Nuclear level densities: Energy distribution of all the excited levels: challenge to our
Energy: The Nuclear Perspective - MIT ESPNuclear Energy Densities • Fission: The splitting of...
Transcript of Energy: The Nuclear Perspective - MIT ESPNuclear Energy Densities • Fission: The splitting of...
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Energy: The Nuclear Perspective
Derek Sutherland
MIT Department of Nuclear Science and EngineeringMIT Department of Physics
12 March 2011
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Nuclear Energy• What makes nuclear energy different from
other energies, such as fossil fuels like coal and oil?
• What is the physics of nuclear energy, and why do we wish to use it for energy production?
• Any questions you may have at the beginning of this lecture?
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Chemical Energy DensitiesChemistry
U = -e2/rDistance ~ 10-10 m
Order of Magnitude ~ eV
The maximum energy for any chemical reaction, which involves the rearrangement of
electrons, is on the order of electron-volts.
Energy Density ~ 30-40 MJ/kg
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E = mc2
Energy-Mass equivalence tells us that mass is able to be “converted” into energy.
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Nuclear Energy Densities• Fission: The splitting of heavy nuclei, normally with
the introduction of a thermalized neutron into U-235. ~ 88,000,000 MJ/kg
• Thermonuclear Fusion: Fusing of light nuclei, like heavy hydrogen deuterium and tritium, in an experimentally created stellar environment. ~576,000,000 MJ/kg
U = -e2/r
Distance ~ 10-15 m
Order of Magnitude ~ MeV ! A million times greater than chemical reactions
fundamentally.
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Huge Amounts of Energy• Obviously, the amount of energy from
nuclear reactions cannot be matched by any chemical reaction due to the fundamental length scales over which each interaction occurs.
• This large amount of energy, the plentiful amounts of fuel, and environmental considerations, are why we want to use it for energy production.
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Fission Power Plants• There are many fission power plants working
around the world today, with some countries, like France, having roughly 80% of their energy coming from them.
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Fission Safety• Present reactors have many redundant
passive safety features that form a negative feedback network, so that if something gets out of line, it drives the reactor to a lower power level and ultimate shutdown instead of a run away power increase, and meltdown.
• The storage of radioactive waste is still a long-term concern.
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Fusion Power Plants?• There are no working commercial fusion
power plants today, due to how much more complicated fusion is than fission to achieve here on Earth.
• Fission occurs at about room temperature with the right reactor set-up.
• Artificial (non-gravitational) fusion occurs at 100,000,000 degrees, in a complicated (and invisible) magnetic “bottle,” but first...
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Plasmas!• A plasma is a quasi-neutral gas of charged and neutral
particles which exhibits collective behavior.
• Occurs at relatively high temperatures, around 160,000 K for hydrogen for example.
• Since plasmas consists of charged particles, magnetic fields can have an effect on the trajectories of these particles per the Lorentz Force.
• Magnetic fields will be used to confine particles in a plasma, which want to expand as fast as they can to regain thermodynamic equilibrium with their surroundings, so we can get a large enough fusion power density.
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Natural Plasmas
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Fusion Reactions
Requires high pressures ~ 5 atms, high temperatures ~ 100,000,000 K, and confinement t ~ 3-4 seconds.
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Confinement • Confinement is really the most dynamic
area of study, which design is the best? Magnetic Confinement Schemes
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Other Confinement Schemes
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Summary of Nuclear Energy• Fission is currently the mode of nuclear
energy production, and probably will be the dominate method throughout the next century. Plenty of fuel to use; storage of waste is still a problem, but no greenhouse problems.
• Fusion is a promising energy, though much work is left to be done before becoming an industry. ITER is presently the leading project in the world for magnetic confinement.