UEET 603
Introduction to Energy Engineering
Spring 2010
Nuclear Power
•Nuclear energy is a way of creating heat through
the fission process of atoms.
•Nuclear energy originates from the fission of
atomic nucleus in a chain reaction.
•Nuclear fission reaction is controlled in a
nuclear reactor to produce thermal energy.
• The fission process takes place when the nucleus
of a heavy atom like uranium or plutonium is
split when struck by a neutron.
• The fission of the nucleus releases two or
more new neutrons.
• It also releases energy in the form of heat.
• The released neutrons can then continue to split
additional nucleus .
- This releases even more neutrons and more
nuclear energy.
- The repeating of the process leads to a chain
reaction.
• All nuclear power plants convert heat into electricity
using steam.
• The heat is created when atoms are split apart – called
fission.
• The heat from fission reaction is used to produce
steam, which is then used to turn a turbine and
produce electricity using a generator.
• Power from nuclear fission accounts for about 19% of
the nation’s total energy.
• Number of operating nuclear power plants is 120 ??
• Mostly safe, successful and well regulated
• No new power plant has been built in last 30 years
• Nuclear power is generated primarily in stationary
applications like in a nuclear power plants, propulsion of
mobile system like naval vessels, especially submarines as
well as several surface vessels.
• Since nuclear plants do not consume oxygen like
conventional plants, it is quite attractive for use under sea.
• Also, ships powered by nuclear plants need to be refueled
only after long period of operation.
• Nuclear power has also been developed for the propulsion
of aircrafts and rockets.
Safe operation of the plant and safe handling and disposal of
nuclear fuels.
Concern of environmentalists about the dangers of storing
the radioactive byproducts of the process.
Cost of building a new nuclear reactor is about $10 billion
each – One of the main reason for a stagnant industry.
Recent reduced cost of other fuels like coal, natural gas and
oil, make the nuclear power production less competitive.
Each project has to pass through a rigorous scrutiny and
check through Nuclear Regulatory Commission (NRC) before
construction can begin.
• Needs economic guarantee from the government
• Without any support from the government it seems
difficult for the utility companies to start any new projects.
• Government recently committed $8.33 billion
in loan guarantees for the construction of two
new reactors at the Alvin W. Vogtle Electric
Generating Plant in Georgia
- Expected to provide electricity to
over a million people by next 5-6 years.
- Expected to create new job opportunities.
Fundamental Particles
The physical world is composed of various subatomic or
fundamental particles.
There are variety of different fundamental particles, and
scientists are still finding newer ones .
However , only few of these are important in nuclear
engineering:
- Electrons - Proton - Neutron
- Photon - Neutrino
Electrons:
m 9.10956 10 28 g
• This particle has rest mass of e
and carries a charge e 1.60219 10 19 coulombs
• Mass of a particle is a function of its speed relative to the
observer
• In giving the mass of fundamental particle, it is necessary to
specify the mass at rest with respect to the observer -
termed as rest mass.
There are two types of electrons:
• Negatrons or negative electrons:
Carries a negative charge
Normal electrons encountered in this
world.
• Positrons or positive electrons:
Carries a positive charge
Relatively rare in this world
These two are identical except the sign of
the charge
Electron Annihilation Process
• When under circumstances, a positron collide
with a negatron, the electrons disappear and
two (occasionally more) photon (particles of
electromagnetic radiation) are emitted.
Proton
• 24
This particle has a rest mass of m p 1,6726110 g
and carries a positive charge equal in magnitude
to the charge on the electron.
• Protons with negative charge have also been
discovered, but these particles are of no
importance in nuclear engineering.
Neutron
• The mass of a neutron is mn 1.67492 10 24 g
which is slightly larger than the mass of the
proton.
• It is electrically neutral.
• The neutron is not a stable particle, except
when it is bound into an atomic nucleus.
• A free neutron decays to a proton with the
emission of a negative electron (Known as β decay
)
Photon
• Particle equivalent of electromagnetic wave.
• This is a particle with zero rest mass and zero
charge, which travels in a vacuum at only one
speed, namely the speed of light c 2.0079 1010 cm/s
Neutrino
• This also a particle with zero rest mass and no electrical
charge.
• This appears in the decay of certain nuclei.
• There are two types of Neutrinos: neutrinos and
antineutrinos
Atoms are the building blocks of all gross matter
Atoms, in turn, consists of a small but massive nucleus
surrounded by a cloud of rapidly moving (negative)
electrons
The nucleus is composed of protons and neutrons
The total number of protons in the nucleus is called
the atomic number (Z) of the atom.
• Total electrical charge of the nucleus is : +Ze
• In a neutral atom there are as many electrons as
protons, i.e. Z-number of electrons moving around the
nucleus.
