Types of Ionizing Radiation • Alpha radiation is a large, relatively slow moving particle released by a radioactive element. It is the nucleus of a Helium atom (2 protons, 2 neutrons) • Beta radiation is small and fast, an electron released from the nucleus of a radioactive element • Gamma radiation is electromagnetic energy (similar to visible light), but much more energetic
Shielding requirements for ionizing radiation • Alpha particles will be stopped by a piece of paper or the dead cells on the surface of your skin • Beta has two forms (fast and slow), fast requires several feet of air to stop, slow can be stopped by less • Gamma requires thick sheets of lead or several feet of concrete
Penetration capabilities • Alpha can not penetrate deeply into living tissue, but it is extremely damaging to those cells it does contact. • Beta can penetrate more deeply, damage is likely. • Gamma can pass completely through an organism. Damage might occur.
What happens when a cell is exposed to ionizing radiation? DNA double helix = potential point mutation
What happens when a cell is exposed to ionizing radiation? Nucleus Nucleus Cytoplasm Cytoplasm Older, mature cell Younger, growing cell This is why, young growing tissues or organisms are at greater risk for damage from ionizing radiation than older tissues or organisms.
Note: turbines exposed to Radioactive steam
Boiling Water Reactor • Note that the water that has come in direct contact with the core also comes in contact with the turbine. This can lead to repair difficulties as the turbine is also considered to be highly radioactive after this.
Pressurized Water Reactor Nonradioactive water Radioactive water
Pressurized Water Reactor • Most frequently used reactor design • Depends upon the availability of lots of water for cooling • Water in contact with turbine is not radioactive!
Uranium Fuel Cycle: Note that each arrow also represents a time where material is shipped
What happens at the mining step? • Open pit mining usually removes uranium ore • Uranium ore is one of the ore in lowest concentrations! Usually still economically viable to mine at concentrations of 0.1% • This leaves 99.9% tailings!
What do you do with these tailings? • Uranium tailings are radioactive • Also a source of radon • Not a good idea to use these for building materials or “fill” on which structures are built • Thus these become part of radioactive waste problem
Milling • Usually happens at the mine location • Have to crush rock and get more concentrated Uranium ore (also known as “yellowcake” for its color)
Conversion and Enrichment • Uranium ore contains U235 and U238 • Need to concentrate U235 as it is useful in a power plant reactor and U238 is useful only in a breeder reactor • Breeder reactors are used for power in France, but only for weapons manufacture in U.S. • Also convert fuel into pellet form
Used at Power Plants • In the process of fission, Uranium releases neutrons which bombard other Uranium atoms. When an atom is struck it breaks apart into fission fragments, neutrons and releases heat. We use the heat to make steam which makes electricity • When fission fragments accumulate too much fuel is no longer useful and needs to be reprocessed • Fuel then goes back for reprocessing • When fuel can no longer be reprocessed…..
We’re going to have to put it someplace very, very safe! • Half life for uranium and plutonium is very long! • Uranium235 half life is 7 x 108 years! • Uranium238 half life is 4.5 x 108 years! • Plutonium half life is 24, 000 years
How do you design a waste facility that will be safe for millions of years? Yucca Mountain Nevada – an old volcano
See your text for a good description of a waste disposal facility • Currently, Yucca Mtn., Nevada is the site that has been chosen by Congress to receive the nation’s waste
How’s the waste going to get there? Highway and rail – using semitrucks and trains
Finally, remember this… • Nuclear power is used solely for the generation of electricity • How much of our total energy demands are electrical? Recall from lecture prior to last exam………..……8% • Economic cost/benefit analyses have not been positive for nuclear power, but may change with natural gas price crisis.