Nuclear Energy

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Nuclear Energy
http//www.teachnet.ie/dkeenahan/2004/Images/Radia
tion20symbol20220J.jpg
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History of Nuclear Energy in the US

• During the 1940s and 1950s nuclear power was
  viewed as a solution to energy problems
• The Price-Anderson Act of 1957 exempted these
  companies from any legal liabilities incurred.
• By 1975 there were 53 plants operating in the US
  producing about 9 of the electricity.
• Similar nuclear development occurred in other
  industrialized nations (France, UK, USSR, etc.)
• By the end of the 1970s, interest in nuclear
  power substantially waned. Interest in nuclear
  power dropped off, and the public perception of
  nuclear energy grew more suspicious

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Figure 13-2
Note the major gap in the 1970s
This graph reflects public perceptions about
nuclear energy over time!
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Nuclear Power, The US and Worldwide

• According to DOE, there are 104 nuclear power
  plants in operation in October of 2005. No
  applications for new nuclear power plants have
  been submitted.
• The last nuclear power plant constructed was in
  1996 in Watts Bar, Tennessee http//www.eia.doe.go
  v/cneaf/nuclear/page/nuc_reactors/reactsum.html
• Worldwide 441 operating nuclear power plants.
• Nuclear power is restricted to those
  industrialized nations that have the
  technological know-how to enrich Uranium
  (described later)

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What Happened to the Promise of Nuclear Energy?

• The public became (and still is) suspicious of
  nuclear energy.
• Actual accidents like Three-Mile Island (1979)
  and Chernobyl (1986)
• Cinema, TV, and science fiction novels (e.g. The
  China Syndrome and Them)
• Better awareness of what a nuclear meltdown will
  do.

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Nuclear-Related Movies
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Nuclear Energy

• Nuclear reactions
• Fission one large atom splits into smaller
  daughter atoms
• Fusion two smaller atoms fuse to form a larger
  atom

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Fission and Fusion

• Fission or fusion of an atom produces energy as
  the conversion from one large into many small
  (fission) or many small into one large (fusion)
  doesnt occur cleanly.

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• Note that both reactions produce energy,
  neutrons, alpha particles, beta particles, gamma
  rays, etc.

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Fission

• Fission the weight of the large atom (parent)
  prior to splitting does not equal the combined
  weights of the daughter atoms.

Weight of A ? B C
B
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Fusion, similar process

• The weight of the two initial atoms weighs
  different from the daughter atom

Weight of A B ? C
A
C
B
Energy
The difference in mass is accounted for by the
release of energy
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Fission and Fusion

• An example of such a radioactive isotope is
  uranium 235. Uranium 238 is the more stable and
  more abundant isotope.
• Fusion occurs within the sun where hydrogen atoms
  fuse to form helium.

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Radioactive Isotopes

• Some Isotopes are unstable and will decay to more
  stable forms (via fission). For example,
  carbon-14 will decay into carbon-12 at a fixed
  rate (known as a half-life).
• Unstable isotopes are called radioisotopes and
  the process of breaking down into more stable
  atoms is called radioactive decay. Radioactive
  decay releases energy.

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Uranium

• One of the most common atoms used in nuclear
  reactors is uranium. Uranium is found abundantly
  in nature, with the majority of uranium being the
  more stable isotope U-238.
• Uranium also has a radioactive isotope U-235,
  which is very rare. In nature the percent of
  U-235 of all uranium isotopes is lt 0.05 to 0.3.
• Raw uranium (mostly U-238) is mined
• The radioactive uranium (U-235) has to be
  distilled from the raw uranium (U-238) through a
  process called enrichment.
• For uranium to be used in nuclear power plants,
  the goal is to increase the abundance of U-235
  via enrichment to about 4. Enrichment has to be
  much higher for nuclear weapons

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Uranium to Fuel Rod

• Uranium processing and enrichment
• First the raw uranium is mined, then it is
  chemically leached to form a uranium oxide powder
  known as yellowcake
• The yellowcake is converted to uranium
  hexafloride, then it is enriched
• The enriched uranium exists as a powder uranium
  dioxide
• The powder is pressed into pellets and the
  pellets are stuffed into hollow tubes and sealed.
  This tube filled with enriched uranium pellets
  is a fuel rod. The fuel rod is used within a
  nuclear power plant.