• It is the number electrons that dictates thechemical
behavior of atoms and gives identify of a element.
Hydrogen (H) has one electron
Helium (He) has two electrons
Lithium (Li) has three electrons
• The number of neutrons in a nucleus is known as
the neutron number (N)
Atomic mass number: A = Z+N
The various species of atoms whose nuclei contain
particular numbers of protons and neutrons are called
nuclides.
Each nuclides is denoted by the chemical symbol of the
element (this specifies Z) with the atomic mass number
as superscript.
This determines the number of neutrons N = A-Z
1
H : Hydrogen nuclide with ( Z=1) a single proton
as nucleus
2
H is the hydrogen nuclide with a neutron and as well
as a proton in the nucleus. This called the deuterium
of heavy hydrogen .
4
He is the helium nuclides whose nucleus consists
of two proton (two electron) and two neutrons.
For better clarity, Z is also included in the symbol
as a subscript.
Atoms such as 1 H and 2 H whose nuclei contains
same number of protons but different numbers of
neutrons ( Same Z but different N and hence
different A) are known as isotopes.
Naturally occurring elements may exist in the
nature with some stable isotopes and some
unstable isotopes and expressed as
percentage atoms of the element.
• Oxygen, for example, has three stable isotopes 16 O ,
17
O , 18O ( Z = 8, N = 8, 9 , 10 ) and five known unstable ( i.e.
20
radioactive) isotopes O , O , O , O and O (Z = 8, N=5, 6,
13 14 15 19
7, 11, 12).
• The stable isotopes ( and a few of the unstable isotopes) are
found as naturally occurring elements in nature.
• However, they are not found in equal amounts; some isotopes
of a given element are more abundant than others.
For example: 99.8 % of naturally occurring
oxygen atoms are the isotope 16 O . Rest are:
0.037% O and 0.204%
17
Einstein’s theory of relativity
• Mass and energy are equivalent and
convertible, one into other.
•Complete annihilation of a particle or other body
of rest mass m 0 releases an amount of energy
which is given by Einstein’s formula
E rest m0 c 2
c is the speed of light
For example, the annihilation of 1g of matter would lead to a
release of
E 1 2.9979 10
10 2
8.9874 1020 erg 8.984 1013 joules
- This is equivalent to 25 million kilowatt-hours
Another unit of energy that is often used in nuclear engineering
is the electronVolt (eV)
This is defined as the increase in the kinetic energy of an
electron when it falls through an electrical potential of one volts.
This is in turn is equal to the charge of the electron multiplied by
the potential drop
1eV 1.60219 10 19 Coulomb 1 Volt 1.60219 10-19 Joule
When a body is in motion, its mass increases relative to
an observer according to the formula
m0
m
v2
1
c2
Total energy of a particle, that is, its rest mass plus its
kinetic energy
Etotal mc2
Kinetic energy is given as
1
For v<< c Same as in Classical
E mc 2 m0 c 2 m0 c
2 1 Mechanics
1 v
E m0 v 2
c2
2
Energy of Atomic particles
1
Neutron: E m0 v 2 v 2.383 106 E
2
Photon: Travels at the speed of light and has no
rest mass, its total energy is given as
E hv
Particle Wave Length
For Neutron
9 For Photon and all other
2.869 10
particles of zero rest mass
E
1.240 10 4
Where E is the kinetic E
energy in eV
Excited States and Radiation
The z atomic electrons that cluster about the nucleus
move in a well defined orbits
However, some of these electrons are more tightly
bound in the atom than other.
For example only 7.38 eV is required to remove the
outermost electron from a lead (Z=82), while 88 keV
(or 88,000 eV) is required to remove the inner most or
the k-electron.
The process of removing an electron from an atom is
call ionization and 7.38 eV and 88k3V are known as
the ionization energies.
This leads to a excited state for the atom –has more
energy than the ground state.
It slow decays back to the ground state.
When such transition occurs, a photon is emitted by
the atom with an energy equal to the difference in the
energies of the two states.
Depending on the energy level of the excited state or
the removed electron orbit level, radiation wavelength
( ultraviolet etc. ) can be determined.
•Light -Water Reactor (LWR)
•Gas Cooled Graphite moderated Reactor
- High temperature gas cooled reactor (HTGR)
•Heavy -Water Reactor (HWR)
•Breeder Reactor (BR)
• The first generation of reactor that is There are two
moderated and cooled by ordinary (light) types of light
water.
- water
• Water has excellent moderating reactors:
properties as well as thermodynamic
properties to produce steam. Pressurized-
water reactor
• Water also absorbs neutrons to such an (PWR)
extent that it is not possible to fuel a LWR
with natural uranium – it simply would not
become critical. Boiling-water
reactor (BWR)
• Uranium in LWR must always be
enriched to some extent.
