LECTURE 9 NUCLEAR POWER GENERATION

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LECTURE 9NUCLEAR POWER GENERATION
Dr. Rostamkolai

• ECE 371
• Sustainable Energy Systems

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INTRODUCTION

• If the current coal usage continues, the coal
  supply in the world will be depleted in 155 years
• Nuclear energy as it is known today was
  highlighted by Einstein in 1905
• E mc2

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INTRODUCTION

• Theoretical research in controlled fission
  resulted in the first successful demonstration of
  a self-sustained chain reaction at the University
  of Chicago in 1942 as a part of the Manhattan
  Project
• Nuclear power plants were first developed for
  naval propulsion and energy production in 1950s
  (higher-specific-energy fuels)

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INTRODUCTION

• Expansion in US halted in 1970s
• Overbuilt generation
• Reduction in load growth
• Most nuclear plants are light water reactors
• Pressurized Water Reactor (PWR) Most Common
• Boiling Water Reactor (BWR)

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PWR

• 2300 psi, 315oC

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BWR

• 1000 psi, 285oC

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HISTORICAL PERSPECTIVE

• The worlds first nuclear-powered electric
  generating plant was constructed by Soviet Union
  in 1954 5 MW
• The first US PWR was constructed and placed in
  service by Westinghouse at Pennsylvania in 1957
• The first US BWR was constructed and placed in
  service by GE at California in 1957 5 MW

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HISTORICAL PERSPECTIVE

• The following figure shows the number of nuclear
  plant orders placed annually

1973 Arab Oil Embargo
1979 Three Mile Island 2
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INTRODUCTION
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HISTORICAL PERSPECTIVE

• There are 439 nuclear plants in the world, with
  104 of them in 31 US states

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HISTORICAL PERSPECTIVE
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HISTORICAL PERSPECTIVE
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BACKGROUND

• Nuclear energy is obtained from the atom nuclei
  through a controlled reaction
• The possibility of harvesting the nuclear energy
  was first recognized in the 1930s and early 1940s
• The idea of obtaining large amounts of energy
  from small amounts of material was very exciting
  to the scientists

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BACKGROUND

• An elements chemical nature is determined by the
  number of electrons in its atom
• In a neutral atom, the number of electrons is
  equal to the number of protons in the nucleus
• The positive charge of protons are cancelled by
  the negative charge of electrons

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BACKGROUND
Radioactive
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BACKGROUND

Mass Number (Number of Protons)
(Number of Neutrons)
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BACKGROUND

• The number of protons in a nucleus determines the
  elements
• The number of neutrons determines the isotope
• Example
• Uranium nucleus has 92 protons
• If it has 143 neutrons, it is Uranium-235
• If it has 146 neutrons, it is Uranium-238

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BACKGROUND

• There are 14 known isotopes of uranium
• Approximately 1000 distinct isotopes have been
  identified experimentally
• They are grouped into 103 elements with names
• There are 4 more elements shown in charts, but
  two are un-named

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BACKGROUND

• Of all identified isotopes, 279 of them are
  stable
• They are nuclei that do not experience natural
  decay (disintegration)
• The rest have some intrinsic nuclear imbalance
  which eventually causes them to change their
  structure
• Such changes always lead to a more stable isotope
  and involve the emission of some disintegration
  product

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BACKGROUND

• The emitted particles are
• Electron beta decay
• Helium nuclei alpha decay
• All nuclei, except hydrogen H1, can be excited
  without altering its basic nuclear structure
• They eventually return to their natural state by
  emitting one or more protons

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BACKGROUND

• These protons are very high energy and called
  gamma rays
• Nuclei can be excited artificially by bombarding
  them with
• Photons
• Neutron
• Helium nuclei

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BACKGROUND

• Nuclei can also have their isotopic
  identification changed by bombardment and capture
• These changes are called isotopic transmutation
  and play a central role in the physics of nuclear
  reactors

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BACKGROUND

• A chemical reaction is a reaction which involves
  electrons
• Nuclear reaction is a reaction which involves the
  nucleus of an atom
• Nuclear reactions produce more energy per atom
  than chemical reactions

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BACKGROUND

• This is because nuclear forces holding the
  nucleus together are much stronger than the
  electrostatic forces that are holding electrons
• The most commonly observed from a nuclear
  reaction is the radioactive decay
• The radioactive decay causes a heavy atom to
  transform to a lighter atom of a different element

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BACKGROUND

• For example, in the following a radioactive decay
  of Uranium 238 decomposes it to Thorium with the
  release of an alpha particle (He nuclei)

