The document discusses different types of nuclear reactors, including their components, operation, and advantages/disadvantages. It describes pressurized water reactors (PWR), boiling water reactors (BWR), CANDU reactors, liquid metal cooled reactors, organic moderated reactors, and liquid metal fast breeder reactors. Key points covered include how each reactor type moderates and cools the nuclear fuel, controls the fission reaction, and uses the generated heat for power production. Advantages include efficient use of uranium and ability to produce additional fissile material, while disadvantages relate to safety, cost, and waste issues.

1. Nuclear Power Plant
By
Prof. P.W.Ingle
Sanjivani College of Engineering Kopargaon

2. The reserve of coal and petroleum though tremendous are limited to a
few hundred years. The quantity of fuel required is huge leading to
transportation and ash disposal problem for coal. But nuclear energy
is one source which require a very low quantity of fuel.
The fuel uranium alone has a huge potential and its reserve contains
more energy than the coal and petroleum
Advantages: no green house gases emission, no pollution of air, little
solid waste generated, large fuel reserve because very little fuel is
needed 1 kg of uranium is equal to 200 tonnes of coal, plants are not
affected by adverse weather conditions and reliable
Disadvantages:- Capital cost high, maintenance cosy high, cost of
decommissioning of plant high, risk of major accident, nuclear waste
disposal is a big problem

3. Nuclear fission:- When a neutron collides with the nucleus of certain
fissile material causing the original nucleus to split into two or more
fragments which carry most of the energy of fission. Thus fission is
accompanied by the release of considerable energy which exceeds
many time that produced by radioactive disintegration.

4. If such a continuous reaction is controlled, it would results in a
continuous release of energy at a steady state rate, the rate depending
upon the number of fissions occurring in a particular time. A reaction
of this type is known a chain reaction.
The fission fragments resulting from the fission process are
radioactive and decay by the emission of gamma and beta
rays to a lesser degree alpha particles and neutrons. The
neutrons emitted after fission are known as delayed
neutrons. These are important because they permit the chain
reaction to be controlled easily.
The total energy released due to fission of one nucleus of
Uranium-235 is 193 mev ( millielectronvolt)

5. A chain reaction is one in which the number of neutrons keeps on
increasing in geometric progression during progression till all
fissionable material is disintegrated. The chain reaction will sustain
only if, for every neutron absorbed, at least one fission neutron is
available to cause fission of another nucleus.
The ratio of number of neutrons in any fission to the number of
neutrons generated in the preceding generation is known as
multiplication factor K. If K is less than 1, the number of fission
decreases rapidly and process dies down i.e. Stop If K is greater than
1, the rate of rection is very fast and may result in sudden explosion
as it occurs in an atomic bomb.
Hence it is necessary to keep the value of K=1, but there will be loss
of neutrons due to leakage, capture in control rod, etc. which requires
to keep value of K around 1.04

6. Components of Nuclear reactor
Moderator:- is used to slow down the fast neutrons. The fast
neutrons collide with the nuclei of the moderator material and
slow down by losing their energy. A moderator can be in the
form of solid, liquid or gas.
It should not react with neutrons, because neutrons captured in
nuclear reaction are lost to the fission process and reactor
becomes inefficient.
It should not be costly
It should be chemically stable. The moderators used in nuclear
reactor as graphite, heavy water (deuterium). Helium and
beryllium can also be used but they are costly

7. Reflector:- It is generally placed round the core to reflect some of
the neutrons that leak out from the surface of core. Reflectors are
generally made of the same material as that of moderator.
Coolant:- As the name suggests, it is a medium used to take heat from
the reactor core. The coolant should not absorb more neutrons. The
coolant used are either liquid or gas. The coolant should have a good
heat transfer coefficient. It should not corrode to metal. Liquid metal
coolant should have low melting point. It should have low viscosity.
Control rod:- the reaction rate , starting and shutting down of a reactor
is controlled by the control rods. The thermal and breeder reactors use
control rods. Boron steel and cadmium strips are used for absorbing
excess neutrons. They are good absorbers of slow neutrons and have
the advantage of not becoming radioactive due to neutron capture

