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Chapter 12 Nuclear Energy Introduction to Nuclear Energy Nuclear energy – Nuclear fission Nuclear fusion – Atoms and Radioactivity Nucleus – Electrons (-) orbit around nucleus Neutral atoms – Atomic mass – Atomic number – – Isotope – Usually an atom has an equal number of neutrons and protons – If the number of neutrons is greater than the number of protons = isotope Radioactive Isotope Unstable isotope Radioactive Decay – – Example – Each isotope decays based on its own half-life – time required for one half of the total amount of a radioactive substance to change to a different element. Uranium isotopes U-238: U-235: 0.71% of ore, used in conventional nuclear fission but must be refined to 3% (enrichment) (Bomb grade is 20%) U-234:<0.01% of ore. Not used in fission. Uranium found predominantly in Radioactive Isotope Half-lives Nuclear Fission Nuclear Fuel Cycle – Nuclear Fission U-235 The nucleus absorbs neutrons 2-3 neutrons are emitted and bombard another U-235 atom How Electricity is produced Breeder Nuclear Fission A type of nuclear fission in which non-fissionable U-238 is converted into fissionable Pu-239 Plutonium also used in nuclear weapons Pros – Pros and Cons of Nuclear Energy Pros (continued) – Carbon-free source of electricity– Cons – – – Cost of Electricity from Nuclear Energy Cost is very high 20% of US electricity is from Nuclear Energy – Affordable due to government subsidies Expensive to build nuclear power plants Fixing technical and safety issues in existing plants is expensive Safety Issues in Nuclear Power Plants Meltdown – Sites of major accidents: – Three Mile Island – Chornobyl (Ukraine) Three-Mile Island 1979 50% meltdown of reactor core – – – Elevated public apprehension of nuclear energy – Led to cancellation of many new plants in US Chornobyl 1986- Worst accident in history 1 or 2 explosions destroyed the nuclear reactor – Spread across large portions of Europe Death toll is 10,000-100,000 Nuclear Energy and Nuclear Weapons These countries have access to spent fuel needed to make nuclear weapons Safe storage and handling of these weapons is a concern Radioactive Waste Low-level radioactive waste- High-level radioactive waste- Radioactive Wastes Long term solution to waste – Deep geologic burial –Yucca Mountain (closed) – As of 2004, site must meet EPA million year standard (compared to previous 10,000 year standard) – Possibilities: Temporary storage solutions – In nuclear plant facility (require high security) Case-In-Point Yucca Mountain 70,000 tons of high-level radioactive waste Tectonic issues have been identified-near earthquake fault line and volcano Transportation of waste an issue Decommissioning Nuclear Power Plants Licensed to operate for 40 years – Power plants cannot be abandoned when they are shut down Three solutions – Storage – – Entombment– Decommissioning (dismantling)Fusion Fuel= isotopes of hydrogen (heavy hydrogen or deuterium) Combining 2 lighter atoms into one large one producing very large amounts of energy Fusion Way of the future?? – – Problems – It takes very high temperatures (millions of degrees) to make atoms fuse – Confining the plasma after it is formed super heated ionizing gas (plasma) has a tendency to expand and nuclei aren’t close together and will lose energy when they hit the container wall. Scientists have yet to be able to create energy from fusion