Mechanical Engineering
Introduction to Nuclear Engineering
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Lecture 1
Introduction to Nuclear Engineering
Objectives
In this lecture you will learn the following
In this lecture the population and energy scenario in India are reviewed.
The imminent rapid growth of nuclear power is brought out.
Subsequently a bird’s eye view of the various principles involved are presented.
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Lecture 1
Introduction to Nuclear Engineering
Role of Nuclear Engineering
Before we can start understanding about nuclear power, it is essential to look at the
motivation.
We shall realise that if India has to meet its aspirations of providing decent living to its
people, it is necessary that nuclear has to grow fast.
If this is planned properly and executed, there are tremendous opportunities for nuclear
engineers.
Let us show this in a brief manner.
Population Growth
The source for the information on facts and figures are taken from a recent publication by
Grover and Chandra (R.B. Grover and S. Chandra, “Scenario for growth of energy in India”, Energy
Policy, Vol. 34, 2006, pp 2834-2847).
Energy is generated for people to use it and hence we need to have a good picture of the
population dynamics before we can project the energy requirements.
The population statistics past, present and projected are given in the following Table:
Year Population Growth Rate (per
(Billions) year)
2001 1.027 1.50
2011 1.19 1.02
2021 1.32 0.7
2031 1.41 0.4
2041 1.47 0.2
2051 1.50 0.0
We expect to stabilise around 2050.
We need to provide electricity for 1.5 billion people.
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Lecture 1
Introduction to Nuclear Engineering
Electricity Production
Year Power Production (Mwe)
1947 1363
1981 30214
1991 66086
2003 138730
From the above table, we see that the average growth rate is 8.6% and is impressive.
However, per capita power production is still small compared to global average.
Total Energy Scenario
In 2001, total energy consumed by the world was 382 EJ (1 Exa Joule = 1018 J).
Indians consumed 3.4% with a population share of 16.6%.
USA consumed 24.5% with 4.6% population.
Indian consumption was 1/5 th of the world average.
Thus to improve the quality of life there has to be a growth in energy production and
consumption.
Energy Split
In 2003, Indians consumed 18.96 EJ.
Domestic resources accounted for 15 EJ and imported 3.96 EJ.
71% of the above was for commercial purposes and 29% was for domestic purposes.
Of the commercial, 92% was from fossil, 6% hydro, 1.7% nuclear and 0.2% wind.
The import content was 8% for coal, 71% for oil and 13% for nuclear.
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Lecture 1
Introduction to Nuclear Engineering
Energy Growth Rate Projection
Year Total Energy (%) Electrical Power (%)
2002-22 4.6 6.3
2022-32 4.5 4.9
2032-42 4.5 4.5
2042-52 3.9 3.9
For a sustainable development a model has been evolved for electricity production. This is
summarised in the table shown above.
The contributions from coal, Hydrocarbon, Hydel, Renewable and Nuclear are 46%, 16%, 8%,
4% and 26% respectively. Thus nuclear has to grow fast if we have to meet our energy
demands.
Nuclear Perspective
For the projections given, if we have to succeed, several new technologies have to be
demonstrated.
The foremost among them is the Fast Breeder.
Demonstration of Accelerated Driven Systems with thorium as fuel.
It is important to note that India has to take the leadership role as the rest of the world does
not have much interest in thorium based cycle.
Having understood the need for accelerated growth of nuclear power, let us now learn the
fundamentals of the subject.
Before going into the details, a small overview is given to appreciate the details of the subject
that will be taught.
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Lecture 1
Introduction to Nuclear Engineering
Discovery of Fission
Rutherford described as the father of nuclear physics, bombarded alpha particles on Nitrogen
to eject a proton and thus started the business of splitting atom in 1917.
James Chadwick is credited with discovering neutron in 1932. Being neutral, it can easily
penetrate the Columb barrier and interact directly with the nucleus.
Enrico Fermi, considered to be one of the most brilliant physicist, postulated and succeeded in
producing transuranic elements by bombarding neutrons on Uranium. However, he did not
realise that he had fissioned Uranium in 1934.
Otto Hahn, Fritz Strassman and Lise Meitner in 1938 conducted experiments similar to Fermi.
They noticed that instead of a heavy element formation they found lighter elements in the
product.
They were the first ones to postulate fission and pointed the large energy that will be released.
We shall see later how this energy release is made possible.
Rutherford’s Model
Rutherford, based on experimentation, had proposed a model for the atom.
It has a central positively charged nucleus consisting of protons and neutrons.
It has electrons revolving around to make the atom neutral.
The charge and mass are summarised in the following table.
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Lecture 1
Introduction to Nuclear Engineering
Binding Energy
Binding energy of a nucleus is defined as the energy required to break a nucleus into its
constituents.
It increases with the number of nucleons in a nucleus.
It is often plotted in per nucleon basis as shown below
We shall understand this figure in more detail in a later lecture.
Higher the binding energy per nucleon, more stable is the nuclei.
Iron is the most stable nuclei.
We also note that as light elements fuse or heavy elements undergo fission, the products are
more stable.
