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