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Nuclear Implications and Applications. Nuclear Power. Diablo Canyon Power Plant, California. Source: Jim Zimmerlin, http://www.zimfamilycockers.com/DiabloCanyon.html. Nuclear Power. Nuclear fission reactions release heat (kinetic energy of products)
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Nuclear Power Diablo Canyon Power Plant, California Source: Jim Zimmerlin, http://www.zimfamilycockers.com/DiabloCanyon.html
Nuclear Power • Nuclear fission reactions release heat (kinetic energy of products) • Heat boils water, powers turbine to generate electricity • No greenhouse gas production
Fission Chain Reaction Source: Griffith
Criticality • Reaction self-sustaining if each fission on average induces another • Critical mass depends on geometry, moderation, reflection, many other factors
Poll Question Which shape of fission fuel will be the most likely to reach criticality? • A sphere. • A plate. • A long, thin cylinder.
Fissile Nuclei • Required for reactors and bombs • Fission started by absorption of thermal neutrons • Only fissile nuclei are U-233, U-235, and Pu-239 • U-235 is less than 1% of natural uranium (rest is U-238)
Plutonium Breeding Source: Griffith
Breeder Reactors • Transmute U-238 to Pu-239 or Th-232 to U-233 • Increase amount of usable fuel
Nuclear Waste Source: Savannah River Site
Nuclear Fuel Cycle • Fission chain reaction produces fission products and neutron capture products • Certain fission products absorb neutrons • Fuel becomes unusable after ~1% burnup • Must be reprocessed or discarded
Poll Question The amount of nuclear waste generated would be reduced if • spent fuel were reprocessed and reused. • all reactors were shut down. • reactors with higher “burn-up” were used. • any of these.
Spent Fuel Hazards Source: Cohen, B. L. Rev. Mod. Phys. 1977, 49, 1–20.
Reprocessing • Recover U, Pu from spent fuel • Discard fission product waste • Possibility of U, Pu diversion
Advanced Reactor Designs • Evaporating moderator • Melt-proof fuel pellets • Higher-burnup design • On-site rapid reprocessing • Fast neutron fission of non-fissile nuclei • Accelerator-based systems
Stellar Fusion NASA photograph, Skylab, 10 December 1973
Think Question What sort of nucleus releases energy by fusion? • Nuclei lighter than iron. • Nuclei about as heavy as iron. • Nuclei heavier than iron.
Fusion in the Sun Source: Seeds, Horizons: Exploring the Universe Net reaction: 4 p+ 4He + 2 e+ + 2 n+ 2 g
Fusion in Hotter Stars Source: Seeds, Horizons: Exploring the Universe Net reaction: 4 p+ 4He + 2 e+ + 2 n+ 3 g
Fusion Life of Massive Stars • Massive star’s hot core fuses atoms to ever-higher masses • Greater nuclear charges require higher temperatures, pressures • Less energy per nucleon from fusing massive nuclei • Fusion energy exhausted at iron
Fusion Death by Supernova • Iron core does not produce energy to resist gravitational collapse of star • High temperature and pressure in shock wave creates more massive nuclei • Some products scattered by explosion All Fe, Cu, W, I, Ag, Au, Pb, U, etc. were released by supernovas!
Fission Weapons Grable 15-kT yield artillery shell, Nevada Test Site, 25 May 1953. U.S. Department of Energy photo.
Gun Device (“Little Boy”) Source: Griffith
Implosion Device (“Fat Man”) Source: Griffith
Fusion Weapons Dakota 1.1 MT shot, Enewetak, 25 June 1956. U.S Department of Energy photo.
Fusion in Weapons • Require high temperatures to bring nuclei together (thermonuclear) • Heated by fission bomb “pit” 2H + 3H 4He + n