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Nuclear Energy: Fission: Conversion of Mass To Energy MC

Nuclear fission occurs when a neutron strikes certain radioactive heavy nuclei like Uranium-235, causing it to split into lighter elements and releasing energy and neutrons. This can start a self-sustaining chain reaction if the amount of U-235 is above a critical mass. Controlled fission reactions in nuclear power plants generate electricity, while uncontrolled reactions cause nuclear explosions. Plutonium-239 produced from Uranium-238 absorption can also undergo fission and be used in nuclear weapons or power if enriched sufficiently. Nuclear waste is highly radioactive and poses long-term storage and environmental challenges.

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55 views10 pages

Nuclear Energy: Fission: Conversion of Mass To Energy MC

Nuclear fission occurs when a neutron strikes certain radioactive heavy nuclei like Uranium-235, causing it to split into lighter elements and releasing energy and neutrons. This can start a self-sustaining chain reaction if the amount of U-235 is above a critical mass. Controlled fission reactions in nuclear power plants generate electricity, while uncontrolled reactions cause nuclear explosions. Plutonium-239 produced from Uranium-238 absorption can also undergo fission and be used in nuclear weapons or power if enriched sufficiently. Nuclear waste is highly radioactive and poses long-term storage and environmental challenges.

Uploaded by

Sheena Gagarin
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© © All Rights Reserved
We take content rights seriously. If you suspect this is your content, claim it here.
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Download as PDF, TXT or read online on Scribd
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NUCLEAR ENERGY:

FISSION
CONVERSION OF MASS TO
ENERGY = mc2
Nuclear Fission (1)
• Neutron + Radioactive Heavy Nucleus 
Stable Lighter Nuclei + ENERGY
• 10n + 23592U  14256Ba + 9136Kr + 3 10n
• This is one fission pathway for U-235.
There are nearly 400 fission pathways for
U-235. τ1/2 = 7.04E+8 yrs.
• Sum of mass number and sum of atomic
number must be conserved. Note Ex.17.4
Nuclear Fission (2)
• 10n + 23592U  14256Ba + 9136Kr + 3 10n
• The 3 product neutrons can induce 3 more
fission reactions. These 3 reactions can
cause 9 more fission reactions. This is
called a Chain Reaction
• If amount of U-235 is large enough (critical
mass = 56 kg), the chain reaction can be
self-sustaining. An external neutron
source is not needed.
Nuclear Fission (3)
• U-235 is naturally occurring in UO2 ores at
0.7% abundance level. It is the only
isotope of U that can undergo fission.
• In a controlled fission reaction, the energy
(1.68E+10 kJ/mol) produced can be
captured and used for generating
electricity.
• Nuclear power require fuel rods enriched
to 3.0% U-235.
Nuclear Fission (4)
• If the amt of U-235 is in a small enough
volume, the energy release is so rapid as
to create a nuclear explosion or atomic
bomb.
• Nuclear bombs require the fuel to be
enriched to 90.0% U-235.
Plutonium - 239
• The most abundant isotope of uranium is U-238
(99.3%). It is not fissionable but is radioactive.
• U-238 in fuel rods absorbs neutrons to form
highly radioactive U-239 which decays to give
highly radioactive Pu-239. (p 639)
• Pu-239 has a long τ1/2 = 2.4E+4 yrs, is
radioactive (emits α particles) and is fissionable.
• Pu-239 is not naturally occurring.
• If enriched to 93%, Pu-239 can be used in an
atomic bomb.
Nuclear Waste
• Nuclear plant waste is highly radioactive
and must be secured, stored and
monitored.
• The big challenges are: How, where, for
how long?
Other Issues
• Reprocessing spent fuel to obtain Pu-239.
• The world supply of Pu-239 is growing.
• Breeder reactors maximize production of
Pu-239 to be used for nuclear power
plants instead of U-235.
• Public acceptance of nuclear energy is low

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