1. Chapter 25 Nuclear Chemistry 25.3 Fission and Fusion
25.1 Nuclear Radiation
25.2 Nuclear Transformations
25.3 Fission and Fusion
25.4 Radiation in Your Life
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2. Where does the sun’s energy come from?
CHEMISTRY & YOU
Where does the sun’s energy come from?
The sun is about halfway through its life cycle. It has been producing energy for about 5 billion years and is expected to continue to produce energy for about 5 billion more.
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3. What happens in a nuclear chain reaction?
Nuclear Fission
Nuclear Fission
What happens in a nuclear chain reaction?
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4. Nuclear Fission
When the nuclei of certain isotopes are bombarded with neutrons, the nuclei split into smaller fragments.
This process is called fission.
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5. Nuclear Fission
The figure below shows how uranium-235 breaks into two smaller fragments of roughly the same size when struck by a slow-moving neutron. U
Uranium-235
(fissionable)
235 92
Uranium-236
(very unstable)
236 Ba
Barium-142
142 56 Kr
Krypton-91 91 36
3 n 1
Neutron
More neutrons are released by the fission.
These neutrons strike the nuclei of other uranium-235 atoms, which causes a chain reaction.
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6. Nuclear Fission
In a chain reaction, some of the emitted neutrons react with other fissionable atoms, which emit neutrons that react with still more fissionable atoms.
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7. Nuclear fission can release enormous amounts of energy.
The fission of 1 kg of uranium-235 yields an amount of energy equal to that produced when 20,000 tons of dynamite explode.
An atomic bomb is a device that can trigger an uncontrolled nuclear chain reaction.
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8. Nuclear reactors use controlled fission to produce useful energy.
Nuclear Fission
Nuclear reactors use controlled fission to produce useful energy.
The reaction takes place within uranium-235 or plutonium-239 fuel rods.
A coolant absorbs heat produced by the controlled fission reaction and transfers the heat to water, which changes to steam.
The steam drives a turbine, which drives a generator that produces electricity.
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9. Nuclear reactors use controlled fission to produce useful energy.
Nuclear Fission
Nuclear reactors use controlled fission to produce useful energy.
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10. Nuclear Fission
Neutron Moderation
Nuclear moderation is a process that slows down neutrons so the reactor fuel can capture them to continue the chain reaction.
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11. Nuclear Fission
Neutron Moderation
Nuclear moderation is a process that slows down neutrons so the reactor fuel can capture them to continue the chain reaction.
Moderation is necessary because most of the neutrons produced move so fast that they would pass right through a nucleus without being captured.
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12. Nuclear Fission
Neutron Moderation
Nuclear moderation is a process that slows down neutrons so the reactor fuel can capture them to continue the chain reaction.
Moderation is necessary because most of the neutrons produced move so fast that they would pass right through a nucleus without being captured.
Water and carbon in the form of graphite are good moderators.
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13. Nuclear Fission
Neutron Absorption
To prevent the chain reaction from going too fast, some of the slowed neutrons must be trapped before they hit fissionable atoms.
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14. Nuclear Fission
Neutron Absorption
To prevent the chain reaction from going too fast, some of the slowed neutrons must be trapped before they hit fissionable atoms.
Neutron absorption is a process that decreases the number of slow-moving neutrons.
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15. Nuclear Fission
Neutron Absorption
Control rods, made of materials such as cadmium, are used to absorb neutrons.
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16. Nuclear Fission
Neutron Absorption
Control rods, made of materials such as cadmium, are used to absorb neutrons.
When control rods extend almost all the way into the reactor core, they absorb many neutrons and fission occurs slowly.
As the rods are pulled out, they absorb fewer neutrons and the fission process speeds up.
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17. Nuclear Fission
Neutron Absorption
Control rods, made of materials such as cadmium, are used to absorb neutrons.
If the chain reaction were to go too fast, heat might be produced faster than the coolant could remove it.
Ultimately, a meltdown of the reactor core might occur.
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18. Nuclear Fission
Nuclear Waste
Fuel rods from nuclear power plants are one major source of nuclear waste.
The fuel rods are made from a fissionable isotope, either uranium-235 or plutonium-239.
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19. Nuclear Fission
Nuclear Waste
Fuel rods from nuclear power plants are one major source of nuclear waste.
The fuel rods are made from a fissionable isotope, either uranium-235 or plutonium-239.
During fission, the amount of fissionable isotope in each rod decreases.
Eventually the rods no longer have enough fuel to ensure that the output of the power station remains constant.
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20. Spent fuel rods are classified as high-level nuclear waste.
Nuclear Fission
Nuclear Waste
Spent fuel rods are classified as high-level nuclear waste.
All nuclear power plants have holding tanks, or “swimming pools,” for spent fuel rods.
Water cools the spent rods and also acts as a radiation shield to reduce the radiation levels.
