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When a slow neutron is captured by a nucleus of U235 or Pu239, the nucleus fissions or splits into two fission fragments and on average 2.5 neutrons are released as well as the energy which we use as heat. In the reactor, some of these are absorbed by the moderator, some escape from the core at the boundaries, but if just one of them is then captured by another nucleus, the process is self repeating, it goes on at a steady rate which can be described as a chain reaction, a type of endless chain. For the reaction to continue at a steady rate, the number of neutrons buzzing about in the core must be constant, this is called the neutron flux, so many neutrons per sq cm per second. The fine control of neutron absorption is done by control rods of absorbing material, usually boron steel alloy, and these are adjusted so that the flux is constant, giving constant power. Note that the reaction is self starting due to the fact that U235 and Pu239 give off a small number of spontaneously produced neutrons, this happens whatever the state of the reactor and continues when it is fully shutdown, so as soon as the control rods are withdrawn the neutron flux starts to increase. You don't have to ignite the fuel to start, as you do with fossil fuels.
Wiki User
∙ 15y ago
Chain reactions happen in nuclear fission because when a uranium atom is split, it releases neutrons that can then strike other uranium atoms, causing them to split as well. This process continues, releasing more neutrons and creating a self-sustaining cascade of reactions that generate a large amount of energy.
Wiki User
∙ 15y agoFission of heavy nuclei can release alpha and beta particles, as well as neutrons. All of these particles are capable of initiating the fission of a heavy nucleus that they collide with.
In a large enough sample of a fissionable element (critical mass), there is a high probability that these particles, when released by spontaneous decay, will initiate a self-sustaining nuclear chain reaction.
This reaction, moderated by neutron absorbers such as carbon or gadolinium, is what releases the energy in nuclear power plants.
In an even larger (or denser) sample (supercritical mass), this reaction progresses geometrically (1, 2, 4, 16, 256, etc) and enormous amounts of energy are released.
This type of reaction is what occurs when an atomic bomb detonates.
Wiki User
∙ 13y agoThe fact that for every fission of U-235, on average 2.5 neutrons are released. By slowing these down with a moderator, at least one can be captured by further U-235 nuclei, thus making the chain reaction possible.
Wiki User
∙ 13y agoThe fact that when a nucleus of U-235 or Pu-239 fissions, free neutrons are emitted, about 2.5 per fission on average. So if you can arrange to absorb one of these in another nucleus, causing another fission, the process will continue and a chain reaction results.
Wiki User
∙ 10y agoThis occurs through the control of the number of available neutrons through the use of high neutron capture control material.
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Do nuclear chain reactions happen in only uranium?
No, nuclear chain reactions can happen in several types of fissile materials, not just uranium. Other examples include plutonium and thorium. These materials can undergo fission reactions and sustain a self-sustaining chain reaction.
A nuclear fission process in which neutrons produced by fission trigger more fissions?
nuclear chain reactionNote: there are also chemical chain reactions (e.g. polymerization), of course they involve no neutrons
What is it called when nuclear fission is repeated?
When nuclear fission is repeated in a self-sustaining chain reaction, it is called a nuclear reactor or a nuclear power plant.
What particle is used to start nuclear fission?
In actuality, a spontaneous fission event begins a nuclear chain reaction. It kick starts a nuclear chain reaction. And a neutron from that fission will initiate another fission to continue and rev up that nuclear chain reaction.
What products do you gain by nuclear fission?
The products of nuclear fission are typically two or more smaller nuclei, along with the release of energy in the form of gamma radiation and kinetic energy of the fission fragments. Fission of a heavy nucleus can also produce neutrons, which can go on to induce further fission reactions in a chain reaction.
Do nuclear chain reactions happen in only uranium?
No, nuclear chain reactions can happen in several types of fissile materials, not just uranium. Other examples include plutonium and thorium. These materials can undergo fission reactions and sustain a self-sustaining chain reaction.
Is fusion a chain reaction?
Not exactly, nuclear chain reactions are a series of nuclear fissions initiated by neutrons produced in a preceding fission.
A nuclear fission process in which neutrons produced by fission trigger more fissions?
nuclear chain reactionNote: there are also chemical chain reactions (e.g. polymerization), of course they involve no neutrons
Do chain reaction takes place in nuclear reactor?
Yes, chain reactions take place in nuclear reactors. In a nuclear reactor, the chain reaction involves the splitting of uranium atoms (fission) which releases energy and more neutrons, leading to further fission reactions. Control rods are used to regulate and maintain the chain reaction at a steady rate.
The process in which each split atom gives up neutrons?
The act of an atom splitting is called nuclear fission. In nuclear fission where we see neutrons emerge with fission fragments, and we then see those neutrons initiate other fission reactions is called a nuclear fission chain reaction.
What type of reaction happens inside a nuclear power plant?
A nuclear chain reaction nuclear fission
Can fission happen on earth?
Yes, all natural radiation (in the rocks) is a result of fission (but this fission is not part of a chain reaction like in a fission bomb). However, it is theoretically possible for natural processes to concentrate radioactive elements (uranium) to the extent where a natural nuclear fission reactor (a chain reaction like in a nuclear power plant) will form. Oklo in in Gabon is the only known location for this to have happened and consists of 16 sites at which self-sustaining nuclear fission reactions took place approximately 1.7 billion years ago.
What is it called when nuclear fission is repeated?
When nuclear fission is repeated in a self-sustaining chain reaction, it is called a nuclear reactor or a nuclear power plant.
What particle is used to start nuclear fission?
In actuality, a spontaneous fission event begins a nuclear chain reaction. It kick starts a nuclear chain reaction. And a neutron from that fission will initiate another fission to continue and rev up that nuclear chain reaction.
Fossil fuels form from nuclear chain reactions?
Fossil fuels do not form from nuclear chain reactions. Fossil fuels are formed from the decay of organic matter over millions of years in the Earth's crust. Nuclear chain reactions refer to the process of nuclear fission in which atomic nuclei split, releasing energy.
If carbon were used as nuclear fuel it would be best?
Carbon is not commonly used as nuclear fuel because it does not readily undergo nuclear fission reactions. Elements such as uranium and plutonium are more suitable for use as nuclear fuels due to their ability to sustain nuclear chain reactions.
What reaction keeps going on its own once it starts?
A chain reaction is a type of reaction that keeps going on its own once it starts due to the products of the reaction continuing to fuel the reaction. Nuclear fission reactions in nuclear power plants and explosions are examples of chain reactions that continue on their own once initiated.
