NUCLEAR POWER PLANTS
Nuclear power is the
use of sustained or controlled nuclear fission to generate heat and
do useful work. Nuclear Electric Plants, Nuclear Ships and Submarines use
controlled nuclear energy to heat water and produce steam, while in space,
nuclear energy decays naturally
in a radioisotope thermoelectric generator. Scientists are
experimenting with fusion energy for
future generation, but these experiments do not currently
generate useful energy.
Nuclear power provides about 6%
of the world's energy and 13–14% of the world's
electricity, with the U.S., France, and Japan together accounting for about 50%
of nuclear generated electricity.
Also, more than 150 naval vessels
using nuclear propulsion have been built. Just as many conventional thermal
power stations generate electricity by harnessing the thermal energy released
from burning fossil fuels, nuclear power plants convert the energy released
from the nucleus of an atom, typically via nuclear fission.
LAYOUT OF NUCLEAR POWER PLANT:
NUCLEAR REACTOR
A nuclear reactor is an apparatus
in which heat is produced due to nuclear fission chain reaction. Fig. shows the
various parts of reactor, which are as follows:
1. Nuclear
Fuel
2. Moderator
3. Control
Rods
4. Reflector
5. Reactors
Vessel
6. Biological
Shielding
7. Coolant.
1. Nuclear Fuel
Fuel of a nuclear reactor should
be fissionable material which can be defined as an element or isotope whose
nuclei can be caused to undergo nuclear fission by nuclear bombardment and to
produce a fission chain reaction. It can be one or all of the following U233,
U235 and Pu239.
Natural uranium found in earth
crust contains three isotopes namely U234, U235 and U238
and their average percentage is as follows:
U238
- 99.3%
U235
- 0.7%
U234
- Trace
2. Moderator
In the chain reaction the
neutrons produced are fast moving neutrons. These fast moving neutrons are far
less effective in causing the fission of U235 and try to escape from the
reactor. To improve the utilization of these neutrons their speed is reduced.
It is done by colliding them with the nuclei of other material which is
lighter, does not capture the neutrons but scatters them. Each such collision
causes loss of energy, and the speed of the fast moving neutrons is reduced.
Such material is called Moderator. The slow neutrons (Thermal Neutrons) so
produced are easily captured by the nuclear fuel and the chain reaction
proceeds smoothly. Graphite, heavy water and beryllium are generally used as
moderator
3. Control Rods
The Control and operation of a
nuclear reactor is quite different from a fossil fuelled (coal or oil fired)
furnace. The energy produced in the reactor due to fission of nuclear fuel
during chain reaction is so much that if it is not controlled properly the
entire core and surrounding structure may melt and radioactive fission products
may come out of the reactor thus making it uninhabitable. This implies that we
should have some means to control the power of reactor. This is done by means
of control rods.
Control rods in the cylindrical
or sheet form are made of boron or cadmium. These rods can be moved in and out
of the holes in the reactor core assembly. Their insertion absorbs more
neutrons and damps down the reaction and their withdrawal absorbs less
neutrons. Thus power of reaction is controlled by shifting control rods which
may be done manually or automatically.
4.Reflector
The neutrons produced during the
fission process will be partly absorbed by the fuel rods, moderator, coolant or
structural material etc. Neutrons left unabsorbed will try to leave the reactor
core never to return to it and will be lost. Such losses should be minimized.
It is done by surrounding the reactor core by a material called reflector which
will send the neutrons back into the core. The returned neutrons can then cause
more fission and improve the neutrons economy of' the reactor.
Generally the reflector is made up of graphite and beryllium.
5. Reactor
Vessel
It is a.
strong walled container housing the cure of the power reactor. It contains moderator, reflector, thermal
shielding and control rods.
6. Biological
Shielding
Shielding the radioactive zones in the reactor roan possible
radiation hazard is essential
to protect, the operating men
from the harmful effects. During fission of nuclear fuel, alpha particles, beta
particles, deadly gamma rays and neutrons are produced. Out of these gamma rays
are of main significance. A protection must be provided against them. Thick
layers of lead or concrete are provided round the reactor for stopping the
gamma rays. Thick layers of metals or plastics are sufficient to stop the alpha
and beta particles.
7. Coolant
Coolant flows through and around the reactor core. It is used
to transfer the large
amount of heat produced in the
reactor due to fission of the nuclear fuel during chain reaction. The coolant
either transfers its heat to another medium or if the coolant used is water it
takes up the heat and gets converted into steam in the reactor which is directly
sent to the turbine.
Advantages
Ø Need less
space.
Ø Fuel
consumption is small, hence transportation and storage charges are low.
Ø Well
suited for large power demands.
Ø Less work
men required.
Disadvantages
Ø Capital
cost very high.
Ø Radioactive
wastes, if not disposed properly have adverse effect on environment.
Ø Maintenance
cost high.
Related Topics
Privacy Policy, Terms and Conditions, DMCA Policy and Compliant
Copyright © 2018-2023 BrainKart.com; All Rights Reserved. Developed by Therithal info, Chennai.