How A Nuclear Reactor Works in Steps Explained

A nuclear reactor works through a process of fission, heating, fluid conveyance, electricity generation, cooling and recycling. The same process can be used to describe how a nuclear power plant works; because the nuclear reactor is a central component of the NPP and performs most of its core functions. This article discusses how a nuclear reactor works in steps, as outlined below;





1). Fission (in Explanation of How a Nuclear Reactor Works)

Nuclear fission is the splitting of radioactive atoms into smaller atoms called 'fission products'; and it works by the bombardment of a parent nuclide by neutrons which provide the required energy and excitation for splitting to occur [4].

Fission differs from fusion, which is the joining and radioactive combination of light atoms like hydrogen, to form a larger atom like helium.

Unlike fusion which is less practical and still undergoing development, fission reactors are possible and are the conventional type of nuclear reactors being used for energy conversion and electricity generation.

Control rods in a nuclear reactor are elongate components (plates, tubes, or rods) that are made from neutron-absorbent materials like boron which actively absorb neutrons released from the reactor core, in order to control the fission process and prevent unsustainable reaction conditions.

In most nuclear reactors, fission is the first major step in the process of nuclear power generation.

Neutron bombardment is what starts a nuclear reactor, and the mechanism, core design and composition by which this initial bombardment is achieved depends on the type of reactor involved.

How a Nuclear Reactor Works: Fission as Part of the Nuclear Reactor Process (Credit: Fastfission 2006)
How a Nuclear Reactor Works: Fission as Part of the Nuclear Reactor Process (Credit: Fastfission 2006)





2). Heating

Heat is generated in a nuclear reactor by the fission of nuclear fuel in the core, which is in turn a result of neutron bombardment [3].

Nuclear is used in heating through radioactive reactions that occur between fuel nuclides and bombarding neutrons, as well as between fuel nuclides and reaction products.

This implies that the chain reactions in a nuclear reactor are the basis of nuclear energy release, which usually occurs in the form of heating.

However, this heating must be controlled, by regulating the rate of neutron bombardment and nuclear fission using control rods.

If a nuclear reactor gets too hot, it can cause core damage, fuel rod melting, high vapor pressure, hydrogen gas production by hydration of uranium, and nuclear hazard in the form of explosion and radioactive pollution.

While heating is arguably the basis of nuclear power generation, it is also arguably the basis of nuclear power's potential environmental impact. This is because heating initiates vapor formation and fuel fission in the reactor, both of which must be contained effectively to protect the ecosystem.





3). Fluid Conveyance (in Explanation of How a Nuclear Reactor Works)

Fluid conveyance refers to the function of heat exchangers and coolant fluids in nuclear reactors.

Some materials used as coolant in nuclear reactors include water, carbon dioxide, air, liquid sodium, helium, sodium-potassium alloys and liquid halogen salts.

Without coolant fluids, a nuclear reactor will be unable to transfer heat generated from fission at the core. This will lead go overheating and core damage.

Most fully-operating reactors are designed to perform an emergency shutdown and core cooling, or to reduce their fuel-fission rate when coolant fluid volume reduces, also known as a loss of coolant accident (LOCA) [2].





4). Electricity Generation

Electricity generation is another important step in the outline of nuclear reactor operations.

It occurs typically when nuclear heat from the core is converted to mechanical energy that drives and electric generator to generate electricity.

The conversion pathway from nuclear heat to mechanical energy may differ from one reactor type to another.

For many reactors however, this pathway involves steam generation.

Some reactors may generate steam directly from water in the reactor vessel through boiling, while other reactors make use of a steam generator for this purpose.

The steam that is generated is then transferred to a turbine system, where it drives the turbine to produce mechanical energy which may in turn be used for electricity generation through the electromagnetic effect.

Generators in nuclear power plants are usually designed such that the plant produces AC (alternating current) without need for an external power inverter system.

A nuclear power plant can produce between 100 GWh to 4 TWh of electricity per year, based on hourly capacities of 0.5 MWh to 24.3 MWh. However, the amount of electricity generated under real-life circumstances depends on the capacity factor of the power plant; which is a measure of its timely performance in terms of energy conversion.

Since nuclear power plants in real life do not operate at 100% capacity at all times, the total annual electricity output for a 0.5 MWh plant may be around 89 GWh with proper maintenance.

In general, a capacity factor of above 85% is fair for nuclear reactors working in full operation mode for extended periods.

The amount of electricity produced by a nuclear power plant also depends on the fuel being used.

For example, 1 kg of Uranium produces about 24 GWh, provided it is dominated by U-235 radioisotope, which is highly fissile and constitutes about 0.72% of natural uranium.





5). Cooling and Recycling (in Explanation of How a Nuclear Reactor Works)

Cooling and recycling are distinct but usually simultaneous functions that occur at the end of a complete cycle of nuclear power generation.

Coolant fluid is used to cool down nuclear reactor, by heat transfer, as the fluid is made to flow through a condenser or heat exchange unit.

Nuclear recycling works by effective isolation of all renewable materials in a nuclear reactor system; which include coolant and fuel.

Recycling of the coolant is relatively simple, and occurs when the vaporized or heated fluid is cooled and condensed.

Fuel recycling is a result of the combined function of reactor core and moderator; and its effectiveness is largely determined by the design of the reactor.

Breeder reactors are particularly effective for recycling fuel by re-using fission products, thereby producing nearly unlimited amount of power [1].

Diagrammatic Summary of How a Nuclear Reactor Works in Steps (Credit: Tennessee Valley Authority 2013)
Diagrammatic Summary of How a Nuclear Reactor Works in Steps (Credit: Tennessee Valley Authority 2013)






The summary of how a nuclear reactor works in steps is as follows;

1. Fission

2. Heating

3. Fluid Conveyance

4. Electricity Generation

5. Cooling and Recycling






1). Gill, M. (2016). "The potential impact of fast reactors and fuel recycling schemes on the UK's nuclear waste inventory." Student thesis: Phd. Available at: (Accessed 12 January 2023).

2). Mochizuki, M.; Singh, R.; Nguyen, G.; Nguyen, T. (2014). "Heat pipe based passive emergency core cooling system for safe shutdown of nuclear power reactor." Applied Thermal Engineering 73(1):697-704. Available at: (Accessed 12 January 2023).

3). Nguyen, T. (2020). "Powering Human Settlements in Space." ACS Central Science. Available at: (Accessed 12 January 2023).

4). Seaborg, G. T. (1989). "Nuclear fission and transuranium elements: 50 years ago." Journal of Chemical Education 1989 66 (5), 379. Available at: (Accessed 12 January 2023).

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