Nuclear Reactions: Fission
and Fusion.
Questions to consider
 What is nuclear fission?
 What are the advantages and
disadvantages of nuclear fission?
 What is nuclear fusion?
 What are the advantages and
disadvantages of nuclear fusion?
 What are the risks involved in atomic
energy?
 What are the benefits of atomic energy?
Nuclear Reactions: Fission and Fusion.
 Nuclear fission of a plutonium nucleus already
happens naturally ... we just help it along by allowing
the reaction to proceed faster.
 Nuclear fusion, on the other hand, requires that the fuel
nuclei be moving very fast, or be heated to very high
temperatures.
 Scientists for the last 50 years have been trying to
figure out how to do this, but so far the technology at
our disposal is not equal to the task!
Nuclear fusion
 Nuclear fusion is what provides the sun and the stars
with the energy to shine continuously for billions of
years.
 Fusion reactions power the stars and produce
virtually all elements in a process called
nucleosynthesis.
Nuclear fusion
 Fusion is what happens when two atomic nuclei are forced
together by high pressure ... high enough to overcome the
strong repulsive forces of the respective protons in the nuclei.
 When the nuclei fuse, they form a new element and release
excess energy in the form of a fast-moving neutron.
 The energy is “extra” because the mass of the newly formed
nucleus is less than the sum of the masses of the original two
nuclei.
 The extra mass is converted to energy according to Einstein's
equation E=mc2. This energy can be used to do useful work.
Nuclear fusion
 Nuclear energy can also be released by fusion of
two light elements (elements with low atomic
numbers).
 The power that fuels the sun and the stars is
nuclear fusion.
 In a hydrogen bomb, two isotopes of hydrogen,
deuterium and tritium are fused to form a nucleus
of helium and a neutron.
 This fusion releases 17.6 MeV of energy. Unlike
nuclear fission, there is no limit on the amount of
the fusion that can occur.
Nuclear fusion
http://www.atomicarchive.com/Fusion/Fusion1.shtml
Nuclear Fusion
 For years now people have been turning to fusion as
the "energy of the future."
 Not only does fusion appear to be an extremely
effective source of energy production, it is
environmentally friendly and virtually inexhaustible.
 Too good to be true, you say?
 Perhaps we should look more closely at fusion, both
as a scientific theory and as what may prove to
become mankind’s energy source for the 21st
century and beyond.
What are the advantages of nuclear fusion?
 Fuel for fusion reactions are readily available. Deuterium and
tritium are virtually inexhaustible.
 Unlike the burning of coal or other fossil fuels, fusion does not
emit harmful toxins into the atmosphere. The combustion of
most fossil fuels involves some form of the reaction
C + O2(g) --> CO2(g) + heat
 The carbon dioxide (CO2(g)) emitted by this reaction
contributes to the global warming or so-called "Greenhouse
Effect" that we've all heard so much about. Fusion, however,
produces only helium, a gas that is already in abundance in
the atmosphere and will not contribute to global warming.
 A major concern with the use of fission power is the issue of
nuclear waste, a dangerous material that can both directly
injure people and be manufactured into weapons. Fusion has
no such problems with dangerous by-products.
What are the disadvantages of nuclear fusion?
 Scientists have not yet been able to contain a
fusion reaction long enough for there to be a net
energy gain.
 Many countries are phasing out fusion research
because of the failure to reach a breakthrough.
Nuclear Fission
 Fission is already an established method of energy
production.
 Countries around the world possess fission reactors
capable of powering whole cities.
 The benefits in energy production, however, are
shadowed by disturbing accounts of harm to the
environment and dangerous nuclear waste byproducts.
 Chernobyl, Hiroshima, and Nagasaki are frightening
precedents in the field of fission development and are
not to be ignored.
Nuclear Fission
 Nuclear fission is the process of splitting atoms, or fissioning
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them.
To picture nuclear fission, imagine about 200 marbles lying on a
flat surface, all jumbled together, and roughly forming a circle.
What would happen if someone took another marble and threw it
at them?
They would fly all around in different directions and groups, right?
That is a good visual of what happens in nuclear fission.
The filled circle is like an atom's nucleus. The marble being
thrown is like a "neutron bullet".
The only differences are that the marbles are protons and
neutrons and the protons and neutrons aren't in a filled circle. In
the actual atom they are in the shape of a sphere.
An atom is also a bit more complicated than a bunch of marbles.
Nuclear Fission
http://en.wikipedia.org/wiki/Nuclear_fission
What are the advantages of nuclear fission?
 Relatively little fuel is needed, it is relatively
inexpensive, and it is available in trace amounts
around the world.
 Fission is not believed to contribute to global
warming or other pollution effects associated with
fossil fuel combustion.
What are the disadvantages of nuclear
fission?
 Possibility of nuclear meltdown from an uncontrolled
reaction–leads to nuclear fallout with potentially
harmful effects on civilians.
 Waste products can be used to manufacture
weapons.
 High initial cost because plant requires containment
safeguards.
What are the risks involved in atomic energy?
 The biggest risk is the future of the by-product, which
includes highly-radioactive fuel, containers, tools,
decommissioned plants, and anything that comes
into contact with the fuel.
 Since this material can be dangerous for hundreds of
thousands of years after use, and since no human
artifacts have been in continuous use for that span of
time, it's doubtful humans will find a way to
permanently store these materials.
What are the risks involved in atomic energy?
 There are acute dangers associated with atomic energy,
such as the risk of reactor melt-down where control of
the fissioning process is lost, the containment and safety
systems are breached, and massive amounts of
radioactive material escape into the environment
contaminating a large region for hundreds or thousands
of years.
 Modern advocates of nuclear power claim that the risk of
meltdown is low or nonexistent with modern designs, but
it is hard for a designer to account for all the scenarios
(for example: terrorist attacks, an extreme earthquake or
tsunami, etc.)
What are the benefits of atomic energy?
 First, what is atomic energy? Atomic energy is
energy produced by atoms. (It is used synonymously
with the word “nuclear energy.”)
 Atomic energy offers a clean energy alternative that
frees us from dependence on fossil fuels.