8. Canning materials:- the fuel elements in a nuclear reactor is put in
cans so that the fuel does not contaminate the coolant. Hence
canning eliminates radiation hazards. Selection of canning material
depends on fuel used in reactor. Aluminum, magnesium, beryllium
and stainless steel are the canning material used.
Nuclear reactor is a device in which nuclear chain reaction are initiated,
controlled and sustained at a steady rate.
Heat is produced in a nuclear reactor when neutrons strike Uranium
atoms causing them to fission in a continuous chain reaction. Control
elements, or control rods as they are often called, are pulled out of core,
more neutrons are available and the chain reaction speeds up,
producing more heat. When they are inserted into the core, more
neutrons are absorbed, and the chain reaction slows or stops, reducing
the heat

9. Pressurized water reactor ( PWR )
In a PWR, the nuclear fuel heats the water in the primary coolant loop
by thermal conduction through the fuel cladding. The hot water is
pumped into a certain type of heat exchanger called steam generator
which allows the primary coolant to heat up the secondary coolant.
The pressure in the primary coolant loop is at typically 16 Megapascal,
notably higher than in other reactors. As an effect of this gas law
guarantee that the primary coolant loops water never boils during
normal operation of the reactor.
In PWR, there are two separate coolant loops(primary and secondary),
which are both filled with ordinary water also called light water. A BWR ,
by contrast has only one coolant loop.
Advantages:- very stable , operating with a core containing less fissile
material, use enriched uranium ordinary water as a moderator

10. PRESSURIZED WATER REACTOR

11. Before starting the boiler water in the pressurizer is boiled and
converted into steam by electric heating coil. Pressurizer is
used to maintain pressure of boiled water constant in primary
loop.
Disadvantages:- The coolant water must be heavily pressurized to
remain liquid at high temperature,
Most PWR can not be refueled while operating, water absorbs neutrons
making it necessary to enrich the uranium fuel increases the cost of fuel
production,
Because water act as a neutron moderator, it is not possible to build a
fast neutron reactor with a PWR design.

12. BOILING WATER REACTOR
There is a single circuit in a BWR in which the water is at lower pressure about
75 atmospheric than in a PWR so that it boils in the core at about 285 degree
Celsius. Reactor power is controlled via two methods one by inserting or
withdrawing control rod and other by changing the water flow through the
reactor core.
As control rods are withdrawn, neutron absorption decreases in the control
material and reactor power increases. As control rod inserted, neutron
absorption increases, power decreases.
Changing i.e. increasing or decreasing the flow of water through the core is
the normal method for controlling power when operating between
approximately 70% and 100% of rated power.
As flow of water through the core is increased, steam bubbles( voids) are
more quickly removed from the core, the amount of liquid water in the core
increases, neutron moderation increases, more neutrons are slowed down to
be absorbed by the fuel, and reactor power increases.
As the flow of water through the core is decreased, steam voids remain
longer in the core, the amount of liquid water in the core decreases, neutron
moderation decreases, fewer neutrons are slowed down to be absorbed by the
fuel, and reactor power decreases.

13. Steam produced in the reactor core passes through the steam
separators and dryer plates above the core and then directly to the
turbine, which is part of the reactor circuit.
Because the water around the core of a reactor is always contaminated
with traces of radionuclides, the turbine must be shielded during
normal operation, and radiological protection must be provided
during maintenance
The increased cost related to the operation and maintenance of a BWR
tends to balance the saving due to simpler design and greater thermal
efficiency of a BWR when compared with a PWR
A modern BWR fuel assembly comprises 74 to 100 fuel rods, and there
are up to approximately 800 assemblies in a reactor core, holding up to
140 tones of uranium.

