What is a Nuclear Reactor?

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  • Written By: Mary McMahon
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  • Last Modified Date: 02 October 2019
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A nuclear reactor is a piece of scientific equipment which is designed to generate controlled chain reactions of fissionable elements like uranium. Nuclear reactors can be used for a number of purposes, including the generation of electrical power, the production of nuclear fuels, and scientific research. Nuclear reactors of various designs can be found in many regions of the world, from scientific labs in the United States to the French countryside, with the French relying on nuclear power for around 75% of their power needs as of 2009.

Nuclear reactors rely on a process known as fission, which occurs when a heavy element absorbs a neutron and breaks apart into two lighter elements. In the process, the element releases energy. In a controlled fission reaction, this energy can be harnessed for various activities, and coaxed into establishing a chain reaction which encourages the rest of the fissionable element to break apart as well. An uncontrolled reaction creates a nuclear bomb.


Inside a nuclear reactor, fuel rods made up of a fissionable element are inserted into a moderator, a material which will slow down neutrons to encourage fission. The operator of the nuclear reactor can control the reaction with the use of control rods, rods made from materials which absorb neutrons. When the rods are lowered into the reactor core with the fuel, they absorb the neutrons, slowing or stopping the fission process, and when they are raised, they allow the fuel rods to absorb the neutrons and undergo fission. Periodically, the fuel rods become spent and need to be replaced with fresh fuel, while the spent fuel must be carefully disposed of to avoid generating pollution.

The nuclear reactor also requires a coolant to transfer heat away from the reactor core. Heat, a byproduct of fission, may in fact be the goal of the reactor's operators, because it can be used to generate electricity by generating steam which will push turbines. When a nuclear reactor is being used for scientific research, the heat may be an undesirable byproduct, although some reactors are designed for both research and electrical generation for maximum efficiency.

A huge number of systems are involved in the control and containment of a nuclear reactor. The inherent risk of creating a controlled reaction is that the reaction may cascade out of control. This concern is addressed with numerous failsafes and safety technologies which are designed to keep the reactor safely operating. Relatively few major accidents have occurred with nuclear reactors, and those which do tend to occur in older reactors with insufficient support infrastructure in place.


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Post 3

@framemaker- Here is an overly simplified explanation of a fusion reaction. In one type of nuclear fusion, two isotopes of hydrogen (the most abundant element in the universe) are combined to form helium isotopes. These helium isotopes are then combined to form an unstable beryllium isotope. The unstable beryllium isotope then decays back into a new helium 4 isotope creating energized particles and radiation as a by-product.

Another type of fusion reaction only involves hydrogen isotopes that form a helium isotope and a high-energy neutron particle.

The difficulty with fusion reactions is the conditions required for the reaction to take place. Fusion requires high heat and pressure, on the magnitude of what you would find in the sun, to create the reaction. This makes fusion destructive by nature (to the reactor). The nuclear reactor diagrams I have seen for fusion involve strong electromagnets to stabilize the core.

Post 2

@framemaker- There are three major advantages of a fusion reactor. 1) Fusion reactors produce less radioactive waste than a fission reactor. 2) Fusion reactors will not leak high levels of radiation should a reactor failure occur. 3) Fusion reactors use abundant and readily available fuel.

There are no commercially operational reactors, but there are a few in the experimental stages at various DOE plants across the country. Fusion could be operational in a couple of decades, but at the current time, they consume more energy than they produce. Once a breakthrough occurs, they should be much safer than fission reactors.

Post 1

What is a fusion reactor? What is the basic concept behind a fusion reactor? I hear talk about fusion being the ultimate goal of nuclear least in the near future, but I do not understand it. How does fusion work and what makes it so appealing? Are there any operational fusion reactors? As far as nuclear reactor safety, what is safer: fission or fusion?

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