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UEET 603 Introduction to Energy Engineering Spring 2010 Nuclear Power Nuclear Energy 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.

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slide1

UEET 603

Introduction to Energy Engineering

Spring 2010

Nuclear Power

nuclear energy
Nuclear Energy

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.

slide3
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.

current use of nuclear power
Current Use of Nuclear Power

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

current use of nuclear power5
Current Use of Nuclear power

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.

major concern and obstacles
Major Concern and Obstacles

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.

slide7
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.

atomic and nuclear physics
Atomic and Nuclear Physics

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

fundamental particles
Fundamental Particles

Electrons:

This particle has rest mass of

and carries a charge

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.

slide10
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

slide11
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

 This particle has a rest mass of

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.

slide12
Neutron

The mass of a neutron is

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 )

slide13
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

Neutrino

This also a particle with zero rest mass and no electrical

charge.

This appearsin the decay of certain nuclei.

There are two types of Neutrinos: neutrinos and

antineutrinos

atomic and nuclear structure
Atomic and Nuclear Structure

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.

slide15
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 the chemical 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

theneutron number (N)

Atomic mass number: A = Z+N

slide16
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

: Hydrogen nuclide with ( Z=1) a single proton as nucleus

is the hydrogen nuclide with a neutron and as well as a proton in the nucleus. This called the deuterium of heavy hydrogen .

slide17
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 and whose nuclei contains same number of protons but different numbers of neutrons ( Same Z but different N and hence different A) are known asisotopes.

Naturally occurring elements may exist in the nature with some stable isotopes and some unstable isotopes and expressed as percentage atoms of the element.

stable and unstable isotopes
Stable and Unstable Isotopes

Oxygen, for example, has three stable isotopes ,

, ( Z = 8, N = 8, 9 , 10 ) and five known unstable ( i.e. radioactive) isotopes , , , and (Z = 8, N=5, 6, 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 . Rest are:

0.037% and 0.204%

mass and energy
Mass and Energy

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 releases an amount of energy

which is given by Einstein’s formula

c is the speed of light

slide21
For example, the annihilation of 1g of matter would lead to a release of

- 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

slide22
When a body is in motion, its mass increases relative to an observer according to the formula

Total energy of a particle, that is, its rest mass plus its kinetic energy

Kinetic energy is given as

For v<< c

Same as in Classical Mechanics

energy of atomic particles
Energy of Atomic particles

Neutron:

Photon: Travels at the speed of light and has no rest mass, its total energy is given as

Particle Wave Length

For Neutron

For Photon and all other particles of zero rest mass

Where E is the kinetic energy in eV

excited states and radiation
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.

slide25
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.

type of power reactor
Type of Power Reactor

Light -Water Reactor (LWR)

Gas Cooled Graphite moderated Reactor

- High temperature gas cooled reactor (HTGR)

Heavy -Water Reactor (HWR)

Breeder Reactor (BR)

light water reactor lwr

The first generation of reactor that is moderated and cooled by ordinary (light) water.

  • Water has excellent moderating properties as well as thermodynamic properties to produce steam.
  • Water also absorbs neutrons to such an extent that it is not possible to fuel a LWR with natural uranium – it simply would not become critical.
  • Uranium in LWR must always be enriched to some extent.

There are two types of light - water reactors:

Pressurized-water reactor (PWR)

Boiling-water reactor (BWR)

Light-Water reactor (LWR)
pressurized water reactor pwr
Pressurized Water Reactor (PWR)

The water in a PWR is maintained at a high pressure in the range of 2000-2500 psi to prevent water from boiling.

High pressure water is circulated through the reactor core to pick up heat without any boiling of water.

Pressurize hot water is then circulated through the steam generator where heat is transferred to a secondary water stream that enters as liquid water and exits steam.

slide29
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

slide30

Boiling Water Reactor (BWR)

Referred to as the direct cycle.

Water is boiled directly in the reactor vessel and produces steam to turn the turbine.

Steam is produced directly inside the reactor and there is no need of a separate steam generator.

Steam from the rector goes directly to the turbine to produce power.

More effective in removing heat from the fission reaction using latent heat rather than sensible heat.

slide31
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.

slide32
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.

slide33

Heavy-Water ( )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.

slide34
Such a reactor can operate on natural Uranium because the absorption cross section of deuterium ( D = ) for thermal neutron is very small, much smaller for example than the cross section of ordinary hydrogen ( H = ).

However, deuterium in is twice as heavy as hydrogen in , so that is not as effective in moderating neutrons as .  

They require more collisions and travel greater distances before reaching thermal energies than

slide35
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.

slide36
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

slide37

Breeder Reactor

The world reserve of 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.

slide38
The two most important fissile isotopes produced from conversion are and .

The fissile isotope is obtained from fissile isotope of thorium by the absorption of neutrons.

is obtained from nonfissile , which is one of the major component of natural resource of uranium.

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 .

Practically all of the fuel in these reactors is therefore and conversion of into takes place during the normal operation of the rector.

slide39
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.

slide40
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