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Nuclear Energy
Energy liberated by the nuclear fission of materials like
Uranium (U), Plutonium (Pu).
The heat produced due to fission of U and Pu is used to
heat water to generate steam which is used
for running turbo-generator.
Chain Reaction
When a neutron is captured by a nucleus of an atom of
U235, it splits up roughly into two equal
segments and about 2.5 neutrons are released and a large
amount of energy (nearly 200 MeV) is
produced.
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Energy produced, E=mc
2.5 n 1 n is to sustain the chain reaction
0.9n is captured by U238
0.6n is partly absorbed by control rod, coolant,
moderator, and partly escape.
Fertile Material
It is defined as the material which absorbs neutrons and
undergoes spontaneous changes which lead
238 232
to the formation of fissionable material. U and Th are
the fertile materials.
232 233
Th + n U
238 239
U + n Pu
Main Components
1.Nuclear Fuel
2.Moderator
3.Control rods
4.Reflector
5.Reactor Vessel
6.Biological Shielding
7.Coolant Main Components
1.Nuclear Fuel
2.Moderator
3.Control rods
4.Reflector
5.Reactor 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
233, 235 239
produce a fission chain reaction. It can be one or all
of the following U U and Pu .
Nuclear fuel should not be expensive to fabricate. It
should be able to operate at high temperatures
and should be resistant to radiation damage.
The fuel should be protected from corrosion and erosion
of the coolant and for this it is encased in
metal cladding generally stainless steel or aluminum.
Adequate arrangements should be made for fuel supply charging
or discharging and storing of the
fuel.
Fuel element cladding should possess the following properties:
(i) It should withstand high temperature within the reactor.
(ii) It should have high corrosion resistance.
(iii) It should have high thermal conductivity
(iv) It should not have a tendency to absorb neutrons.
(v) It should have sufficient strength to withstand the
effect of radiations to which it is
subjected.
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.
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A moderator should process the following properties:
(i) It should have high thermal conductivity
(ii) It should be available in large quantities in pure
form.
(iii) It should have high melting point in case of solid
moderators and low melting point in case of
liquid moderators. Solid moderators should also possess
good strength and machinability
(iv) It should provide good resistance to corrosion
(v) It should be stable under heat and radiation
(ii) It should be able to slow down neutrons.
3. Control Rods
The consumption of this fuel and the power level of the
reactor depends upon its neutron flux in the
reactor core. 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.
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 down
manually or automatically.
Control rods should possess the following properties:
They should have adequate heat transfer properties They
should be stable under heat and radiation They should
be corrosion resistant. They should be sufficient strong
and should be able to shut down the reactor almost instantly
under all conditions. They should have sufficient cross
sectional area fro the absorption.
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 strong walled container housing the core of the
power reactor. It contains moderator reflector
thermal shielding and control rods.
6. Biological Shielding
Shielding the radioactive zones in the reactor from 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.
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
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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.
Coolant used should be stable under thermal condition.
It should have a low melting point and
high boiling point. It should not corrode the material
with which it comes in contact. The coolant
should have high heat transfer coefficient.
Coolant Cycle
The coolant while circulating through the reactor passages
take up heat produced due to chain reaction
and transfer to the system.
(i)Direct cycle: In this system coolant, which is water,
leaves the reactor in the form of steam. Boiling water
reactor uses this system.
(ii)Single Circuit System: In this system the coolant
transfers the heat to the feed water in the steam
generator. This system is used in pressurized reactor.
(iii) Double circuit system: In this system two coolant
are used. Primary coolant after circulating through the
reactor flows through the intermediate heat exchanger
(IHX) and passes on its heat to the secondary coolant
with transfers its heat in the feed water in the system
generator. This system is used in sodium graphite
reactor and fast breeder reactor.
Different Types of Reactors
Boiling Water Reactor
Boiling Water Reactor enriched uranium (enriched uranium
contains more fissionable isotope U235
then the naturally occurring percentage 0.7%) is used
as nuclear fuel and water is used as coolant.
Water enters the reactor at the bottom. It takes up the
heat generated due to the fission of fuel and
gets converted into steam. Steam leaves the rector at
the top and flows into the turbine. Water also
serves as moderator.
Advantages of Nuclear Power Plant
The various advantages of a nuclear power plant are as
follows:
1. Space requirement of a nuclear power plant is less
as compared to other conventional power
plants are of equal size.
2. A nuclear power plant consumes very small quantity
of fuel. Thus fuel transportation cost is
less and large fuel storage facilities are not needed.
Further the nuclear power plants will
conserve the fossil fuel for other energy.
