Nuclear power plant - IV Semester PGE Module 3- VTU

Module 3:
Nuclear Power Plants
VTU – 18EE42
Complied
by
Dr. C.V. Mohan
EEE., Sir. MV IT.,
Bangalore
For VTU – 4th Semester, EEE
1

Nuclear Power Plant – Syllabus
 Nuclear Power Plant: Introduction,
 Economics of nuclear plants,
 Merits and demerits,
 Selection of site,
 Nuclear reaction,
 Nuclear fission process,
 Nuclear chain reaction,
 Nuclear energy,
 Nuclear fuels,
 Nuclear plant and layout,
 Nuclear reactor and its control,
 Classification of reactors,
 Power reactors in use,
 Effects of nuclear plants,
 Disposal of nuclear waste and effluent, shielding.
By Dr.C.V. Mohan Sir MVIT., Bangalore 2

Nuclear Power Plant
 A nuclear power plant abbreviated as NPP. It is a thermal
power station in which the heat source is a nuclear reactor.
 This thermal heat is used to generate steam that drives a
steam turbine connected to a generator that produces
electricity.
 As on 2018, the International Atomic Energy Agency
reported there were 450 nuclear power reactors in operation
in 30 countries around the world.
 Nuclear plants are usually considered to be base load
stations since fuel is a small part of the cost of production
and because they cannot be easily or quickly dispatched.
 The cost of proper long term radioactive waste storage is
uncertain.

Nuclear Power Plant
 As of November 2020, India has 22 nuclear reactors in
operation in 7 nuclear power plants, with a total installed
capacity of 6,780 MW
Sl.No Name of the Power Plant State Total
Capacity
in MW
1 Kudankulam Nuclear Power Plant Tamil Nadu 2,000
2 Narora Atomic Power Station Uttar Pradesh 440
3 MadrasAtomic Power Station Tamil Nadu 440
4 RajasthanAtomic Power Station Rajasthan 1,180
5 TarapurAtomic Power Station Maharashtra 1,400
6 Kaiga Nuclear Power Plant Karnataka 880
7 KakraparAtomic Power Station Gujarat 440

The Economics of Nuclear Power
The economics of nuclear power involves several aspects:
• Nuclear power plants are expensive to build but relatively
cheap to run. In many places, nuclear energy is
competitive with fossil fuels as a means of electricity
generation.
• Waste disposal and decommissioning costs are usually
fully included in the operating costs. If the social, health
and environmental costs of fossil fuels are also taken into
account, the competitiveness of nuclear power is
improved.
 Capital Cost
 Plant Operating Cost
 External Cost
 Additional Costs

Capital Cost:
• which include the cost of site preparation, construction,
manufacture, commissioning and financing a nuclear
power plant. Building a large-scale nuclear reactor takes
thousands of workers, huge amounts of steel and
concrete, thousands of components, and numerous other
systems to provide electricity, cooling, ventilation,
information, control and communication.
• To compare different power generation technologies the
capital costs must be expressed in terms of the
generating capacity of the plant. Capital costs may be
calculated with the financing costs included or excluded.
• If financing costs are included then the capital costs
change materially in relation to construction time of the
plant and with the interest rate and/or mode of financing
employed.

Plant Operating Cost:
• Which include the costs of fuel, operation and maintenance
(O&M), and a provision for funding the costs of
decommissioning the plant and treating and disposing of
used fuel and wastes.
• Operating costs may be divided into ‘fixed costs’ that are
incurred whether or not the plant is generating electricity
and ‘variable costs’, which vary in relation to the output.
• Normally these costs are expressed relative to a unit of
electricity for example, Rupees per kilowatt hour to allow
a consistent comparison with other energy technologies.
• To calculate the operating cost of a plant over its whole
lifetime, we must estimate the ‘levelised’(levelised cost of
Electricity- LOCE) cost at present value.
• LCOE: It is the total cost to build and operate a power
plant over its lifetime divided by the total electricity output
dispatched from the plant over that period, hence typically
cost per megawatt hour.)

