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Submarines and Aircraft Carriers:The Science of Nuclear Power
Science Topic: Physics and Social Science
Matter and Energy: Energy From the Atom
Plot your course to the Arctic Sea!
Use Google Earth or Google Maps to determine the distance in miles from Kitsap Naval Base in Washington state to a secret location in the Arctic Sea.
How long underwater?
• Example calculation:– Assume a cruising speed of 20 knots (23 mph)– If you measured 3,750 miles, the time underwater =
3,750/23 = 163 hours• Most non-nuclear submarines cannot remain
submerged that long!• With nuclear power, a submarine is limited only
by its food supply.
Nuclear power is…
• A method of generating electricity• A means of powering large vessels, such as
submarines and aircraft carriers• Based on a process involving atomic nuclei:
nuclear fission
Matter and Energy: Energy From the Atom
Fission
A loose neutron…
…collides with a uranium atom… …destabilizing it.
Fission splits the atom into two new elements, releasing energy, gamma
rays and additional neutrons.
Chain reaction1. A neutron collides with
a uranium atom.2. The collision releases
energy, and three additional neutrons.
3. Each neutron in turn collides with additional uranium atoms.
Nuclear Fission and Power Plants
Generating Electricity
Labels:•Condenser•Containment structure•Control Rods•Electric Generator•Pressurizer•Reactor Vessel•Steam Generator•Turbine
Containment structure
Pressurizer SteamGenerator
ControlRods
ReactorVessel
Turbine
ElectricGenerator
Condenser
See the reactor in action!
Nuclear reactor safety – explosion?
• Could a nuclear explosion occur?
- critical massThe minimum amount of material needed to sustain an uncontrolled chain reaction, and therefore cause a nuclear explosion.
- purity of U-235Nuclear fuel in a reactor is about 5% U-235. For a weapon, U-235 needs to be about 90% pure.
- an explosion cannot occurThe purity of U-235 in nuclear fuel is too low to sustain an uncontrolled chain reaction
Nuclear reactor safety – waste
• Why is radioactivity dangerous?
- meltdownOverheating of reactor core due to loss of cooling ability or control rod function.
- cell damageRadioactivity causes damages cell components and causes mutations.
- regular operationsAs uranium fuel is used, it and its byproducts are highly radioactive.
To deal with radioactive waste: •Protect workers•Store waste safely
Exponential decayNegative power
relationship
Faster decay
Slowerdecay
Results of half-life activity
• What shape are the observed curves? • Which of the lines, the class average or the group
line, is closest to the theoretical line? Why?• What is the difference in the average time for U-
232 and P-238 groups to use up all their candies? • What does this difference represent?
Radioactive decay
Over each half-life…
…radioactivity is halved…
…then again, and…
…again, and…
Half-life of top 10 fission productsElement Name (symbol) Yield
(%)Half-life
Caesium (Cs 133) 6.8 2.1 years
Iodine (I 135) 6.3 6.6 hours
Zirconium (Zr 93) 6.3 1,530,000 years
Molybdenum (Mo 99) 6.1 65.9 hours
Caesium (Cs 137) 6.1 30.17 years
Technetium (Tc 99) 6.1 211,000 years
Strontium (Sr 90) 5.8 28.9 years
Iodine (I 131) 2.8 8.0 days
Promethium (Pm 147) 2.3 2.6 years
CONCLUSION•Most fission products have relatively short half-lives (< 90 years).
Percent yield is the relative amount of each element resulting from fission of U-235.
BONUS FACT•Seven fission products have very long half-lives. (Only two of those are shown.)
Types of radioactive decay
Type of Decay (symbol)
Cause Particle Emitted Example
Alpha (α) Excess neutrons cause repulsion
Helium nucleus Uranium-238 to Thorium-234
Beta (β) Excess neutrons cause conversion
Electron Hydrogen-3 to Helium-3
Gamma (γ) Nucleus energy too high
Photon Cobalt-60 to Nickel-60
Penetrating power of decay particles
Predicting decay products
• How does alpha decay affect an isotope?
• What is the atomic number and atomic weight of helium?
• What is the new atomic mass and atomic number?
Loss of a helium nucleus
Loss of protons changes the element. Transmutation = change from one element into another
Atomic number = 2 Atomic weight = 2
Subtract 2 protons Subtract 2 neutrons
Predict alpha decay – example• Problem: an atom
of 238U emits an alpha particle, undergoing alpha decay. What is the product of this process?
3. Look up the periodic table.
(In the periodic table, the element with atomic number 90 is thorium.)
2. Subtract values for helium from uranium:Atomic mass = 238 – 4 = 234Atomic number = 92 – 2 = 90
1. Write the equation:
Solution:
Answer: The decay product is thorium-234 (234Th)
Radioactive decay chain
Th Ra Rn Po PbUUranium Thorium Radium Radon Polonium Lead
Check the periodic table to find the atomic numbers for each of the elements. Do you see a pattern?
– 1 α particle
How long is radioactive waste dangerous?• It depends on the half-life of the products of
fission and decay• A few decades to millions of years• It can be made safer if stored properly
Matter and Energy: Energy From the Atom
The Science of Nuclear Power
• Example concepts
alpha particle
chain reaction
critical mass
nuclear fission
gamma rays
half-life
nuclear decay
exponential decay
nucleus
radioactivity
transmutation
nuclear reactor
Copyright© 2013 Discovery Education. All rights reserved. Discovery Education, Inc. is a subsidiary of Discovery Communications, LLC.
Energy yield of nuclear fuel
• Fun factoids! – 1 gram of nuclear fuel provides 1.76 million times
the energy from a gram of gasoline– If your car was nuclear-powered it could travel 5
billion miles to the gallon
Type of Engine
Engine Efficiency
Energy Yield (1g)
Diesel 40 – 50% 5 x 104 J
Nuclear 30 – 40% 9 × 1010 J
At Sea: Submarine Warfare
Essential (Guiding) Questions
• How does a nuclear reactor work?• What are the benefits and risks of nuclear
power?• What are basic terms used in the fields of nuclear
power and nuclear physics?• How are quantitative data related to radioactivity
analyzed?• Can you define the key words?
Key Vocabulary• alpha particle• chain reaction• critical mass• exponential decay• gamma rays• half-life
• nuclear decay• nuclear fission• nuclear reactor• nucleus• radioactivity• transmutation