Page 302 - Electrician - TT (Volume 2)

ELECTRICIAN - CITS

5 Maintenance charges are high due to lack of standardisation. Moreover, high salaries of specially trained
personnel employed to handle the plant further raise the cost.
6 Nuclear power plants are not well suited for varying loads as the reactor does not respond to the load
fluctuations efficiently.
7 The disposal of the by-products, which are radioactive, is a big problem. They have either to be disposed off
in a deep trench or in a sea away from sea-shore.
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

Fig 4

i Nuclear reactor
Is a cylindrical stout pressure vessel and houses, fuel rods of Uranium, moderator of graphite and control rods of
cadmium material.

The graphite moderator slows down the neutrons before they bombard the fuel rods. Cadmium is strong neutron
absorber and thus regulates the supply of neutrons for fission. By pulling out the control rods, power of the nuclear
reactor is increased, whereas by pushing them in, it is reduced. The heat produced in the reactor is removed by
the coolant, generally a sodium exchanger.
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.

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CITS : Power - Electrician & Wireman - Lesson 106-116