External Cost:
• The costs of dealing with a serious accident that are
beyond the insurance limit and in practice need to be
picked up by the government.
 The regulations that control nuclear power typically
require the plant operator to make a provision for
disposing of any waste, thus these costs are ‘internalised’
as part of operating costs (and are not external).
Additional Costs:
 Other costs such as system costs and nuclear-specific
taxes.

Merits of Nuclear Power Plant
1. Nuclear power plants can meet large power demand at
moderate cost
2. Space required is less as compared to other power
Plants
3. Performance of Nuclear power plant is high at high
load factors.
4. 1kg of Uranium U 235 can produce as much as energy
as the burning 4500 tons of high grade coal.
5. Since the fuel consumption is very small as compared
to conventional type of power plants, there is saving in
cost of fuel transportation.
6. The operation of nuclear power plant is more reliable.
7. Nuclear power plants are not affected by adverse
weather conditions

Demerits of Nuclear Power Plant
1. The capital cost of a nuclear power station is very high.
2. Nuclear plant cannot be operated effectively for varying
loads.
3. Maintenance cost of the nuclear plants very high.
4. Handling radioactive material requires standardization,
trained and field specialization personnel, which incur
in costs high.
5. Disposal of radioactive waste is a very big problem. If is
not disposed properly will affect the environment .
6. Working conditions in nuclear power stations are always
damaging to the health of workers.

Nuclear plant Site Selection
The following are important for selecting nuclear power
plant:
1. Availability of water supply
2. Disposal of Waste.
3. Distance from populated area.
4. Distance from load center.
5. Transportation facilities.
6. Accessibility

Availability of water supply:
Nuclear plants require a considerably greater qualities
of cooling water than steam power plants because of their
higher turbine heat rates. It is better the plant site should be
located where sufficient quantity of water is available. E.g.
across a river or by sea-side.
Disposal of Waste:
The waste produced by fission in a nuclear power
station is generally radioactive which must be disposed off
properly to avoid health hazard. The waste should either be
buried in a deep trench or disposed off in sea quite away
from sea shore.

Distance from populated area:
The site selected for nuclear power station
should be quite away from the populated areas as
there is a danger of presence of radioactivity in the
atmosphere near the plant, generally a dome is used in
the plant which does not allow the radioactivity to
spread by wind or underground water ways.
Distance from load center:
The plant should be located near the load
center. This will minimize the power losses in
transmission lines.

Transportation facilities:
The site selected for a nuclear power station
should have adequate facilities in order to transport
the heavy equipment during erection and to facilitate
the movement of the workers employed in the plant
Accessibility:
There should be reasonable accessibility for
plant personnel, transporting in equipment and
dispatching and receiving heavily dispatching
radioactive materials

Nuclear Reaction
 A Nuclear reaction refers to a processes where one or
more nuclides get produced from the collusion of atomic
nuclei or one atomic nucleus and a subatomic particle.
The nuclides obtained from nuclear reactions are not the
same as of reacting nuclei or parent nuclei. Popularly
these to two reactions named as Nuclear fission and
Nuclear Fusion reaction.
 In nuclear fission, a heavy nucleus tend to absorb neutrons
or relatively lighter particles. And further it splits into two
lighter nuclei.
 Where as Nuclear fusion refers to a process where two
light nuclei collide to form a single heavy Nucleus.

Nuclear Fission Process

Nuclear Energy

Nuclear Chain Reaction
 A chain reaction refers to a process in which neutrons
released in fission produce an additional fission in at least
one further nucleus. This nucleus in turn produces neutrons,
and the process repeats. ... If each neutron releases two
more neutrons, then the number of fissions doubles each
generation.

Nuclear Chain reaction

Nuclear Fuels
 Nuclear Fuel is a material which can be
used or consumed by nuclear fusion or
fission to derive Nuclear energy

Nuclear Fuels
 Uranium is found in small amounts in most rocks, and
even in seawater. Uranium mines operate in many
countries, but more than 85% of uranium is produced in
six countries: Canada, Australia, Namibia, Niger, and
Russia.
 The enriched uranium is transported to a fuel fabrication
plant where it is converted to uranium dioxide powder.
This powder is then pressed to form small fuel pellets
and heated to make a hard ceramic material. The pellets
are subsequently inserted into thin tubes known as fuel
rods, which are then grouped together to form fuel
assemblies. The number of fuel rods used to make each
fuel assembly ranges from around 90 to well over 200,
depending on the type of reactor.

