APES 6.6 Nuclear Power

Enduring Understanding:

• Humans use energy from a variety of sources, resulting in positive and negative consequences.

Learning Objective:

• Describe the use of nuclear energy in power generation.
• Describe the effects of the use of nuclear energy on the environment.

Essential Knowledge:

• Nuclear power is generated through fission, where atoms of Uranium-235, which are stored in fuel rods, are split into smaller parts after being struck by a neutron.  Nuclear fission releases a large amount of heat, which is used to generate steam, which powers a turbine and generates electricity.
• Radioactivity occurs when the nucleus of a radioactive isotope loses energy by emitting radiation.
• Uranium-235 remains radioactive for a long time, which leads to the problems associated with the disposal of nuclear waste.
• Nuclear power generation is a nonrenewable energy source.  Nuclear power is considered a cleaner energy source because it does not produce air pollutants, but it does release thermal pollution and hazardous solid waste.
• Three Mile Island, Chernobyl, and Fukushima are three cases where accidents or natural disasters led to the release of radiation.  These releases have had a short-and long-term impacts on the environment.
• A radioactive element’s half-life can be used to calculate a variety of things, including the rate of decay and the radioactivity level at specific points in time.

Process

• Uses ore of Uranium-235
• U-235 is placed into fuel rods with water
• The rods are stuck by an outside neutron
• The process a splitting a U-235 atom releases a large amount of heat
• Heat makes water boil and turn into steam
• The steam turns a turbine
• The turbine powers a generator where mechanical energy turns into electrical
• The steam cools afterward and can be used again
• Heat is released

Fission

• An incident neutron is shot at a very high speed towards a U-235 nucleus
• The nucleus is ripped apart, releasing energy and high speed neutrons
• This causes a chain reaction where those runaway neutrons split other nuclei, and so on

Advantages and Disadvantages

Benefits

• There are no harmful gas emissions
• It produces a high amount of energy
• It does not cost much after initial construction
• There is no mining for fossil fuels involved
• There are no primary or secondary air pollutants

Drawbacks

• The hazardous waste produced is present for a very long time
• There is thermal pollution
• The initial cost can be billions
• There is mining involved for construction and Uranium
  • Mining Uranium is also an extremely dangerous process
• It is nonrenewable
• There are rare but notable chances of nuclear meltdown

Environmental Concerns

Radioactive Energy

• Nuclear energy comes from breaking down U-235
• The isotope is always losing energy, but this energy is radioactive and therefore very dangerous
• Once U-235 has broken down, it remains radioactive but can no longer be used
• It gathers neutrons, becoming heavier like plutonium
• It will remain radioactive for up to 24,000 years (10 half lives)
• There is nothing we can do with it except store it safely and hope no radiation leaks out

Half-Life

• Half-life is a measure of time for half of an atomic nucleus to decay
• The nucleus will decay into another atom, emitting radiation
• Ten half-lives is generally when a radioactive atom becomes safe

Storage

• We have to find a place to store the material for a long time
• Often times we store the waste on site, deep underground
• More sites means more chances of radioactivity leaking into the environment
• A federal site called Yucca Mountain, Nevada, was commissioned to hold nuclear waste
  • Due to the Not In My Backyard movement/concern, it did not fulfill this purpose
  • There were other concerns as well

Accidents

• The most notable accidents are:
  • Three Mile Island, Pennsylvania, USA, 1979
  • This accident started in the non-nuclear portion of the reactor
  • A water pump failed, meaning the reactor was not cooling down
  • The fuel began to melt partially
  • There was no explosion or long-term high radiation exposure
  • Chernobyl, Ukraine, 1986
  • The accident arose from a safety test accident
  • The power was turned off during a simulation
  • Extra power from turbine was supposed to keep the reactor powered enough to cool
  • When the test was complete, control rods did not drop
  • There was an explosion, releasing the most radiation ever from a nuclear accident
  • Fukushima, Japan, 2011
  • This accident was caused by a natural disaster
  • A tsunami caused the reactor to shut down
  • The influx of water flooded four reactors
  • Three of the four ended up melting down
  • The accident was deemed preventable
  • They identified all faults and put many safety enhancements in place to prevent this from happening again
• Causes can be natural or human error