Here we are providing the short notes on Chemistry which will be help to crack science part in may examinations like SSC, Railway and other competitive exams.
NUCLEAR REACTOR
A nuclear reactor is a device 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.
Role of extra neutron –
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 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 or Atom 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 nuclearfission. It contains the fuel elements in 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 steam. 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 high absorption of capacity 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.
