Nuclear Reactors
- A nuclear reactor is a system that contains and controls sustained nuclear chain reactions.
- In nuclear reactors, the nuclear fission is controlled by controlling the number of neutrons released during the fission.
- The energy liberated in a controlled manner is used to produce steam, which can run turbines and produce electricity.
Fuel : (uranium 235 , Plutonium-239 )
The fissionable material is used in the reactor along with a small neutron source.The solid fuel is made into rods and is called fuel rods.
The role of the neutrons:
- These neutrons, in turn, can initiate fission processes, producing still more neutrons, and so on. This starts a chain reaction.
- Slow neutrons (thermal neutrons) are much more likely to cause fission in uranium 235 than fast neutrons.
- Fast neutrons liberated in fission would escape instead of causing another fission reaction.
- If the chain reaction is uncontrolled, it leads to explosive energy output, as in a Nuclear Bomb.
- Each time an atom splits, it releases large amounts of energy in the form of heat.
Moderators: (water, heavy water (D2O) and graphite)
Light nuclei called moderators are provided along with the fissionable nuclei for slowing down fast neutrons.
Core :
The core of the reactor is the site of nuclear fission. It contains the fuel elements in a suitably fabricated form.
Reflector :
The core is surrounded by a reflector to reduce leakage. The energy (heat) released in fission is continuously removed by a suitable coolant.
Coolant: (water, heavy water, liquid sodium, helium, Liquid oxygen)
The coolant transfers heat produced during fission to a working fluid which in turn may produce a stream. The steam drives turbines and generates electricity.
Control rods: (Cadmium, Boron)
The reactor can be shut down by means of rods (made of, for example, cadmium, Boron) that have a high absorption of neutrons.cadmium and boron can absorb neutrons to form the corresponding isotopes, which are not radioactive.
Shield:
The whole assembly is shielded with heavy steel or concrete to check harmful radiation from coming out.
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