Nuclear Reactor-Basic Components

A nuclear reactor is a machine that starts and stops a nuclear chain reaction. They can be used for a lot of different things. Nuclear fission or nuclear fusion can be used to generate thermal energy in these reactions (in development). Aside from generating electricity, nuclear reactors can be used for propulsion in vehicles like submarines or naval boats, production of valuable isotopes or neutrons, research, and training.

All tools that can start and control nuclear fissions are known as nuclear reactors. Nuclear reactors are used for research, production of radioactive isotopes, and most notably, nuclear power plants’ energy supply sources.

Nuclear reactor components

The nuclear reactor’s components are explained in this section.

FUEL

• The primary source of energy is uranium. 

• Uranium oxide (UO2) pellets are often placed in tubes to form fuel rods. In the reactor’s core, the rods are organised into fuel assemblies. 

• The fuel for a nuclear reactor must be compatible with the reactor’s overall architecture and the systems that drive its operations. 

In the next section, a brief description of the fuel materials and reactor layouts used in nuclear reactors is offered.

Low-pressure water reactor

The most frequently utilised type of light-water reactor (LWR) for commercial power generation uses sintered uranium dioxide pellets fed into zirconium alloy or other advanced cladding material cladding tubes.

Heavy water reactor:

• Natural uranium pellets are used in the CANDU (Canada Deuterium Uranium) reactor, which is the most common form of the heavy-water reactor. 

• Using lengthy tubes, these pellets are placed in a lattice.

• It is estimated that a CANDU reactor fuel assembly is about 40 inches long. The reactor core is filled with several assemblies stacked one on top of the other. 

• The neutron scattering is improved by using heavy water instead of light water as the moderator. Fuel material fission probability increases as a result.

Graphite reactor for High-Temperature Use

• At the core is a uranium dioxide microsphere, which is surrounded by concentric shells of carbon, silicon carbide, and carbon in a high-temperature graphite reactor’s fuel. 

• Each fuel sphere is protected from the outside world by these shells. 

• It is then enclosed in micrographic graphite cladding, which blends the particles with graphite.

Research Nuclear Reactor

• In research reactors, uranium-aluminium alloy plates with aluminium cladding are the most frequent types of fuel. 

• The uranium is reinforced to a level of about 20%. In comparison to other cladding materials, aluminium’s melting point is lower. 

• However, because the plates are only 1.25 mm thick, the flat plate design maintains a low fuel temperature. 

• Fuel for TRIGA (a class of nuclear research reactor) is a mixture of zirconium hydroxide and uranium hydride, plus a small amount of erbium condensate, and stainless steel.

CORE

• The core of a nuclear reactor, which includes the nuclear fuel components, is where nuclear reactions occur and heat is generated. 

• Low-enriched uranium is typically used as fuel in hundreds of fuel pins. Structural components to reduce neutrons, manage reaction, and transport fuel heat outside the core are also included in the core.

• This centre core houses the fuel, coolant (which also serves as a moderator), and cladding. 

• The core of a nuclear reactor is where the fission energy is produced.

Reactors using water as a mediating agent

• The core of a pressurised water reactor or a boiling water reactor contains four-metre-long fuel rods. “Fuel assemblies” are bundles of hundreds of components.

• Pellets of uranium, or uranium oxide, are piled one on top of the other in the fuel rods. In addition, the core contains control rods packed with neutron-capturing pellets of boron, hafnium, or cadmium.

• Flowing water from the core shroud cools the nuclear reactions taking place in the core.

• Fission reaction heat is dissipated by water, while neutron reactions are regulated by water.

Graphite-moderated reactors

• The neutron moderator in a graphite-moderator reactor is solid nuclear graphite, and the coolant is ordinary water.

• There is a graphite neutron moderator in the Advanced Gas-Cooled Reactor (AGCR) core, where the fuel assembly is located. As a cooling agent, carbon dioxide gas is used. 

• The heat is dissipated as it circulates through the core.

REFLECTORS

• Many neutrons are scattered or reflected back into the core by the reflector, which is a layer of material around the core. 

• By further fusing the neutrons that have been reflected, the reactor’s neutron economy is improved. 

• Graphite, water, beryllium, and natural uranium are among the most common reflector materials.

MODERATORS AND COOLANTS

• To protect the environment and generate power, the heat generated by nuclear fission in reactors needs to be caught and transported. 

• Reactors use coolants to remove heat from the core, where the fuel is digested, in order to accomplish this. 

• Coolants also help to keep the core’s pressures under control.

Water

• There are two primary types of water-cooled reactors: PWR and boiling water reactor (BWR). Both use light water, but the cooling procedures are slightly different. 

• To generate electrical power, the steam turbines of a boiling-water reactor are directly fed with water from the core of the reactor.

• It is more economical to employ heavy water (liquid D2O) as cooling and moderator than hydrogen since its cross-section is three times smaller. However, it is also extremely pricey.

The alloy of Sodium and Zinc

• Fast breeding reactors use molten sodium as their cooling medium. 

• Liquid sodium is also compatible with stainless steel due to its high strength density and lack of corrosivity.

Molten Salt

• Liquid metal can be replaced with molten salt. 

• Using this coolant at higher temperatures may reduce the mechanical load on the reactor and increase its inherent safety. 

• There is efficient heat transfer through molten salt.

Containment system

Reactors are built to function without releasing radioactive material into the environment. However, it’s possible that something goes wrong. These mishaps need the use of numerous fission product barriers. The fuel ceramic, the reactor vessel, the metal fuel cladding tubes, and the coolant system are all examples of barriers. Finally, the reactor is housed in the containment chamber.

Conclusion

We have learned about the nuclear reactor and its basic components. Each component is useful and has its utilities in nature, be it fuel, water, an alloy of sodium or zinc, etc. All nuclear reactors follow the same basic principles for generating electricity. In either gas or water, the heat generated by the fission of the fuel atoms is utilised to generate steam.