Nuclear Fuels
Nuclear fuel in its powder and pellet form

Nuclear Power Plant Layout
Water

Layout or Schematic arrangement of NPP

Nuclear Power Plant Operation
• Nuclear power plants generate electricity in a similar way
to other traditional power plants like Thermal power plant,
differing in the type of fuel used. In SPP electricity
generation by burning coal for heating water into steam,
which drives a turbine connected to a generator and
subsequently produces electricity.
• Uranium, a naturally radioactive element used as fuel to
electric power in nuclear plant or nuclear reactors. In a
nuclear reactor, uranium atoms are split into smaller parts
by fission process. The energy released during this split
creates heat to produce steam, which is used by a turbine
generator to generate electricity.
• One uranium pellet, the size of a fingertip, produces the
same amount of energy as 1 ton of coal.

The whole arrangement can be divided into the
following main stages
(i) Nuclear Reactor.
(ii) Heat Exchanger.
(iii) Steam Turbine.
(iv) Condenser.
(v) Alternator.

1. Nuclear Reactor:
Reactor is the heart of the nuclear plant. In nuclear reactor,
nuclear fission of radioactive material takes place. This
liberates large amount of heat energy. This heat is taken up
by the coolant circulating through the reactor core. After
absorbing the heat, the coolant becomes hot to produce
steam
2. Heat Exchanger or Steam generator:
The hot coolant coming from nuclear reactor flows
through the tubes of heat exchanger or steam generator, In
the heat exchanger, hot coolant gives up to feed water, so
that it can be converted into steam

3. Steam Turbine:
The steam produced in the heat exchanger is sent to steam
turbine. The steam undergoes expansion in steam turbine
and produces useful work in the steam turbine.
4. Steam Condenser:
In condenser, the steam is cooled and condensed with the
help of cooling water coming from cooling tower. Exhaust
steam is converted to water.
5. Alternator:
Output of steam turbine is coupled to alternator which
convers mechanical energy into electrical energy

Nuclear Reactor:
• A nuclear reactor, formerly known as an atomic pile, is a
device used to initiate and control a fission nuclear chain
reaction or nuclear fusion reactions.
• Nuclear reactors are used at nuclear power
plants for electricity generation. When a large fissile atomic
nucleus such as uranium-235 or plutonium-239 absorbs a
neutron, it may undergo nuclear fission.
• The heavy nucleus splits into two or more lighter nuclei,
(the fission products), releasing kinetic energy, gamma
radiation, and free neutrons.
• A portion of these neutrons may be absorbed by other fissile
atoms and trigger further fission events, which release more
neutrons, and so on. This is known as a nuclear chain
reaction.

Layout or Schematic arrangement of NPP
 To control such a nuclear chain reaction, control
rods containing neutron poisons and neutron
moderators can change the portion of neutrons that will go
on to cause more fission.
 Nuclear reactors generally have automatic and manual
systems to shut the fission reaction down if monitoring or
instrumentation detects unsafe conditions.
 Important parts of Nuclear Reactor
(i) Reactor Core
(ii) Reflector
(iii) Control Mechanism
(iv) Modulator
(v) Coolants
(vi) Thermal Shielding

Important parts of Nuclear Reactor
 Reactor Core :
This is the main part of the reactor which contains
fissionable material called reactor fuel. Fission energy is
liberated in the form of heat for operating power
conversion equipment. The fuel element are made of plate
of rods of uranium. In this reactor the nuclear fission
processes takes place
 Reactor reflector:
The region surrounding the reactor core is known as
reflector. Its function is to reflect back some of the neutron
that leak out from the surface of the core

 Control rods:
The rate of reaction in a nuclear reactor is controlled by
control rods. Since the neutron are responsible for the
progress of chain reaction, suitable neutron absorber are
required to control the rate of reaction.
i. For starting the reactor.
ii. To keep the production at a steady state
iii. For shutting down the reactor under normal or
emergency conditions.
iv. Cadmium and Boron are used as control rods.

