NUCLEAR POWER PLANT

NUCLEAR POWER PLANT

A nuclear power plant (NPP) is a thermal power station in which the heat source is one or more nuclear reactors.

The schematic arrangement of a nuclear power station is shown above.
The whole arrangement can be divided into following main stages.
(i)Nuclear Reactor (ii)Heat Exchanger (iii)Steam Turbine (iv)Alternator
(i)Nuclear Reactor
It is an apparatus in which nuclear fuel(U235)is subjected to nuclear fission.It controls the chain reaction that starts once the fusion is done.If the chain reaction is not controlled,the result will be an explosion due to the fast increase in the energy released.
A nuclear reactor is a cylindrical stout pressure vessel and houses fuel rods of Uranium moderator and control rods.The fuel rods constitute the fission materials and release huge amount of energy when bombarded with slow moving neutrons.The moderator consists of graphite rods which enclose the fuel rods.The control rods are of Cadmium and and are inserted in the reactor.Cadmium is strong neutron absorber and thus regulates the supply of neutrons for fission.When the control rods are pushed in deep enough,they absorb most of fission neutrons and hence few are available for chain reaction, which therefore stops.However,hence they are being withdrawn,more and more of these fission neutorns cause fission and hence the intensity of chain reaction is increased.Therefore by pulling out the control rods,power of nuclear reactor is increased,whereas by pushing them in,it is reduced.In actual practice,the lowering or raising of control rods is accomplished automatically acoording to the requiremen t of load.The heat produced by the reactor is removed by the coolant, generally a sodium metal.The coolant carries heat to the heat exchanger.
(ii)Heat Exchanger
The coolant gives up the heat to the heat exchanger which is utilised in raising the steam.After giving up heat,the coolant is again fed to the reactor.
(iii)Steam Turbine
The stean produced in the heat exchanger is led to the steam turbine througha valve.after doing a useful work in the turbine,the steam is exhausted to the condenser.The condenser condense the steam which is fed to the heat exchangerthrough feed water pump.
(iv)Alternator
The steam turbine drives the alternator which converts mechanical energy into electrical energy.The output from the alernator is delivered to the bus bars through tansformers,circuit brakers and isolators.

A nuclear reactor is a device to initiate and control a sustained nuclear chain reaction.