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Fuel Rods, Full of Enriched Uranium
www.fernald.gov/.../Aug01/images/7368-D0359.jpg
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Uranium Fission within Fuel Rods

• The U-235 in fuel rods will undergo fission
  through a chain reaction.
• Enriching the uranium is one of the most
  technologically difficult operations to master..
• Currently Iran is in the processes of developing
  uranium enrichment this has been very
  controversial (later in the lecture we will come
  back to this point). Also North Korea has
  learned how to enrich uranium both for nuclear
  power plants and for nuclear weapons.

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Uranium-235 Fission, a Chain Reaction (Figure 13-6

• Fission of U-235 can occur through a chain
  reaction.
• When a U-235 is bombarded by a neutron, it forms
  U-236
• U-236 instantaneously breaks down
• Part of the fission process releases more
  neutrons, which bombard additional U-235 atoms.
  This occurs numerous times in a chain reaction
• This is what is going on inside a fuel rod

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Nuclear Reactor

• A nuclear reactor for a power plant is designed
  to sustain a continuous chain reaction but not
  allow it to amplify into a nuclear explosion.
• A chain reaction can be achieved using a
  moderator, which slows down the neutrons that
  produce fission, so that they are traveling at
  the right speed to trigger another fission.
• Moderators in US nuclear reactor plants water.
  Graphite is used as a moderator in former Soviet
  plants.
• Nuclear power plants, like those in the US, have
  to be located near a water source to have access
  to water. Water is both a moderator and a
  coolant.

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Fuel Rods and Energy

• Groups of fuel rods are placed close together to
  form a reactor core.
• The reactor core is contained within a fortified
  reactor vessel that holds moderator, reactor
  core, coolant, safety equipment, control rods,
  etc .
• Heat given off from the reactor core is used to
  boil water and generate steam. The steam is used
  to turn turbines to generate nuclear power.
• Spent Fuel Rods have to be replaced (after
  about 10 years) with fresh new ones.

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Control Rods

• Control rods are used to regulate the fission
  reaction.
• They absorb neutrons
• When inserted in between the fuel rods they slow
  down the chain reaction.

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The chain reaction is controlled by rods of
neutron-absorbing materials.
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Figure 13-8 design of a nuclear power plant
The Cooling Towers are the infamous nuclear
icons seen on the landscape
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Cooling Towers
What you see being emitted from the cooling
towers is steam, not radioactive pollution.
http//www.picture-newsletter.com/nuclear/cooling-
tower-ub4.jpg
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Reactor Core Fuel Rods Plus Control Rods
Image from Wikipedia.org
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Advantages of Nuclear Energy

• Well-run nuclear power plants produce very minute
  amounts of pollution. As a matter of fact,
  radiation levels near coal-burning power plants
  are significantly higher (100 times more!) than
  around nuclear power plants
• Nuclear fuel produces no greenhouse gases
• no need to be reliant on foreign oil.
• The amount of uranium needed is relatively small
  compared to coal-burning power plants.
• No sulfur dioxides or other acid-rain progenitors
  are released, whereas coal plants produce over
  300,000 tons of sulfur dioxide.
• The coal plant produces 600,000 tons of ash
  requiring land disposal nuclear power produces
  only 250 tons of radioactive waste requiring safe
  storage.

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The Dark Side!
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Radiation Exposure

• People exposed to radiation can become very sick
• Radioactive decay produces direct products and
  indirect products
• Direct products daughter elements (30 possible
  ones, such as radioactive isotopes of iodine,
  strontium, cesium, cobalt, etc.)
• Indirect products alpha particles, beta
  particles, gamma rays, errant neutrons.
• Any material in and around radioactivity will
  absorb these indirect radioactive emissions.
• These radioactive byproducts cause significant
  harm to the body.

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Possible Biological Effect of Radiation

• Immediate Death radiation destroys cells and
  burns tissues
• Stops cell division organic tissues that absorb
  radioactive emissions will cease cell division,
  which leads to radiation sickness. Red blood
  cells (RBC) are continuously being produced, for
  example, and if a person is exposed to too much
  radiation this will stop the production of new
  RBCs. Without new RBCs a person will die.
  Skin and hair cells will also stop dividing.
• Long-term effect mutation of DNA and higher
  risk of cancer. Birth defects are also possible.