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NUCLEAR REACTION

• It is a reaction that changes the number of
  protons or neutrons in the nucleus of an atom
• There are several kinds of nuclear reactions
• Fragmentation of large nuclei into smaller ones
• Nuclear fission
• Building up of small nuclei into larger ones
• Nuclear fusion

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NUCLEAR FISSION

• It is a nuclear reaction in which nucleus of an
  atom splits into smaller parts
• This process often release neutrons
• Self-sustaining chain reaction, if slowed
  (concept of moderator invented by Fermi)
• It also releases enormous amount of energy in the
  form of heat

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NUCLEAR FISSION

• In 1939 Hahn and Strassman in Berlin bombarded a
  Uranium-235 isotope with neutrons and
  demonstrated nuclear fission for the first time

Barium
Krypton
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NUCLEAR FISSION

• The naturally mined uranium contains 0.7 of
  U-235 and 99.3 of U-238
• Separation is difficult
• Bohr found that nuclear fission was much more
  likely to occur in Uranium-235 isotope than in
  Uranium-238
• The process of enrichment was developed to
  increase concentration of U-235 in the mixture

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NUCLEAR POWER PLANT

• In a nuclear power plant, a nuclear reactor
  produces and controls the release of energy from
  splitting the atoms of elements such as uranium
  and plutonium
• The energy released as heat from the continuous
  fission of the atoms in the fuel is used to make
  steam

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NUCLEAR POWER PLANT
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CORE

• Reactor core is the portion of the nuclear
  reactor which contains the nuclear fuel where the
  nuclear reaction takes place
• The main function of a core is to create an
  environment which establishes and maintains the
  nuclear chain reaction
• It provides a means for controlling the neutron
  population and removing the energy released
  within the core

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MODERATOR

• Moderator is a material which slows down the
  released neutrons from the fission process
• Slow moving neutrons are much more likely to be
  absorbed by uranium atoms to cause fission than
  fast moving neutrons
• Newly released neutrons after a nuclear fission
  move at 300,000 km/sec

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MODERATOR

• It must be slowed down or moderated to speeds
  of a few km/sec
• This is necessary to cause further fission and
  continue the chain reaction

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MODERATOR

• The most commonly moderators are
• Water - H2O
• Light water reactor
• Not efficient it slows neutrons and also
  absorbs them
• Heavy water D2O (formed by a heavier isotope of
  hydrogen with atomic mass 2)
• Heavy water reactor
• Efficient
• Graphite

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FUEL

• The most common fuel is
• Uranium-235
• Plutonium-239
• Light water reactors use uranium oxide (UO2)
  pellets which are arranged in zirconium alloy
  tubes to form fuel rods (melting point of UO2 is
  2800oC)

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FUEL

• Pellets are 1 cm in diameter and 1.5 cm long

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FUEL

• The fuel rods are placed in fuel assemblies in
  the reactor core

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CONTROL ROD

• It is made of neutron-absorbing material
• Cadmium
• Hafnium
• Boron
• Rods are used to control the rate of reaction
• They are inserted or withdrawn from the core to
  decrease or increase the rate of fission

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CONTROL ROD
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CONTROL ROD

• Inserting the rod slows down the reaction by
  absorbing the neutrons and reducing the available
  neutrons for fission
• Withdrawing them has the opposite effect
• Allowing the rate of fission to grow beyond a
  certain point can be very dangerous (Chernobyl)

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COOLANT

• It is a liquid or gas circulating around or
  through the core
• It carries the heat away from the reactor
• It generates steam in the steam generator
• The most common coolant is pressurized water

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STEAM GENERATOR

• It is a heat exchanger
• Uses heat from the core which is transported by
  the coolant
• Produces steam for the turbine

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CONTAINMENT

• It is the structure around the reactor core
• It protects the core from outside intrusion
• Protects outside environment from effects of
  radiation in case of a malfunction
• Typically it is a meter thick concrete and steel
  structure

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SPENT FUEL POOL

• It stores the spent fuel from the nuclear reactor
• About 1/4 to 1/3 of the total fuel is removed
  from the core every 12 to 18 months and replaced
  with the fresh fuel
• The removed fuel rods still generate a lot of
  heat and dangerous radiation

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SPENT FUEL POOL

• The fuel bundles freshly removed from the core
  are separated for several months for initial
  cooling
• Then they are sorted in other parts of the pool
  for final disposal
• Metal racks keep the fuel in safe positions to
  avoid the possibility of a nuclear chain reaction

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SPENT FUEL POOL

• The spent fuel is typically stored underwater for
  10 to 20 years before being sent for disposal or
  reprocessing

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PRODUCTION COST OF NUCLEAR POWER