Lecture 57: Conventional NRG

We Use as Variety of NRG Sources

  • Renewable/replenishable/inexhaustible
  • Hydro
  • Biomass NRG
  • Solar
  • Wind
  • Geothermal
  • Tidal
  • Chemical fuels (hydrogen)

Hydro, Nuclear, and Biomass are "ceonventional" NRG Alternatives

  • Fuelwood and other traditional biomass sources provide ~10% of the world's NRG, nuclear ~6.3, hydro ~2.2
  • Nuclear NRG and hydro each account for nearly 16\frac{1}{6} of the world's electricity generation
  • Canada relies heavily on hydro (60% hydro for electricity gen)
  • Each of these sources has benefits and drawbacks

Modern Hydro Uses 2 Approaches

  • Hydro uses the kinetic NRG of moving water to turn turbines and gen electricity
  • 2 approaches (the 1st is much more common)
  • Dams harness kinetic NRG by storing water in reservoirs and then releasing it "impounding approach"
  • Run-of-river generates NRG by diverting it without greatly impacting ecosystem
  • Diverts water from river, then returns it back into the chanel

Hydro is Clean and Renewable

  • Hydro has advantages over fossil fuels for electricity
  • It is renewable
  • It is clean (no CO2)
  • It is efficient: EROI is 10:1, as high as any modern day thing oil is only 5:1

It Takes NRG to Make NRG

  • One way to measure the relative efficiency of NRG sources is by calving EROI → NRG obtains/NRG invested
  • Different NRG sources have different EROI

Hydro Negative Impacts

  • Dams
  • Destroy habitats
  • Disrupts natural cycles of flooding and sedimentation
  • Causes thermal pollution that can eliminate fish pops
  • Block passage of fish, fragmenting the river and reducing biodiversity
  • Have geological impacts
  • Have other social and econ impacts on local communities

Nuclear Should Have Been the Next Wave NRG in the NRG Transition

  • Public concerns and the costs of addressing them have constrained the spread of nuclear
  • 20% of US electricity comes from nuclear sources
  • Canada gens 16% of its electricity with nuclear power
  • France receives 78% of its electricity from nuclear power
  • Public support in Japan decreased dramatically after Tohoku earthquake and tsunami in 2011

Nuclear Power Comes from Processed and Enriched Uranium

  • Nuclear reactor → Device in a nuclear power plant, in which nuclear chain reactions are initiated
  • Radioisotopes emit subatomic particles and high NRG radiation as they decay into lighter radioisotopes
  • Nuclear fuel cycle: production of fuel from mines, use in reactor, disposal of final product

Fission Releases Nuclear NRG

  • NRG that holds together protons and neutrons within the nucleus of an atom
  • Nuclear fission → Splitting apart of atomic nuclei

Breeder Reactors Make Better Use of Fuel but Have Some Safety Issues

  • Use U-238 which goes unused as a waste product in conventional fission
  • Canadian CANDU reactor
  • Makes better use of fuel, generates more power, produces less waste
  • CANDU uses "heavy" water instead of light water for cooling
  • Heavy water absorbs less waste neutrons which increases efficiency

Nuclear Power is Cleaner than Fossil Fuels

  • Avoids emitting CO2
  • Avoids health impacts of smog in air
  • Less dmg to landscape and less waste than coal mining
  • Better safety record than coal mines and fire plants

Safety and Cost are the Big Concerns for Nuclear Power

  • Drawbacks of nuclear power
  • Nuclear waste is radioactive
  • Disposal has not been addressed satisfactorily
  • Accidents can be catastrophic
  • Very small chance though
  • Enormously expensive to build, maintain, operate, and ensure the safety of nuclear facilities
  • Electricity is more expensive than from coal and other sources

Nuclear Power Poses Small Risks of Large Accidents

  • Meltdown
  • When coolant water drains from the reactor vessel, temperatures rise uncontrollably in the reactor core
  • Metal casements surrounding the uranium fuel rods can begin to melt
  • Radiation can be released
  • Chernobyl
  • Fukushima

Chernobyl Worst Nuclear Accident Ever

  • Explosion at the chernobyl plant
  • Almost matched in severity by fukushima
  • For 10 days, radiation escaped from the plant while crews tried to put out the fire
  • Soviet union evacuated 100k residents
  • Landscape around the plant is still contaminated
  • Killed 31 people directly and several thousand developed fatal cancers
  • To get rid of waste, geological isolation (bury it deep in the earth)

Cold Fusion Remains a Dream

  • Nuclear fusion → Forcing together nuclei of lightweight elements under extreme high temps and pressure
  • Scientists have not yet achieved "cold" fusion useable for commercial power gen
  • If we could control fusion, we could produce vast amounts of NRG from water

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