Group Work 1.Should nuclear power capacity be increased or reduced? Why?

Announcements Get 3 scraps paper per person in addition to whiteboard and marker Standards retakes today 11–mn Last Exam 3 today–6 PM tomorrow Final (makeups) Tuesday 10:15–12:15

Nuclear Implications and Applications Chapter 34

Nuclear Power Source: Jim Zimmerlin, Diablo Canyon Power Plant, California

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.A sphere. B.A plate. C.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 A.spent fuel were reprocessed and reused. B.all reactors were shut down. C.reactors with higher “burn-up” were used. D.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 Passive cooling systems Melt-proof fuel pellets Higher-burnup design On-site fast reprocessing Fast neutron fission of non-fissile nuclei Accelerator-based systems

Group Work 2.What should be done with nuclear waste?

Stellar Fusion NASA photograph, Skylab, 10 December 1973

Think Question What sort of nucleus releases energy by fusion? A.Nuclei lighter than iron. B.Nuclei about as heavy as iron. C.Nuclei heavier than iron.

Fusion in the Sun Source: Seeds, Horizons: Exploring the Universe Net reaction: 4 p +  4 He + 2 e + + 2 + 2 

Fusion in Hotter Stars Source: Seeds, Horizons: Exploring the Universe Net reaction: 4 p +  4 He + 2 e + + 2 + 3 

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!

Nuclear Weapons

Fission Weapons Grable 15-kT yield artillery shell, Nevada Test Site, 25 May 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 U.S Department of Energy photo.

Fusion in Weapons Require high temperatures to bring nuclei together (thermonuclear) Heated by fission bomb “pit” 2 H + 3 H  4 He + n

Thermonuclear Device