Nuclear Energy

• nuclear power generation


  a nonrenewable energy source
• Fission


  process of splitting an atom apart

  -Releases a lot of energy (radiation)

  -Have to harness the energy safely
• Nuclear Fuel


  -Uranium ore: deposit with a high concentration of uranium

  -Yellowcake: processed uranium ore

  -U isotopes (235U vs 238U) separated

  -centrifuges

  -separated to keep uranium 235
• Want the fuel enriched in 235U rel to 238U

  • Power plants 3-5% enrichment

  • Weapons- 90% enrichment
• Why is 235U needed?

  -Firing neutrons takes time and energy

  -Splitting 235U atoms starts a chain reaction

  --Chain reaction is controlled by control rods

  --Cooling system removes the heat energy by pumping water through the plant to create steam which is used for electricity
• Requires lots of water


  -4 million gal/yr in some plants

  -Water can be recycled once it is cooled by a cooling tower
• Nuclear Advantages


  1- Large US Reserve

  -Est 130+ yr supply assuming current production rate

  2- Reduce C emissions

  3- Decrease fossil fuel dependence

  4- Produces tremendous amounts of energy

  -1 kg of U produces 3 million times more energy than 1 kg of coal

  5- Good safety record***
• Current US Use


  - ~100 plants, ~20% of US electricity

  Use declining since 1996

  -Half the active plants will close by 2020

  -No new reactors ordered btwn 1978- ~2010

  --48% of the ones ordered before 1978 were never built
• Nuclear Disadvantages


  1- Nuclear electric price tripled between 1970-1990

  2- reactor safety

  3- Nuclear proliferation Iran: making electricity or making weapons?

  4- Nuclear waste disposal
• Radioactive Waste


  -Avg power plant creates 25-30 tons of waste per yr

  -2017: US has 71,000 tons of stored radioactive waste

  -Radiation levels vary, so safety protocols also vary
• Types of Nuclear Waste

  Low Level (LL) Waste


  low levels of radiation; usually have been exposed to radiation

  -Ex: tools that have been exposed to radiation

  -4 classes

  --Class A, B, C, and GTCC

  (A is the lowest levels of radiation and goes up from there)

  -GTCC = Intermediate Level Waste in Europe
• High Level (HL) Waste: high levels of radiation; natural radioactive

  -Main type from power plants/weapons research

  -Heavy shielding & deep burial

  -Globally we generate ~ 12,000 tons/yr


  1- Spent Nuclear Fuel: used up fuel cells from the power plant

  -Has to be changed out 3-4 times a year

  - ~20 tons/yr/plant

  2- Trans-uranic waste: highly dangerous from high levels of radiation and things in this category have a long half life of minimum 20 years

  -generated primarily during weapons research

  -Military use
• Q: What Do We Do with Radioactive Waste?

  Option 1- Store It

  -Want to ensure stability and safety
• LL Waste Sites


  Only 3 Low-Level nuclear waste sites in the US:

  1- Clive, Utah

  -Only accepts Class A

  2- Richland, Washington

  -Accepts Class A-C from 11 NW states

  3- Barnwell, South Carolina

  -Class A-C waste from the other 39 states

  -2008: closed it gates to all but 3 states
• HL Waste Sites


  Spent Nuclear Fuel

  -Yucca Mountain: US's 1st site for spent nuclear fuel

  -Supposed to open in 1985, still not started

  --Geologic concerns (faults, seismic activity)

  --Legal challenges: "not in my backyard effect"

  
  

  Trans-uranic Waste Fuel

  -Waste Isolation Pilot Plant (WIPP)

  --Carlsbad, NM

  -Only US site for trans-uranic waste disposal

  -20 yrs planning

  -1999-2006: over 5,000 shipments deposited
• Inside WIPP


  - ~ ½ mi underground, carved into 3,000 ft thick salt deposit

  -Containers cannot be high-temperature, cannot contain fluids, and must be ventilated to prevent explosion
• Long-Term Plans at WIPP

  -Site expected to be full by 2070

  -Monitored for safety until 2170

  -Marked as off-limits for drilling, excavation, & development until 12,170 (!)
• Other Storage Ideas


  1- Dump in the ocean

  2- Put in subduction zones

  3- Launch into space
• Option 2- Use It

  Transmutation: take something worthless and turn it into something useful

  -Big in 1970s until banned in the US

  -Currently being re-visited, esp in Europe
• Transmutation


  -Some new reactors capable of using nuclear waste as fuel

  -Hard since they have to function with little U-235

  -241Am used for smoke detectors

  -137Cs used for food irradiation
• Radiation Levels & Safety

  Lots of units, easy to get confused: Curies, Becquerels, Grays, Rads, Sieverts, etc

  
  

  -Rem: how likely it will cause biological problems
• Background Levels


  Annual exposure from natural sources in millirems (mrem):

  -Cosmic rays- 30

  -Radon- 95

  -Medical- 100

  -Fallout- 4

  -Terrestrial- 55

  Total ~ 300 mrem

  (= 0.3 rem)
• How Much is Safe/Unsafe?

  (per episode of exposure)

  -< 5 rem/yr: no problems

  -5-20 rem: possible long-term problems

  -20-100 rem: mild radiation sickness

  -200+ rem: hair loss, 1/3 chance of death

  -600+ rem: 100% fatality rate w/in 14 days
• Contamination


  -108+ sites in the US are considered unsafe due to radioactive contaminants

  -Accidents, mismanagement, unsecure storage
• Case Study


  -Three Mile island

  -PA 1979- partial core meltdown

  -No serious radiation release reported (still debated)
• Case Study


  -Chernobyl 1986

  -Fallout 30x > than the bombs dropped on Japan

  -336,000 people permanently evacuated

  -19 mile exclusion zone still exists