Section 5 HandoutPhysics 102/15/06
I.Warmup / Questions
A.What is the purpose of a moderator?
B.What is one reason why it is impossible for standard fission reactors to blow up like a fission bomb?
C.How do nuclear power plants (and most electric generators) ultimately produce electricity?
D.If fusion reactors have less inherent danger from radioactivity, why aren’t they used more?
E.How is the intense heat required for fusion generated in a hydrogen bomb?
F.What is the fear of “nuclear winter”? (Discussion question: do you think that this affects the calculations of “mutually assured destruction” or “MAD”?)
G.What were some of the mistakes made in the construction of the Chernobyl plant – and its operation on the day of the disaster? What mistakes were made after the disaster? Do you think such an accident would have / could have occurred in the U.S., Western Europe, or Japan?
H.Was any radioactivity released to the environment in Three Mile Island? How many people died because of this or because of the accident directly?
I.What is a chain reaction, and what characterizes its growth?
II.Feedback Processes
A.Positive & negative feedback
1.Positive feedback is like a chain reaction.
2.Feedback can be positive, but still not lead to instability; this is like a chain reaction in a subcritical mass that “fizzles out.”
3.Negative feedback always encourages stability.
B.Examples of feedback / chain reactions
1.Microphones
2.Snowballs / avalanches / lightning
3.Chemical explosion
4.Lid on boiling water
5.Job interviews / dates
6.Homeostasis / thermostats
7.Canal formation
8.Overfishing
9.Unrestricted population growth
C.Key example: Climate change
1.Clouds
2.Ice
3.Dissolved ocean carbon dioxide
D.Key example: Fission reactors
1.Water (moderated & cooled) reactors
2.Chernobyl
III.Fission Reactors
A.Operation
1.The standard reaction model owes a lot to its use in nuclear-powered submarines.
2.Central Core (see Figure 1)
3.Three ingredients:
a)Control rods
b)Moderator
c)Fuel rods
B.Fuel cycle
1.Enrichment
2.Waste
3.Reprocessing
a)Advantages: expands available world nuclear fuel supply, sharply reduces the volume and lifetime of highly radioactive waste.
b)Disadvantages: may be more expensive (at least while U-235 is not scarce),may increase proliferation risk.
C.Advantages
1.Fuel cycle releases no carbon dioxide or other pollution
2.Centralized and compatible with existing power infrastrcuture (whereas solar may require rethinking how we set up the grid, both technologically and in terms of policy)
3.Ample fuel available domestically (and in other, uhm, stable, friendly countries)
D.Critiques
1.Cost
2.Risks of accident
3.Fears of proliferation
4.Radioactive waste
E.Advanced Designs
1.Called “Generation 3” or “Generation 4”
2.Involve passive instead of active safety features
IV.Fusion Reactors
A.Obstacles
B.What is a tokamak?
C.Other designs
D.“Cold fusion”
V.Nuclear Weapons
A.Fission
1.See figure 2.
2.Uranium
a)(Relatively) Easy to assemble, hard to get the material
b)Gun design
c)Used on Hiroshima
3.Plutonium
a)Hard to assemble, (relatively) easy to get the material
b)Implosion design
c)Used on Nagasaki
B.Fusion
1.Releases far more energy than a fission bomb, but requires more technical sophistication.
2.The biggest fusion bombs constructed had a yield of 50-100 megatons (what is a “megaton?), whereas the bombs dropped on Hiroshima and Nagasaki had less than 1/1000 that energy yield.
3.The blast radius does not increase by the same factor, thankfully.
Figure 1:
Figure 2:
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