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Lecture 1
Introduction to Nuclear Engineering
Fissile Elements
Consider the following equation
6.6 MeV is released on account of nuetron being absorbed or bound to U-234 nucleus.
Thus, Binding Energy of Last Neutron is 6.6 MeV.
Energy necessary to be supplied to induce fission is called Critical Energy for Fission.
The binding energy of last neutron and critical energy for fission for some isotopes are listed
below:
Isotope Critical Energy for Binding Energy of Last
Fission (MeV) Neutron (MeV)
Th232 6.5 5.1
U234 4.6 6.6
U236 5.3 6.4
U239 5.5 4.9
Pu 240 4.0 6.4
Thus when neutron is absorbed in U233 the neutron deposits its binding energy in the
compound nucleus (U 234 ), which is more than what is required to make U234 fission. Hence it
splits spontaneously.
Those elements which can be fissioned by zero energy neutrons are called fissile elements.
Thus U233, U235 and Pu239 are fissile elements.
On the other hand, Th232 and U238 need neutrons with 1.4 MeV and 0.6 MeV respectively for
inducing fission. Hence these are called fissionable nuclei.
Natural Uranium has 99.3% of U238 and 0.7% of U235.
U235 is the only naturally occuring fissile element.
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Lecture 1
Introduction to Nuclear Engineering
Prompt Neutron Spectrum
Nutrons released from fission have an average Energy = 1.98 MeV.
A large fraction of neutron is above the threshold energy of 0.6 MeV (refer table in previous
page) needed to fission U238.
Thus some U238 is also directly fissioned in reactors.
It has been noticed that as the energy of the colliding neutron is high, the probability of
reaction is poor.
This is attributed to the reduced time a neutron spends in the zone of interaction.
Hence the probability of reaction is inversely proportional to the speed of the neutron.
As the interaction decreases rapidly with increase in energy, and that the energy of the
prompt neutrons are high, we need to slow them down.
This is done by the use of moderator.
Moderators and Coolants
Hydrogen in the form of water (H 2O) and heavy hydrogen in the form of heavy water (D 2O)
are the most common moderators.
In gas cooled reactors graphite (C) is used as the moderator.
Coolant is employed to transport the heat generated in the core to the steam generator, where
steam is generated.
In water moderated reactors the same fluid also serves as coolant.
There are some safety advantages if we use gas as a coolant. In such cases CO2 or He is used.
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Lecture 1
Introduction to Nuclear Engineering
Critical Size
We shall see later in the course that all neutrons produced do not get absorbed in the reactor.
Many neutrons leak out of the reactor.
To keep the neutron population steady in a reactor we need to produce more neutrons than
what is absorbed in fuel.
As the number of neutrons produced depends on the volume and number of neutrons leaking
is proportional to surface area, there exists a minimum size below which the reactor cannot
operate (due to excess leakage).
This is called the critical size.
Thus, for a reactor to operate we need a critical size.
This size depends on the concentration of the fissile elements.
The size increases with the reduction in concentration.
Thus conceptually, as fuel burns out we need to increase the size, which is impractical.
To overcome this, the size of the reactor is increased to begin with and to compensate for the
excess production, neutron absorbers are used.
As fuel burns out the absorbers are gradually removed.
Control of Nuclear Reactors
The process of power addition or reduction is done by insertion or
removal of control rods.
Originally when the fuel is fresh and the reactor is not operating,
these rods are fully in.
To start the reactor, these are slowly pulled out and the rector
begins operation when the rods are out by a small amount.
As the fissile elements deplete, to compensate for them these are
continuously pulled out.
When they get pulled out completely, then reactor is stopped and
fresh fuel added.
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Lecture 1
Introduction to Nuclear Engineering
Fast Breeders
We shall show later in the course that we get around 2 effective neutrons from fission induced
by fully moderated neutrons.
However, if we do not fully slow down and allow the neutron to induce fission at higher
speeds, we get more effective neutrons per fission.
While only one neutron is required to get the reactor operating steadily, the excess neutrons
can be used to produce fresh fuel.
This is called breeding.
Since neutrons are not fully slowed down, it is called fast breeder.
Such rectors are usually cooled by sodium.
Power Reactors
Some of the characteristics of nuclear power reactors are summarised in the following Table:
Type Moderator Coolant Pressure Maximum Eff.
(bar) Temp (C) %
Pressurized Water Light Water Light Water 150 320 33
Reactor
Boiling Water Light Water Light Water 70 250 33
Reactor
Pressurised Heavy Heavy Water Heavy Water 80 320 32
Water Reactor
Gas Cooled Reactor Graphite Carbondioxide 15 410 35
High Temperature Graphite Helium 45 800 45
Gas Reactor
Liquid Metal Fast ------- Sodium 1 580 42
Reactor
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Lecture 1
Introduction to Nuclear Engineering
Agenda for the Course
Having realised that nuclear reactors have an important role to play in India’s power
generation scene, we shall now understand the principles of operation of a nuclear reactor.
We shall understand that present and the reactors of immediate future shall operate on fission
process.
We shall understand how reactors are sized, moderated, cooled and controlled.
We shall also understand the safety aspects that have to be kept on mind while designing
these reactors.
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