14. BOILING WATER REACTOR

15. Advantages:- the reactor vessel and associated components operate at
a substantially lower pressure at 75 atm, compared to PWR working
at about 159 atm.
Pressure vessel is subject to significantly less irradiation
operates at lower nuclear temperature.
Disadvantages:- Complex operational problems due to the utilization of
the nuclear fuel in the fuel elements during power production due to
two phase flow i.e. Water and steam
Much larger pressure vessel than PWR
Contamination of turbine by fission product.
Shielding and access control around the steam turbine are required
during normal operation due to radiation enters with steam

16. CANDU Reactor
A reactor designed and developed by Canadian engineers is
called as CANDU reactor. It uses pressurized heavy
water(PHW) which is 99.8% an primary coolant while fuel
used as natural uranium. The deuterium D2O as moderator
can also use enriched uranium, mixed fuels, and even
thorium.
Natural uranium fuel is in the form of small cylinder pallets.
These are packed in a corrosion resistant zirconium alloy
tubes in the form of fuel rod. These short rods are combined
in 37 bundles of 37 rods and 12 bundles are placed end to
end in each pressure tubes. This type of arrangements helps
in refueling the reactor while in operation

17. CANDU REACTOR

18. Reactor vessel is a steel cylinder called calandria. It is placed
horizontally. The active core is about 6 m high and 7 to 8 m in
diameter. In primary circuit, the D2O coolant enters the array of
pressure tubes at 260 degree Celsius and 110 bar pressure. It flows
through the fuel elements leaves the pressure tubes at about 370
degree Celsius after absorbing the heat generated by fission of fuel
material.
The coolant at 110 bar and 370 temperature leaving the reactor enters the
steam generator where generated steam used in conventional steam power
plant.
Ad:- heavy water used has low fuel consumption, enriched fuel is nit required,
cost and time of construction is less, it has good neutron economy. Disad:-
heavy water used has high cost, leakage problem, plant size large, requires
high standard of design, manufacture and maintenance

19. Liquid metal cooled reactor (LMCR) or Sodium Graphite
reactor(SGR)

20. In primary circuit the heat is absorbed by liquid sodium in the reactor.
The sodium become radioactive while it passes through the core and
reacts chemically with water.
Therefore the heat absorbed by sodium is transferred to secondary
coolant sodium potassium NaK in the primary heat exchanger. Which in
turn transfers the heat in the secondary heat exchanger called steam
generator. Steam generated in steam generator up to a temperature of
540 degree Celsius is for expansion in turbine.
Ad:- high temp of steam obtained, system need to be pressurized,
thermal efficiency high, cost of pressure vessel and piping system
reduced due to low pressure sodium in primary circuit.
Disad:- sodium react with water and air, intermediate HE required
increase cost, primary and secondary HE are needed to shield with
concrete against radiation, leakage of sodium coolant is highly
dangerous

21. Organic moderated and cooled reactor (OMCR)
It uses hydrocarbon like polyphenyls inste.ad of liquid sodium as coolant.
Polyphenyls contains carbon and hydrogen and are good moderators. These
are used as coolant as well as moderators.
Ad:- compact in design, use wide variety of fuel like uranium or its oxides or
alloys, Disad:- low HT coefficient, inflammable, leave slurry deposits on fuel
surface.

22. Liquid metal fast breeder reactor (LMFBR)
Fast breeder reactor is a fast neutron reactor designed to breed fuel by
producing more fissile material than it consumes. The FBR is one possible type
of breeder reactor.
FBR usually use a mixed oxide fuel core up to 20 % plutonium dioxide and at
least 80 % uranium dioxide. The plutonium used can be from reprocessed civil
or dismantled nuclear weapons sources. Surrounding the reactor core is a
blanket of tubes containing non fissile uranium 238 which by capturing fast
neutrons from the reaction in the core, is partially converted to fissile
plutonium 239 which can then proceed well with fast neutrons.
Fast reactors typically used liquid metal as the primary coolant, to cool and
heat the water used to power the electricity generating turbines. Sodium is the
normal coolant for large power station, but lead and NaK have both been used
for smaller power plant units. Some early FBR used mercury.
This type of reactors are important since they are not only produce heat but
also produce more secondary fissile fuels like plutonium more than fuel
consumed in the reactor