Copyright 2007 – John Sayles Background: Historical View of Energy Use  Pre-industrial man used very little energy  Modern man needs HUGE amounts of energy –so where does it come from? –

Copyright 2007 – John Sayles Background: Energy Sources  Most energy on Earth is ultimately nuclear –So nuclear is NOT unnatural –From nuclear fusion in the Sun  fossil fuels (coal, oil, natural gases)  solar  hydroelectric  wind –Nuclear energy – man-made  fission  fusion

Copyright 2007 – John Sayles Nuclear Fission  Same reaction as in atom bomb, only controlled  U n  U-236 * + 3n   U n  U-236 *  2 FP’s  + ENERGY + 3n 

The Fission Chain Reaction  nuclear-fission_en.jar nuclear-fission_en.jar  Z4 Z4 Z4 Copyright 2007 – John Sayles

Fission Reactor Components  Fuel rods  Control rods  Moderator  Coolant  Turbine  Generator  Containment

Copyright 2007 – John Sayles Fuel Rods  Either U-235 (natural) or Pu-239 (man-made)  Approximately 3% U-235, 97% U-238  Fuel pellets are stacked in alloy tube –cladding is first level of containment  Reactor core contains many fuel rods –all shooting neutrons at each other –1 fission  3 fissions  9 fissions  27 fission

Copyright 2007 – John Sayles

Control Rods  Control rods are interspersed with fuel rods  Control rods contain neutron absorbing material (silver, indium, boron)  The rate of the process is controlled by raising and lowering the control rods  When 2 of every 3 neutrons is absorbed, the reaction is critical –running at a steady rate

Copyright 2007 – John Sayles Control Rods

Copyright 2007 – John Sayles

Moderator  Material that slows down (thermalizes) neutrons so they can be captured by U-235  Water is most common moderator –good coolant, too –good coolant, too  Graphite was used at Chernobyl –flammable   Boron sometimes added to water  In subs, bubbles are used to fine-tune moderation

Copyright 2007 – John Sayles Coolant  Carries energy from core to steam turbine  Keeps fuel from melting  Meltdown is the ultimate nuclear disaster –coolant failure –fuel melts and falls to bottom –forms supercritical mass that goes bananas –tremendous heat burns through all containment –China Syndrome

Copyright 2007 – John Sayles

Turbine and Generator  Expansion of steam spins turbine  Turbine spins generator producing electricity –an electric motor in reverse  motion in, electricity out  Same as turbine and generator in a fossil fuel power plant or hydro-electric power plant

Nuclear Reactor Copyright 2007 – John Sayles

Advantages of Nuclear Fission  We know how to do it  Plenty of fuel  Get LOTS of energy  No greenhouse gases

Copyright 2007 – John Sayles Nuclear Fusion and Nuclear Energy Reactor Design Present and Future

Copyright 2007 – John Sayles Disadvantages of Nuclear Fission  Fuel problems –must mine uranium ore –or build a breeder reactor (which work too well?)  Fuel must be enriched –VERY difficult and expensive  NASTY waste products –mix of short half-life and long half-life radioisotopes  The reaction can get away from you! –1  3  9  27  81  243  729  2187  6561  … –Meltdown

Do we want to build more (fission) nuclear reactors? Copyright 2007 – John Sayles

Nuclear Fusion  Use tremendous heat to fuse two small nuclei together (  NOT a chain reaction –

Copyright 2007 – John Sayles Making Tritium fuel  The tritium is made on the fly

Copyright 2007 – John Sayles Nuclear Fusion Weapons  Use an Atom Bomb (fission) as the detonator in a Hydrogen Bomb

Copyright 2007 – John Sayles Nuclear Fusion  We know how to make fusion bombs –use fission bomb to supply heat and compression –no need to control the reaction  but that’s not an issue with fusion anyway  We don’t know how to make a fusion reactor –We have not yet figured out how to reach the break-even point  requires more energy to start than you get out –The containment challenge

Copyright 2007 – John Sayles Pro’s and Con’s of Nuclear Fusion  Most energy per gram of ANY process  Endless supply of safe fuel (several options)  No nasty products  Can’t get out of hand But …  We don’t know how to do it