 Moderator:
The main function of a reactor is to slow down the fast
neutron. The commonly used moderator are Ordinary water or
Heavy Water and Graphite
The moderator should have following features
(a) High slowing down power
(b) Non corrosiveness
(c) Chemical and radiation stability.
(d) High thermal conductivity.
(e) Abundance in pure form
(f) High melting point for solids and low melting point for
liquids.

 Control Rods:
The control rods are used to control the chain
reaction. They are very good absorbers of neutrons. The
commonly used control rods are made up of elements like
boron or cadmium. The control rods are inserted into the
core and they pass through the space in between the fuel
tubes and through the moderator. By pushing them in or
pulling out, the reaction rate can be controlled.

 Coolant System:
The cooling system removes the heat generated in the
reactor core. Ordinary water, heavy water and liquid sodium
are the commonly used coolants.
A good coolant must possess large specific heat
capacity and high boiling point. The coolant passes through
the tubes containing the fuel bundle and carries the heat from
the fuel rods to the steam generator through heat exchanger.
The steam runs the turbines to produce electricity in power
reactors.
The coolant and the moderator are the same in the
PHWR and PWR. In fast breeder reactors, liquid sodium is
used as the coolant. A high temperature is produced in the
reactor core of the fast breeder reactors. Being a metal
substance, liquid sodium is a very good conductor of heat and
it remains in the liquid state for a very high temperature as its
boiling point is about 1000o C.

Thermal Shielding:
The fission reaction is accompanied by emission of
radiation like α, β and Ƴ. Exposure to these radiations is
dangerous. In order to protect the persons working near the
reactor from these harmful radiations the reactor is
enclosed in steel and concrete structure which are capable
of stopping these radiations. Shielding prevents radiations
to reach outside the reactor, Coolant flows over the
shielding to take away the heat.

Control of Nuclear Reactor
It is very very important to control the heat produced
by nuclear reactor. This is achieved by controlling the neutron
flux by
(i) Control rods. (ii) Control through flow of coolant.
(i) Control rods:
For normal operation, the multiplication constant must
be maintained at unity. This will ensure the neutron flux is
held at constant value. Neutrons may be absorbed by inserting
some material having high absorption cross-section. Such
materials are boron, hafnium and cadmium. They are
generally alloyed with steel and made into control rods which
can be moved in and out of channels in the core. To ensure
even distribution of neutron flux it is necessary to employ
large number of rods( hundred or even more). When rods are
fully inserted, the neutron absorption will be maximum.

Control of Nuclear Reactor
(ii) Control through flow of coolant:
In addition to control by using control rods, it is
necessary to maintain an appropriate relation between
mass flow of coolant and power. At constant temperature
the power output is proportional to the rate of flow of
coolant. Coolant temperature recorders and coolant flow
indicators recorders and coolant flow indicators and
operating switches are necessary for this purpose.

Classification of Reactor
 Based on neutron energy
a. Fast Reactor
b. Slow or Thermal Reactor
c. Intermediate Reactor
 Based on fuel used
a. Enrich Uranium
b. Natural Uranium
c. Plutonium.
d. Thorium.
 Based on type of Core used
a. Homogenous Reactor :  moderator and fuel mixed together
b. Heterogeneous Reactor:It has large number of fuel rods with
the coolant circulating around them
and carrying heat produced.

Classification of Reactor
 Based Moderator used
a. Graphite Reactor.
b. Beryllium Reactor.
c. Light water Reactor.
d. Liquid metal cooled Reactor.
e. Organic liquid cooled Reactor.
 Based on Coolant used
a. Ordinary water cooled Reactor.
b. Heavy water cooled Reactor.
c. Gas cooled Reactor.
d. Liquid metal cooled Reactor.
e. Organic liquid cooled Reactor.

Power Reactors in Use
Main types of nuclear Reactor
i. Pressurized water Reactor.(PWR)
ii. Boiling water Reactor.(BWR)
iii. Heavy water Cooled and Moderated Reactor.(CANDU)
iv. Gas cooled Reactor.
v. Fast Breeder Reactor.

Pressurized water reactor (PWR)
Pictorial explanation of power transfer in a pressurized water reactor.

