Overview of Chapter

• Began with "cartoon of a reactor"
  • fuel elements (pellets of enriched Uranium)
  • moderator (graphite, water) -- to slow the neutrons
  • control rods (cadmium, typically)
    • to absorb neutrons and slow the rate of fusion
    • can vary power production by withdrawing or inserting control rods
    • can cause emergency shut down by inserting rods ("scramming")
      • on problem at Chernobyl-- reactor overheated, cracked the graphite, and the holes for the control rods were no longer available = total loss of control.
  • this is the reactor assembly-- the part that gets hot (it is enclosed in a steel shell)
  • the rest of the plant is almost same as a coal fired plant
    • (exception: nuclear plant indirectly transfers heat to the water to keep the water from passing through the radioactive area in the reactor core.)
    • heat is used to generate steam
    • steam runs turbine which runs a generator
    • turbine and spent steam has heat that must be lost
  • largest part of a nuclear reactor is the heat exchanger or cooling tower.

• Nuclear Power is an important economic force
  • __% of US electricity (25%?)
  • __% in France, for example (75%)
• Economic Reasons
  • fuel and transportation costs less than coal
  • typically fewer, larger power plants
  • no fossil fuels-- no CO₂, SO₂, NO_x
• Objective Evaluations
  • sometimes hard to come by
• Compare a Coal vs. a Nuclear Electrical power Plant
  • a typical coal plant releases more radioactivity
    • traces of heavy elements in fly ash
  • both are similar beyond the heat source
    • heat boils water
    • steam drives turbines
    • turbines drive electrical generators
    • heat is exchanged with surroundings
      • river or lake water
      • large air cooled heat exchangers
  • can build small/medium/large coal fired generators
  • generally impractical to make small nuclear plants
    • can make them small
    • (submarines and aircraft carriers)
    • but not cheap

• tied into national power grids
  • critical for large reactors-- major power supplier
    • go off line, perhaps unexpectedly
    • go off line to refuel or upgrade
      • often weeks, months, years

• Downside of Nuclear Power Plants
  • fear of radiation (NIMBY)
    • hard to get sites approved
    • last new US facility: 19xx
  • fear of catastrophic failure
    • Chernobyl and 3Mi Island
    • Kursk and other seagoing disasters
    • US design: containment vessels
    • coal plant accidents more common
      • but damage is local, short term
  • fear of small leakage
    • system closed, nothing should escape
  • intense scrutiny
  • needs more highly trained technical staff

• 1. failure modes and risk assessment
• 2. spent fuel
• 3. actual economics
• 4. lifetime of a nuclear plant

Spent Fuel

• The fuel is enriched uranium
• 0.7% ²³⁵U upgraded to, say, 25%
• U-ore is relatively cheap and abundant
• enrichment is expensive
• Fuel would be to supply power for decades
  • but reaction products accumulate
  • they collect and divert needed neutrons
  • fuel is useless after, perhaps, 25% of ²³⁵U is used
• Must refuel
  • shut down and remove old fuel
  • install new fuel and restart
• Used Fuel
  • can be chemically processed
  • impurities are not U, chemically separated
  • fuel is still enriched 235U
• Processing
  • difficult since the fuel is highly radioactive
  • processing is by machinery, remove control
  • serious problems if any leakage
  • costly process
• plants like Fernault (near Cincinnati) disasters
  • economically worse than fresh Uranium
  • environmental disasters

Spent Fuel

• now mostly just stored for disposal
• too radioactive for routine disposal
• (treatment residues also need storage)

• Storage Facilities
  • None- for high activity wastes
    • now stored on site at each reactor facility
    • (temporary storage, 20-30 years now)
  • Need secure location for thousands of years
    • no ground water
    • no earthquakes
    • no human habitation for time > human society to date
  • Underground, sealed
    • encapsulate wastes (e.g., in glass or concrete)
    • Yucca Mountain ?

Relicensing of Nuclear Reactors

• Most were designed for 30-40 year life
• design life, in part, period before failure is likely
• Most were built in the 60's
• Most nearing the end of their design period
  • Now, push to grant 10-20 year extensions
  • Some say, automatically
  • (Also true of Aircraft-- many commercial airliners are 30-40 years old.)
  • Continuous testing, replacement of critical components

Shutting down and Dismantling

• No real history of decommissioning
  • some Naval reactors simply deep sixed
• Core components radioactive for 1000 years
• probably costs $0.5-1 billion to decommission
  • costs less to refurbish and run