Unit 8 – Nonrenewable Energy
What is Fission?
Learning Objectives
• Explain how long supplies of nonrenewable minerals
might last.
• Outline and assess environmental impacts of fossil fuel
use.
• Describe the advantages and disadvantages of using
nuclear energy.
Agenda
• Quiz
• Notes
Homework
• Larger atoms of
certain elements are
split into two smaller
atoms of different
elements.
• Fission is the process
that nuclear plants
use.
• Unit 8 Reading Assignment due Sunday March 6th
• Unit 8 Current Event due Sunday March 6th
What is Fusion?
• Two smaller atoms are combined to make one
larger atom of a different element.
• Fusion is the process that powers the sun and
other stars.
How are fusion and fission alike?
• In each case, the mass
of the end product(s)
is less than the mass
of the starting
material(s).
How can we use this?
• Nuclear reactions produce 100,000 times more
energy per atom than chemical (fossil fuel)
reactions.
– In nuclear bombs, this energy is released all at once,
producing a huge surge of heat and power that
destroys everything in its vicinity.
– When nuclear reactions are controlled, it can be
converted to electricity.
What is the Fuel Source?
• Uranium ore is a
nonrenewable
mineral in the
sedimentary rock
in the Earth’s crust.
– It is found in
Australia, Africa,
and N. America.
Nuclear Fuel Cycle
• Mine the uranium
• Process the uranium
to make the fuel
• Use it in the reactor
• Safely store the
radioactive waste
• Decommission the
reactor
• Uranium contains three isotopes, U-238, U-235,
and U-234.
– U-235 is used in conventional nuclear reactions.
– However, this isotope is only .71% of the ore, and must
be refined after mining to a concentration of 3%.
– This energy-intensive refinement is called enrichment.
• After enrichment, the
uranium fuel used in a
nuclear reactor is processed
into small pellets of
uranium dioxide.
– Each pellet contains the
energy equivalent to 1 ton of coal!
• The pellets are placed in fuel
rods (closed pipes)
• The fuel rods are grouped in
fuel assemblies (about 200
rods each).
• A typical nuclear reactor
contains 250 fuel assemblies
How is Electricity Produced
from Nuclear Energy in a
Power Plant?
In Callaway: 193 fuel assemblies
composed of over 50,000 fuel rods
and some 18 million fuel pellets!
Nuclear Power Plants in the U.S.
Typical Nuclear Power Plant
• 99 operating
nuclear reactors
in the U.S.
• A typical nuclear
power plant has
four main parts:
– It is expected
that 4-6 new
units may come
on line by 2020
1. Reactor core
2. Steam
generator
3. Turbine
4. Condenser
a. Fission occurs in the reactor core.
b. Heat produced by fission produces steam from liquid
water in the steam generator.
c. The turbine uses steam to generate electricity.
d. The condenser cools the steam, converting it back to
liquid.
The Process
• The reactor core contains the fuel
assemblies with uranium inside.
• The U-235 is hit with a neutron,
which is absorbed and causes the
atom to become unstable.
• It splits into two smaller atoms
and neutrons are thrown from
the uranium atom.
• They collide with other U-235
atoms, causing a chain reaction
─ Continuous fission reactions from
the release of neutrons as uranium
atoms split
How do we Control a Chain
Reaction?
• Above each fuel assembly is a control rod made
of a special metal alloy that is capable of
absorbing neutrons.
• The plant operator signals the control rod to
move either up out of or down into the fuel
assembly.
– If it is out, the free neutrons collide
with the fuel rods and uranium
fission takes place.
– If it is in the assembly,
free neutrons are
absorbed and fission no
longer occurs.
A typical plant has three water circuits.
1.Primary water circuit: heats water using energy in fission
reaction
• It is a closed system, so it cannot become steam due to high
pressure.
2. Secondary Water circuit: Water is converted to steam
by the first water circuit at the steam generator
• The steam turns a turbine that spins a generator to produce
electricity.
• Then the steam goes to a condenser where it is converted to
liquid.
Power Plant colorsheet
3. Tertiary water circuit (cooling water): provides cool
water to the condenser (cools the steam)
• As the water in the tertiary circuit is heated it moves to a cooling
tower, where it is cooled before circulating back to the
condenser.