Water can be used as a moderator and coolant for
power reactors. The fuel used is slightly enriched uranium in
the form of thin rods or pallets and cladding is either of
stainless steel or zircaloy.
Water under pressure is used as both moderator and
coolant. This type of reactor is extensively developed in
USA. The most important limitation in PWR is the critical
temperature of water.
The coolant pressure must be greater than the
saturation pressure to suppress boiling which is maintained at
about 155 bars. A circulating pump is used to maintain the
water round the core, which absorbs heat.
The coolant picks up the heat from the reactor
and transfers it to the working fluid to generate steam to run
the turbine generator system similar to the steam power plant

Advantages:
a. It is cheap as ordinary water is used as moderator and
coolant.
b. It is very compact in size compared to other reactors.
c. Power density of reactor is relatively high.
d. Reactor takes care of the load variation by using the
pressurizer and surge tank.
Disadvantages:
a. Low thermal efficiency (approximately 25%)
b. Greater heat loss due to the heat exchanger.
c. Due to high pressure, a strong pressure vessel is
required
d. More safety devices are required.

Fuel Assembly Removal

Refueling

Boiling water reactor (BWR)

This is the simplest type of water reactor. It utilizes
enriched uranium as the fuel and light water as both
moderator and coolant. A BWR operates at a relatively lower
pressure of about 76 bar in such way that water boils in the
core at about 285 degree centigrade. Steam mixture leaves
the core, with water separated from steam in a steam
separator. A BWR assembly comprises 90 -100 fuel rods.
Advantages:
a. The reactor vessel and associated components operate at
a substantially lower pressure of about 70 to 75 bar.
b. Can operate at lower core power density levels using
circulation without forced flow.
c. Simple in construction.
d. Elimination of heat exchanger circuit resulting in
reduction in cost and gain in thermal efficiency.

Disadvantages:
a. The steam is passing through the reactor, the
radioactive contamination of turbine mechanism is
possible.
b. Water of steam will also lower the efficiency of the
plant.
c. It is not suitable for meeting a sudden increase in load.

Heavy water Cooled and Moderated Reactor
1. Fuel bundle
2. Calandria (reactor core)
3. Adjuster rods
4. Heavy-water pressure reservoir
5. Steam generator
6. Light-water pump
7. Heavy-water pump
8. Fueling machines
9. Heavy-water moderator
10.Pressure tube
11.Steam going to steam turbine
12.Cold water returning from turbine
13.Containment building made of reinforced concrete
CANDUType

Heavy water Cooled and Moderated Reactor
Heavy water(D2O)has almost the same characteristic
as that of ordinary water. Its boiling point at atmospheric
pressure is 101.4 o C and its density at room temperature is
only10% above the density of water. Heavy water moderated
and cooled reactors are extensively developed and used in
Canada and are called Canadian Deuterium Uranium
(CANDU) reactors. These reactors use pressurized heavy
water (PWH) and suitable for those countries which do not
produced the enriched uranium.
Advantages:
1.No control rods and low fuel consumption
2. Moderator is more effective in slowing down neutrons.
3. The Construction and equipment's occupy less space.
Disadvantages:
1. Cost of the reactor is very high.
2. Proper safety design is required to limit leakage issues.

Gas – Cooled Reactor

Gas – Cooled Reactor
 In gas – cooled reactors, gas is used as a coolant and
graphite is used as a moderator.
 The Inherent advantages of gas cooling is that the
maximum temperature of the working fluid can be selected
independently, raising temperature does not necessarily
imply raising of coolant pressure, as with the liquid cooled
reactors. Normally carbon dioxide or helium is used as
coolant.
 Although gases are inferior to water in heat transfer, but
offers several advantages such as safer then water cooled
reactors, less severe corrosion problems and natural
uranium can be used as fuel.
 Helium can be used instead of CO2 for higher efficiency.

Fast Breeder Reactor (FBR)
 The Fast Breeder Reactor are available in two designs
(i) Loop type:
In which the primary coolant is circulated through
primary heat exchangers outside the reactor tank.
(ii) Pool type:
In which the primary heat exchangers and pumps
are immersed in the reactor tank

 The Breeder reactors are capable of producing more
fissile material than they consume during fission chain
reaction ( by converting fertile U-238 to Pu 239 or Th-
233 to U-233).Thus a uranium breeder reactor, once
running can be refueled with natural or ever depleted
uranium and a thorium breeder reactor can be refueled
with thorium, however, an initial stock of fissile material
is required.
 In fast breeder reactor the average neutron yield of a
fission caused by a fast neutron is greater than in thermal
reactors.
 The absorption cross-section are low and conversion
factor is high also no moderator is needed in this reactor.