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21. Spent fuel rods are classified as high-level nuclear waste.
Nuclear Fission
Nuclear Waste
Spent fuel rods are classified as high-level nuclear waste.
At some nuclear power plants, the storage pool has no space left.
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22. Spent fuel rods are classified as high-level nuclear waste.
Nuclear Fission
Nuclear Waste
Spent fuel rods are classified as high-level nuclear waste.
At some nuclear power plants, the storage pool has no space left.
Finding appropriate storage sites is difficult because high-level waste may need to be stored for a long time.
Plutonium-239, for example, will not decay to safe levels for 20,000 years.
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23. How does the fission of a uranium-235 nucleus cause a chain reaction?
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24. How does the fission of a uranium-235 nucleus cause a chain reaction?
When slow-moving neutrons bombard uranium-235, the atom splits and releases more neutrons. These neutrons then collide with more uranium atoms, and so on.
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25. How do fission reactions and fusion reactions differ?
Nuclear Fusion
Nuclear Fusion
How do fission reactions and fusion reactions differ?
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26. The energy emitted by the sun results from nuclear fusion.
Fusion occurs when nuclei combine to produce a nucleus of greater mass.
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27. The energy emitted by the sun results from nuclear fusion.
Fusion occurs when nuclei combine to produce a nucleus of greater mass.
In solar fusion, hydrogen nuclei (protons) fuse to make helium nuclei.
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28. The energy emitted by the sun results from nuclear fusion.
Fusion occurs when nuclei combine to produce a nucleus of greater mass.
In solar fusion, hydrogen nuclei (protons) fuse to make helium nuclei.
The reaction also produces two positrons.
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29. Nuclear Fusion
Fusion reactions, in which small nuclei combine, release much more energy than fission reactions, in which large nuclei split apart and form smaller nuclei.
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30. Nuclear Fusion
Fusion reactions, in which small nuclei combine, release much more energy than fission reactions, in which large nuclei split apart and form smaller nuclei.
However, fusion reactions occur only at very high temperatures—in excess of 40,000,000°C.
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31. Nuclear Fusion
The use of controlled nuclear fusion as an energy source on Earth is appealing.
The potential fuels are inexpensive and readily available.
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32. Nuclear Fusion
The use of controlled nuclear fusion as an energy source on Earth is appealing.
The potential fuels are inexpensive and readily available.
The problems with fusion lie in achieving the high temperatures needed to start the reaction and in containing the reaction once it has started.
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33. Nuclear Fusion
The high temperatures required to start fusion reactions have been achieved by using a fission bomb.
Such a bomb is the triggering device used for setting off a hydrogen bomb, which is an uncontrolled-fusion device.
This process is of no use, however, as a controlled generator of power.
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34. CHEMISTRY & YOU
The high temperatures needed to support fusion exist within the sun’s core. Late in the sun’s life cycle, other fusion reactions will occur. What element would form when two helium nuclei fuse?
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35. CHEMISTRY & YOU
The high temperatures needed to support fusion exist within the sun’s core. Late in the sun’s life cycle, other fusion reactions will occur. What element would form when two helium nuclei fuse? Be 8 4
He He 2 →
Two helium nuclei fuse to form an unstable isotope of beryllium.
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36. Choose the correct words for the spaces
Choose the correct words for the spaces. In solar fusion, _______ nuclei fuse to form _______ nuclei.
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37. Choose the correct words for the spaces
Choose the correct words for the spaces. In solar fusion, _______ nuclei fuse to form _______ nuclei.
Hydrogen nuclei fuse to form helium nuclei.
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38. Key Concepts
In a chain reaction, some of the emitted neutrons react with other fissionable atoms, which emit neutrons that react with still more fissionable atoms.
Fusion reactions, in which small nuclei combine, release much more energy than fission reactions, in which large nuclei split apart to form smaller nuclei.
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39. Glossary Terms
fission: the splitting of a nucleus into smaller fragments, accompanied by the release of neutrons and a large amount of energy
neutron moderation: a process used in nuclear reactors to slow down neutrons so the reactor fuel captures them to continue the chain reaction
Bullet #2: it was “nuclear moderation” earlier; which is correct?
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40. Glossary Terms
neutron absorption: a process that decreases the number of slow-moving neutrons in a nuclear reactor; this is accomplished by using control rods made of a material such as cadmium, which absorbs neutrons
fusion: the process of combining nuclei to produce a nucleus of greater mass
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41. Electrons and the Structure of Atoms
BIG IDEA
Electrons and the Structure of Atoms
During fission and fusion, atoms change their chemical identity as the number of protons in their nuclei change.
In fission, large nuclei split into two or more smaller nuclei.
In fusion, smaller nuclei combine to form larger nuclei at extremely high temperature and pressure.
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42. END OF 25.3
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