1. Nuclear energy comes from the energy stored in the nucleus of atoms and can be released through nuclear fission or fusion. Fission involves splitting heavy atoms while fusion combines light atoms. 2. There are two main nuclear processes for energy production - fission and fusion. Fission of atoms like uranium is used in nuclear power plants today while fusion promises more energy but has not been achieved commercially. 3. A nuclear power plant uses fission in a reactor to heat water and produce steam that drives turbines to generate electricity. Pakistan operates 5 nuclear reactors producing around 3.6% of its total electricity.

1. GOVERNMENT COLLEGE OF TECHNOLOGY LAHORE 1
Nuclear energy
Nuclear energy is the energy that holds together the nucleus of atoms. Atoms are the most
simple blocks that make up matter. Every atom has in its center a very small nucleus. Normally,
nuclear energy is hidden inside the atoms. However, some atoms are radioactive and send off
part of their nuclear energy as radiation. Radiation is given off from the nucleus of
unstable isotopes of radioactive substances.
Nuclear energy can also be freed in two other ways: nuclear fusion and nuclear fission. Nuclear
fusion is the combining of two light atoms into a heavier one and nuclear fission is the splitting of
a heavy atom. Both ways make big amounts of energy. They sometimes take place in nature.
Fusion is the source of heat in the sun. Fission is also used in nuclear power plants to
make electricity. Both fusion and fission can be used in nuclear weapons.
Fission and Fusion
There are two fundamental nuclear processes considered for energy production: fission and
fusion.

2. GOVERNMENT COLLEGE OF TECHNOLOGY LAHORE 2
 Fissionis the energetic splitting of large atoms such as Uranium or Plutonium into
two smaller atoms, called fission products. To split an atom, you have to hit it with a
neutron. Several neutrons are also released which can go on to split other nearby
atoms, producing a nuclear chain reaction of sustained energy release. This nuclear
reaction was the first of the two to be discovered. All commercial nuclear power plants in
operation use this reaction to generate heat which they turn into electricity.
Fusionis the combining of two small atoms such as Hydrogen or Helium to produce
heavier atoms and energy. These reactions can release more energy than fission without
producing as many radioactive byproducts. Fusion reactions occur in the sun, generally using
Hydrogen as fuel and producing Helium as waste (fun fact: Helium was discovered in the sun
and named after the Greek Sun God, Helios). This reaction has not been commercially
 developed yet and is a serious research interest worldwide, due to its promise of nearly
limitless, low-pollution, and non-proliferative energy.

3. GOVERNMENT COLLEGE OF TECHNOLOGY LAHORE 3
How Does A Nuclear Power Plant Work?
Heavy elements such as Uranium (U235
) or Thorium (Th232
) are subjected to nuclear fission
reaction in a nuclear reactor. Due to fission, a large amount of heat energy is produced which is
transferred to the reactor coolant. The coolant may be water, gas or a liquid metal. The heated
coolant is made to flow through a heat exchanger where water is converted into high-temperature
steam. The generated steam is then allowed to drive a steam turbine. The steam, after doing its
work, is converted back into the water and recycled to the heat exchanger. The steam turbine is
coupled to an alternator which generates electricity. The generated electrical voltage is then
stepped up using a transformer for the purpose of long-distance transmission.
Basic Components of A Nuclear Power Plant

4. GOVERNMENT COLLEGE OF TECHNOLOGY LAHORE 4
Nuclear Reactor
A nuclear reactor is a special apparatus used to perform nuclear fission.
Since the nuclear fission is radioactive, the reactor is covered by a protective shield. Splitting up
of nuclei of heavy atoms is called as nuclear fission, during which huge amount of energy is
released. Nuclear fission is done by bombarding slow moving neutrons on the nuclei of heavy
element. As the nuclei break up, it releases energy as well as more neutrons which further cause
fission of neighboring atoms. Hence, it is a chain reaction and it must be controlled, otherwise it
may result in explosion. A nuclear reactor consists of fuel rods, control rods and moderator. A fuel
rod contains small round fuel pallets (uranium pallets). Control rods are of cadmium which absorb
neutrons. They are inserted into reactor and can be moved in or out to control the reaction. The
moderator can be graphite rods or the coolant itself. Moderator slows down the neutrons before
they bombard on the fuel rods.
a) Fuel rods
Fuel is contained in these fuel rods as fuel pellets. These fuel rods
contain a number of fuel pellets, and neutrons hit these fuel pellets to start and continue the
fission reaction.
b) Moderator
Moderator is the liquid contained in the pressure vessel at high pressure. It is
generally heavy water. The main function of moderator is to slow down the highly energized
neutrons so that they can again collide with uranium atom. More importantly it’s the appropriate
velocity of neutron which is required to split the uranium atom. If the first neutron which hit the
uranium atom has got a energy of 0.04ev then the resulting 3 neutrons will have 1ev of energy,
which is needed to be slowed down to 0.04ev again that is where moderator comes into play.
c) Control rods
Control rods are the most important part of a nuclear reactor in nuclear power
plant, and are made up of Barium or Cadmium. It controls the ongoing nuclear reaction by absorbing
the neutrons and we can also control the energy production as per the requirement, by inserting the
control rods accordingly.
Two types of nuclear reactors that are widely
used
1) Pressurized Water Reactor (PWR)
This type of reactor uses regular water as
coolant. The coolant (water) is kept at very high pressure so that it does not boil. The heated
water is transferred through heat exchanger where water from secondary coolant loop is