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Radioactive Waste

• Radioactive materials can cause substantial harm.
  Moreover, spent fuel rods have to be replaced
  with new ones. How do we dispose of the spent
  fuel rods without exposing people to
  radioactivity?
• Traditionally, spent fuel rods are placed within
  containers and then stored on-site within
  containment ponds or containment-pools. The
  immersed containers are surrounded by water,
  which absorbs the radioactive emissions.
• How long will the waste be radioactive?
• It depends on the half-life of the material.
• The next table (Table 13-1) shows radiation
  levels for various substances. Read the textbook
  explanation of measuring radioactivity
  Radioactive Emissions pg 358.

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Half-life

• The half-life of carbon 14 is approximately 5700
  years. By knowing the rate of decay, which is a
  fixed value, scientists are able to radiocarbon
  date objects from the past. By knowing the ratio
  of C14 to C12 in organic matter and by knowing
  the half-life, you can backtrack the age of the
  organic material to determine when it was alive
  and when it was incorporating both C12 and C14
  within similar amounts.
• Plutonium has a half life of 24,000 years
• The following table (Table 13-2) reports the
  half-lives of some of the uranium fission
  daughter products. Note how some, like
  plutonium, take a long time to decompose and
  thats just half of the radioactive material!
  The complete decomposition takes 10,000s of
  years.

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Where are the spent fuel rods stored?

• Again, most fuel rods are stored on-site at the
  nuclear power plants. But available storage is
  rapidly diminishing. Some nuclear power plants
  have been operating for decades, and the amount
  of storage space is running out.
• Some nuclear power plants are researching how to
  reuse spent fuel rods. The following slide is an
  excerpt form a Morning Edition report on
  recycling fuel rods.

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Storing Spent Fuel Rods

• The US Government has invested billions of
  dollars to build a long-term nuclear waste
  disposal site, Yucca Mountain in Nevada
  (discussed a little later).
• The Yucca Mountain site will be used to safeguard
  nuclear waste from nuclear reactors, and it will
  start accepting the spent fuel rods by 2017 (11
  years).
• One major concern regarding this is that fuel
  rods from across the country will have to be
  shipped to Nevada along Americas roadways.

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Nuclear Meltdown

• Perhaps the biggest fear of nuclear energy is a
  meltdown of the reactor and the contamination of
  the environment by radioactive waste.
• Nuclear plants generate a lot of internal heat to
  be converted into power. As stated, a coolant is
  used to convert the heat energy into steam to
  turn a turbogenerator.
• Reactors in the US use water as a coolant and as
  a moderator.
• If there is a loss of the coolant (it leaks out
  of the double-loop structures), the heat within
  the reactor will continue to rise. Because the
  water also acts as a moderator to slow the
  neutrons, the loss of the coolant will result in
  the nuclear reaction continuing unabated. The
  reactions start to occur way too fast and cannot
  be controlled.
• The internal heat of the reactor core (physical
  location of where the fuel rods, control rods are
  within a nuclear reactor) will heat up to such a
  degree that the whole system will melt. This is
  the actual meltdown. Examine Figure 13-8, all
  those things in the containment building
  basically overheat and melt.

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Meltdown (continued)

• The melting of the reactor core from the loss of
  coolant will accomplish several things
• melt away and destroy all the safety features.
• The melting reactor core will collapse into the
  remaining pool of water and will cause an
  explosion of steam.
• The worst case scenario of a meltdown is termed a
  China Syndrome.

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Nuclear Disasters

• There have been two major nuclear disasters to
  date
• 1979 Three-Mile Island in Pennsylvania
• Partial meltdown, no major release of radiation,
  no one got really hurt, but it scared the
  you-know-what out of the public
• 1986 Chernobyl, Ukraine (former USSR)
• Meltdown, conflagration and radiation killed
  100s of people directly
• The release of a radioactive cloud of fission
  products across much northern Central Europe
  forced the evacuation of 150,000 people
• Long-term affects on the population are still
  being monitored and increased cancer risk and
  birth defects are a major concern.

