Nuclear Energy

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Nuclear Energy
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Nuclear Energy

• New form of energy to be introduced since the
  beginning of civilization
• After Chernobyl and Three mile accidents,
  construction of new plants is opposed by people
  in many countries
• N.E. accounted for about 16 of world's
  electricity, and 19 (1998)of US

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Nuclear Shares of National Electricity
Generation, 1998
Source eia
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US Nuclear Energy
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Atomic Structure

• Matter is made up of little building blocks
  called atoms
• Atoms are made up of smaller units called
  protons, neutrons and electrons
• Chemical Vs Nuclear Reaction

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Periodic Table

• Elements are listed in a periodic table by atomic
  number
• Example

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Atomic Mass and Charge
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Radioactivity

• The nuclei of most atoms are stable.
• Some nuclei are unstable and emit radiation to
  gain stability. These nuclei are said to be
  radioactive.

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Three Common Modes of Decay

• Alpha Particle Emission
• Alpha particles are the nuclei of fast moving
  helium atoms.
• Beta Particle Emission
• Beta particles are fast moving electrons
• Gamma Ray Emission
• Gamma rays are electromagnetic radiation of very
  high frequencies.

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Writing Nuclear Reactions-1
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Writing Nuclear Reactions-2
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Writing Nuclear Reactions-3
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Writing Nuclear Reactions-4
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Summary

• In all nuclear reactions, the sum of the mass
  numbers on the left side of the equation equals
  the sum of the mass numbers on the right side of
  the equation. The same is true for the atomic
  numbers.

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Principles

• U235 n1 --------gt Ba144 Kr89 3n1
• 85 of the fission energy is released as kinetic
  energy
• This kinetic energy is passed into the
  surroundings and heat builds up.
• This heat is used to generate steam in a nuclear
  plant.

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Binding Energy

• Binding energy of
• an atom is minimum amount of energy required to
  break up its nucleus into individual components

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Main Components of a Reactor

• Fuel, usually 235U at 3-4 concentration
• Control System
• Moderator
• Cooling system
• Radiative shield

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Controlling the Reaction

• Material (like Boron or Cadmium)
• High ability to absorb neutrons and thereby
  control the reaction
• Three possible conditions
• Critical - fission at constant rate
• Subcritical - decreasing rate
• Supercritical - increasing rate

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Chain Reaction
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Moderator

• We need to control the speed of the neutrons to
  control a nuclear reactor, this is what a
  moderator does.
• A moderator sits between the fuel rods and slows
  the neutrons so the reaction can be sustained.
  (they are fast so could pass the other rods)
• Water, heavy water, graphite are or have been
  used as moderators

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Moderator

• Problems
• Graphite can burn at high temperatures
• In Built Protection
• Steam is a poor moderator, more steam less
  moderated neutrons the reaction slows down
• All US nuclear reactors have water as the
  moderator

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Nuclear Power ?

• http//www.pbs.org/wgbh/pages/frontline/shows/reac
  tion/interact/getclose.html

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Fissionable Uranium

• Only one naturally occurring fissionable isotope,
  U - 235
• Naturally occurring Isotopes of Uranium of
  Total
• U - 234
  0.006
• U - 235
  0.714
• U - 238 99.280

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Man-made fissionable Isotopes

• Two man-made fissionable isotopes
• U - 233 and Pu - 239
• U - 233 can be made from Th - 232
• Pu - 239 from U - 238
• Therefore, Uranium and Thorium are the sources of
  our fission energy fuels

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Breeding Cycle
U-238 and Th-232 can be converted to fissionable
material. Therefore, the U-238 and Th-232 are
called "fertile"
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Breeder Reactors

• Normally U238 (97 of the mined uranium) is of no
  use in the nuclear industry but with a neutron
  can form plutonium Pu239.
• This can be used as a nuclear fuel or worse in
  nuclear weapons!
• Reactor designed to maximize generation of Pu239
  are called breeder reactors

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Storage of Fuel Rods

• Currently in the US rods are stored in deep water
  pools at the reactor site. However, many sites
  are getting close to capacity.
• Reprocessing separates the fuel from the rod,
  plutonium is removed (fuel or bomb material),
  unused U235 is removed and reused
• Long term solution (US) is storage at Yucca
  mountain

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Nuclear Reactors in the US
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Three Mile Island Incident

• Three Mile Island in 1979, caused an average
  exposure of 1.5 millirem to people within 50
  miles of the plantabout what they'd get from a
  cross-country airplane flight.

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Nuclear Time Line

• 1945 First atom bomb test Little Boy dropped
  on Hiroshima and Fat Man on Nagasaki
• 1951 First generation of electricity from nuclear
  power
• 1953 Atoms for Peace
• 1957 First Full Scale Reactor Shippingport PA,
  (60 MW)
• 1960 Nuclear powered weather stations and sea
  bouys

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• 1973 US orders 41 nuclear power plants
• 1979 Three Mile Island
• 1986 100th nuclear plant in the US
• 1986 Chernobyl
• 1988 US electricity demand is 150 of 1973

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Fatalities
Fatality Comparison Statistics US Coal Mining
1931-1995 33,134 Oil / Gas Industry 1992-1995 7
19 Chemical Manufacturing 1992-1995 201 US
Automobile 1899-1995 2,903,036 Smoking per
year 419,000 US Civil Aviation 1938-present 54,0
00 US Nuclear Power Historical 0
Source http//www.pbs.org/wgbh/pages/frontline/s
hows/reaction/maps/ chart1.html
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Nuclear Power

• No Carbon dioxide
• No SOx or NOx or particulates
• Small quantities of waste
• 32 Countries have Nuclear Power
• 20 of the US electricity comes from Nuclear
  Power
• Equivalent to 100 million barrels of oil per
  year
• Security of fuel supply
• Can use nuclear weapons as fuel sources
• SAFE ?!

