Nuclear Energy

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Fossil Fuel vs. Nuclear Fuel Fossil Fuel: Provides energy by

chemical reactions (No change in atoms)

Uranium: There is a change in structure of atom (energy release I given in terms of binding energies)

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Atom Atomic Number = # of

protons (P) Mass Number =# neutrons

+ protons (A=n+P) The nucleus of an atom of

carbon has 6 protons and 8 neutrons

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Binding Energy per Nucleon Fission (breaking up the heavy atoms) Fusion (fusing the light atoms)

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Isotopes Isotopes are unstable atoms having the

same number of protons, but different number of neutrons (different A and same P).

U-235 has 92 protons and 143 neutrons, U-236 has 92 protons and 144 neutrons. Normal hydrogen has 1 proton and 0 neutron, deuterium has 1 proton and 1 neutron, tritium has 1 proton and 2 neutrons

Nomenclature

( number of protons) 92U235 (atomic mass number)

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Isotopes

Isotopes are chemically identical but physically are very different

Isotopes are radioactive Isotopes are rare

(0.05%) H (99.28%) U

(0.15%) H (0.714%) U

(99.80%) H (0.006%) U

31

23892

21

23592

11

23492

Fission

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History 1896 – Antone Bequerel (France)

uranium salt darkened photographic plates even in total dark

1900 – Maria Curie (Poland)radioactivity consisted of three components

1911 - Ernest Rutherford (New Zealand)first planetary model of atom of hydrogen

1945 - First atomic explosionAlamogordo, New Mexico, July 16

1945 – Fist Atomic BombHiroshima, August 6

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U.S. Nuclear Industry 103 Power plants as of 1996

providing 20 % of the US electric power 90% are in Northeast and Midwest Oil Embargo – 1973 No new plants since - 1976 Accident at Three Miles Island - 1979 Operating licenses for many power plants

will expire in the next ten years.

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Nuclear Plants

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Fission

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Basic Physics Reactions

U-235 + n U-236Many ways that U-236 can decompose, e.g. U-236 Ba-137 + Kr-97 + 2n + energy U-236 Xe-140 + Sr-94 + 2n + energy

Energy is in the form of gamma-rays

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Nuclear Energy Energy E= m. C2

Nuclear energy from 1-kg of uranium = Chemical energy from 2000 tons (2 million kg) of coal

Mass is usually expressed as atomic mass unit1 amu= 1/12 of the mass of C-12 atom=1.66x10-7 kg

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Uranium Uranium ore is only .7% U-235, rest is U-238 U-235 must be enriched to 3% before it can be

used as nuclear fuel. Only U-235 is fissionable (fertile). If neutron

not acquired by U-235, it will be acquired by U-238

The slower the neutron, the more chance that U-235 will acquire it.

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Fuel Cycle

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Nuclear Power Plant

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Basic Components of Conventional Nuclear Reactors

Fuel Rods (3% U-235, 97% U-238)

Control Rods (Boron/ Cadmium)

B-10 + n Li-7 + He-4

Moderator (Graphite / Water) If neutron is too fast short contact time If neutron is too slow not enough energy

Coolant (Water / Sodium)

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Types of Reactors Coolant

LW, HW, Gas, Liquid Metals Moderators

Water, Graphite Pressure

Low Pressure (LWR) Pressurized (BWR)

Fuel Uranium-235 Plutonium-239 MOX

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Classification Light Water Reactors Pressurized Water Reactors Boiling Water Reactors High Temperature Gas Cooled

Reactors Fast Breeder Reactors Pebble Bed Modular Reactors

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Breeder Reactors Convert Non-fissionable U-238 to

fissionable Pu-239 Can use either U-235 or Pu-239

U-238 + n Np-239 Pu-239 Mainly in Europe and Russia Must use sodium (instead of water) as

coolant/moderator Does not slow down neutron (as water does) Much higher heat capacity Disadvantages are:

Sodium is highly explosive Plutonium is bomb-grade quality

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Breeder Reactors

238U + n 239U 239Np 239Puuranium-238 + neutron plutonium-239

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Pebble Bed Reactors

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Nuclear Safety Nuclear Regulatory Commission is in

charge of all nuclear safety issues Major factors are:

Design Steel-reinforced containment must withstand severe

hurricanes and earthquakes, and direct hit by a large jetliner

Multiple backup systems must be in place Automatic shutdown in case of loss of coolant

Training TMI accident was attributed to deficient personnel

training Clear operating procedures

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Three Miles Island (Harrisburg, PA)

Near meltdown in March 28, 1979 Over 3 billion dollars in cleaning

costs Two million people (within 50

miles radius) were exposed to low level radiation (no statistical way of determining how many will die from cancer)

Nuclear Industry created a watchdog agency, Institute for Nuclear Power Operation (INPO)

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Chernobyl, Ukraine April 26, 1986 explosion followed by fire in

reactor#4 Fire extinguished by dropping 5000 tons of sand and boron. Eventually encased in 300,000 tons of concrete. Remaining Chernobyl reactors decommissioned in 1999.

Why? RBK-1000 design unstable at low powers Poor training Inadequate containment Reactor was used as a research facility as well as power

production

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Chernobyl – Consequences 8000 have already died. No estimate on the ultimate

death toll from the accident 160,000 people were forced to leave their homes 1500 acres of surrounding forest died instantly; 5 million

acres of prime farmland were contaminated; 20% of farmland and 15% of the Belarus forests cannot be used over 100 years.

Rate of thyroid cancer in Ukrainian children have climbed 30-fold.

Higher rate of spontaneous abortion by Belarusian women Wild life is blooming. Field mice are undergoing

evolutionary changes that took other species 10 million years.

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Nuclear Fusion

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Hydrogen Isotopes

Abundance:Normal 99.8%

Deuterium .015%

Tritium .005%

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Fusion vs. Fission

Fusion:D + T He + n + energy (E=4x1011 BTU/kg deuterium)

Fission

U + n Kr + Ba +3n + energy (E=7x1010 BTU/kg U-235)

Coal (recall)C+O2 CO2+ energy (E=3.3x104 BTU/kg coal)

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Fusion

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Fusion Reactions D+D He-3 + 3.3 MeV (79 MJ/g)

@ 400 million oC

D+T He-4 + 17.6 MeV (331 MJ/g) @ 45 million oC

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Breakeven Point

Where plasma can be raised at sufficiently high temperature and particle density, and long enough so the rate of energy production exceeds the rate of energy required for sustained reaction.

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Challenges Ignition

Very high temperatures to overcome repulsive forces of positively charged nuclei

Confinement Very high pressures to increase probability

of collision And for times long enough for producing

energy more than that required for heating and compression (sustained reaction)

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Confinement No solid vessel Magnetic confinement Inertial confinement (laser)

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Magnetic Confinement