nuclear reactor

• Nuclear energy


  The energy that exists within the nucleus of an atom
• Types of nuclear energy

  • Nuclear fission
  • Nuclear fusion

  
• Nuclear fission


  The splitting of a large nucleus, releasing HUGE amounts of energy

  
• Nuclear fusion


  The combining of smaller nuclei to form heavier nuclei, releasing HUGE amounts of energy

  
• How nuclear fission energy is produced

  1. Nuclear reactions in a nuclear power plant occur at a controlled, manageable pace and release energy slowly

  2. Heat is generated and used to boil water, creating steam

  3. The steam turns turbines which rotate electric generators, creating electricity

  4. Steam is released from the cooling towers

  
• Nuclear power


  • It is an extremely rich energy source
  • One gram of Uranium-235 delivers as much energy as 3.5 metric tons of coal
  • One in every 5 houses in the U.S. is supplied with nuclear energy
• Enrichment


  The process of increasing the fraction of 235U in natural uranium from 0.72% to 3-5% to enable a self-sustaining nuclear reaction

  
• How a nuclear fission reactor works

  1. Nuclear fission is used as a heat source to boil water

  2. The steam turns a turbine, which turns a generator

  3. Efficiency is limited by Carnot efficiency (about 30-40%)
• Nuclear reactor core


  • Contains the uranium fuel rods and control rods that absorb neutrons to control the reaction

  
• Fuel packaging


  Uranium is packaged in long rods, bundled into assemblies, to provide lots of surface area and allow the water coolant to carry away heat
• Control rods


  Absorb neutrons to control the rate of the nuclear reaction

  
• Types of nuclear waste

  • High-level waste
  • Transuranic waste
  • Low and mixed low-level waste
  • Uranium mill tailings
• High-level waste


  The most dangerous radioactive waste, including spent fuel from nuclear reactors and liquid/solid waste from plutonium production
• Transuranic waste


  Includes clothing, tools, and other materials contaminated with plutonium, neptunium, and other man-made elements heavier than uranium
• Low and mixed low-level waste

  Includes radioactive and hazardous wastes from hospitals, research institutions, and decommissioned power plants
• Uranium mill tailings


  Residues left from the extraction of uranium ore
• Fuel cycle options


  • Once-through cycle
  • Closed cycle
  • Mixed/hybrid cycle
• Once-through cycle


  • Store all of the fuel assembly as waste
• Closed cycle


  • 'Recycle' most of the fuel for reuse, store the rest
• Mixed/hybrid cycle


  • 'Recycle' some of the fuel
• Nuclear fuel


  Natural uranium is only 0.71% U-235, the main fissile fuel. It must be enriched to 3-5% U-235 to enable a self-sustaining reaction. After use, the fuel contains many new radioactive isotopes.

  
• Waste storage options


  • Spent fuel pool
  • Interim storage
  • Geological repository
  • Deep borehole
  • On-site storage
• Thorium


  • Thorium is mostly Th-232, which is not fissile but can be converted to the fissile U-233. Thorium reactors can be fast or thermal breeder reactors, and produce less long-lived radioactive waste.
• The Three Mile Island nuclear accident occurred


  1979
• The Chernobyl nuclear disaster occurred


  1986
• The Fukushima nuclear accident occurred following the Sendai earthquake and tsunami


  2011
• The Three Mile Island accident was the worst nuclear reactor accident in U.S. history, but had little environmental impact
• The Chernobyl disaster was caused by blatant disregard for safety and an inherently unstable reactor design, resulting in a major radioactive release and many deaths
• The Fukushima accident was caused by the Sendai earthquake and tsunami disabling the backup generators, leading to core meltdowns and hydrogen explosions