G Mujtaba Ahsan iqbal Zafar Bakhshi
• NUCLEAR REACTOR
• Components of Nuclear Reactor
• TYPE OF REACTOR
• Device designed to maintain a chain
reaction producing a steady flow of
neutrons generated by the fission of
• It is an apparatus in which heat is
produced due to nuclear fission chain
reaction for the generation of the
Pressure Vessel / Tubes
Usually a robust steel vessel containing the
reactor core and moderator/coolant.
Or it may be a series of tubes holding the fuel and
conveying the coolant through the surrounding
It consists of fuel elements, control rods, coolant,
Cores generally have shapes of right circular
cylinders with diameters ranging from 0.5 to 15
It is placed
round the core,
to reflect back
some of the
leak out from
Uranium-235 is the
Usually pellets of
(UO2) are arranged
in tubes to form fuel
Usually made up of
cadmium or boron.
Slow down the rate of
reaction to a
controllable limit .
Other wise chain
reaction blows up like a
Raising and lowering
the control rods allow
operators to control the
rate of the nuclear
To slow down neutrons
from high velocities and
hence high energy level
which they have on being
released from fission
process so that probability
of neutron to hit the fuel
Main moderator used:
Water H2O Heavy water
D2O Graphite Beryllium
Coolant is used to remove intense heat
produced in the reactor and that heat can be
transferred to water in a separate vessel which
is converted into steam and runs the turbine.
Main coolant used: Water H2O , CO2, Hg, He
The structure around the reactor and
associated steam generators which is designed
to protect it from outside intrusion and to
protect those outside from the effects of
radiation in case of any serious malfunction
It is typically a meter-thick concrete and steel
For Starting Reactor
To start a reactor, a neutron from a source is
ejected through thermal means and the control
rods are taken upwards so that the control rods
can not disturb the reaction.
Hence neutron hits the fuel rods, break it into
lighter nuclei, energy is released, number of
neutron keeps on increasing since K will be
greater than 1 for this time period and hence
reaction starts and its rate also increases.
Hence reaction starts and its rate also increases.
Meaning of K
K (the effective neutron multiplication factor)
is the average number of neutrons from one
fission that cause another fission.
The remaining neutrons either are absorber in
non-fission reactions or leave the system
without being absorbed.
The value of K determines how a nuclear chain
For Maintaining the reaction at
When rate of reaction achieves a permissible
value then control rods are inserted between
the fuel rods in such away that K becomes
equal to 1.
Hence the rate of reaction achieves a finite
For Shutting Down Reactor
To shut down the reactor either in normal or
emergency conditions, the control rods are
inserted in such away that K becomes less
Hence the number of neutrons keeps on
decreasing i.e. rate of reaction decreases, so
the reaction stops after a certain interval of
Classification of Nuclear Reactor:
• 1. On the basis of Neutron
• a) Fast Reactors
• b) Thermal Reactors
• 2. On the basis of Fuel used
• a) Natural fuel
• b) Enriched Uranium
• 3. On the basis of
• a) Water Moderator
• b) Heavy water Moderator
• c) Graphite Moderator
• d) Beryllium Moderator
• 4. On the basis of Coolant
• a) Water cooled reactor
(Ordinary or Heavy)
• b) Gas cooled reactor
• c) Liquid metal cooled
• d) Organic liquid cooled
1. Boiling Water Reactor
• In the boiling water reactor (BWR), the water
which passes over the reactor core act as
moderator and coolant. It is also the steam
source for the turbine.
• A typical operating pressure for BWR is about 70
atm at which the water boils at about 285°C
temperature. This operating temperature gives a
efficiency of only 42% with a practical operating
efficiency of around 32%, somewhat less than the
Pressurized Water Reactor(PWR)
• Possibility of radioactive contamination in the
• Safety precautions are needed which can turn
out to be costly.
• Wasting of steam and resulting of lower
• Only 3% - 5% by mass can be converted to
steam per pass.
2. Pressurized Water Reactor
• Uranium (Uranium – 235) as fuel.
• Chain reaction produces high level of heat.
• Heat tubes pass the heat to the primary
cooling system water simply by contact.
• Primary cooling system is a closed circuit of
• Primary water enters the reactor vessel at 296
°C and exit at 327 °C.
• Water used as coolant, moderator and reflector is
cheap and available in plenty.
• The reactor is compact and high power density
• Hardly 60 control rods are required in 1000 MW
• Inspecting and maintaining of turbine, feed
heaters and condenser during operation.
• Reducing fuel cost and extracting more energy.
• Requires high pressure vessel and high capital
• Thermodynamic efficiency of plant is as low as
20% due to low pressure.
• Corrosion problems are more severe. Use of
stainless steel for vessel is necessary.
• Fuel recharging requires a couple of months