reactor core and a secondary circuit in which the steam produced helps turn the turbine. The water in the main circuit is prevented from boiling by high pressure. The water in the secondary circuit is under less pressure so it boils, turning the turbine to generate electricity.
PWR reactors only require regular water as a moderator instead of expensive heavy water. They are also very stable as they tend to reduce capacity as temperature increases. PWRs can also operate with cores containing less fissile material, reducing the possibility of uncontrolled power surges, increasing safety.
However, they still have some limitations such as requiring very sturdy pipes and good pressure vessels, making PWR construction quite expensive. Most reactors need to be refueled every 18 months or so and must be shut down for several weeks of refueling. Hot water from the main circuit with dissolved boric acid is corrosive to stainless steel, causing (radioactive) corrosion products to flow through the main circuit. This reduces the life of the reactor and requires special systems to filter out the corrosion products.
Boiling Water Reactor (BWR) is the second most popular type globally, accounting for 15% with about 60 reactors, total capacity of 60 GW. Unlike the PWR, this design has a single circuit in which the water is kept at a pressure that can boil. The generated steam is fed directly into the turbine. BWR is mainly distributed in the US, Japan, and Sweden.
Because there is only one circuit, the design of the BWR is simpler and easier to operate. The pressure inside the reactor is much lower than with PWR because the water is allowed to boil. Therefore, the tank is lighter and does not need to withstand high pressure. The reactor also does not use boric acid, which helps reduce corrosion in the reactor vessel and pipes.
However, BWR requires more complex calculations to adjust nuclear fuel consumption during operation. The reactor core also requires more equipment. Another disadvantage is that the steam produced is slightly radioactive, so pipes and turbines need to be carefully shielded.
With nearly 50 reactors and 11% of the world, pressurized heavy water reactor (PWHR) is the third most popular type of nuclear power reactor, contributing a total capacity of 25 GW. The design uses heavy water, a chemically distinct form of water, to cool and control nuclear reactions. Heavy water reactors are mainly built in Canada and India.
The big advantage of PHWR is the ability to refuel during operations, increasing availability. Thanks to heavy water, PWHR can use natural uranium as fuel instead of having to use enriched uranium like PWR and BWR. In addition, the reactor is also considered very safe.
Although fuel costs are reduced, PHWRs cost more to produce heavy water. Besides, the energy content of natural uranium is lower than that of enriched uranium, requiring more frequent fuel replacement. The increased rate of fuel passing through the reactor also results in a higher mass of spent fuel compared to reactors using enriched uranium.
The Beloyarsk nuclear power plant in Russia has two sodium-cooled fast reactors. Image: Rosatom
Most reactors today use water to cool the core, but scientists are still researching and developing reactors that use liquid metal, molten salt or gas as coolant. Their development could help provide nuclear power more efficiently with new, exciting applications. Many waterless reactors have been operating successfully for many years, mainly at the experimental level.
For example, liquid metal fast reactor (LMFR) uses liquid metals such as sodium, lead… to cool the core. They can use uranium as fuel in metallic form instead of the currently common ceramic form, as well as recycled nuclear waste. The rare fast reactors in operation are the sodium-cooled BN-600 and BN-800. Both are located in the Beloyarsk nuclear power plant, Russia.