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France and Nuclear Power

• "no oil, no gas, no coal, no choice.
• France has 56 working nuclear plants, generating
  76 of her electricity.

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Three Mile Island (1979)

• http//www.pbs.org/wgbh/pages/frontline/shows/reac
  tion/readings/tmi.html

• A valve was closed preventing water from
  reaching the steam generator
• Emergency feed water did not enter the reactor
  (another closed valve)
• Pressure in the reactor increased, a safety
  valve opened but stayed open
• Lower pressure and high temperature boiled the
  water
• Radiation escaped with the steam
• Loss of coolant activated an emergency system of
  water injection
• It was stopped prematurely due to a faulty
  reading that the coolant level was restored.
• Partial meltdown occurred.

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Chernobyl (1986)

• An unauthorized experiment went very badly.
• Several safety features were deliberately turned
  off.
• Power was reduced to 1 and then increased too
  quickly (moderator rods removed)
• The heat vaporized the cooling water and blew off
  the roof.

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Chernobyl (1986)

• A meltdown occurred
• There was an explosion from hydrogen from the hot
  metals reacting with the steam
• The graphite rods burned.
• 31 people were killed
• 135,000 people evacuated (a week after)
• Numerous others impacted by radiation

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Chernobyl

• Chernobyl, 80 miles north of Kiev in the Ukraine,
  
• A toxic radioactive explosion took place
  immediately killing 31 people, hospitalizing
  another 150 for severe radiation sickness, and
  evacuating approximately 130,000 people from a
  30-square-kilometer zone around the atomic plant.

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Chernobyl

• Most of the world did not learn of the accident
  until two days later
• Researchers in Sweden detected radiation over a
  nuclear power plant there.
• Radiation levels reached 100,000 times the normal
  amount in Poland
• 10,000 times the normal amount in Scotland.

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Reactor
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Reactor Damage
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Improve Nuclear Safety in FSU65 Reactors at 20
Nuclear Power Plants in 8 Countries
Problems Inadequate operating procedures and
training Design deficiencies Lack of
infrastructure to sustain safe
operation Inadequate nuclear regulatory authority
Percent of Electricity from Nuclear Power
80
83
60
45
44
42
41
37
40
20
13
20
0
Russia
Czech Republic
Ukraine
Bulgaria
Hungary
Slovakia
Lithuania
Armenia
IG98040040.23
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Radioactive Waste

• 99.9 of fuel ends up as radioactive waste
• Must be stored until radioactivity is no longer
  harmful
• Cumulative wastes produced so far
• 1965 - 2,000 tons 1975 - 5,000 tons
• Close to 85,000 tons of spent fuel in holding
  tanks by 1990

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Nuclear Waste

• Almost 100 million gallons of liquid defense
  wastes
• 95 of the spent fuel rods is U-235, U-238,
  Pu-239. Therefore, spent fuel rods are waste only
  by government decree

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Radioactive Waste
There is low level and high level waste.
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Nuclear Weapons

• Often use Plutonium
• Require a critical mass, below which a nuclear
  explosion will not occur.
• 8 kg of plutonium is the critical mass
• India and Pakistan are the latest to join the
  nuclear club

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Natural vs. Man-Made
Natural background radiation is nearly 85 percent
of our total annual exposure. Where does the
rest come from? You probably get about 50
millirem a year from X-rays and radioactive
materials used for medical diagnosis and therapy.
Another 10 millirem come from consumer products,
like your household smoke detector, color
television set, and luminous dial clock.
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Radiation and Rems

• Radiation is measured in units called rem or
  millirem
• An average person is exposed to 360 millirem
  each year.
• Natural background radiation 85

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Natural (Background) and Man-Made Radiation
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Illustration of the concept of half-life of
radioactive isotopes
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Half Lives
Half life 0.7 / Decay Constant
As the unstable radioactive elements decay they
leave behind stable atoms. When 50 of the
original radioactive elements are gone then the
half live is reached.
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Half Lives

• Uranium235 0.7 x 109 YEARS
• Plutonium 239 24,000 YEARS
• Radon 222 3.8 days
• Polonium 218 3 min
• Thus, radioactive waste storage will be a problem
  for a very long time!

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U.S.Legislation on Radiation Exposure
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Acute Biological Effects of Exposure to Radiation
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Problems with Nuclear Energy

• After 30 years of nuclear energy use there is no
  official plan for their disposal
• Radioisotope Pu-239, for example, with half-life
  of 24,000 years is dangerous for quarter of a
  million years, or 12,000 generations
• HLW accounts for less than 1 of the volume of
  all the radioactive wastes in the US but for 95
  of the radioactivity

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Problems with Nuclear Power

• Public perception
• What to do with the waste
• Nuclear weapons from nuclear reactors
• Chernobyl
• Cancer ?!

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Nuclear Fusion
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Heating Requirements for Fusion
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Main Reaction
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Challenges-Nuclear Fusion

• Heating the mixture of reactants to a very high
  temperature to overcome the repulsive forces
  between positively charged nuclei.
• Thermonuclear reaction
• Compressing the mixture to a very high density so
  that the probability of among the nuclei can be
  high.
• Confinement problem

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Challenges

• Keeping the reaction mixtures together long
  enough for the fusion reaction to produce energy
  that is greater than the energy put in to heat
  and compress.
• Confinement problem