Submarines and Aircraft Carriers The Science of Nuclear

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 reaction 1. 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

Containment structure Pressurizer Steam Generator Control Rods Electric Generator Turbine Reactor Vessel Condenser See the reactor in action! Labels: • Condenser • Containment structure • Control Rods • Electric Generator • Pressurizer • Reactor Vessel • Steam Generator • Turbine

Nuclear reactor safety – explosion? • Could a nuclear explosion occur? - critical mass The minimum amount of material needed to sustain an uncontrolled chain reaction, and therefore cause a nuclear explosion. - purity of U-235 Nuclear fuel in a reactor is about 5% U-235. For a weapon, U-235 needs to be about 90% pure. - an explosion cannot occur The purity of U-235 in nuclear fuel is too low to sustain an uncontrolled chain reaction

Nuclear reactor safety – waste • Why is radioactivity dangerous? - meltdown Overheating of reactor core due to loss of cooling ability or control rod function. - regular operations As uranium fuel is used, it and its byproducts are highly radioactive. - cell damage Radioactivity causes damages cell components and causes mutations. To deal with radioactive waste: • Protect workers • Store waste safely

Exponential decay Negative power relationship Slower decay Faster decay

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 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 …radioactivity is halved… …then again, and… …again, and… Over each half-life…

Half-life of top 10 fission products Element Name (symbol) Yield (%) Half-life Cesium (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 Cesium (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 Percent yield is the relative amount of each element resulting from fission of U-235. CONCLUSION • Most fission products have relatively short half-lives (< 90 years). 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 Helium nucleus repulsion Uranium-238 to Thorium-234 Beta (β) Excess neutrons cause Electron conversion Hydrogen-3 to Helium-3 Gamma (γ) Nucleus energy too high Cobalt-60 to Nickel-60 Photon

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 Atomic number = 2 Atomic weight = 2 Subtract 2 protons Subtract 2 neutrons Loss of protons changes the element. Transmutation = change from one element into another

Predict alpha decay – example • Problem: an atom of 238 U emits an alpha particle, undergoing alpha decay. What is the product of this process? Solution: 1. Write the equation: 2. Subtract values for helium from uranium: Atomic mass = 238 – 4 = 234 Atomic number = 92 – 2 = 90 3. Look up the periodic table. (In the periodic table, the element with atomic number 90 is thorium. ) Answer: The decay product is thorium-234 (234 Th)

Radioactive decay chain Uranium Thorium Radon Polonium Lead U Th Ra Rn Po Pb – 1 α particle Check the periodic table to find the atomic numbers for each of the elements. Do you see a pattern?

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 nucleus nuclear reactor chain reaction alpha particle nuclear fission critical mass gamma rays radioactivity exponential decay half-life transmutation nuclear decay

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Energy yield of nuclear fuel • Fun factoids! Type of Engine Efficiency Energy Yield (1 g) Diesel 40 – 50% 5 x 104 J Nuclear 30 – 40% 9 × 1010 J – 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

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 make a Quizlet to 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