5. GOVERNMENT COLLEGE OF TECHNOLOGY LAHORE 5
converted into steam. Thus, the secondary loop is completely free from radioactive stuff. In a
PWR, the coolant water itself acts as a moderator. Due to these advantages, pressurized water
reactors are most commonly used.
2) Boiling Water Reactor (BWR)
In this type of reactor only one coolant loop is present.
The water is allowed to boil in the reactor. The steam is generated as it heads out of the reactor
and then flows through the steam turbine. One major disadvantage of a BWR is that, the coolant
water comes in direct contact with fuel rods as well as the turbine. So, there is a possibility that
radioactive material could be placed on the turbine.
Heat Exchanger
In the heat exchanger, the primary coolant transfers heat to the
secondary coolant (water). Thus, water from the secondary loop is converted into steam. The
primary system and secondary system are closed loop, and they are never allowed to mix up
with each other. Thus, heat exchanger helps in keeping secondary system free from radioactive
stuff. Heat exchanger is absent in boiling water reactors.
Steam Turbine
Generated steam is passed through a steam turbine, which runs due to
pressure of the steam. As the steam is passed through the turbine blades, the pressure of
steam gradually decreases and it expands in volume. The steam turbine is coupled to an
alternator through a rotating shaft.
Alternator
The steam turbine rotates the shaft of an alternator thus generating electrical
energy. Electrical output of the alternator is the delivered to a step up transformer to transfer it
over distances.
Condenser
The steam coming out of the turbine, after it has done its work, is then converted
back into water in a condenser. The steam is cooled by passing it through a third cold water
loop.
Advantages & Disadvantages of Thermal Power
Plant
Advantages:
1. Fuel cost of thermal power plant is relatively low.
2. We can produce thermal energy almost everywhere in the world.

6. GOVERNMENT COLLEGE OF TECHNOLOGY LAHORE 6
3. Heat production System is simple compared to other system.
4. Overall system cost effective.
5. Easy mechanism.
6. Same heat could be reused.
7. Easier Maintenance of power station.
8. Use of water is prominent here, therefore, any places with ample supply of water is a perfect
location for installing a thermal power station.
9. Thermal power plant requires comparatively small space to be installed.
Disadvantages:
1. Huge production of Carbon-di-oxide (CO2) in the atmosphere.
2. Exhausted gases harms outside environment badly.
3. Low overall efficiency.
4. Thermal engines require huge amount of lubricating oil that is very expensive.
5. Nuclear thermal power plant demands excessive amount of water for cooling purpose.
6. Coal type thermal power plant requires comparatively larger duration before it supply
generated power to the grid.
7. This type of power station ultimately responsible for raise in sea water level.
Power Plants in Pakistanwith capacities:
List of nuclear reactors in Pakistan
Nam
e
Un
it
No
.
Reactor
Status
Capacity in
MW
Construc
tion start
Commer
cial
operatio
n
Clos
ure
Ty
pe
Mod
el
N
et
Gro
ss
Chash
ma
1 PWR
CNP-
300
Operatio
nal
300 325
1 August
1993
15
September
2000
2 PWR
CNP-
300
Operatio
nal
300 325
28
December
2005
18 May
2011

7. GOVERNMENT COLLEGE OF TECHNOLOGY LAHORE 7
List of nuclear reactors in Pakistan
Nam
e
Un
it
No
.
Reactor
Status
Capacity in
MW
Construc
tion start
Commer
cial
operatio
n
Clos
ure
Ty
pe
Mod
el
N
et
Gro
ss
3 PWR
CNP-
300
Operatio
nal
315 340
28 May
2011
15 October
2016
4 PWR
CNP-
300
Operatio
nal
315 340
18
December
2011
1 July 2017
5 PWR
Hualon
g-1
Planned
108
0
1150
Karach
i
1
PHW
R
CAND
U-137
MW
Operatio
nal
90 100
1 August
1966
7
December
1972
2 PWR
Hualon
g-1
Under
construct
ion
108
0
1150
23 May
2013
(2021)
3 PWR
Hualon
g-1
Under
construct
ion
108
0
1150
21 August
2015
(2022)

8. GOVERNMENT COLLEGE OF TECHNOLOGY LAHORE 8
Reactor Province Type MWe net Construction
start Commercial operation Planned close
Karachi 1 Sindh PHWR 125.............. 125 1966 December 1972 2019
Chashma 1 Punjab CNP-300............. 300 1993 June 2000 2040
Chashma 2 Punjab CNP-300............. 300 2005 May 2011 2051
Chashma 3 Punjab CNP-300 .............315 May 2011 December 2016 2056
Chashma 4 Punjab CNP-300.............. 315 Dec 2011 September 2017 2057
Total (5) 1355
Total share of nuclear energy In Pakistan
Electricity
The electricity generated by commercial nuclear power plants
constitutes roughly ~3.6% of electricity generated in Pakistan,
compared to ~62% from fossil fuel, ~33% from hydroelectric
power and ~0.3% from coal electricity.