Schematic Arrangement of Nuclear Power Station

Schematic Arrangement of Nuclear Power Station:

The schematic arrangement of a nuclear power station is shown in Figure.The whole arrangement can be divided into the following main stages :

(i) Nuclear Reactor

(ii) Heat Exchanger

(iii) Steam Turbine

(iv) Alternator

Schematic Arrangement Of Nuclear Power Station

(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 fission 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 (See Figure).The fuel rods constitute the fission material and release huge amount of energy when bombarded with slow moving neutrons.The moderator consists of graphite rods which enclose the fuel rods. The moderator slows down the neutrons before they bombard the fuel rods. The control rods are of cadmium and are inserted into 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of fission neutrons and hence few are available for chain reaction which, therefore, stops.However, as they are being withdrawn, more and more of these fission neutrons cause fission and hence the  intensity  of chain reaction (or heat produced) is increased. Therefore, by pulling out the control rods, power of the 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 according to the requirement of load.The heat produced in the reactor is removed by the coolant, generally a sodium metal.  The coolant carries the heat to the heat exchanger.

Nuclear Reactor

(ii) Heat Exchanger. The coolant gives up heat to the heat exchanger which is utilized in raising the steam. After giving up heat, the coolant is again fed to the reactor.

(iii) Steam Turbine. The steam produced in the heat exchanger is led to the steam turbine through a valve.  After doing a useful work in the turbine, the steam is exhausted to condenser. The condenser condenses the steam which is fed to the heat exchanger through feed water pump.

(iv) Alternator. The steam turbine drives the alternator which converts mechanical energy into electrical energy.The output from the alternator is delivered to the bus-bars through transformer, circuit breakers and isolators.