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Three Mile Island
Photo from Wikipedia, United States Department
of Energy
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Three-Mile Island

• Worst nuclear disaster in the US
• 25,000 people live within 5 miles of the plant
• The partial meltdown occurred from a loss of
  coolant (LOCA).
• Complicating factors associated with this
  disaster (Synopsis)
• Many safety features were not working properly
• The reactor core did melt, but the containment
  building that holds the reactor core never fully
  melted and the meltdown never breached the outer
  walls.

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Three-Mile Island (continued)

• No one was really hurt from the accident
• There was a release of radioactive cloud from the
  reactor.
• The public within a 10 mile radius was exposed to
  about 1 millirem, far less radiation then normal
  background exposure.
• The accident didnt result in a worst-case
  scenario, it actually was pretty minor
  considering what could have happened.
• Public perception of nuclear power, however,
  changed forever!
• There was a major loss of confidence in nuclear
  power in the country after Three-Mile Island.

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Chernobyl

• THE WORST NUCLEAR DISASTER, EVER
• The meltdown at Chernobyl (April 26, 1986) was a
  worst-case scenario and the molten reactor core
  and ensuing steam explosions breached the reactor
  vessel and contaminated the environment.
• Making matters even worse, was that the reaction
  was due to human error. A planned experiment to
  run the generator without coolant was conducted
  late at night. The experiment was run by a
  nightshift skeleton crew that didnt know what
  they were doing. The experiment was to see if
  they could generate enough power to fuel the
  safety systems without using external
  electricity.

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Chernobyl
library.thinkquest.org/.../fission/dangers.html
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Note the accumulation in Neighboring Belarus
From Wikipidia.org, Smithsonian Institution 1
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The World Finds Out

• The USSR didnt immediately admit to the
  accident. A Swedish nuclear plant started
  picking up high radiation levels. They shut down
  their plant thinking that they had a leak. Once
  the determined that there was no leak, they
  looked at the upper level wind patterns. Global
  attention then turned to the USSR as being the
  culprit for higher radiation levels. They
  finally admitted to it several days after the
  accident.

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Result of Meltdown

• 31 people died immediately, mostly firefighters
  exposed to the radiation and fire
• Residents had to be evacuated leaving behind all
  possessions and pets. In order for the
  evacuation to occur more quickly the USSR
  government told the citizens that the evacuation
  was only temporary (a lie). 135,000 had to be
  evacuated.
• The reactor was encased in a sarcophagus of
  concrete and steel. A barbed-wire fence now
  surrounds a 1000- square-mile exclusion zone
  around the reactor site.
• More than 4000 workers that participated in the
  cleanup have since died.
• Concerns of elevated cancer will be a concern for
  the area for the next 70 years!! However to date
  there has been no significant rise in leukemia
  and only a slight rise in thyroid cancer.
• Long term estimates from 140,000 475,000 cancer
  deaths worldwide from the accident.

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Synopsis of Three-Mile Island and Chernobyl

• The disasters were both related to human error
  and faulty designs. Also both disaster occurred
  late at night.
• From this it is easy to conclude that nuclear
  power is perfectly safe, IF
• Workers are not tired nor otherwise in a bad mood
• Everyone is properly trained and knows exactly
  what to do
• All gauges read correctly and all systems are
  working properly, never breaking down of needing
  repair
• Security is tight and security screening is 100
• No guerilla warfare or terrorism
• No natural or human disasters occur, e.g.
  earthquakes, tornadoes, plane crashes,
• So, you have nothing to worry about

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Nuclear Power Today?

• Energy Policy Act 2005 (EPACT)
• Section 1306, Credit for Production from Advanced
  Nuclear Power Facilities under Title XIII -
  Energy Policy Tax Incentives

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Dream or Delusion?

• Questions to think about (just think about them,
  you dont have to turn answers in or debate them)
• Is nuclear power the solution to our energy
  problems?
• Does the promise of cheap, clean energy outweigh
  the costs of a meltdown?
• Will public perception of nuclear energy ever
  change?
• Can we make nuclear energy safer?
• Where do you stand on nuclear energy?