3. There is increased reliability of operation.
4. Nuclear power plants are not effected by adverse weather
condition
5. Nuclear power plants are well suited to meet large
power demands. They give better
performance at higher load factors
6. It does not require large quantity of water.
Disadvantages
1. Initial cost of nuclear power plant is higher as compared
to hydro or steam power plant
2. Nuclear power plants are not well suited for varying
load conditions.
3. Radioactive wastes if not disposed carefully may have
bad effect on the health of workers
and other population.
4. Maintenance cost of the plant is high
5. It requires trained personnel to handle a nuclear power
plants.
Site Selection
The various factors to be considered while selection the
site for nuclear plant are as follows:
1. Availability of water: At the power plant site an ample
quantity of water should be available
for condenser cooling and make up water required for steam
generation. Therefore the site
should be nearer to a river, reservoir or sea.
2. Distance from load centre: The plant should be located
near the load center. This will
minimise the power losses in transmission lines
3. Distance from populated area: The power plant should
be located far away from populated
are to avoid the radioactive hazard.
4. Accessibility to site: The power plant should have
rail and road transportation facilities.
5. Waste disposal: The wastes of nuclear power plant are
radioactive and there should be
sufficient space near the plant site for the disposal
of wastes.
6. Safe guard against earth quakes.
Hydro-Electric Power Plant
Hydro Power
Harnessing power from water flowing under pressure.
Hydroelectricity is electricity produced by hydropower.
Most hydroelectric power comes from the potential energy
of dammed water driving a water
turbine and generator.
Hydroelectricity is a renewable energy source.
Pros
1.Running cost of hydro power plant is low.
2.Reliability is greater than that of other power plants.
3.The hydraulic turbines can be put off and on in matter
of minutes.
4.Life expectancy more.
5.Steam power plants have problem of ash disposal where
as hydro power plant has no
comparable problem
6.Modern hydro generators give very high efficiency over
a considerable range of load.
Cons
1.The power produced by the plant depends upon quantity
of water.
2.Initial cost of the plant is high.
3.Requires long transmission lines to deliver power.
4.It takes long time for the erection of such plants.
5.Hydroelectric projects can be disruptive to surrounding
aquatic ecosystems.
Main Components of Hydro-Electric Power Plant
1.Water reservoir
2.Dam
3.Forebay
4.Trash rack
5.Water way
6.Draft tube
7.Surge tank
8.Spill way
9.Power house & equipment.
Dam
a.Gravity dam
b.Arch dam
c.Buttress dam
d.Earthen dam
e.Rock fill dam
Classification of Hydro-electric Power Plant
1.Quantity of water
a. Run of river plant b. Storage plant c. Pump
storage pump
2. Availability of head of water
a. Low head plant b. Medium head plant c. High head
plant
3. According to topography
a. Low land b. Hilly area c. Mountainous
region
4. According to load supplied
a. Base load plant b. Peak load plant
5. According to capacity of plant
a. Micro hydel plant (up to 5MW) b. Medium capacity plant(5
to 100 MW)
c. High capacity plant(101 to 1000 MW) d. Super plant
(above 1000 MW)
6. According to turbine characteristic
a. High specific speed b. Medium specific speed
Selection of Turbines
1.Working Head
2.Nature of Load
3.Output
4.Specific Speed
Turbines Type:
Impulse Turbine (Pelton wheel),
Reaction Turbine (Francis turbine,
Kaplane and Propeller Turbines
Hydrology
Deals with the distribution of water on land beneath the
surface of earth. It deals with
the solid, liquid and vapor forms of water.
Hydrologic Cycle
The various processes involved in the transfer of moisture
from the sea to the land
and back to the sea again.
Hydrologic equation is expressed as follows
P=R+E P=Precipitation
R=Run-off
E=Evaporation
Hydrograph
Graphical representation between discharge (cubic meter
per second)
through a river and time.
A hydrograph may be plotted for several weeks or even
months.
Hydrograph indicates the power available from the stream
at different
times of the day week or year. It depends on the characteristics
of the
catchment and precipitation over the catchment. A hydrograph
has a rising
limb peak and receding limb or recession curve.
Factors Affecting Run-Off
1.Precipitation Characteristics
2.Meteorological Characteristics
3.Catchment Characteristics
Run-Off Estimation
Information Needed
1.Annual, Monthly or Seasonal run-off
2.Extreme low flows
3.Flood run-off
Following methods to determine the run-off
1.Empirical Method
2.Rational Method
3.From Hydrograph
Calculation of Power from Head and Discharge
Let H = net head of water in meters
?= discharge m3/sec
h= overall efficiency of hydro-power plant
w= specific weight of water in kg/m3
HP = horse power developed HP = ?fH.?
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Disclaimer Typo, inconsistency, omission should be checked
and corrected by he readers, thereby. Please consult with
the textbook and with the eference books for any inconsistency
found in the contents.
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