The water in a PWR is
maintained at a high pressure
in the range of 2000-2500 psi
Containment Structure to prevent water from boiling.
Steam
Control Generator High pressure water is
Rods circulated through the reactor
core to pick up heat without
any boiling of water.
Turbine
Pressurize hot water is then
Generator circulated through the steam
generator where heat is
transferred to a secondary
water stream that enters as
Condenser liquid water and exits steam.
Reactor Vessel
High pressure and high temperature steam is then turns
a turbine to produce electric power.
Large PWR system uses as many as four steam
generators, which produce steam at about 560 F and
900 psi.
This gives an overall efficiency of 32-33 % for a PWR
plant.
The condenser is cooled by a cooling water loop using
pumps and cooling tower that rejects heat to
environment
Boiling Water Reactor (BWR)
•Referred to as the direct cycle.
Containment Structure
•Water is boiled directly in the
Steam reactor vessel and produces
Control Generator steam to turn the turbine.
Rods
•Steam is produced directly
inside the reactor and there is
Turbine
no need of a separate steam
generator.
Generator
•Steam from the rector goes
directly to the turbine to
produce power.
Condenser
•More effective in removing
Reactor Vessel r
heat from the fission reaction
using latent heat rather than
sensible heat.
Less water is pumped through the reactor than a PWR
for the same net power output
However, the water becomes radioactive in passing
through the reactor core.
Since this radioactive water is utilized in the electricity
producing side of the plant, all of the components like
the turbines, condensers, reheaters, pumps, piping be
shielded in a BWR Plant.
The pressure in a BWR is approximate 1000 psi, about
half the pressure in a PWR.
As a results the wall of the pressure vessel for a BWR
need not be as thick as it is for a PWR.
However the power density (Watt/cm^2) is smaller in a
BWR than a PWR, and so overall dimension of a
pressure vessel for BWR must be larger than for PWR.
Heavy-Water ( D2O )Reactor
Heavy-water moderated and cooled reactor
(HWR) has been under development in several
countries, especially in Canada.
Heavy-water moderated reactor is suitable for use with
natural uranium.
Canada has large resources of natural uranium.
Removes the need for expansive uranium enrichment
plant.
•Such a reactor can operate on natural Uranium
because the absorption cross section of
deuterium ( D = 2 H ) for thermal neutron is very small,
much smaller for example than the cross section of
ordinary hydrogen ( H = 2 H ).
•However, deuterium in D2O is twice as heavy as
hydrogen in H 2 O, so that D2O is not as effective in
moderating neutrons as H 2 O .
•They require more collisions and travel greater
distances before reaching thermal energies than
H 2O
•The core of an HWR is therefore considerably larger
than that of an LWR, but much smaller than a natural
uranium, gas cooled graphite moderated reactor.
•In order to avoid the use of large and expensive
pressure vessel, Canadian design uses pressure tube
concept that encapsulated fuel within a hollow tubes.
•The coolant passes through the tubes and coolant do
not come in direct contact with the heavy water
moderator.
•In Canadian HWR design, heavy water is also used as
the coolant.
•One important thing about the HWR is that the reaction
is not inherently stable.
•Thus an accidental increase in power leads automatically
to further increase in power and rapid external
intervention is required to bring reactor under control
Breeder Reactor
• The world reserve of 235
U are not adequate to meet the
indefinite needs of the growing nuclear power industry ( may be
for 100 years)
•Only the advent of the breeder reactor can achieve the full
potential of the world’s uranium and thorium supply.
•It is possible to manufacture certain fissile isotopes from
abundant non-fissile materials by a process know an
conversion.
The two most important fissile isotopes produced from conversion
are 233 U and 239 .
Pu
The fissile isotope 233 U is obtained from fissile isotope 232
U of
thorium by the absorption of neutrons.
239
Pu is obtained from nonfissile 238 U , which is one of the major
component of natural resource of uranium.
238
U has to be irradiated in a reactor, which normally occurs in
most the reactors. So most of the reactor are fueled with uranium
which is only slightly enriched in 235 U .
Practically all of the fuel in these reactors is therefore 238 U and
conversion of 238 U into 239 Pu takes place during the normal
operation of the rector.
The conversion process is described in terms of conversion
ratio or breeding ratio
- Defined as the average number of fissile atoms
produced in a reactor per fissile fuel atom consumed.
In a breeder reactor every effort is made to prevent fission
neutrons to slow down. So, light-water is excluded from
the core.
There is no moderator in the core and the core contains
only fuel rods and coolant.
In these reactors, different other types of coolants such as
sodium are used.
Types of Breeder Rectors:
• Liquid-metal Cooled fast Breeder Rector
(LMFBR)
• Gas cooled fast breeder Reactor (GCFR)
• Molten salt breeder reactor (MSBR)
• Light water breeder reactor