Nuclear Energy
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…..
What happens when we’re done
with nuclear fuel?
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
That’s the job of these folks
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.