What is a requirement for any nuclear chain reaction?

The chain reaction requires both the release of neutrons from fissile isotopes undergoing nuclear fission and the subsequent absorption of some of these neutrons in fissile isotopes.

Is the moderator used in the nuclear?

The moderator of a nuclear reactor is a substance that slows neutrons down. In traditional nuclear reactors, the moderator is the same thing as the coolant: it’s water! When fast neutrons strike the hydrogen atoms in H2O, they slow down a lot (like a billiard ball striking another).

Why moderator is not used in breeder reactor?

No moderator is used to slow down the neutrons, because fast neutrons transmute uranium-238 much more efficiently than slow neutrons. Using water as a coolant would reduce the neutron abundance, since neutrons are absorbed by water. Therefore liquid sodium is used instead.

How is a nuclear chain reaction controlled?

To maintain a sustained controlled nuclear reaction, for every 2 or 3 neutrons released, only one must be allowed to strike another uranium nucleus. Most reactors are controlled by means of control rods that are made of a strongly neutron-absorbent material such as boron or cadmium.

Can a nuclear reaction be stopped?

The only way to control or stop a nuclear chain reaction is to stop the neutrons from splitting more atoms. Control rods made of a neutron-absorbing element such as boron reduce the number of free neutrons and take them out of the reaction. In that case, the chain reaction stops.

Why is moderator necessary in nuclear reactor?

Neutron moderators are a type of material in a nuclear reactor that work to slow down the fast neutrons (produced by splitting atoms in fissile compounds like uranium-235), to make them more effective in the fission chain reaction.

Why do nuclear reactors need a moderator?

The moderator helps slow down the neutrons produced by fission to sustain the chain reaction. Control rods can then be inserted into the reactor core to reduce the reaction rate or withdrawn to increase it. The heat created by fission turns the water into steam, which spins a turbine to produce carbon-free electricity.

Why dont fast reactors need a moderator?

Nuclear reactors can be either thermal or fast. Currently, almost all operating reactors are thermal and thus require a moderator to slow down fast neutrons to the thermal level so that nuclear fission can continue. However, in fast reactors a moderator is not needed, and the neutrons within it move much more quickly.

How can we stop nuclear reactions?

To get a chain reaction in the first place, enough of the neutrons that are being produced have to reach enough of the nuclei that are waiting to decay. To shut the Fukushima reactors down, the designers installed neutron absorbing control rods that can be inserted between fuel rods to halt the chain reaction.

Why it is necessary to control this reaction?

If fission reaction in nuclear power plants is not controlled, then enormous amount of heat released during this process will lead to explosion of the plant and cause fatal destruction to environment and mankind. Thus, it is absolutely necessary to control the fission reaction in nuclear power plants.