 A coolant with excellent heat transfer properties is
required to minimize temperature from the fuel surface
to the coolant and also it must be non moderating.
Hench the best coolants for fast breeder reactor are
liquid metals such as sodium(Na). Such reactor is also
called Liquid metal cooled reactor (LMCR).
 In pool type system, the reactor core, primary pump and
intermediate heat exchangers are placed in a large pool
of liquid sodium contained reactor vessel, where as in
loop type system all are placed outside of vessel.(Liquid
metal fast breeder reactor- LMFBR)

Effects of Nuclear Power Plants
 A nuclear reactor produces α, β and Ƴ rays and neutrons
which can disturb the normal working of human beings
and animals and it enforces need of special safety
measures.
 Ƴ-rays are electromagnetic radiation of very short
wavelength, have high energy and ae very penetrating.
They are capable of causing considerable damage to
organic materials.
 Overexposure of Ƴ-rays caused the blood disease,
undesirable genetic effects, anemia etc.,
 Large exposure may cause death within hours of exposure.
 Nuclear power stations are prohibited to build close to
residential buildings.
 The level of radiations of this NPP area is checked
periodically.

Disposal of NuclearWaste and Effluent
What is Nuclear Waste ?
Nuclear wastes are wastes that contain radioactive material.
Nuclear wastes are usually by product of nuclear power
generation and other application of nuclear fission or
nuclear technology.
Nuclear Waste classification
1. Solid wastes
2. Liquid wastes
3. Gaseous Wastes

Solid Waste:
 Solid waste consists of scrape materials or discarded
objects contaminated with radioactive matter.
 These wastes if combustible are burnt and the
radioactive matter is mixed with concrete, drummed and
shipped for burial.
 Non combustible solid wastes are always buried deep in
the ground

Liquid Waste: The disposal of liquid waste in done in two ways
1. Dilution:
The liquid waste ae diluted with large quantities of water
and then released into the ground. This method suffers from a
drawback that there is a change of contamination of underground
water, if the dilution factor is not adequate.
2. Concentration to small volumes and storage:
When the dilution of radioactive liquid waste is not
desirable due to amount or nature of isotopes, the liquid wastes
are concentrated to small volumes and stored in underground
tanks. The tanks should be of assured long term strength of
leakage of liquid from the tanks should not take place other wise
leakage of contents from the tank may leads to significant
underground water contamination

 Gaseous Waste:
Gaseous wastes can most easily results in
atmospheric pollution. Gaseous wastes are generally
diluted with air passed through filters and the released to
atmosphere through large chimneys.

Shielding
 Adequate shielding has be provided to guard personnel
and delicate instruments form radioactive wastes. The
various materials used for shielding are
 Lead: It is a common shielding material has high
density 11.3 gm/cm3 and is invariably used due to its low
cost.
 Concrete: Its density is 2.4 gm/ cm3 and is less efficient
than lead.
 Steel: Its density is 7.8 gm/cm3. It is not an efficient
shielding material but has good structural properties. It
is sometimes used for attenuating shield.

Shielding
 Cadmium: Its density is 8.65 gm/cm3. It can absorb
slow neutrons by a nuclear reaction.
No single material is effective in shielding against
all types of radioactive radiation.
In nuclear power reactors a thermal shielding of
several cm’s thick steel surrounded by about 3 meters thick
concrete is used.

0 10 20 30 40 50 60 70 80 90
France
Lithuania
Slovak Republic
Belgium
Switzerland
Ukraine
Bulgaria
Armenia
Slovenia
South Korea
Hungary
Switzerland
Germany
Czech Republic
Japan
Finland
Spain
USA
UK
Russia
Canada
Percent
Source: www.iaea.org/programmes/a2/index.html
Nuclear Share of Electricity

Nuclear power plant - IV Semester PGE Module 3- VTU

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